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US20070068605A1 - Method of metal performance improvement and protection against degradation and suppression thereof by ultrasonic impact - Google Patents

Method of metal performance improvement and protection against degradation and suppression thereof by ultrasonic impact Download PDF

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US20070068605A1
US20070068605A1 US11/342,846 US34284606A US2007068605A1 US 20070068605 A1 US20070068605 A1 US 20070068605A1 US 34284606 A US34284606 A US 34284606A US 2007068605 A1 US2007068605 A1 US 2007068605A1
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ultrasonic
corrosion
metal
impact
degradation
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Efim Statnikov
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UIT LLC
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UIT LLC
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Priority to US11/342,846 priority Critical patent/US20070068605A1/en
Assigned to U.I.T., L.L.C. reassignment U.I.T., L.L.C. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: STATNIKOV, EFIM S.
Priority to CN2006800439116A priority patent/CN101558174B/zh
Priority to PCT/US2006/037154 priority patent/WO2007038378A2/fr
Priority to KR1020087009584A priority patent/KR101362019B1/ko
Priority to JP2008532465A priority patent/JP5682993B2/ja
Priority to TW095135182A priority patent/TWI336730B/zh
Publication of US20070068605A1 publication Critical patent/US20070068605A1/en
Abandoned legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D10/00—Modifying the physical properties by methods other than heat treatment or deformation
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F3/00—Changing the physical structure of non-ferrous metals or alloys by special physical methods, e.g. treatment with neutrons
    • C22F3/02—Changing the physical structure of non-ferrous metals or alloys by special physical methods, e.g. treatment with neutrons by solidifying a melt controlled by supersonic waves or electric or magnetic fields

Definitions

  • the invention relates to a method and algorithm of improving the performance of metal and protecting the metal against degradation and suppression thereof by ultrasonic impact.
  • the invention addresses the problems of degradation of metal properties during prolonged service under external forces, thermodynamic fluctuations and negative environmental factors.
  • the invention protects against, i.e., prevents, and suppresses the danger of material failure due to unfavorable change in performance over time. These problems commonly occur because of the damage of the original structure of the material/metal under known conditions that accompany the processes of environmental degradation of metals.
  • MS mechanical systems
  • TS technical systems
  • Breakdown of MS and life depletion of the components are characterized by breakdown and limiting state criteria.
  • the operational safety and necessary lifetime are attained by reserves of working capacity and load-bearing capacity, diagnostic and prediction techniques that compensate for a scatter in external actions and a random nature thereof.
  • a parametric reliability theory is based on calculating reliability parameters, including physico-mechanical failure models. This theory suggests that output parameters of a product change due to wear and damage of individual components. However, in many cases the output parameter is not susceptible to a damage value until some critical instant when functioning is terminated or safe operation conditions are violated. For example, cracking occurs in vessels, pipes and other components where functioning is terminated because of through-wall cracking or brittle or ductile fracture.
  • the breakdown of MS is a final stage preceded by failure of one or several components, which, in turn, is caused by the damaged material that reached the critical value.
  • Various parameters are taken as a damaging measure, depending on the material properties and external factors.
  • the damage parameters characterize the change in physical, chemical and mechanical properties of the material, as well as surface and structural conditions.
  • the current measurement techniques do not detect initial damage stages due to their local application or because the industry lacks the necessary technical means and this should be considered during MS development. This brings a problem of identifying direct and indirect diagnostic features and developing diagnostic means needed to evaluate and predict the state during testing and in service.
  • MS and TS multiple effects on MS and TS, especially in chemistry, petrochemistry, nuclear engineering, bioengineering and pipeline infrastructure, cause a great variety of degradation processes that are responsible for complex damage of the material, life depletion and breakdown of MS. Identifying possible degradation processes is the most important objective during pre-design investigations and design work.
  • a widely used and well-studied reliability method such as structural redundancy is not applicable for MS where reliability cannot be provided or correctly assessed based on the strength and life criteria.
  • the main failure criterion for pipelines, tubular devices and pressure vessels is seal failures due to through-wall damages or component failures, leading to leakage or atmospheric injection.
  • Any damage process may be described by its mechanism, kinetics and dynamics.
  • the mechanism of the damage process implies the combination and interaction of the factors determining the process; the kinetics implies damages such as micro and/or macroscopic events occurring as a result of summing or accumulating elementary motion events; and dynamics implies the process velocity change over time.
  • the damage mechanism (degradation mechanism) is identified with a number of factors affecting the components material; kinetics and dynamics are identified with material response within micro- and submicrovolumes to a given effect in time; and damage parameters are identified with consequences of external effects within component volume.
  • Each damage process is a collective process that is accompanied by a complex of effects with special cause-and-effect relations. Any damage process has a minimum number of dominant factors that are typically taken as a basis to assign a class to the process.
  • Identifying the nature and causes of MS component material failure is fundamental as this presents the following: a basis for a design model to assess the strength and lifetime; a criterion of correct choice of test methods and conditions; the initial information to validate diagnostic, prediction and improvement methods for MS.
  • the material damage is described as a multi-stage, statistical and large-scale process due to various damage micromechanisms, statistical relationships of heat fluctuations in time and simultaneous phenomena at nuclear, dislocation, substructural and structural levels.
  • the use of purely mechanical criteria to assess the strength and life under combined action of loads and media does not ensure accuracy nor allow improving these criteria and affecting the damage process.
  • Table 2 shows the classification results of the most common and hazardous type of damage parameters that have substantial effect on MS life and characterized by cracking.
  • TABLE 2 Cracking Parameters Intensification Classification Parameter Crack Crack surface Type of Type of front structure Crack failure at failure shape in in develop- Branching microcrack at macro- fracture fracture ment path type tip crack tip Semi- One- Intra- Strongly Dislocation Chip; circular; focus; granular; branching; type; fracture; semi- multi- inter- weakly growth and cut elliptic; focus granular; branching; coalescence linear combined non- of pores; branching dislocation type and local corrosion
  • NASH National Aeronautics and Space Administration
  • NMAB National Materials Advisory Board
  • a NMAB study committee was established to (1) provide an overview of long-term exposure effects on future high-performance aircraft structures and materials; (2) recommend improvements to analytical methods and approaches to accelerate laboratory testing and analytical techniques to characterize and predict material responses to likely aircraft operating environments; and (3) identify research needed to develop and verify the required testing, predictive analytical capabilities, and evaluation criteria.
  • the general degradation mechanisms i.e., the physical event or chain of events that underlie observed degradation effects, that must be considered include:
  • Determination of the most critical degradation mechanisms depends on what properties are important in a particular application. For example, if strength is critical, coarsening of the matrix precipitates during elevated-temperature service will be important; if toughness is critical, grain-boundary precipitation or the development of a precipitate-free zone will be important; and if creep or fatigue are critical, the nucleation, growth, and coalescence of microcracks will be important.
  • Potential damage mechanisms associated with high-temperature applications of aluminum alloys include microstructural changes, fatigue, creep, and environmental effects.
  • Elevated-temperature exposure under applied stress can introduce a number of microstructural changes including coarsening of the matrix precipitates (important in strength-critical applications) and grain-boundary precipitation or the development of a precipitate-free zone (important in toughness-critical applications).
  • Fatigue resistance is degraded by the nucleation, growth, and coalescence of voids or microcracks.
  • High-cycle fatigue resistance is sensitive to the nucleation of microcracks at microstructural inhomogeneities, while fatigue crack growth thresholds are affected by the level of residual stresses and crack tip shielding produced by variations in microstructure. Creep resistance appears to improve with increasing grain size.
  • cold work reduces creep resistance in precipitation-strengthened and dispersion-strengthened aluminum alloys. Degradation mechanisms due to service environmental interactions that need to be considered for aluminum alloys include corrosion, stress corrosion cracking, hydrogen embrittlement, solid-metal embrittlement, and liquid-metal embrittlement.
  • the three primary factors that need to be considered in long-term, elevated-temperature applications of high-strength and high-toughness titanium alloys for HSCT applications, include:
  • Creep is one of the most serious high temperature damage mechanisms. Creep involves time-dependent deformation. High temperature creep cracking generally develops in an intercrystalline manner in components of engineering importance that fail over an extended time and includes boiler superheater and other components operating at high temperature, petrochemical furnace and reactor vessel components and gas turbine blades. At higher temperatures, as can occur with local overheating, deformation may be localized, with large plastic strains and local wall thinning. At somewhat lower temperatures and under correspondingly higher stress levels, fracture can be transgranular in nature.
  • Microstructural degradation is a damage mechanism that can lead to failure by some other process such as creep, fatigue or more rapid fracture. Microstructure degradation is a mechanism of damage as it can result in a significant loss in strength in a material.
  • Fatigue involving repeated stressing, can lead to failure at high temperature as it does at low temperature.
  • fatigue often arises through temperature changes that can lead to cyclic thermal stresses, which can lead to thermal fatigue cracking.
  • the cracking tends to develop in areas of high constraint, and the detailed mechanism may be one of local creep deformation.
  • Creep-fatigue interaction is a complex process of damage involving creep deformation and cyclic stress and the predominant damage mode can range from primarily fatigue crack growth at higher frequencies and lower temperatures to primarily creep damage where hold times are long and temperature is at the high end of the scale.
  • Embrittlement from precipitation can arise in a number of different ways. For example, sigma phase formation in austenitic stainless steels maintained at high temperature or cycled through the critical temperature range (approximately 565 to 980° C.) causes loss of ductility and embrittlement. Ferritic stainless steels may be subject to an embrittlement phenomenon when held at or cooled over the temperature range 550 to 400° C. If the temperature conditions are considered likely to lead to such effects, metallographic checks are advisable after extended exposure prior to an unexpected rupture developing.
  • carburization can produce brittle material when a component is exposed to a carburizing atmosphere for extended time at high temperature.
  • Hydrogen damage arising particularly in petrochemical plant, can occur in carbon steels through diffusion of atomic hydrogen into the metal, where it combines with the carbon in the Fe 3 C to form methane and to eliminate the pearlite constituent. This is a special case of microstructural degradation, and is much less common today than in the past because of the use of low-alloy steels containing elements that stabilize carbides.
  • Graphitization can take place in ferritic steels after exposure to high temperature for extended time, owing to reversion of the cementite in the pearlite to the more stable graphite phase. It is a particular form of microstructural degradation that was formerly observed relatively frequently in petrochemical components. With the development of more stable CrMo steels, it is not often seen today, but occurs from time to time both in petrochemical plants and in steam generators in which the temperature is high and the material is not entirely stable.
  • Thermal shock involves rapid temperature change producing a steep temperature gradient and consequently high stresses. Such loading can produce cracking, particularly if the shock loading is repetitive. Cracks generated in this manner progress by a process of thermal fatigue. Such conditions are not encountered in thermal generating plants and refineries under normal operating conditions, but may arise during emergencies or with an excursion in the operating conditions. Brittle materials are much more susceptible to thermal shock and ceramic components, as are becoming more common in advanced gas turbines for example, are susceptible to such damage.
  • Erosion can occur in high temperature components when there are particles present in flowing gases. This is a not uncommon situation in coal-fired power plants in which erosion by fly-ash can lead to tube thinning and failure in economizers and reheaters, and soot blower erosion can produce thinning in superheaters and reheaters in those tubes that are in the paths of the blowers.
  • the solution to fly ash erosion depends in part on improving boiler flue gas distribution, and cutting down on local excessively high gas velocities.
  • the control of soot blower erosion depends on many factors including excessive blowing pressure, poor maintenance and the provision of effective tube protection where required.
  • Liquid metal embrittlement can occur with a number of liquid-solid metal combinations, and one that can have serious consequences for the refining industry is LME of austenitic stainless steel by zinc. Rapid embrittlement can occur at temperatures above 750° C., and has been observed to produce widespread cracking in stainless steel components after a fire when there is a source of Zn present such as galvanized steel structural parts, or when there is contamination from Zn-based paints. This latter source led to considerable cracking at the time of the Flixborough disaster (Flixborough, North Lincolnshire, England; 1974). Cracking can be extremely rapid (m/s) and stress levels can be as low as 20 MPa for such cracking to take place.
  • Minimization of corrosion in alloys for high temperature applications depends on the formation of a protective oxide scale. Alternatively, for alloys with very high strength properties at high temperature, a protective coating may need to be applied.
  • the oxides that are generally used to provide protective layers are Cr 2 O 3 and Al 2 O 3 . Corrosion protection usually breaks down through mechanical failure of the protective layer involving spalling of the oxide as a result of thermal cycling or from erosion or impact.
  • specimens were taken from operating pipelines, emergency reels and emergency stock.
  • the useful life was between 4 and 44 years.
  • the metal used in current production of Orsko-Khalilovsk metallurgical works and pipes from emergency stock were taken as the initial condition.
  • FIG. 1 shows the effect of life on the brittle state (T 50 ) transformation temperature for pipe metal of steel 17MnSi (sign ⁇ means that there are cases of brittle state transfer at above +20° C.).
  • the change in structural state of pipe metal may result from the process of defect accumulation due to stress effects, corrosion environment and hydrogen. Corrosion processes change surface condition of pipe metal, saturating metal with hydrogen, which entails formation of internal microcrack-like defects.
  • the process of accumulation of microcrack-like defects and fracture under static or quasistatic stress, which is lower than the ultimate fracture stress and yield stress of steel, is commonly termed the delayed fracture.
  • the delayed fracture is the cause of the premature brittle fracture of critical high-strength steel details exposed to corrosion environment, for example, tighten bolts, strained reinforcing wire, etc.
  • Delayed fracture tests were carried out in accordance with a specially developed procedure under simultaneous exposure to stresses, corrosion environment and hydrogen.
  • the delayed fracture has three phases: incubation period (crack nucleation phase), slow growth of a stable crack and quick fracture.
  • incubation period crack nucleation phase
  • slow growth of a stable crack slow fracture.
  • the most important assessment is to find the resistance to crack nucleation and propagation (not quick as in shock testing, but slow), which is why the level of impact strength does not reflect the crack formation resistance for pipes.
  • FIG. 2 shows the relationship between time to fracture, t f , and initial stress intensity coefficient, K i , for pipes of steel 17MnSi: 1—as-manufactured; 2—working pipe; 3—emergency pipe.
  • the prolonged service affects the inclination of pipe metal to delayed fracture, moving the K i -versus-t f curve to the region of lower time to fracture.
  • the time to fracture for as-manufactured pipes is much greater than that for working and emergency pipes as shown in FIG. 2 .
  • the stable crack propagation rate also depends on lifetime.
  • the metal of as-manufactured pipes has the lowest stable crack propagation rate of (1-3) ⁇ 10 ⁇ 4 mm/min.
  • Strain aging of iron and low-carbon steels is observed only when a solid solution contains carbon and nitrogen atoms of certain concentration. Strain aging results in improved tensile strength, yield strength, hardness; a yield plateau on SN curve; increased critical brittle temperature in shock tests; and lower plasticity. The tendency to strain aging is an important property of metals.
  • FIG. 3 From FIG. 3 follows that during prolonged service the tendency of steel to strain aging is reduced, i.e., the smaller growth of the yield strength, ⁇ 5 , and reduction of area in aged condition. This is the most intensive during the first 15-30 years of service.
  • the effect of service on the tendency to deformation aging, ⁇ s is shown in FIG. 3 and the reduction of area of aged pipes, ⁇ s , is shown in FIG. 4 .
  • IFTD internal friction temperature dependence
  • the IFTD curves for specimens cut out from pipes after long service of 30 years have two maximums at 60 and 200-220° C., as shown in FIGS. 5 and 6 .
  • the temperature dependence of internal friction, Q ⁇ 1 , of pipe metal of 17MnSi steel after prolonged service of 30 years is shown in FIG. 5 and in emergency stock is shown in FIG. 6 .
  • the maximum at 60° C. is higher.
  • the Snoek maximum in IFTD curves in known to be observed when interstitial impurity content is greater than 2-10 ⁇ 4 %.
  • the carbon and nitrogen content in solid solution of the pipes being in service for 30 years, approximates 2 ⁇ 10 ⁇ 4 %, i.e., under pipeline conditions the carbon and nitrogen content in a free solid solution tends to decrease.
  • the carbon and nitrogen content decreases during pipe service due to plastic deformation that results in fresh dislocations being fixed by carbon and nitrogen atoms, forming so-called “atmospheres” of impurity atoms on dislocations and reducing the mobility thereof.
  • the tendency of developing deformation aging under pipeline conditions is also evidenced by the increase in IFTD curve maximum at 200-250° C. which is observed only when the metal is subject to plastic deformation and subsequent aging.
  • the reliability assessment criteria should include the properties susceptible to local structural changes, for example, those obtained by delayed fracture tests and tests on cracked or sharp notched specimens at low temperatures.
  • Clarifying general and localized corrosion effects the effects of atmospheric exposure, high-temperature gases, soil, water, weak and strong chemicals, liquid metals and nuclear radiation are disclosed.
  • This disclosure also shows how improvements in component design can reduce corrosion; details of the high- and low-temperature effects of oxidizing agents, such as oxygen, sulfur and water vapor, the halogens and CO 2 ; investigates the instantaneous and delayed failure of solid metal in contact with liquid metal; highlights the influence of hydrogen on metal, including the loss of ductility and internal flaking, blistering, fissuring and cracking; profiles radiation effects on metal, such as irradiation growth, void swelling, and embrittlement and more.
  • the disclosure covers the following subjects: types and prevention of aqueous corrosion, tarnishing and scaling processes (thermodynamic aspects of metal-oxidant system; kinetic aspects and rate equations; defect chemistry of oxides and other inorganic compounds; mechanisms of tarnishing and scaling processes; scale growth by lattice and grain boundary diffusion; formation of voids, porosities and other macrodefects in oxide scale and in the substrate; development of stresses and strains in the growing scales; dissolution and diffusion of oxidant in metals; effect of metal surface preparation and pretreatment), alloy oxidation, liquid metal attach, and hydrogen damage.
  • types and prevention of aqueous corrosion, tarnishing and scaling processes thermodynamic aspects of metal-oxidant system; kinetic aspects and rate equations; defect chemistry of oxides and other inorganic compounds; mechanisms of tarnishing and scaling processes; scale growth by lattice and grain boundary diffusion; formation of voids, porosities and other macrodefects in oxide scale and in the substrate; development of stresses and strains in the growing scales
  • Accelerated Degradation by Brigitte Battat (AMPTIAC, Rome, N.Y. 2001), which discloses a brief description of materials degradation, and the methodology for accelerated degradation. Testing through accelerated degradation or aging measures product performance as a function of time, at overstress conditions.
  • Table 4 (based on a compilation of data from Nelson's book on acceleration testing (see Nelson, W., Accelerated Testing: Statistical Models, Test Plans and Data Analyses, Wiley Series in Probability and Mathematical Statistics, 1990, p.11-49)) provides a breakdown of the degradation mechanisms, the materials they affect, the accelerated stress factors used, and the measured properties that gauge the response. For example, fatigue occurs in metals, plastics, etc, and accelerated stress factors can be temperature, load, or chemical reactions. The measured properties are residual life and cumulative damage effect. This information helps to generate models that can be extrapolated to determine residual life. As such, this is different from accelerated life testing which spans the full extent of the material or component life.
  • Accelerated aging implies accelerated exposure to generate end-of-life microstructure or damage states for subsequent characterization tests.
  • the coarsening of metal alloy microstructure can accelerate exposure by lowering the strength and toughness of the material.
  • multiple damage mechanisms e.g., thermomechanical fatigue
  • both accelerated aging and accelerated life testing may be required for validation. Accelerated aging can be achieved by: (1) increasing temperature and load; (2) damaging the product before performing the test; (3) increasing the number of hold times between exposures; and (4) increasing the concentration of the chemical agent causing degradation.
  • Accelerated degradation tests compared to accelerated life tests have the advantage of analyzing performance before the material or the component fails. Degradation tests determine how much life there is left in a material or in components, and such knowledge enables life extension. Extrapolating performance degradation to estimate when it reaches failure level enables analysis of degradation data. However, such analysis is correct only if a good model for extrapolation of performance degradation and a suitable performance failure have been established.
  • Accelerated aging for cases where multiple degradation mechanisms are involved, should be performed in series: the sample should be exposed incrementally to conditions that bring about the degradation mechanisms one at a time, until the end-of-life condition is reached.
  • Degradation mechanisms for aluminum alloys include: microstructural and compositional changes; time-dependent deformation and resultant damage accumulation Environmental attack and the accelerated effects of elevated temperature; and synergistic effects of the above mechanisms. Damage mechanisms associated with high-temperature applications of aluminum alloys (e.g., microstructural changes, fatigue, creep, environmental effects) are illustrated in FIG. 7 .
  • life may be of the order of millions of cycles, or several years. Life depends on degradation processes, such as corrosion, fatigue, creep, etc. Certain components, such as aircraft parts, are made for the life of the system, while others, subject to fatigue, have a much tighter life schedule.
  • the object of accelerated testing is to determine the life for the dominant failure mode under normal operating conditions, using information and testing obtained from stressed operating conditions. To achieve this, a mechanistic understanding of the failure mode is needed.
  • temperature, load and duty cycle determine the life models that predict failure modes. Life testing may be accelerated by increasing the temperature, or by increasing load and duty cycle, or by using a combination of all effects. Under stressed conditions, the model predicts failure within a few hours (or minutes). Once verified, the same model is used to predict the life under nominal conditions of operation.
  • Life on the other hand, relates to failure modes and to the maintenance of performance and robustness over the lifetime of the item, as prescribed by the specification. Failures can occur due to shortfall of performance, or due to hard and catastrophic breakdown, that necessitate replacement. In this connection, accelerated testing may be used to determine and extend life, but it may also be employed to identify directions for performance improvement.
  • accelerated testing is a methodology for predicting future material and component performance from testing procedures performed in the present time. This is obtained by using a test environment more severe than that experienced in the normal use environment.
  • the current projects include: damage localization mechanisms in aqueous chloride corrosion fatigue of aluminum-lithium alloys; measurements and mechanisms of localized aqueous corrosion in aluminum-lithium alloys; an investigation of the localized corrosion and stress corrosion cracking behavior of alloy 2090; deformation and fracture of aluminum-lithium alloys—the effect of dissolved hydrogen and the effect of cryogenic temperatures; and elevated temperature crack growth in advanced powder metallurgy aluminum alloys.
  • the oxide layer on the bare alloy was found to consist of Al 2 O 3 , Cr 2 O 3 , and NiAl 2 O 4 .
  • the microstructural degradation of both the plain aluminide and platinum aluminide coatings during oxidation was seen to occur in three distinct stages which, however, differed for each coating. This stagewise degradation, which involves final obliteration of the interdiffusion layer in each case, is disclosed therein in detail.
  • Oxidation - Induced Degradation of Coatings on High Temperature Materials An Overview , by Jedlinskia, Jerzy, (Proceedings Symp. Elevated Temp Coatings: SCI & TECH, 1994, Vol. 1, pp. 75-83), which discloses that interaction between an aggressive environment and coated materials leads to the accelerated degradation of the latter.
  • An understanding of the mechanisms of degradation plays a crucial role in the design of materials with improved service properties.
  • Corrosion and Environmental Degradation by Schtze, Michael; Editor: Robert W. Cahn; Peter Haasen (2000), which provides a sound and broad survey on the whole subject—from the fundamentals to the latest research results.
  • Corrosion and corrosion protection is one of most important topics in applied materials science. Corrosion science is not only important from an economic point of view, but, due to its interdisciplinary nature combining metallurgy, materials physics and electrochemistry, it is also of high scientific interest.
  • corrosion science even gets new impetus from surface science and polymer chemistry.
  • the detailed topics include: Corrosion Behavior of Aluminum Alloys, Inhibition and Protection of Aluminum and Magnesium Alloys; Inhibition and Protection of Metals in Process Industries; Assisted Cracking of Steels: Stress Corrosion Cracking, Corrosion Fatigue, and Hydrogen Damage; Electrochemical and Monitoring Techniques; Durability of Materials: Coatings and their Performance.
  • Aluminum aircraft structures are susceptible to corrosion and fatigue damage, which interact mainly at structural joints. Interactions between corrosion and fatigue may represent a serious threat for the structural integrity of the aircraft, especially as the aircrafts become older.
  • Present day considerations of the corrosion induced structural degradation relate the presence of corrosion with a decrease of the load bearing capacity of the corroded structural member, as well as with the onset of fatigue cracks.
  • corrosion-pitting damage has been quantified and related to the decrease in fatigue life of 2024-T3 specimens corroded in alternate immersion corrosion process.
  • MSD Multiple Site Damage
  • Corrosion attack of aluminum alloys has been classically attributed to the complex processes of oxidation. Yet, recent investigations performed on a series of aircraft alloys have provided evidence that corrosion is not limited to the well known surface damage process, which affects yield strength and fatigue life through the occurrence of corrosion notches, but it is also the cause for a diffusion controlled material hydrogen embrittlement.
  • the fatigue and damage tolerance behaviour of pre-corroded aluminum 2024 T351 alloy specimens have been investigated and discussed under the viewpoint of a synergistic effect of corrosion and corrosion-induced hydrogen embrittlement.
  • the performed experiments included fatigue tests to obtain S-N curves, fatigue crack growth tests and fracture toughness tests.
  • the fatigue crack growth tests were performed for different values of the stress ratio R.
  • all experiments were carried out also for the uncorroded material.
  • the results have demonstrated the essential effect of existing corrosion on the fatigue and damage tolerance behaviour of the 2024 alloy as well as the need to account for the effect of corrosion on the mechanical properties in fatigue and damage tolerance analyses of the corroded areas of a structure.
  • a series of measurements of pitting density and the dimensions of pits for Al 2024 T351 subjected to exfoliation corrosion solution for 36 hours has shown an average pitting diameter of 2.586 ⁇ 10 ⁇ 3 mm and a pitting density of 920 samples per 100 mm 2 .
  • the measurements were made using the stereoscopic image analysis.
  • Metallographic corrosion characterization has shown that for 36 hours of exposure to exfoliation corrosion, some intergranular corrosion may be expected as well.
  • the presence of essential corrosion pitting and intergranular corrosion facilitates essentially the onset of fatigue cracks and, hence, reduces the fatigue life of the corroded specimens appreciably.
  • the fatigue endurance limit drops from 175 MPa for the uncorroded material to 95 MPa for the pre-corroded specimens. Fitting curves for both, uncorroded and corroded material were derived using regression analysis.
  • Crack growth may be interpreted to occur incrementally and to correspond to the failure of material elements ahead of an existing crack after a certain number of low cycle fatigue.
  • the fracture toughness value of the corroded material will be lower.
  • the fracture toughness reduction of the corroded material was confirmed by fracture toughness measurements which will be discussed in a following paragraph. The above considerations may explain the higher crack growth rates and the steeper crack growth increase at the stage of accelerated crack growth.
  • the reduced fracture toughness values for the corroded material explain the reduced crack length at failure and, with regard also to the higher crack growth rates at the stage of accelerated crack growth rate, the reduced fatigue lives for the corroded specimens.
  • the fracture toughness of the corroded material decreases significantly and it is necessary to evaluate local fracture toughness values associated with the reduction of strain energy density.
  • the involvement of multiscaling approaches is very efficient for facing the complex interactive corrosion hydrogen embrittlement process and it was suggested to examine the effect of corrosion-induced hydrogen embrittlement on multiple site damage (MSD) problems where the distance of the rivet holes is such that allows local volumetric embrittlement of the material.
  • Hydrogen embrittlement of austenitic steels can be divided into two broad types: (1) the combination of high hydrogen fugacity, low diffusivity (i.e., low temperature) and austenitic stability leads to severe internal strains, spontaneous transformation to alpha and epsilon martensites and extensive intergranular and transgranular surface cracking, and (2) the combination of composition, temperature and fugacity are such that hydrogen is absorbed without accompanying gross structural changes.
  • Hydrogen has a diverse range of harmful effects on metals. Hydrogen induced degradation of metals is caused by exposure to atmosphere, where hydrogen is absorbed into the material and results in reduction of its mechanical performance. The severity and mode of the hydrogen damage depends on: source of hydrogen—external (gaseous)/internal (dissolved), time of exposure, temperature and pressure, presence of solutions or solvents that may undergo some reaction with metals (e.g., acidic solutions), type of alloy and its production method, amount of discontinuities in the metal, treatment of exposed surfaces (barrier layers, e.g., oxide layers as hydrogen permeation barriers on metals), final treatment of the metal surface (e.g., galvanic nickel plating), method of heat treatment, and/or level of residual and applied stresses.
  • the hydrogen damage may be classified as hydrogen embrittlement, hydride embrittlement, solid solution hardening, creation of internal defects, and can further be subdivided into various damaging processes as shown in FIG. 8 .
  • the degree of hydrogen attack depends on temperature, hydrogen partial pressure, stress level, exposure time, steel composition and structure. Hydrogen attack has been reported in plain carbon steel, low alloy steels and even some stainless steels operating above 473K. Hydrogen attack is one of the major problems in refineries, where hydrogen and hydrocarbon streams are handled up to 20 MPa and approximately 810K level. In order to prevent hydrogen attack from occurring at high temperature and/or pressure, a high alloy element content is required. Chromium (Cr), Molybdenum (Mo), Tungsten (W), Vanadium (V), Titanium (Ti), Niobium (Nb), which are carbide forming elements, are used in steel to provide desired resistance.
  • API 941's Nelson Curves provide guidance universally used for alloy selection.
  • the appropriate alloy to select is shown as the curve immediately to the right or above the temperature-hydrogen partial pressure coordinates, which represent anticipated parameters of operation.
  • Heat treatment influences steel resistance to hydrogen attack.
  • quenched and tempered 2-1/4Cr-1Mo steel has increased susceptibility to hydrogen cracking due to low resistance of martensitic and bainitic structures to hydrogen damage.
  • the heat treatments that would produce excessive yield strength levels should be avoided or used with caution.
  • Hydrogen attack is caused by exposure of steel to a hydrogen environment.
  • the severity of the damage depends on the time of exposure, temperature, hydrogen partial pressure, stress level, steel composition and structure.
  • steels with elements forming stable carbides should be used.
  • a heat treatment should be carefully applied to avoid producing structures with low resistance to hydrogen attack (martensite, bainite).
  • Proper inspection and quality control systems are necessary during the manufacturing process of hydrogen and hydrocarbon handling equipment. Hydrogen undamaged and damaged samples of steel used in plant equipment should be available for the hydrogen attack testing purposes.
  • oxide films formed under four different DH conditions in simulated primary water of PWR was carried out using a grazing incidence X-ray diffractometer (GIXRD), a scanning electron microscope (SEM) and a transmission electron microscope (TEM).
  • GIXRD grazing incidence X-ray diffractometer
  • SEM scanning electron microscope
  • TEM transmission electron microscope
  • the synchronotron radiation of Spring-8 was used for GIXRD.
  • the oxide film is mainly composed of nickel oxide, under the condition without hydrogen.
  • needle-like oxides are formed at 1.0 ppm of DH. In the environment of 2.75 ppm of DH, the oxide film has thin spinel structures.
  • the condition around 1.0 ppm of DH corresponds to the boundary between stable NiO and spinal oxides, and also to the peak range of PWSCC susceptibility. This suggests that the boundary between Nio and spinel oxides may affect the SCC susceptibility.
  • Intergranular corrosion of aluminum alloys occurs because of incorrect heat treatment and sometimes due to a prolonged exposure to sunlight in many environments such as sea water, marine and industrial atmosphere.
  • the intergranular corrosion theory holds that Al—Cu solid solution breaks down with precipitation primarily at grain boundaries during artificial aging of aluminum alloys or under other thermal effects produced during heat treatment in the temperature range between 90° C. and 270° C.
  • the composition of the precipitate is close to intermetallic compound CuAl 2 . This results in a copper-depleted region near the boundaries. Within grains, intermetallic compounds precipitate to a lesser degree, hence the solid solution is less exhausted of copper in regions removed from boundaries.
  • the surface of the aluminum alloy can no longer be considered homogeneous from the electrochemical standpoint.
  • a potential difference between the grain boundaries and a grain may be up to 100 mV, which ultimately causes the electrochemical corrosion.
  • the aluminum alloys may generally be prevented from intergranular corrosion by subjecting to appropriate heat treatment that provides a favorable potential distribution over the surface. Correct heat treatment is to make the alloy more homogeneous and transfer as much copper as possible into a solid solution, which is fixed by a rapid quench process. Duralumin has optimum corrosion resistance when quenched from 480-500° C. in cold water (40° C.) with further natural aging.
  • Corrosion cracking occurs when alloys are simultaneously affected by a corrosive environment and static tensile stresses.
  • the stresses may be both external and internal.
  • Some aluminum alloys are apt to stress corrosion cracking.
  • the susceptibility of alloys to such hazardous corrosion damage depends upon the metal structure, the magnitude and nature of stresses and corrosive environment.
  • the corrosive environments that selectively attack alloys contribute to corrosion cracking.
  • Exfoliation corrosion is a specific type of sub-surface corrosion that develops mainly parallel to the vector of deformation, produced in shaping a semi-finished article, and is attended by crack formation in this direction, exfoliation of individual metal particles or complete failure of samples or components. This corrosion may develop along grain boundaries or deformed boundaries of dendrite cells, as well as transgranularly. Exfoliation corrosion is substantially typical of deformed semi-finished articles. In some exceptional cases, this may be observed in conventional castings with directional liquation, for example, in Al—Mg—Li alloy with high manganese content.
  • Corrosion exfoliation is attributable to a specific structural state, orientation of the second phases and solid solution crystals in a direction of deformation, high content of alloy elements or impurities and the nonuniform distribution thereof, internal stresses, and certain physical-and-chemical state of the surface that depends on the nature of the corrosive environment.
  • the corrosion resistance of aluminum alloys in service is determined by the following criteria: surface finish, internal compressive (favorable) stresses, and specific structure of alloy near the surface, which is produced by certain quenching conditions.
  • surface finish internal compressive (favorable) stresses
  • specific structure of alloy near the surface which is produced by certain quenching conditions.
  • the ultrasonic treatment applied to the surface of aluminum alloys is very likely to combine all the above favorable factors.
  • the alloying of aluminum changes the kinetics of the anodic process.
  • a stationary potential of the alloy with 1% iron content corresponds to the passive region. This determines a fairly low corrosion rate of such an alloy, though this is higher than that of pure aluminum.
  • the corrosion rate of the alloy increases proportionally to the iron content, starting from 0.004%.
  • the alloying of aluminum with copper affects the kinetics of the anodic process (solution of aluminum alloy) to a greater extent than in the case of iron.
  • a slight increase in corrosion rate in a 3% sodium chloride solution is observed as the copper content increases up to 0.01%.
  • the corrosion process intensifies significantly with further increase in copper content.
  • the alloying aluminum with nickel reduces the hydrogen and oxygen over.
  • the acceleration of the cathodic process due to nickel introduction increases stationary potentials of alloys.
  • a standard potential of the alloy containing 0.2% nickel corresponds to the passive region; the corrosion rate in this case is low.
  • the stationary potential corresponds to the overpassivation region; the corrosion rate is naturally increases.
  • the content of an alloying element up to 1% has the largest effect on the kinetics of the electrode processes.
  • the aluminum alloys contain intermetallides of these elements.
  • the electrode potentials of intermetallides are more positive than the stationary potential of aluminum and work as cathodes in aluminum alloys.
  • the stationary potential of the alloy is shifted in the negative direction in neutral and acid environments.
  • the stationary potential of the alloy is virtually unaffected by further increase in zinc content.
  • the addition of 0.16% zinc to aluminum has little effect on the cathodic process rate.
  • the alloying of aluminum with zinc up to 2.05% does not increase, but even decreases somewhat the corrosion rate.
  • Magnesium in amounts up to 5% does not increase aluminum corrosion significantly. In neutral or acid environments, the stationary potential decreases when aluminum is alloyed with magnesium. The same is the case with lithium.
  • the calcium content of 0.08% reduces somewhat the resistance of commercial aluminum in neutral environment; 0.5-1.0% sodium speeds up aluminum corrosion significantly in 0.5-n alkaline solution (n designates the normality of a solution).
  • the calcium impurity is especially hazardous in the presence of silicon.
  • the alloying of aluminum with cadmium suppresses the adverse action of copper.
  • Lead has little effect on the aluminum resistance.
  • the titanium content above 0.01% intensifies corrosion in acid environments. Cerium, cobalt, platinum, silver, thorium and vanadium have an adverse effect.
  • aluminum alloy with 40% silver failed completely after a few days of testing in the atmosphere at 100% relative humidity (RH).
  • RH relative humidity
  • a high corrosion rate is caused by effective operation of Ag 2 Al intermetallides as cathodes.
  • chromium, tin and cadmium have no effect, but sometimes these intensify corrosion.
  • Antimony improves the corrosion resistance of aluminum.
  • a mercury-containing aluminum protector has sufficiently negative potential and is virtually not passivated with time.
  • the alloying affects the dependence of a stationary potential and corrosion resistance upon pH environment. In alkali environments, pure aluminum and most of aluminum alloys are not resistant. Under such conditions, the alloy doped with 0.5% magnesium has the smallest corrosion rate.
  • an oxide film develops at the metal surface. This film contains magnesium hydrate, which is insoluble in alkali. In diluted alkalis, the alloy resistance improves with increase in magnesium content. In concentrated alkalis, magnesium does not improve the aluminum resistance.
  • the alloying with magnesium and manganese enhances the resistance in ammonia. In ammonia-containing coke waters, 99-99.5% aluminum and aluminum alloys with 1.25% manganese or 3% magnesium are resistant to corrosion.
  • silicon intensifies and cadmium suppresses corrosion of aluminum.
  • Zinc and manganese have an unfavorable effect.
  • Magnesium and tin enhance the corrosion resistance.
  • 1% silicon does not impair metal resistance in nitric acid; in heterogeneous alloys, 1% silicon impairs the resistance significantly in 65% nitric acid. Copper in amounts of 1%, even if this is not completely dissolved in aluminum, intensifies corrosion significantly in 25% acid.
  • Impurities and alloying elements have a significant effect upon pitting corrosion in aluminum and its alloys.
  • corrosion is very rarely observed in fresh water.
  • 99.5-99.8% aluminum the depth of corrosion may reach 0.3 mm within a week.
  • a reduction in aluminum purity from 99.99% to 99% increases the cathodic process rate in the oxygen ionization area, as well as the rate of limiting diffusion current and hydrogen ion discharge. This intensifies pitting corrosion.
  • Corrosion pits are usually oriented in the rolling direction which corresponds to the arrangement of intermetallides. Pitting corrosion is also observed in scratch areas where intermetallides appear.
  • Plastic deformation which disrupts the integrity of the impure intergranular substance, improves the resistance of aluminum doped with iron and nickel to intergranular corrosion.
  • a reduction in intergranular internal adsorption or breakdown of solid solution at grain boundaries is attained by using lower heating temperature before quenching and aging.
  • some aluminum alloys for example alloys doped with magnesium or magnesium and zinc, suffer a specific form of attack typically termed corrosion cracking or stress corrosion. This form of attack is usually observed in environments containing chlorides. Corrosion cracking of aluminum alloys may be explained by precipitation of an intermetallic phase Mg 2 Al 3 at grain boundaries. This intermetallide was found by metallographic and electron-microscopic investigations to exist at grain boundaries of magnesium-doped aluminum alloys that suffered corrosion cracking.
  • the corrosion cracking process of magnesium-doped aluminum alloys is as follows.
  • the ⁇ -phase at crystallite boundaries is not passivated in chloride solution and dissolves intensively.
  • the intermetallide may precipitate either during manufacture and treatment of an alloy or under tensile stresses.
  • the dissolution of the ⁇ -phase and formation of submicroscopic cracks result in formation of concentrators and precipitation of new intermetallides.
  • the process propagates intensively deep into the metal.
  • Deaeration of the environment or cathodic polarization shifts the potential in the negative direction and diminishes the dissolution of the ⁇ -phase and hence the corrosion cracking process.
  • the anodic polarization or contact with more precious metals increases the dissolution rate of the ⁇ -phase (that is not passivated in chlorides) and hence intensifies corrosion cracking.
  • the corrosion cracking process is the fastest when the surface of the alloy is etched in acid or alkali. Surface polishing increases the alloy life to failure. With pH increase from 0 to 6, the specimen life to failure increases.
  • Aluminum alloys doped simultaneously with magnesium and copper are less apt to corrosion cracking than magnesium-copper binary alloys.
  • the additional alloying with 0.5-1.5% zinc enhances the corrosion cracking resistance of the alloy containing 7-8% magnesium; the tempering temperature and degree of deformation increase to values when the alloy becomes susceptible to corrosion cracking.
  • alloys may fail due to corrosion fatigue. Chlorides speed up the failure of aluminum alloys because of corrosion fatigue. In 3% solution of sodium chloride, the fatigue limit of 2024 alloy is 3.5 kg/mm 2 at 10 7 .
  • oxidizing agents for example chromates and dichromate
  • chromates may be used to protect aluminum and its alloys against corrosion in neutral, alkali and weak-acid environments. If 0.5-1.0 g/l sodium chromate or potassium chromate is added to water containing at most 50-100 mg/l of salts, the corrosion rate of aluminum and its alloys will decrease greatly. With a greater salt concentration, especially copper, the chromate protective properties are reduced and pitting corrosion may occur.
  • Some other compounds are used as inhibitors to protect aluminum parts of cooling systems.
  • 3% sodium nitrate, 0.03% sodium phosphate and 3% acid phosphate sodium to river water containing 35 mg/l of chlorides at 80° C.
  • the corrosion rate is reduced by 2-3 times;
  • 0.03% sodium nitrate and sodium silicate, 3% sodium benzoate corrosion is reduced by 6-8 times.
  • duralumin The electrochemical protection of duralumin was demonstrated by G. V. Akimov. Visual observations showed that the 4 m long duralumin plate, secured at ends by zinc strips, did not have any corrosion damages after sea water testing.
  • the cathodic polarization with potential ⁇ 0.8 V across chloride-silver electrode protects duralumin in sea water during 6 months.
  • duralumin ship hulls may be corrosion protected by protectors. Magnesium protectors are uniformly located over the ship bottom and fastened on vinyl-plastic pads by steel zinc-coated bolts.
  • a protective oxide film on the surface of aluminum alloys may be developed in treating the metal in water or aqueous solutions at high temperatures.
  • the high resistance of aluminum alloys in sea water may be achieved by cladding with pure aluminum.
  • the clad layer not only isolates the alloy from corrosive environment, but also protects it electrochemically.
  • enameling may be used. Enamels are fairly durable in water, acids, alkalescent detergents, and city air. Bituminous, polymeric and paint coatings, as well as greases are used for corrosion protection of aluminum and its alloys in the atmosphere and soil.
  • the ability of metals to resist corrosion attack of gases at high temperatures is called heat resistance.
  • Another important behavior of metals at high temperatures is high-temperature strength, which defines the ability of the material to retain good mechanical properties under such conditions.
  • the metal may be heat resistant but may not have good high-temperature strength (for example, aluminum alloys at 400-450° C.) At 600-700° C., high-speed tungsten steel is heat resistant but not high-temperature strong.
  • the oxygen molecules that reached the metal are adsorbed, i.e., captured by its surface.
  • the oxygen adsorption in metal is usually represented as follows. The physical adsorption occurs on a clean surface, weakening the bonds between oxygen atoms and molecules. The molecules dissociate and oxygen atoms draw electrons away from the metal atoms.
  • a chemical adsorption stage occurs when the shift of electrons toward oxygen with the formation of O ⁇ 2 ions is equal to the nuclei formation of the metal-oxygen compound (oxide).
  • the product of the oxygen-metal interaction provides the surface with an oxide film which reduces its chemical activity.
  • the films on metals may be classified as thin (invisible) of thickness up to 40 nm, average (visible as temper colors) of thickness 40-500 nm, or thick (visible) of thickness more than 500 nm.
  • thin (invisible) of thickness up to 40 nm average (visible as temper colors) of thickness 40-500 nm, or thick (visible) of thickness more than 500 nm.
  • temper colors visible as temper colors
  • thick (visible) of thickness more than 500 nm for example, in the case of aluminum:
  • the gas corrosion rate is influenced by the external factors such as the composition, pressure and velocity of the gaseous environment, the temperature and heating condition, as well as the internal factors such as the nature, chemical and phase composition of alloys, mechanical stresses and deformations.
  • Oxidative properties of oxide films are substantially dependent upon the nature and composition of alloys. Chromium, aluminum and silicon considerably retard the steel oxidation process, which occurs due to the formation of films with high protective properties. Deformation of metals during heating may cause film discontinuity, increasing thereby the oxidation rate. Preliminary deformation has little effect on oxidation rate only at temperatures below recrystallization temperature.
  • the surface of the actual alloy is always heterogeneous, i.e., has areas that substantially differ in electric potential.
  • the metal surface may differ not only in structural microirregularity (grain boundaries, impurities), but also in submicroirregularity (imperfections of a crystalline structure, foreign atoms in a lattice, etc.). This localizes the anodic and cathodic processes and causes local corrosion to develop (for example, development of pitting)—the theory of work of micro-galvanic elements under electrochemical corrosion.
  • the modern electrochemical corrosion theory termed kinetic theory of electrochemical corrosion, emphasizes that the electrochemical failure of metals may occur when the metal-electrolyte interphase is available.
  • the fact of corrosion does not depend on the electrolyte nature, whether in the case of super-pure water or concentrated water solution.
  • the amount of electrolyte also has little importance: this may be the moisture film several microns thick.
  • the only condition for corrosion to occur is a possible combination on the metallic surface of the anodic reaction of metal ionization and the cathodic reaction of recovery of some or the other ions or molecules. This is the case if the equilibrium potential of the anodic reaction is more negative than that of at least one of the possible cathodic reactions.
  • the (stationary) potential produced in this case will take an intermediate position. This condition should be met regardless of the corrosion type.
  • FIGS. 10 and 11 show the schematic representation of the double electrochemical layer formation. More particularly, FIG. 10 shows a metal atom ion transforming into solution; FIG. 11 shows a cation transforming from the solution to the metal surface.
  • the cations may be discharged from the electrolytic solution (the bonding energy in a lattice is greater than the hydration energy). As a result, the metal surface obtains a positive charge and forms a double electric layer with solution anions.
  • the electrode potential values substantially affect the nature of the corrosion process.
  • the electric current flow during work of a corrosion microelement is caused by the initial potential difference between the cathode and anode.
  • the potential difference decreases.
  • Such a change of potentials as a result of the current flow is termed polarization.
  • electrochemical corrosion may be classified in the following types: with hydrogen polarization (recovery of hydrogen ions on the cathode)—in acids; with oxygen recovery—atmospheric, in water, in salt solutions, etc.; or with recovery of other oxidants.
  • Passivity is a relatively high corrosion resistance state caused by the retardation of the anodic reaction of metal ionization in a certain region of potentials.
  • the passive state generally occurs when metals are in contact with strong oxidants. However, for some metals even water may be rather strong oxidant (e.g., for titanium).
  • the film theory of passivity is still one of basic theories. There is an adsorption theory that holds that the passivity occurs as a result of the oxygen adsorption at the metal surface. It has been found that passivity occurs even when the amount of adsorbed oxygen is such that the surface cannot be even covered with a layer one molecule thick. This is explained by blocking the active surface areas, which are limited.
  • the adsorption theory presents the adsorption of solution anions on movable dislocations and other structural imperfections. This reduces the surface energy and facilitates the breakdown of atomic bonding of metals.
  • the crack nucleation may occur as a result of a wedging action of surface-active substances in adsorption thereof in microcrevices on the metal surface (Rebinder effect).
  • the electrochemical theory holds that the main factor of crack development is the accelerated anodic dissolution of a metal at the crack base.
  • the primary stress concentrator that cannot relax easily in high-strength material
  • the cathode of such a pair is the crack side surface and partially the external surface of a specimen, the anode is a crack tip.
  • a significantly localized dissolution process maintains the crack sharpness at atomic level and hence the maximum stress concentration at the crack tip.
  • Atomic dissolution at the crack tip is supposedly a notch of a gain or structural block, which occurs with relatively low linear velocity.
  • this notch is realized by the subsequent brittle breakdown of a block or grain with very high linear velocity, but with possible delay in movement on the next block or grain, and then again with a slower electrochemical notch thereof, etc.
  • the crack development will occur fairly uniformly until alternation of electrochemical notches and mechanical breakdowns is so frequent that this will go into the avalanche brittle fracture of the remaining section of a specimen.
  • the crack grows with continuous activation of the anodic process by mechanically increasing tension of the lattice in the crack tip zone. This activation is especially high if the initial state of the metal corresponds to the passive state and superposition of tensile forces results in local activation at the crack tip.
  • macromechanical failures increase in avalanche fashion and the fracture occurs under conditions when a mechanical factor prevails.
  • Corrosion cracking of metals in many environments has long been known in practice, for example, so-called seasonal cracking of brass products such as condenser tubing, brass boxes, rifle shells; and corrosion cracking of steel products such as propellers, rods, diesel engines, turbine blades, etc.
  • Low-carbon steels containing nitrogen are very susceptible to corrosion cracking.
  • the effect of nitrogen on corrosion cracking of high-strength steels is obviously associated with the change in internal stresses.
  • Nitrogen forms interstitial solid solutions with alpha-iron and gamma-iron.
  • the introduction of titanium in steel promotes nitrogen bonding in strong nitrides and prevents the formation of the interstitial solid solution, reducing internal stresses and improving high-strength steel resistance to corrosion cracking.
  • the submicrocrack development period The dislocation density is saturated and the dislocation structure is transformed: many grains have, mainly near the surface, very elongated cells whose walls are comparable with the grain size. Such a structure was termed a band structure.
  • the whole surface of a specimen is covered by a thick network of submicrocracks, which however do not go beyond the grain boundaries. The damage so far accumulated cannot be regarded as irreversible yet, since this does not dramatically reduce the resistance to brittle fracture, ductility, etc.
  • the fatigue limit is favorably influenced by such structural changes that simultaneously increase the strength and ductility of the material (grain refinement or formation of a developed substructure), metal pureness along non-metallic inclusions (internal concentrators).
  • the surface layers condition is of special importance.
  • the most effective are the treatments that harden the surface and at the same time induce residual compressive stresses in the surface layers.
  • the fatigue crack nucleation and propagation resistance is improved simultaneously. Hardening impedes the slip development and compressive stresses prevent surface crack opening, reducing the effect of the tensile component.
  • Corrosion - fatigue Strength of Steel by A. V. Ryabchenkov (Moscow, Mashinostroeniye, 1953), which discloses that the process of corrosion fatigue of a metal may be described as follows. First, the lattice elastic distortions accumulate at some portions of the metal surface due to dislocation density increase. Then submicroscopic cracks appear in the metal volumes, where a critical dislocation density is attained during mass slipping of separate blocks. Finally, microcracks grow into macrocracks. As this takes place, a brittle fracture occurs along one microcrack that develops most intensively.
  • Adsorption of surface-active substances, causing wedging along a microcrevice, may accelerate the environmental attack. If hydrogen is formed in the corrosion process, it may be easily diffused into the metal. The metal embrittlement in the pre-fracture zone (deep in a crack) also accelerates the failure. In plastic deformation, the hydrogen diffusion into the metal along slip planes zones may accelerate. The metal embrittlement under hydrogen attack is explained by dislocation blocking by atomic hydrogen interstitial in the metal lattice.
  • the corrosion fatigue in electrolytes is a mechano-electrochemical process.
  • the electrochemical protection such as a zinc protector and anodic metallic coatings (zinc, cadmium) is feasible.
  • Cathodic metallic coatings (lead, copper) are quite effective only if these are continuous.
  • the metal surface processing is also effective that results in compressive stresses in the surface layer.
  • Hydrogen Embrittlement of Metals by B. A. Kolachev (Moscow, Metallurgia, 1985), which discloses that the change in mechanical properties as a result of hydrogen pickup is termed hydrogen embrittlement. Hydrogen pickup is especially detrimental to the properties of high-strength steels. During 2 hours of etching of high-performance steel 40 CrSiNi with strength of about 2000 MPa in 15% hydrochloric acid, the reduction of area is decreased from 47 to 0.63% and elongation from 10.1 to 1.65.
  • the long-term strength of the hydrogenated steel is reduced.
  • the hydrogenated steel may be subjected to delayed brittle fracture under stress of only 300 MPa. Delayed brittle fracture means the fracture of details or specimens awhile after applying static tensile stresses without further increase thereof. This is especially dangerous, since the fracture may begin without visible plastic deformation under stresses far below the tensile strength.
  • a delayed brittle fracture which was termed hydrogen cracking, may also take place. This is associated with increased embrittlement of steel due to the atomic hydrogen adsorption at its surface (Rebinder effect) or an increased hydrogen concentration in the region of maximum triaxial tensile stresses.
  • the time to cracking in hydrogen pickup depends on the level of applied tensile stresses: the greater the stresses, the shorter the time to cracking.
  • the cracks forming during hydrogen cracking of high-strength steels are of a brittle nature and propagate along the boundaries of former austenite and their direction is almost perpendicular to tensile stresses.
  • hydrogen may be present: in lattice interstices, forming an interstitial solid solution; in pores, cracks and other irregularities in the form of molecules; in the form of chemical compounds with impurities; and/or in the form of chemical compounds with solvent metal—hydrides.
  • the sources of hydrogen penetration in metals include original charge materials, environment where technical operations are carried out at all stages of metal obtaining and processing (melting, hot plastic deformation, welding, heat treatment); electrochemical processes such as metal deposition on the cathode, acid etching, etc.
  • Molten metals absorb hydrogen very intensively. At elevated temperatures, hydrogen is absorbed by many metals even in solid state (e.g., titanium).
  • the reduction in ductility may vary in a wide range: from percentages to almost complete loss of ductility. There is no unified hydrogen embrittlement mechanism.
  • the steel susceptibility to hydrogen embrittlement depends on many factors such as the strength level and then the condition, composition and structure of steel, as well as properties of individual heats.
  • the hydrogen-induced change in properties is generally eliminated by hydrogen desorption from steel during maturing or annealing.
  • high-strength steels as small as 5 cm 3 /100 g content of hydrogen results in irreversible changes that remain upon removal of hydrogen.
  • the hydrogen embrittlement manifests itself as follows:
  • Hydrogen corrosion develops in carbon steels under long exposure to high-pressure hydrogen environment at high temperature. This is based on the interaction between hydrogen and carbon with methane formation. This reaction begins from the surface, resulting in decarburization and formation of cracks that gradually propagate into the metal, reducing the strength and ductility.
  • Hydrogen disease occurs as a result of the interaction between hydrogen diffused from the metal surface and oxygen or oxides dissolved in the metal.
  • the resultant water vapors create microscopic discontinuities.
  • plastic deformation occurs in metals at high temperature during creep: (1) sliding and slip (dislocation pattern), (2) twinning, (3) flexure mechanism, (4) lamellation, (5) rotation and relative movement of grains, (6) rotation and relative displacement of mosaic blocks, (7) cell formation mechanism, (8) diffusion plasticity, and/or (9) recrystallization mechanism.
  • Erosive wear consists in detachment of solid particles from the body surface as a result of the body contact with a moving liquid or gaseous environment or particles entrained thereby or as a result of the impact of solid particles.
  • the following types of erosion wear may be specified:
  • the plastic deformation processes are localized in a certain portion of the volume, where structural defects accumulate, the stress concentration occur and the fracture source nucleates.
  • the plastic deformation processes differ, preserving their dislocation nature, first of all by complex stress distribution over the entire contact zone. Throughout the surface layer and in any point thereof, the participation of all portions of metal in the contact zone in plastic deformation and fracture is equiprobable, resulting in stress deconcentration.
  • Another feature is that during wear, the plastic deformation and fracture cycles continuously overlap when the next cycles occur following the entrainment of the wear debris.
  • the constitution and structure of a thin surface layer may substantially differ from the structure of a metal in volume.
  • Wear and tear is the process of the gradual change in body dimensions during friction, consisting of detachment of the material from the friction surface and/or residual deformation thereof.
  • a sharp increase in the corrosion rate can occur under radiation.
  • the atmospheric corrosion rate of iron, copper, zinc, nickel and lead may increase by 10-100 times.
  • Catastrophic corrosion which is accompanied by cracking, develops in uranium alloys.
  • radioactive emission has considerable effect on the kinetics of corrosion processes without a fundamental change in corrosion mechanism.
  • the radiolysis effect is caused by irradiation on water and accelerates the cathodic process. This is observed in metals whose surface has no thick oxide films.
  • the destructive effect consists in elastic and thermal interaction between the surface and radiating particles, resulting in defects in the metal surface layer and oxide film. This effect is hazardous for the metals whose corrosion resistance is governed by the formation of phase protective films (for example, for aluminum alloys). Also, this facilitates the anodic process and has the most profound effect on the corrosion rate.
  • Corrosion cracking and corrosion fatigue develop according to mechano-electrochemical mechanisms: crack development—electrochemical process, complete fracture—avalanche mechanical failure of the remaining section; in so doing the processes are accompanied by hydrogen embrittlement of the material at the crack tip.
  • the difference is in load application: tensile loads during corrosion cracking and cyclic loads in the case of fatigue.
  • the type of cracks on microsections and the type of rupture are different.
  • Hydrogen embrittlement of a metal has many forms of manifestation—the effect of the porosity and hydrides on the impact strength prior to cracking at the expense of methane being formed or corrosion cracking and flakes (clouds of small cracks in forgings).
  • Hydrogen may have an unfavorable effect on the creep process as well, causing premature failure of structures operating under constant loading at elevated temperatures.
  • the failure process is caused in most cases by crack formation due to vacancy diffusion and the growth of porosity into microcracks.
  • degradation of the material or structures provides the process of the irreversible change in properties thereof, resulting in cessation of functioning of a component or structure and safety violation of their further service.
  • All multiple types of damage, occurring due to material degradation and resulting from various process mechanisms, are divided into the following groups: local and extensive corrosive damages, single and multiple cracks, microcracks, pores at grain boundaries and substructures, mechanical wear and change in surface relief, creation of residual stresses, and change in mechanical and physical properties.
  • the operational factors which lead to degradation and have separate or combined effect, may be divided as follows: contact interaction with the external environment, static stresses, low- and high-cycle stresses, interaction with active external environment in non-electrolytes or electrolytes, constantly high (or low) or cyclically changing temperature, and exposure to radiation.
  • Degradation mechanisms causing the above types of damage are grouped as follows: corrosion cracking, hydrogen embrittlement, corrosion fatigue, mechanical fatigue, chemical corrosion, electrochemical corrosion, erosion, creep, and radiation embrittlement.
  • a systematic strategy for designing a hipping rejuvenation cycle for Ni-base superalloys is disclosed. Once a rejuvenation cycle is designed, the mathematical relationships can then be used to analyze the extent of the rejuvenation of microstructure and creep properties in reheat-treated or hot isostatically pressed-service exposed turbine blades. The influence of trace amounts of Zr on creep properties of service exposed IN738LC turbine blades is also disclosed.
  • variable loading conditions Under variable loading conditions, the technical examination of welded structures in low and average strength steels-should constitute the process of registering the accumulated damage (defect, foreign inclusion, discontinuity) in the metal volume being examined with simultaneous obtaining of the failure resistance parameters.
  • a plastic hysteresis loop in stress-deformation coordinates and cyclic creep are registered in the material.
  • the availability of damage stimulates plastic deformation in local volumes of metal and increases the closed plastic hysteresis loop parameters.
  • the area of the loop is equal to the energy dissipated in the material, while its width equals non-elastic deformation per cycle.
  • the development of local plastic deformation gives rise to new discontinuities and hence the damage density within unit volume of metal increases.
  • D ⁇ two levels may be arbitrarily noted: hereditary density of damage D 1 n stemming from the metal quality and acquired density of damage D 2 Z which is the function of the hereditary damage occurred during metal reshaping in manufacturing a structure and its operating conditions. It is natural that the first level of damage will control the intensity of the second level increment.
  • the actual materials feature the combination of typical linear scales linked with different levels of their structure, micro- and macrotexture.
  • the need to take account of the material structure in describing the deformation and fracture processes is essential in the fracture mechanics.
  • the defects of 7-10 categories i.e., 10 ⁇ 5 -10 ⁇ 4 m long, which are comparable with sizes of structural components.
  • the structural material volume being diagnosed shall be sufficient to reflect how the reshaping and manufacturing technique, service conditions, which cause the main crack formation, affect the material.
  • the main crack is meant one of existing microcracks, which under given conditions develops at a greater rate compared to the remaining cracks and causes the controlled failure of the structure.
  • the structural element i.e., the grain may present the necessary and sufficient volume of metal, while microhardness measurement on the surface of the object being diagnosed may be an instrument recording the changes in physical-and-mechanical properties of structural elements subjected to reshaping technology and loading conditions.
  • the microhardness measuring results will objectively reflect the mechanical properties, the stressed-deformed state and the presence of damage (microcracks) in a structural element.
  • the combination of the microhardness data, i.e., the completeness of the sufficiently large data selection will make it possible to characterize the condition of the metal volume being diagnosed.
  • the load on the indenter is chosen from the range, wherein the Kirpichev-Kick-Davidenko's impression similarity condition is not available for steels of this structural category.
  • each microhardness measuring result obtained from the unit surface is processed in accordance with the method of one of three variations:
  • the indenter gets into the structural element that does not have microcracks along the contour; the adjoining structural elements of the first row are also not damaged. In this case, the basic microhardness value of the element is observed.
  • the indenter gets into the structural element that has microcracks at boundaries.
  • the microcracks have time to develop as the indenter movement speed is substantially lower than the microcrack development rate in a given volume under additional deformation from the indenter.
  • the volume continuousness is broken and the microhardness drops abruptly.
  • the completeness of the microhardness data selection may indicate the degree of reduction in load-carrying capacity of the material, i.e., record the onset of necessary and sufficient conditions for main crack formation in the metal volume under examination under current loading conditions. If the completeness of the microhardness measurement data selection is presented in the form of bar charts where data are distributed along the microhardness scale, then the bar charts for the current instant of service will be shifted relative to those for initial condition of the material.
  • K p ⁇ a i f j
  • N ⁇ n j —the total number of grains; n j —the number of the results in a given interval of microhardness data.
  • the design method for weighting coefficients, a j is based on the linear approximation of the distribution diagram from 0.1 to 1.0.
  • the weighting coefficients should be calculated preserving the numeration of intervals for initial condition bar chart.
  • the reduced frequency of the microhardness measurement bar chart of the in-service metal, K p increases on a constant basis, while the damage accumulation coefficient, k p , is always greater than 1 and also increases.
  • the controlled rolled steel pipes from Urengoi gas-condensate field were selected for study.
  • the mechanical properties of emergency stock pipes were compared to those of pipes after 20 years of service.
  • the metal of the pipes was close in chemical composition and mechanical properties to the steel of strength grade Cr65.
  • the metallographic analysis of specimens cut from portions of pipe after 20 years of service showed that the metal has no cracks detectable by non-destructive examination methods.
  • microhardness may be measured on the surface of the object being diagnosed in the area of the structural-processing and service stress concentrators in order to evaluate the metal degradation degree and establish the correlation relationships between the completeness of the microhardness data selection and the resistance properties of the macro-failure nucleation and development in a structure.
  • Zinc concentration is decreased to the permissible limit that does not increase the radiation buildup of activated Zn-64, i.e., less than 1 ppb according to the analysis of reactor water at Onagawa-1, and a synergistic effect of mixed metal elements to reduce corrosion and radiation buildup on stainless steel surfaces is expected.
  • high temperature autoclave testing was performed to investigate the effects of mixed metal addition on the oxide film characteristics and the corrosion of stainless steel in the simulated BWR environments. The results suggest that the mixed metal addition could be an alternative technique to zinc single injection.
  • Ultrafine-grained (UFG) materials have attracted significant scientific interest. These materials are structurally characterized by very fine grain size (nano- and submicron-order) and large amount of grain boundary area (and volume). UFG materials have unusual and extraordinary mechanical and physical properties that are fundamentally different from, and often far superior to those of their conventional coarse-grained polycrystalline counterparts. Severe plastic deformation (SPD) is an effective processing method for the fabrication of various UFG structures by imposing intense plastic strains into metals and alloys. The production of UFG materials by SPD offers two significant advantages over other techniques such as inert gas condensation, high-energy ball milling, and sliding wear. First, it is possible to produce large bulk samples. Second, these samples are free from any residual porosity and contamination.
  • SPD Severe plastic deformation
  • the resultant microstructures introduced by SPD are substantially grain refined along with high internal stresses and high-energy nonequilibrium boundaries.
  • Several techniques are now available for producing the requisite high plastic strain of the order of several hundreds of percent, including equal-channel angular pressing (ECAP), high pressure torsion (HPT), multipass-coinforge, multi-axis deformation, and repetitive corrugation and strengthening (RCS).
  • ECAP equal-channel angular pressing
  • HPT high pressure torsion
  • RCS repetitive corrugation and strengthening
  • the understanding of the microstructural evolution mechanism involved in SPD is an essential issue of the research topic having great importance from academic and technological points of view.
  • the mechanism should account not only for the grain refinement but also for the generation of high-angle boundaries with increasing strain.
  • Previous investigations have demonstrated that during repetitive deformation, the grain size refinement is most pronounced at the initial stage of the process, for example low and medium strain, and remain virtually unchanged upon further straining. However, at large strains, boundary misorientations dominate. Exposure of deforming surfaces to random and multidirectional deformation could effectively enhance evolution of low-angle boundary misorientations into high-angle ones.
  • Recent studies reported the grain refinement associated with the slip systems and their interactions. Ultrafine dislocation cells enclosed by planes are produced by operation of multi-slip systems during ECAP.
  • the principle of the USSP technique was as follows. A high-energy ultrasonic generator of high frequency (20 kHz) vibrated the reflecting chamber where the stainless steel shots of 7.5 mm diameter resonated. The shots then performed repetitive, high-speed, and multi-directional impact onto the surface of materials. Resultantly, severe strains were imparted into the surface by contact loading. A strain gradient changing from zero far into the matrix to the maximum at the top surface will simultaneously be established. Details of the equipment were reported in previous articles. In the present investigation, the USSP processing was conducted under vacuum at room temperature for 15 minutes.
  • Dislocation gliding, accumulation, interaction, tangling, and spatial rearrangement cause grain subdivision in order to accommodate plastic strains during deformation in polycrystalline materials.
  • the repetitive USSP could impart high strains of high strain rates into the surface layer. Severe plastic straining could produce a high density of dislocations, which are effective at blocking slip at increasing strains and as a result, the mechanism responsible for accommodating large amounts of plastic straining is to subdivide original grains into subgrains with dislocations forming their boundaries. The subdivision of grains takes place on a macroscopic scale with the formation of MBs at low strains. With further straining, subgrains may further break up into smaller CBs. The submicro- and nano-sized subgrains could be produced under much larger strains.
  • the multi-directional peening may lead to the change of slip systems with the strain path even inside the same subgrain, much different from the deformation mode caused by other SPD processes.
  • the dislocations not only interact with other dislocations in the current active slip systems, but also interact with inactive dislocations generated in previous deformation. This will promote the formation of subgrains. As a consequence, the effectiveness of grain refinement is enhanced.
  • the development of equiaxed, highly misoriented grains consists of two steps, i.e., the formation of subgrains through grain subdivision and the subsequent evolution of boundary misorientations.
  • the subgrains resulted from the grain subdivision have a critical size before leveling off, relevant to a certain value of straining.
  • the grain subdivision does not continue indefinitely, and eventually, after a given amount of deformation, the continued straining can no longer reduce the subgrain size.
  • slip systems within adjacent subgrains will be activated in response to applied straining in order to rotate those subgrains into a more energetically favorable orientation.
  • Shot peening provides the multi-directional strain path and high strain rate, which are especially effective at promoting subgrain rotation.
  • the mechanism for the development of high misorientations should be the subgrain rotation. Therefore, the accumulated rotation of subgrains appears to be the primary mechanism as a means of accommodating further deformation, resulting in highly misoriented, equiaxed grains.
  • Deformation of subgrains is controlled by the activation of slip systems, where the critical resolved shear stress has been achieved.
  • slip systems where the critical resolved shear stress has been achieved.
  • different slip system combinations would be activated in each individual subgrain.
  • Adjacent misoriented subgrains will have different activated slip systems because of their different orientations.
  • Certain slip systems will be selectively activated to minimize the internal energy in the subgrain.
  • the adjacent misoriented subgrains will rotate into coincidence to minimize the energy across the sub-boundaries under the driving force of the selectively activated slip systems.
  • With increasing strain subgrains can no longer accommodate deformation by dislocation glide along the same slip systems and, therefore, begin to rotate independently. The rotation angles increase, eventually becoming highly misoriented grains.
  • USSP produces a high strain rate, which plays a significant role in lattice rotation during deformation.
  • the high strain rate results in significantly higher flow stresses for an equivalent increment in strain relative to low strain rates.
  • Computer simulation revealed that the higher strain rates promote lattice rotation in simple shear to a greater extent than lower strain rates due to the reduced plastic spin component and the great number of activated slip systems. It is observed that the average misorientation angle between the subgrains increased for the same strain, with an increase in strain rate from 6 ⁇ 10 ⁇ 6 to 6 ⁇ 10 1 s ⁇ 1 during tension of pure aluminum.
  • USSP provides a simple and effective procedure for producing a UFG structure on the surface layer of aluminum alloy 7075.
  • the development of microstructures during the USSP process is characterized by the sequence of elongated microbands (MBs) with dislocation cells (DCs), equiaxed submicro- and nano-grains, respectively, with increasing straining.
  • the grain refinement and microstructural evolution during the process of USSP is as follows. During plastic straining, the formation of subgrains through grain subdivision occurs in order to accommodate the strain. The highly misoriented boundaries are generated by the subgrain rotation for accommodating further deformation.
  • CSP controlled shot peening
  • LSP laser shock peening
  • the beneficial effect of the compressive residual stress can be compromised by the development of subsurface cracking, usually in the regions where tensile residual stress balances the compressive residual stress field.
  • Subsurface cracking may even be detrimental in smooth fatigue specimens or in components where, surface initiation is not considered to be the critical nucleation site. Roughening of the surface is the major detrimental effect of CSP. Surface roughness, owing to the local intensification of the far-field stress, can account for the premature initiation and propagation of short fatigue cracks.
  • Controlled shot peening was performed using a Tealgate peening machine.
  • the peening intensity was 4 A and it was achieved using a S110 (diameter 0.279 mm and hardness 410.5-548.5 Hv) spherical cast steel shot, incidence angle of 45° and a coverage rate of 200%. These conditions were recommended in a study of maximum, near surface, residual stress profile to counterbalance the increased surface roughness profile.
  • Laser shock peening was performed in water confinement using a Continuum YAG Laser (Powerlite plus) operating in the green wavelength (0.532 ⁇ m) regime.
  • the output energy was approximately 1.3 J with pulse duration in the 6-7 ns regime.
  • All specimens were protected from the thermal effects of LSP by a 70 ⁇ m aluminum coating.
  • the laser intensity was set to 10 GW/cm 2 (estimated pressure of 5 GPa) with a focal point of 2 mm.
  • the analysis suggests a counterbalance residual stress between 90-125 MPa within the first 50 ⁇ m of depth for applied stress levels between 220-300 MPa.
  • the above indicates that the remaining part of the residual stress profile should give some fatigue life increase.
  • FIGS. 13-18 show the crack nucleation site and early crack growth of all six test groups at a maximum stress of 300 MPa.
  • FIG. 13 shows surface crack initiation and crack growth of pristine material with mirror finish.
  • the fractograph clearly indicates the faceted growth (shear mode growth).
  • FIG. 14 shows surface crack initiation and crack growth of pristine material with EDM finish. The near surface region shows evidence of multiple crack nuclei, possibly caused by the irregular surface.
  • FIG. 15 shows the site of corner crack initiation and crack growth morphology of a S110-200%-45° CSP specimen. The faceted area extends to a depth of approximately 150 ⁇ m. The faceted area is surrounded by cleavage like fatigue fracture.
  • FIG. 16 shows crack initiation and crack growth of LSP 10 GW/cm 2 (2 passes). The fractograph indicates surface crack initiation and crack branching at 50 ⁇ m.
  • FIG. 17 shows crack initiation and early crack growth of LSP 10 GW/cm 2 (3 passes)
  • the fractograph indicates surface crack initiation and crack branching at 90 ⁇ m.
  • the propagation path of Crack A is almost parallel to the direction of stress.
  • FIG. 18 shows crack initiation and early crack growth of dual treatment. The fractograph indicates surface crack initiation from a typical shot peening dent. Crack branching is also evident.
  • the lack of surface stress concentration features in the specimen with the mirror like finish leads to a single crack nucleus (possible at an inclusion) and to a surface crack of an almost semi-circular shape (see FIG. 13 ).
  • the rough surface of the EDM finish promotes multiple crack nucleation sites which join at an early stage and the crack adopts an elongated semi-elliptical shape (see FIG. 14 ).
  • the fracture surface of the 4 A CSP shows limited faceted crack growth and extensive evidence of cleavage like fatigue growth which can not be explained by the faster growing corner crack. The above reinforces the initial assumption of ductility loss. Ductility loss can be attributed to a very high and irregular dislocation density in the near surface region caused by work hardening.
  • the fracture surfaces indicate branching of the crack.
  • a part of the crack was observed to propagate almost parallel to the direction of the stress indicating slow crack growth rate.
  • Close examination of the crack paths and the corresponding residual stress profiles indicates the tendency of the “parallel” crack to propagate along the minimum in the residual stress profile.
  • the “perpendicular” crack shows an extensive amount of faceted growth, especially in the case of 2 passes.
  • the dual treatment shows evidence of fracture more similar to LSP (crack branching). In contrast to CSP, the dual treatment shows no evidence of cleavage like fracture.
  • both the CSP and the dual treatment provided strain hardening of the near surface layer and also that only the CSP showed evidence of ductility loss
  • the residual stresses, created by the LSP compensated for the possible ductility loss by possible rearrangement of the near surface dislocations.
  • residual stress relaxation is time and stress level dependent.
  • a better understanding could be obtained by relating the residual stress relaxation pattern to crack length.
  • Pre-stressing the material can increase the magnitude of the residual stress profile while at the same time stabilizes the residual stresses.
  • crystals For crystals, the following crystal systems are established depending on the slope of the coordinate axis and relative length of parameters: cubic, tetragonal, rhombic, monoclinic, etc.
  • Aluminum for example, has face-centered cubic lattice (the metals with this type of lattice are generally well susceptible to plastic deformation), iron has face-centered cubic lattice and body-centered cubic lattice.
  • the cubic lattice is characterized by that all the angles between axes are 90°, all parameters being the same.
  • the typical figure of the polyhedron is cube.
  • cubic lattice examples include space-centered (or body-centered) lattice, which differs from a simple cubic lattice by that in addition to atoms at corners of a cube, it has one atom in the center of the cube, as shown in FIGS. 19 and 20 , and face-centered lattice, which has atoms located at each of the corners and the centers of all the cubic faces, i.e., presents the cube with centered faces, as shown in FIGS. 21 and 22 .
  • FIGS. 19 and 20 show body-centered lattice in lattice form and in cell form, respectively.
  • FIGS. 21 and 22 show face-centered lattice in lattice form and in cell form, respectively.
  • each metal-element is a crystalline body or crystal.
  • the geometric regularity of the particles arrangement in crystalline bodies imparts some characteristics thereto that distinguish them from non-crystalline or amorphous bodies.
  • anisotropy or vectoriality implies the difference of properties according to the direction.
  • Another characteristic of crystalline bodies is the existence of slip planes or cleavage, along which the particles slip or detach under mechanical action upon the crystal. This breaks the crystal (if brittle) or deforms it, i.e., changes the exterior form non-destructively.
  • the fracture of metal piece has clear planes, along which the crystals break more easily.
  • planes are termed cleavage planes, as shown in FIGS. 23-25 .
  • Crystallization from liquid always begins when this is overcooled and crystallization centers are available. This results in crystalline formations of different types. In some exceptional cases, a geometrically regular full-weight or full-face crystal may form. However, this requires certain favorable conditions. Typically, the crystals are formed of irregular exterior shape and therefore termed crystallites.
  • crystals There are two types of crystals.
  • the exterior shape which approximates more or less to the geometric regularity of the polyhedron, takes a rounded shape.
  • Such crystals are termed grains or granules.
  • crystalline formations have a branching shape with unfilled spaces and are termed dendrites, which generally present the initial phase of a crystal being formed.
  • Any metal is a polycrystal comprising many grains.
  • the neighboring grains have differently oriented lattices.
  • the grain boundaries are called high-angle boundaries, since the crystallographic directions in neighboring grains form angles of up to tens of degrees.
  • Each grain consists of individual subgrains that form a so-called substructure.
  • Substructures are off-oriented relative to each other at angles ranging from fractions to units of degrees—low-angle boundaries.
  • Subgrains are measured 0.1-1 microns, which is one-three orders less than grain sizes.
  • the boundaries between individual crystals (grains) are generally a transition region of width up to 2-3 interatomic distances. Atoms in such a region are arranged differently than in grain volume.
  • impurities tend to concentrate at grain boundaries of technical metals and this further disturbs a regular atomic arrangement. Somewhat lesser disturbances are observed at subgrain boundaries.
  • the dislocation density in metal increases with increase in a subgrain off-orientation angle and decrease in subgrain size.
  • the grain size affects the metal properties substantially. Large grains are mainly accompanied by lower mechanical quality of metal. Also, the other properties may change which may be explained by more or less extension of boundaries between grain-crystals. On the whole, the effect of grain boundaries on metal properties is manifested first of all by that these boundaries are surfaces that divide grains, wherein the particles (atoms) of the metal itself are different in energy terms from the atoms located in the lattice inside the grain. The particles between grains are believed to have higher energy representing the surface energy that plays an important role in phenomena occurring in various bodies, including metals and their alloys. Thus, the interlayer between grains in the form of randomly arranged atoms, which is sometimes considered as an amorphous metal film, may affect the properties of the entire piece of metal as a whole.
  • the metals used in practice always have impurities that may also be located in spaces between grains in the form of films or inclusions and influence the metal properties. For example, if such films are weak (brittle), the bond between grains will be weakened and the metal will break under mechanical action at grain boundaries. In this case, intercrystalline fracture of metal will be observed. If fracture occurs inside grains, then intracrystalline fracture will happen.
  • a fine grain may be obtained from a coarse grain thermally (by only heating and cooling in a solid state) only in metals that experience allotropic changes. Such changes constitute a transition from one lattice to another, i.e., atomic rearrangement from one location to another.
  • Each type of lattice is an allotropic alteration or modification of the metal, which is often called a phase, while metals, existing in several modifications, are termed polymorphous metals.
  • Each modification has its own region of temperatures, at which this is stable and hence at certain temperatures there should be a transition from one modification to another. In this manner the crystallization process occurs, which is termed secondary crystallization, in contrast to primary crystallization which occurs during solidification of a liquid.
  • Polymorphous metals include iron.
  • iron there are several allotropic changes between a solidification point (1540° C.) and a usual temperature. Of most practical value is a change at 910° C. that is responsible for transition of a y modification into an ⁇ modification during cooling (and vice versa during heating).
  • the essence of this change is that the atoms of the ⁇ -iron lattice, which constitutes a cube with centered faces, rearrange into a centered cubic lattice which is typical for ⁇ -iron.
  • This change of internal structure is accompanied by the change in external shape of grain-crystals, i.e., recrystallization takes place. In recrystallization, the grain size decreases significantly. The new crystals are closely adjacent to each other, increasing the metal strength.
  • FIGS. 26-27 An example of such a microstructural change of the coarse-grain cast iron into the fine-grain, heat treated or annealed iron is shown in FIGS. 26-27 . More particularly, FIG. 26 shows a microstructure of cast (x20) iron and FIG. 27 shows a microstructure annealed (x100) iron.
  • grains may not be refined in the manner described above (heat treatment only).
  • the only method is the preliminary mechanical shaping that induces a so-called plastic deformation of a metal. Thereafter, grains of various sizes may be obtained by heating.
  • This method may be applied only to ductile metals, i.e., those capable of withstanding mechanical effect and changing their external shape (deformation) without failure.
  • the metal may be mechanically shaped by various methods including rolling, drawing, forging, pressure forming, etc. Each case has some characteristic metal behavior depending on the method applied; however in all cases main process occurs, which is plastic deformation of the metal that consists of changing the exterior shape of the metal without the loss in integrity and strength.
  • Metal deformation is accompanied by an increase in its strength with reduction of ductility (i.e., the ability for further deformation).
  • the metal hardness improves simultaneously with increased strength.
  • the metal becomes “rigid.”
  • Such a state of the metal, obtained as a result of deformation, is usually termed cold work.
  • the cold work state is induced chiefly by displacements or slips of lattice particles that take place during mechanical effect upon grain crystals in a metal.
  • FIGS. 28-30 Similar slips in tension of single-crystal round specimen are schematically shown in FIGS. 28-30 , i.e., slips in single crystal zinc. Tension of the specimen lies in multiple slips of thin metal layers (termed packs or blocks) relative to each other. More particularly, FIG. 28 shows the single crystal-of zinc in the form of a hexagonal prism (the base (cross section)). This plane is an easiest slip plane and FIGS. 29 and 30 show the blocks of particles in the crystal-specimen slipped along this direction.
  • thin metal layers gradually change their direction relative to the tension force, tending to take, by their planes, the location which is less convenient for slipping, i.e., with the greatest resistance to slipping.
  • the stress required for further deformation increases.
  • an increased stress in metal during slipping may be caused by some other factors associated with irregular location of particles near slip sites (lattice distortion, plane warp, formation of the finest fragments, voids, etc.).
  • the resistance to slip along easiest slip planes reaches the value, wherein slips stop and begin along different directions or secondary slip planes that were less convenient and favorable directions for slipping. Slipping along these secondary directions does not reach such a great extent as in the case of primary slips and occurs with substantially increasing stresses until the latter causes a separation of sliding layers from each other, which may result in specimen failure.
  • each grain elongates (or flattens in compression) and consists of multiple slip blocks, oriented predominantly in one direction and presenting “fragments” of the former integral grain.
  • FIG. 31 shows the microstructure of deformed iron (x100) and FIG. 32 shows the microstructure of non-deformed iron (x300).
  • x100 the microstructure of deformed iron
  • FIG. 32 shows the microstructure of non-deformed iron (x300).
  • fibrous a structure of the deformed metal is called fibrous.
  • fibers in this structure are the same initial metal grains, only with changed configuration due to slipping and lattice distortion. There is still no grain refinement as such.
  • the structure has no distinctive individual fine grains and only elongated boundaries of former (initial) grains are visible.
  • the structure may be little different from the initial one, since grain elongation is small and grain boundaries are not broken.
  • a structural indication of ongoing plastic deformation is slip lines occurring on the deformed metallographic section of the metal in the form of parallel or intersecting lines that spread throughout the grain section.
  • An example of slip lines on non-etched metallographic section of iron (x300) is shown in FIG. 33 .
  • recrystallization the temperature at which new finest grains with non-distorted lattice start to occur is called a recrystallization threshold or recrystallization temperature.
  • recrystallization threshold the temperature at which new finest grains with non-distorted lattice start to occur.
  • this temperature varies and may be approximately determined in relation to the metal melting temperature.
  • Absolute recrystallization temperature has been shown to be about 0.4 of the absolute melting temperature.
  • a recrystallization diagram which is plotted in space, may represent the relationship between grain size and the two factors such as the heating temperature and the extent of prior deformation.
  • mechanical treatment deformation
  • heating recrystallization
  • recrystallization diagrams can help to consider the main factors accurately and obtain grains of desired size and hence various metal properties.
  • the metal may be plastically deformed by various methods such as ball and roller burnishing, shot peening, laser strengthening, and high-intensity ultrasound. Some of these methods are characterized below. Also, effects are discussed that accompany the influence of plastic deformation upon the structure of such metals as aluminum alloys and steel.
  • Aluminum Alloys Structure and Properties , by L. F. Mondolfo (Butterworths, London, 1976), which discloses the fundamental characteristics of aluminum alloy vs. steel. Both metals are complex alloys. On cooling from melt, they may have a different structure depending on conditions (temperature, cooling rate). Impurities in alloys add complexity. They simultaneously precipitate in the form of various fine components mainly at boundaries of crystallites of the basic structure.
  • Al—Cu alloy (duralumin) differs in that its strength and hardness, with a specific weight close to conventional aluminum, is not less than those of mild steel (up to about 45-50 kg/mm 2 of ⁇ TS and up to 130 HB) with elongation, ⁇ , about 20%.
  • the structure of the aged alloy consists of a solid solution and non-soluble ferric and manganic compounds. Natural aging takes 1400 hours and more. Hence, artificial aging at 150-170° C. is used.
  • duralumin materials are characterized by low corrosion resistance—susceptible to pitting, intergranular corrosion (when CuAl 2 precipitates at grain boundaries), corrosion cracking, corrosion fatigue and crevice corrosion.
  • the ultrasonic energy was applied to specimens by direct contact or directly with an oscillator, or via a metal concentrator.
  • the dislocation structure of austenitic steel 1Cr8Ni9Ti was studied by transmission electron microscope using foil. A comparison was made at 20° C. between the dislocation structure after ultrasonic treatment and after plastic deformation by tension and compression. In tensioned and compressed specimens, dislocations are smoother, while ultrasonically treated specimens had more twisting dislocations with a great number of thresholds and kinks. This is testimony to intersection, transverse slip and climb of dislocations under ultrasonic effect. As the temperature rises, the number of grains with higher dislocation density increases and there is a tendency to form a cell structure, a great number of dislocation jogs and kinks. The data evidence that the grain boundaries and carbide precipitates are the sources of dislocation.
  • ultrasound In addition to dislocation rearrangement, ultrasound also causes atomic diffusion in metals. Self-diffusion of iron was studied in steels having various lattices. In steels with body-centered cubic (bcc) and face-centered cubic (fcc) lattices, ultrasound accelerates self-diffusion of iron at deformation amplitudes exceeding some threshold values. Also, the ultrasonic effect results in accelerated self-diffusion of iron regardless of the lattice type.
  • bcc body-centered cubic
  • fcc face-centered cubic
  • the most promising technique is the surface treatment by ultrasonic tool, which is effected by impact action of the “deforming element” that receives the energy from the ultrasonically oscillating transducer.
  • This technique provides significant surface microhardness, residual compressive stresses and sliding friction resistance.
  • the surface is plastically deformed at impact with indenters (“deforming elements”).
  • the deformation properties are defined by a quick ultrasonic action and simultaneous introduction into the material (via a plastic deformation saturation region) of high-power ultrasonic oscillations that initiate therein a high-intensity ultrasonic wave at the level of cyclic stresses in the intense creep region and relaxation of the material stressed state.
  • SPD surface plastic deformation
  • Ultrasonic impact treatment is one of the most promising SPD methods.
  • the plastic deformation resistance of the material is temporarily reduced when ultrasonic oscillations are excited therein and a large depth of a strengthened layer is achieved. This results in high degree of plastic deformation and high level of residual compressive stresses induced by treatment.
  • UIT is also accompanied by the effects of surface thermomechanical and subsurface relaxation in the material of a treated product.
  • Corrosion in aircraft structures is a significant economic and safety problem affecting military and civilian aircraft fleets.
  • Corrosion has many forms and affects most structural alloys found in airframes today.
  • One of the most common problems is exfoliation corrosion, which affects rolled plates and forged alloys. Exfoliation is commonly found in upper wing skins around fastener holes where it originates at the exposed end grains in the countersink and hole bore surfaces.
  • exfoliation corrosion is defined as corrosion that proceeds laterally from the sites of “initiation” along planes parallel to the surface, generally at grain boundaries, forming corrosion products that force metal away from the body of the material, giving rise to a layered appearance.
  • exfoliation is a form of severe intergranular corrosion, which occurs at the boundaries of grains elongated in the rolling direction. This form of corrosion is associated with a marked directionality of the grain structure.
  • exfoliation corrosion is most common in the heat-treatable Al—Zn—Mg—Cu (7000 series), Al—Cu—Mg (2000 series), and Al—Mg alloys, but it has also been observed in Al—Mg—Si alloys.
  • the generation of exfoliation corrosion products forces layers apart and causes the metal component to swell. Flakes of metal may be pushed up and may even peel from the surface.
  • FCGR fatigue crack growth rate
  • CPC corrosion preventive compounds
  • the pipeline premature failure is mainly caused by stress concentrations of mechanical origin (scratches, notches, structural defects, etc.) and defects formed by metal contact with corrosive environment.
  • a prolonged service leads to degradation of the pipe metal properties due to a change in metal structural state, and failure is possible even under stresses below the upper stress limit.
  • a reduced damage resistance may be associated with metal aging processes, increase in hydrogen content and internal stresses and accumulation of defects such as microcracks.
  • the grade composition of steels 17MnSi, 17Mn1Si and 19Mn differs by carbon and manganese content.
  • the chemical analysis of pipe samples showed that the actual composition of steels is often inconsistent with industrial certificates and hence the basic statistical analysis was conducted just for these steels, further called as steels of 17MnSi type.
  • 106 samples were studied, 86 from pipes in operation, 9 from emergency stock, 7 from emergency pipes, 3 from backup lines and one sample was taken from the as-manufactured pipe.
  • a number of welded pipe specimens were studied, a majority of which were factory longitudinal welds. All field welds and eight factory longitudinal welds had defects.
  • the standard tensile characteristics are insufficient to evaluate the condition of main pipelines.
  • the reliability evaluation criteria should include the properties susceptible to local structural changes, for example, those obtained from low temperature tests, delayed fracture tests and tests on cracked or sharp notched specimens. All failure resistance characteristics of metal were found to decrease upon sharp notch bending test of specimens after 25 years in service. The fracture energy is reduced by half chiefly due to the reduction in work of crack nucleation. Cold-shortness threshold shifts to the positive temperature area. The crack critical opening is reduced by 1.5 times. The tendency of steel to delayed fracture under simultaneous action of stresses, corrosion environment and hydrogen was found to be the most susceptible to structural changes. The reduction in fracture resistance of pipe metal during long service is associated with the deformation aging process and accumulation of defects and internal microstresses.
  • Phase I included collection and evaluation of plant degradation occurrences, an assessment of the available technical information on age-related degradation, and a scoping study to identify which structures and components should be studied in the subsequent phases of the research program. Based on the results of Phase I, selected structures and passive components are evaluated in Phase II to assess the effects of age-related degradation using existing and enhanced analytical methods. Phase III will utilize the results of the analyses to develop recommendations to the NRC staff for making risk-informed decisions related to degradation of structures and passive components. The results of Phase I of the research program are disclosed.
  • the information in the database includes details of when and how the cracks were detected, their dimensions and cause, as well as system and component details.
  • the database also has a comprehensive reference list of all the related documentation associated with a crack or group of cracks.
  • the database is described and its use illustrated with the trends found in the reactor coolant pressure boundary (RCPB) of the Swedish boiling water reactors (BWR).
  • RCPB reactor coolant pressure boundary
  • BWR Swedish boiling water reactors
  • the components and structures used in almost all areas of engineering are susceptible to degradation.
  • the degradation problem is most serious for engineering systems whose failures may result in catastrophic consequences such as death of people, ecological damage, and severe material losses.
  • These include: transport (bridges, tunnels, railways, load-carrying structures of transportation and load lifting facilities); oil & gas and chemical plants (main pipeline systems, pumping stations, distillation and other chemical facilities); flying vehicles (aircrafts of various types and purpose); power systems (nuclear power installations of nuclear power plants and power supply systems thereof, heat power plants); space systems (space vehicles, launching and rocket systems); and large military facilities.
  • metal degradation is the process of breakdown of metallic materials due to the formation and development of microdefects and cracks, which results in macrocracks and the loss of the load-carrying capacity of a component.
  • the whole structure, comprising such a component may fail.
  • the failure was regarded as an inevitable event.
  • Each material was believed to have a certain structural strength.
  • the material breakdown is the process that may be controlled.
  • UIT application One of promising directions to retard degradation of structural materials and recover their properties is UIT application.
  • SPD methods such as high level of compressive stresses, increased microhardness and suppression of stress concentration effect
  • UIT is also accompanied by relaxation of residual stresses; ultrasonic diffusion in the material; recovery of the degraded material properties; and amorphization of the material structure under the action of the ultrasonic impact.
  • the invention relates to a method and algorithm of improving the performance of metal and protecting the metal against degradation and suppression thereof by ultrasonic impact.
  • the method and algorithm address the problems of degradation of metal properties during prolonged service under external forces, thermodynamic fluctuations and negative environmental factors.
  • the invention also relates to the technologies oriented to protect against (prevent) and to suppress the danger of materials failure due to unfavorable change in performance over time. These problems commonly occur because of the damage of the original structure of materials under known conditions that accompany the processes of environmental degradation of metals.
  • the well-known methods of “combating” metal degradation cover a wide range of technologies from metallurgical alloying during melting, casting, welding and application of coatings to various thermal treatments and effects on the surface.
  • the invention provides a new versatile method and algorithm of addressing degradation problems in all cases mentioned above. This method and algorithm of processing the object being affected are detailed hereafter.
  • the response of the metal boundary layer to the effect and the properties and condition thereof before and after the technical effect substantially influence the characteristics of the subsurface layer, which define, either singly or in the aggregate with the surface characteristics, the technical effectiveness of the method.
  • the effectiveness of the method and/or algorithm means the degree of the effect on material performance due to the directed change in properties and structure of a material, the stress-deformed state of the structure and hence the ability of the material to resist external forces, temperature changes and environmental effects.
  • the method and/or algorithm of the present invention address the surface and the material thereunder as two independent but interrelated substances and, in this context, provides the method of increasing the object's ability to resist the unfavorable factors that cause degradation of its performance.
  • the requirements to the condition of the treated surface and subsurface material determine, as two related but independent technical effectiveness criteria of the method, the features of the technique of affecting the surface of the object being affected and the material therethrough. Accordingly, the method and/or algorithm of ultrasonic impact and the variations of its versatile and specific application in areas of engineering with different causes of degradation in performance of the object's material is detailed hereafter.
  • the task of improving metal degradation resistance is also addressed by the method and/or algorithm of the invention.
  • the method and/or algorithm initiates organizing and controlling, as defined by the task, of “soft” and force normalized phases of the ultrasonic impact and attains the technological effectiveness (which results therefrom) of practical application to suppress degradation (according to the method of the invention using ultrasonic impact control).
  • “Soft” is in reference to the phase and parameters of the ultrasonic impact that correspond to the task and directly govern the predetermined or experimentally established state of the material at the time the impact resistance of the material is possible to be identified and when in the treated area of the material a certain minimum impact resistance occurs depending on the impact phase, resulting in maximum possible strengthening (plastic deformation) while retaining the treated material mesostructure integrity.
  • the main phases of organizing and controlling of “soft” and force normalized phases of the ultrasonic impact preferably include the following:
  • FIG. 1 shows the effect of life on the brittle state (T 50 ) transformation temperature for pipe metal of steel MnSi.
  • FIG. 2 shows the relationship between time to fracture, t f , and initial stress intensity coefficient, K i , for pipes of steel 17MnSi, (1) as-manufactured, (2) working pipe, and (3) emergency pipe.
  • FIG. 3 (Prior Art) shows the effect of service on the tendency to deformation aging.
  • FIG. 4 (Prior Art) shows the reduction of area of aged pipes.
  • FIG. 5 shows the temperature dependence of internal friction, Q ⁇ 1 , of pipe metal of 17MnSi steel after prolonged service of 30 years.
  • FIG. 6 shows the temperature dependence of internal friction, Q ⁇ 1 , of pipe metal of 17MnSi steel in emergency stock.
  • FIG. 7 (Prior Art) shows the potential damage mechanism associated with high temperature applications of aluminum alloys.
  • FIG. 8 (Prior Art) shows various classifications of hydrogen damage.
  • FIG. 9 shows a schematic representation of an electrochemical corrosion process.
  • FIG. 10 shows a schematic representation of a double electrochemical layer formation of a metal atom ion transforming into solution.
  • FIG. 11 shows a schematic representation of a double electrochemical layer formation of a cation transforming from a solution to a metal surface.
  • FIG. 12 shows the completeness of the surface microhardness data obtained on the surface of pipe portions (steel X65) of emergency stock pipe and pipe after 20 years of service.
  • FIG. 13 shows surface crack initiation and crack growth of pristine material with a mirror finish with the fractograph clearly indicating the faceted growth (shear mode growth).
  • FIG. 14 shows surface crack initiation and crack growth of pristine material with EDM finish with the near surface region showing evidence of multiple crack nuclei.
  • FIG. 15 shows a site of corner crack initiation and crack growth morphology of a S110-200%-45° CSO specimen with the faceted area extending to a depth of approximately 150 ⁇ m and the faceted area surrounded by cleavage like fatigue fractures.
  • FIG. 16 shows crack initiation and early crack growth of LSP 10 GW/cm 2 (2 passes) with the fractograph indicating surface crack initiation, crack branching, and propagation path.
  • FIG. 17 shows crack initiation and early crack growth of LSP 10 GW/cm 2 (3 passes) with the fractograph indicating surface crack initiation, crack branching, and propagation path.
  • FIG. 18 shows crack initiation and early crack growth of dual treatment with the fractograph indicating surface crack initiation from a typical shot peening dent and crack branching.
  • FIGS. 19 and 20 show space-centered or body-centered cube lattice.
  • FIGS. 21 and 22 show face-centered cube lattice.
  • FIGS. 23-25 show main slip cleavage planes in simple cubic lattice.
  • FIG. 26 (Prior Art) shows a microstructure of cast iron.
  • FIG. 27 (Prior Art) shows a microstructure of annealed iron.
  • FIGS. 28-30 (Prior Art) show slips in tension of single crystal round specimens of zinc.
  • FIG. 31 (Prior Art) shows the microstructure of deformed iron.
  • FIG. 32 (Prior Art) shows the microstructure of non-deformed iron.
  • FIG. 33 (Prior Art) shows slip lines on non-etched metallographic section of iron.
  • FIGS. 34 and 35 show an oscillating system wherein ultrasonic impact is accompanied by the movement of an oscillating system under elastic recovering force caused by the rebound of the oscillating system off of a treated surface and ultrasonic oscillations of the oscillating system end connected to an indenter.
  • FIG. 36 shows plastic deformation distribution during ultrasonic impact of the invention.
  • FIG. 37 shows a frequency diagram of ultrasonic impact.
  • FIG. 38 shows stochastic ultrasonic impacts arbitrarily aligned.
  • FIG. 39 shows a fragment of a diagram of an oscillating system movement in time.
  • FIGS. 40 a - 40 c show the advance, soft contact and lag/soft impact of vectors of the velocities of the oscillating system at the oscillating system end reduced to an indenter butt.
  • FIG. 41 shows vector diagrams of the velocities of the oscillating system of FIGS. 40 a - 40 c.
  • FIG. 42 shows oscilloscope pictures of ultrasonic impacts arbitrarily aligned.
  • FIG. 43 shows the traditional area of UIT of a welded joint before groove formation by UIT.
  • FIG. 44 shows mesodefect at the groove edge due to local overstrengthening under random impact conditions during UIT.
  • FIG. 45 shows mesodefect in the center of a groove due to local overstrengthening under random impact conditions during UIT.
  • FIG. 46 shows the mesostructural defect after conventional strengthening peening.
  • FIG. 47 shows the state of groove mesostructure after UIT in accordance with the method of the invention.
  • FIG. 48 shows independent and specified uniform (in time) distribution of a 30 ⁇ m amplitude.
  • FIG. 49 shows specified distribution of ultrasonic amplitude over a convex parabola.
  • FIG. 50 shows specified distribution of ultrasonic amplitude over a concave parabola.
  • FIG. 51 shows specified increase in amplitude from 0 ⁇ m in accordance with a linear law.
  • FIG. 52 shows a graph of microhardness distribution for cast iron.
  • FIG. 53 shows a graph of residual stress distribution for cast iron.
  • FIG. 54 shows corrosion strength of a cast iron structure of an untreated specimen at a depth of 100 ⁇ M.
  • FIG. 55 shows improved corrosion strength of a cast iron structure of a UIT treated specimen at a depth of 100 ⁇ m.
  • FIG. 56 shows a comparison of specimens treated and not treated by UIT and tested in tap water regarding corrosion.
  • FIG. 57 shows a graph of improved fatigue resistance of welded specimens of steel as welded, after UIT using 5 mm pins, after hammer peening, after shot peening, after TIG dressing, after TIG dressing followed by UIT, and after UIT using 3 mm pins.
  • FIG. 58 shows a graph of improved fatigue resistance of welded specimens of steel.
  • FIG. 59 shows a graph of improved corrosion fatigue strength of steel.
  • FIG. 60 shows a graph of test results of improved impact strength of steel.
  • FIG. 61 shows a subdivided structure of high strength steels showing grain reduction range.
  • FIGS. 62 and 63 show a white layer in 10Mn2VNb steel weld joint of a main pipe line and in specimens of high strength steel SUJ2.
  • FIGS. 64 and 65 show the effect of UIT on weld metal crystallization in weld carbon ship building steel.
  • FIGS. 66 and 67 show improved mechanical properties of steel specimens.
  • FIG. 68 shows a graph of S-N curves for 8 mm butt welds showing the fatigue limit of specimens made of aluminum alloy.
  • FIG. 69 shows a graph of S-N curves for 8 mm specimens with longitudinal attachments showing improvement in high cycle fatigue strength of welds in aluminum alloys.
  • FIG. 70 shows S-N curves for 8 mm specimens of lap joints showing improvement in high cycle fatigue strength of welds in aluminum alloys.
  • FIGS. 71 and 72 show suppression of porosity to a depth of up to 2.5 mm and a life extension of cast wheels made of aluminum alloys.
  • FIGS. 73 and 74 show maintained impact strength in treatment of cast wheels made of aluminum alloys.
  • FIGS. 75 and 76 show precipitation of silicon in aluminum alloys.
  • FIG. 77 shows a graph of microhardness distribution of precipitation of silicon in aluminum alloys.
  • FIGS. 78 and 79 show improvement in strength properties of aluminum alloys after corrosion exfoliation.
  • FIG. 80 shows the effect of UIT in accordance with the invention on fatigue resistance of specimens with different degree of corrosion.
  • FIGS. 81 and 82 show refined structure of aluminum alloys.
  • FIG. 83 shows a graph of microhardness distribution during precipitate migration and occurrence of microbands in aluminum alloys.
  • FIGS. 84 and 85 show precipitate migration and occurrence of microbands in aluminum alloys.
  • FIGS. 86 and 87 show an increase in corrosion fatigue strength in bronze.
  • FIG. 88 shows a chart of environmental degradation of metals.
  • the invention relates to a method of improving the performance of metal and protecting the metal against degradation and suppression thereof by ultrasonic impact.
  • the method addresses the problems of degradation of metal properties during prolonged service under external forces, thermodynamic fluctuations and negative environmental factors.
  • the invention also relates to the technologies oriented to protect against (prevent) and suppress the danger of materials failure due to unfavorable change in performance over time. These problems commonly occur because of damage to the original structure of materials under known conditions that accompany the processes of environmental degradation of metals.
  • Environmental degradation of metals includes corrosion, hydrogen damage, liquid-metal attack and radiation damage.
  • Corrosion includes aqueous corrosion and high temperature corrosion.
  • Aqueous corrosion may be a general attack or a localized attack of corrosion.
  • a localized attack of aqueous corrosion may include galvanic corrosion, crevice corrosion, pitting, intergranular corrosion, selective leaching, erosion corrosion, or corrosion cracking.
  • High temperature corrosion includes oxidation of metals and hot corrosion. Oxidation of metals may include hydrogen embrittlement, hydrogen blistering, flakes, fish-eyes and shatter cracks, or hydrogen attack.
  • Hydrogen embrittlement may include loss in tensile ductility, hydrogen stress cracking, hydrogen environment embrittlement, or embrittlement due to hydride formation.
  • Liquid metal attack may include liquid metal embrittlement, grain boundary penetration, and/or liquid metal corrosion.
  • Radiation damage may include radiation growth, void swelling, radiation enhanced creep, and/or radiation strengthening and embrittlement.
  • the well-known methods of “combating” metal degradation cover a wide range of technologies from metallurgical alloying during melting, casting, welding and application of coatings to various thermal treatments and effects on the surface.
  • the invention provides a new method of addressing degradation problems in all cases mentioned above. This method of processing the object being affected is detailed hereafter.
  • the response of the metal boundary layer to the effect and the properties and condition thereof before and after the technical effect substantially influence the characteristics of the subsurface layer, which define, either singly or in the aggregate with the surface characteristics, the technical effectiveness of the treatment method.
  • the effectiveness of the treatment method means the degree of the effect on material performance due to the directed change in properties and structure of a material, the stress-deformed state of the structure and hence the ability of the material to resist external forces, temperature changes and environmental effects.
  • the method of the present invention addresses the surface and the material thereunder as two independent but interrelated substances and, in this context, provides the method of increasing the object's ability to resist the unfavorable factors that cause degradation of its performance.
  • the task of improving metal degradation resistance is addressed by the method of the invention.
  • the method initiates organizing and controlling, as defined by the task, of “soft” and force normalized phases of the ultrasonic impact and attains the technological effectiveness (which results therefrom) of practical application to suppress degradation (according to the method of the invention using ultrasonic impact control).
  • “Soft” is in reference to the phase and parameters of the ultrasonic impact that correspond to the task and directly govern the predetermined or experimentally established state of the material at the time the impact resistance of the material is possible to be identified and when in the treated area of the material a certain minimum impact resistance occurs depending on the impact phase, resulting in maximum possible strengthening (plastic deformation) while retaining the treated material mesostructure integrity.
  • the main phases of organizing and controlling of “soft” and force normalized phases of the ultrasonic impact preferably include the following:
  • a basic tool comprises at least one indenter 103 , a waveguide 102 , a magnetostrictive transducer 101 with a casing 107 which may be a water cooled casing, a spring 106 , and a tool case 105 with a handle.
  • the magnetostrictive transducer 101 , waveguide 102 , indenter 103 , tool casing 105 , spring 106 and casing 107 of the transducer form the oscillating system (OS) with a processing setup structurally fixed thereto.
  • OS oscillating system
  • FIG. 36 shows plastic deformation distribution during ultrasonic impact of the invention.
  • the average statistical ultrasonic impact comprises three time intervals (denoted in FIG. 36 as a, b, and c) of the effect on the object, which define the intensity of the plastic deformation distribution in the treated material during each impact event.
  • intervals include: (a) oscillations of the indenter at increasing frequency above the carrier frequency of the ultrasonic transducer in a narrowing gap between the treated surface and the end of the oscillating system; (b) synchronous and in-phase uninterrupted oscillations in a system “oscillating system-indenter-treated surface”; (c) damped oscillations of the indenter in an increasing gap between the treated surface and the end of the oscillating system as a result of the oscillating system rebound from the treated surface as shown in FIG. 37 .
  • the events of rebounds and impacts of the oscillating system occur randomly relative to the ultrasonic oscillations of the output end of the oscillating system (carrier oscillations of the ultrasonic transducer) and form a stochastic pattern of phases, as shown for example in FIG. 38 , representing the start and the end of the events of each ultrasonic impact and the three time intervals thereof, namely (a), (b) and (c).
  • the oscillating system movement velocity and the velocity of ultrasonic oscillations of the oscillating system end with an indenter are added stochastically, creating a problem of dynamic overloads at the surface affected by the ultrasonic impact beyond the dynamic strength limits of the treated surface material mesostructure.
  • This in turn causes the following: (a) dissipation of the impact energy on surface damages caused by mesostructural disruption, and unfavorable development of these damages at subsequent impacts; (b) reduction in intensity and depth of plastic deformations induced in the surface material and favorable compressive stresses caused thereby; and (c) reduction in ultrasonic oscillation energy and hence ultrasonic stress waves in the material of the object being affected.
  • the degradation of metals is accompanied by disruption of their mesostructure, primarily in the surface layer.
  • the ultrasonic impact treatment process is accompanied by two oscillation modes: (a) low-frequency oscillations of the oscillating system lumped mass and (b) ultrasonic frequency oscillations of coupled resonance elements, namely transducer-waveguide-indenter of the oscillating system.
  • the portion of the diagram of these movements and a specific calculation of the relationships of the amplitude velocities thereof are shown for example in FIG. 39 .
  • Positive amplitude corresponds to the OS approach to TS.
  • the maximum velocity is A ⁇ .
  • the oscillating system movement is accompanied by two frequency categories of oscillating velocities, wherein the carrier ultrasonic oscillating velocity is ahead, by at least an order of magnitude, of the reactive oscillating velocity, at which the oscillating system approaches to the treated surface.
  • the method of the invention comprises the following two main conditions:
  • FIGS. 40 a - 40 c The conditions, under which the method of impact control is formed in phase of the effect upon the material mesostructure, i.e., impact phases, are shown in FIGS. 40 a - 40 c . More particularly, FIG. 40 a shows the “advance” wherein the vectors of oscillating velocities of OS and OSE have one direction and the resultant velocity of OSE, V r , is maximum. When OSE contacts TS, the maximum impact impulse, P imp , is transferred thereto.
  • FIG. 40 b shows the “soft contact” wherein the vectors of oscillating velocities of OS and OSE are opposite and the resultant velocity, V r , is “0” at the instant of contacting TS.
  • FIG. 40 c shows the “lag/soft impact” wherein the vectors of oscillating velocities of OS and OSE are opposite.
  • the resultant velocity of OSE (in the contact region) is minimum.
  • the impact impulse is minimum.
  • the change in ultrasonic oscillating velocity at the end of the oscillating system creates, in a phase matched with OSE, initial prerequisites for controlling impulse of force at the point of impact: from “rigid,” when the oscillating velocities are added, to “soft” contact or impact, when the oscillating velocities are equal or when the ultrasonic oscillation velocity exceeds the oscillating system approach velocity at ultrasonic frequency, respectively.
  • the vector diagrams of such states of the oscillating system according to the method are shown for example in FIG. 41 .
  • FIG. 41 clearly reflect the “soft” impact formation mechanism at a point of the first contact between the oscillating system and the treated surface.
  • the superposition of this mechanism on actual oscilloscope pictures of actual impacts is shown for example in FIG. 42 .
  • the resultant of ultrasonic oscillation velocities of the OS and the tool at the onset of impact is zero (0).
  • the resultant ultrasonic oscillation velocities of the OS and the tool at the onset of impact are negative.
  • the resultant ultrasonic oscillation velocities of the OS and the tool at the onset of impact are maximum.
  • FIG. 43 shows the traditional area of UIT of a welded joint before groove formation by UIT (x10).
  • FIGS. 44 and 45 show the types of mesostructural defects after UIT under random impact conditions, wherein FIG. 44 shows the mesodefect at the groove edge due to local overstrengthening under random impact conditions during UIT (x40) and FIG. 45 shows the mesodefect in the center of the groove due to local overstrengthening under random impact conditions during UIT (x160).
  • FIG. 46 shows the mesostructural defect after conventional strengthening peening, i.e., surface mesodefect after hammer peening (x160).
  • FIG. 47 shows the state of mesostructure, i.e. groove mesostructure, after UIT (x160) in accordance with the method of the invention.
  • the surface and mesostructure of the treated surface are formed without damages that may initiate the propagation of degradation effects in service of a given welded joint. Also, at the depth of at least 1.5 mm, the region of intense plastic deformation is visible and, in turn, creates a sound physical barrier against the occurrence of such damages in the geometrical stress concentrator region under service loads during long period of time.
  • the task of formation of the strengthened layer, after “soft contact” or “soft ultrasonic impact,” is solved by a method that constitutes a part of the method of the invention and involves the reverse task of excitation, in the surface layer and material, of the wave (which is maximum for a given material) of ultrasonic stresses initiated by the ultrasonic impact through the area (with optimal mesostructure) of saturation of plastic deformations caused by the soft ultrasonic impact of maximum (in terms of the treated surface strength) power.
  • the control parameters of high-power controlled ultrasonic impact during treatment of subsurface layer are defined by the task.
  • the “soft” phases of the ultrasonic impact are necessary to protect the treated surface against mesostructural damages and create plastic deformations in the saturation area for optimum continuation of the UIT process with minimum scattering losses at the surface and as a result thereof: (a) effective ultrasonic oscillations of the indenter of the oscillating system with detachment from the surface and synchronously therewith; and (b) excitation under the surface of high-power ultrasonic stress waves which are sufficient, in combination with the protective properties of the modified treatment surface, to suppress the occurrence or propagation of the started process of material properties degradation.
  • FIGS. 48-51 show the results of varying the conditions of treated material plastic deformation under the surface at various ultrasonic impact amplitude change laws after the “soft” onset of the ultrasonic impact.
  • the integrated oscilloscope pictures show the relation between the residual surface plastic deformation and the conditions of the change in the amplitude of 1 ms long ultrasonic impacts after “soft” phases thereof. All the results are given in comparison with the actual free dropping distribution of the amplitude within the range of the actual values thereof as shown in FIG. 48 that also illustrates the same dependence from the specified and actually used amplitude of 30 ⁇ m, which is uniformly distributed in time.
  • FIG. 48 shows independent and specified uniform (in time) distribution of the 30 ⁇ m amplitude.
  • FIG. 49 shows specified distribution of the ultrasonic amplitude over a convex parabola.
  • FIG. 50 shows specified distribution of ultrasonic amplitude over a concave parabola.
  • FIG. 51 shows specified increase in amplitude from 0 ⁇ m in accordance with a linear law.
  • reverse self-diffusion in this case is a means of recovering lost strength and ductility of an alloy under normalized ultrasonic impact during and after a “soft” phase thereof;
  • Each technical task the solution of which involves controlling “soft” phases of the ultrasonic impact and the parameters of the impact itself during synchronous and in-phase ultrasonic oscillations in the acoustic series “oscillating system-indenter-treated surface,” may, depending on the treated material structure susceptibility, set up different requirements to the degree of controlling and matching the approach velocities and the oscillating velocity at the output of the ultrasonic oscillating system.
  • the only criterion of the effective engineering solution of a given task is attaining a desired technical effect of degradation suppression with minimum energy consumption. This condition alone determines the requirements to the necessary degree of controlling the velocities of the action upon the material prior to and during ultrasonic impact.
  • the method also provides surface mesostructure integrity by setting the above-mentioned adjustable parameters of the ultrasonic impact, within a range, including maximum, minimum and compensated value of a resultant of a velocity vector at an onset of the impact, setting and changing oscillating amplitude during ultrasonic impact following the oscillating system contacting the treated surface in accordance with affecting the material structure under the treated surface and based on requirements to rebound of the oscillating system from the treated surface until termination of the ultrasonic impact.
  • the amplitude and the phase of ultrasonic oscillations are set, before the oscillating system contacts the treated surface during approach therebetween, such that at an onset of the impact, the velocity and energy of the impact correspond to the conditions of maintaining mesostructure integrity of the material in a surface layer and creating treated surface plastic deformation not exceeding the saturation level but sufficient to transfer an ultrasonic stress wave into the treated material, with acoustic losses remaining within a range from a level necessary for specified subsequent plastic deformation to a level determined by a Q-factor of the material.
  • the method of the invention further comprises setting a degree of controlling oscillating velocities in phase of the oscillating system approach to the treated surface thereby providing integrity of the material and surface layer mesostructure, based on dynamic strength reserve of the surface material in relation with an allowable rate of deformation thereof; setting ultrasonic oscillation intensity distribution during ultrasonic impacts thereby attaining at least one property and/or state of the structure and material under the treated surface, based on susceptibility of the treated material to an action of ultrasonic impacts in transition to a specified state, wherein the degree of controlling oscillating velocities and ultrasonic oscillation intensity distribution are preliminary determined based on experimental data or expertise as defined by the task.
  • the surface material is deformed at a rate sufficient to fill intergranular defective voids while maintaining the integrity of the surface material and mesostructure thereof during plastic deformation initiated by soft phases of the impact.
  • Structural defect boundaries are closed under forces occurring during plastic deformation of the surface material caused by an action of soft and force phases of the ultrasonic impact.
  • Defect boundary closing surfaces may be activated under elastic residual stresses caused by plastic deformation of the treated surface material. Defect boundary closing surfaces also may be activated under impulses of force caused by impacts at a predetermined repetition rate.
  • Activation of defect boundary closing surfaces may be accompanied by an action of a vector sum of oscillating velocities of movement of the oscillating system lumped mass and oscillating system distributed mass, reduced to an oscillating system end, during ultrasonic oscillations of the ultrasonic system end in a phase, which is set by the program of controlling resultant oscillating velocity, and impulse of force caused by the ultrasonic impact.
  • Activation of defect boundary closing surfaces under friction forces, which are caused by defect boundary displacement during an action of impact impulses and ultrasound.
  • defect boundary closing surfaces Activation of defect boundary closing surfaces is accompanied by an action of ultrasonic oscillations and waves going through a closing boundary during an action of the impulse of force caused by the ultrasonic impact.
  • defect boundary closing is also activated in an area of elevated temperature caused by plastic deformation and friction at boundaries of structural defects and fragments during impulse action, recurring at a repetition rate of ultrasonic impacts in a phase, which corresponds to material properties and task of action.
  • Ultrasonic self-diffusion and annihilation of closing boundaries occur under static pressure of the oscillating system, impulses of force, friction at boundaries, heating, ultrasonic oscillations and ultrasonic stress waves, which are set by conditions of forming and controlling “soft” and force phases of the ultrasonic impact as defined by the task.
  • precipitation of alloying phases provides increased material strength which is attained by controlling the ultrasonic impact.
  • Unstable phases similar to copper in Al alloys, are fixed at a stage of soft ultrasonic contacts and impacts for protection against precipitation in solid solutions and prevention of degradation development.
  • Activation of phase migration preferably occurs as a result of normalized ultrasonic impact after soft onset thereof in accordance with a predetermined change in ultrasonic impact intensity with time.
  • the activation is preferably accompanied by increased fatigue resistance due to redistribution and reduction in density of distribution of potential concentrators of internal stresses at a nanostructural level.
  • self-control of the material structure in rotation, bending, twinning, recrystallization, flow, gliding, yielding and aging is activated by the ultrasonic impact during normalized “soft” phases and subsequent force phases of the ultrasonic impact at a level of fragments of nanostructure, microstructure and macrostructure of metals.
  • Activation of subdivision, uniformization and arrangement of material structure at a microlevel, as a means of increasing degradation resistance, occurs under the effect of the ultrasonic impact during “soft” and subsequent force phases, wherein the parameters are normalized as defined by a task.
  • amorphization as a means of final optimization of surface material structure at a nanolevel, occurs as a result of processes initiated by the ultrasonic impact during “soft” and subsequent force phases, wherein the parameters are normalized based on experimental or expert data as defined by a task allowing for rapid local heating and cooling of a metal in the area of plastic deformation thereof. Controlling soft and force phases of the ultrasonic impact protects the material against degradation nucleation in an original condition, as well as prevents and suppresses degradation in the material of a structure during or after long service thereof.
  • (1) aluminum alloys are protected against corrosion exfoliation and/or (2) properties of an aluminum alloy, which have been damaged by exfoliation, are recovered and/or repaired.
  • the action of the method of the invention in comparison with the known methods of “combating” degradation is illustrated and provides a spectrum of engineering solutions and techniques of degradation suppression based on using “soft” phases of the ultrasonic impact of high power in affecting the surface mesostructure and controlling the ultrasonic impact parameters after a “soft” phase in affecting the properties and condition of the treated material under the treated surface.
  • the following are examples of types of degradation, the symptoms of the degradation, the physics of the degradation, the area of occurrence of the degradation and the application and transformation of the methods of affecting the treated surface and treated material in accordance with the present invention to suppress the degradation.
  • the symptoms of mechanical fatigue include fatigue cracks.
  • the fatigue process includes the following phases: at first, accumulation of elastic distortions of a lattice because of the increased dislocation density; thereafter, appearance of submicrocracks in the metal volumes, where a critical dislocation density is attained during mass slipping of separate blocks; and finally, microcracks growing into macrocracks. As this takes place, a brittle fracture occurs along one microcrack that develops most intensively.
  • Mechanical fatigue occurs most often in bridges, tunnels, railways, load-carrying structures of transportation and load lifting facilities, aviation, and transport (loaded welds, stress concentration regions).
  • the method of the invention provides creation of a compensation protective barrier and recovery of the properties of the damaged material by high-power “soft ultrasonic impact” (PSUI) with adaptive on-off time ratio modulation (O/OTRM) of drive pulses synchronized with the high-power soft ultrasonic impact.
  • PSUI soft ultrasonic impact
  • OFOTRM adaptive on-off time ratio modulation
  • pulse width and amplitude modulation are used, which is initiated when an increase in frequency of synchronized ultrasonic impacts is needed with a small (i.e., insufficient for independent predetermined oscillation suppression) pause therebetween or the length of the transient process that is insufficient for independent recovery of oscillations.
  • control of plastic deformation intensity distribution in time and space during each ultrasonic impact control of surface parameters at scales of mesostructure and crystalline structure, its stressed-deformed state and the depth of penetration in the area of existing or possible damage; and stabilization of phases, homogeneity of structure and properties of a material in the area of instability thereof under external conditions (heating, loading, environment).
  • corrosion fatigue Another type of degradation is corrosion fatigue.
  • the symptoms of corrosion fatigue include fatigue cracks that propagate from the surface.
  • the fatigue failure process accelerated by corrosion mechanisms is initiated by: adsorption of surface-active substances, producing a wedging effect at a microcrevice; and hydrogen diffusion, causing metal embrittlement.
  • Corrosion fatigue occurs most often in bridges, pipelines, tunnels, sea transport, and equipment in the chemical industry (loaded welds and stress concentration regions subjected to environmental aggressive action).
  • the invention provides protection from adsorption and prevention of adsorbing inclusions from contact with structural fragments; an increase in mobility and loss of bonding of adsorbing inclusions and surface-active substances with adsorbing surfaces, as well as in the damaged area of a material or its structure; and optimization of the surface, its mesostructure and roughness, residual stresses in the surface layer and hence the surface material resistance to adsorption (increase in material density in the surface layer).
  • thermal and thermal-mechanical fatigue Another type of degradation is thermal and thermal-mechanical fatigue.
  • the symptoms of thermal and thermal-mechanical fatigue include fatigue cracks. In the fatigue failure process, a component is cyclically deformed due to low- or high-cycle temperature effect and mechanical fluctuating stresses caused thereby. As this takes place, heating may be caused by inherent basic processes of energy obtaining and spending, as well as accompanying causes during service of machinery.
  • Thermal and thermal-mechanical fatigue occurs most often in heat and nuclear power plants, metallurgical plants (boilers, furnaces), motor and railway transport, and handling of machinery (components of braking devices).
  • the invention provides increased resistance to thermal and thermal-mechanical damages in the original condition and in service; maintenance and recovery of the material properties based on creating a compensation barrier of distributed residual stresses, relaxation of the stress and deformation gradient in the areas of accumulated thermal and thermal-mechanical damages, filling of the intergranular space in the areas of structural defects by grain material, and ultrasonic diffusion at grain boundaries; and optimizing the friction couples surface as a means of reducing time and heat losses in braking.
  • chemical corrosion Another type of degradation is chemical corrosion.
  • the symptoms of chemical corrosion include uniform dissolution of a material, pitting and pinpoint corrosion, flaws, crevice corrosion, and corrosion exfoliation.
  • the physics of chemical corrosion include metal-environment chemical interaction (gas or liquid), formation of new chemical compounds on the surface, reduction in material strength and formation of stress concentrators.
  • the negative effects of chemical corrosion occur most often in chemical plants, nuclear power engineering, pipeline transportation (tanks, pipelines, reactors), aviation, and sea, railway and motor transport (skin, hull plating).
  • the invention provides protection of the original surface being affected and recovery of the material properties; modification of meso and crystalline structures, amorphization of the surface material, creation of the compensation barrier of residual compressive stresses in the surface material based on formulating a function of oscillating amplitude changing in the “transducer-indenter-surface” system (TIS) during PSUI; pulse and ultrasonic diffusion at grain boundaries in the region of structural failures caused by intercrystalline corrosion; and plastic deformation of a material, increase in grain size uniformity, filling an intergranular space by grain material, pulse ultrasonic diffusion at grain boundaries.
  • TIS transducer-indenter-surface
  • the mechanism of metal-environment electrochemical interaction includes: anodic process—metal atom ionization with formation of ions aquated in solution and uncompensated electrons in a metal; the process of electron transfer from anodic reaction zones to regions where a cathodic process is feasible in thermodynamic and kinetic terms; the process of oxidant-depolarizer application to cathodic zones (reaction of metal ions and electrolyte ions); the cathodic process—assimilation of excess electrons by the depolarizer and in cathodic zones, the thermodynamic conditions of the recovery process is provided for the depolarizer; and dissolution and disturbance of the surface geometrical homogeneity, weakening of structural bonds and reduction in material strength in this area.
  • Electrochemical corrosion occurs most often in sea transport (hull plating, propellers), the chemical industry (tanks, reactors), pipelines, subsurface and subsea lines.
  • the means of suppressing the negative effects of electrochemical corrosion in accordance with the invention include: creation of an electrochemical corrosion compensation barrier in the original condition of a material and recovery of the properties thereof; optimization of the micro- and macro-geometry of the surface, homogeneity of the surface material crystalline structure, nano crystallization and amorphization of the surface material as a means of retardation of the anodic processes; surface plastic deformation, creation of the area of compressive stress and increased material density to retard the localization of electrochemical corrosion of surface defects; and using the PSUI mechanism to form the above surface conditions in the case of optimum surface mesostructure.
  • thermal corrosion Another type of degradation is thermal corrosion.
  • the symptoms of thermal corrosion include material dissolution and evaporation, and scale formation.
  • the physics of thermal corrosion include high temperature induced metal-environment chemical interaction. Thermal corrosion occurs most often in thermal and nuclear power plants, metallurgical plants (boilers, furnaces), and chemical plants (reactors).
  • the invention provides creation of a chemical corrosion compensation barrier in the original condition of a material and recovery of the properties thereof through the use of the PSUI mechanism to optimize the quality and increase the surface alloying depth in application of protective heat-resistant coatings and in repetition of these operations, if needed, on a scale layer and if the surface material properties need to be repaired.
  • the symptoms of radiation corrosion include corrosion pits and cracks.
  • the mechanisms of the radiation emission effect on the kinetics of corrosion processes include: a radiolysis effect which is caused by irradiation on water and accelerates the cathodic process due to water ionization; and the destructive effect which consists of elastic and thermal metal surface-radiating particles interaction, resulting in defects in the metal surface layer and oxide film. These defects facilitate the anodic process and have the most profound effect on the corrosion rate.
  • the negative effects of radiation corrosion occur most often in nuclear power engineering, military facilities, and space systems.
  • the method of affecting the treated surface and treated material of the present invention provides creation of a radiation corrosion compensation protective barrier in the original condition of a material being affected and recovery of the properties thereof using the PSUI mechanism to: optimize the quality and increase the surface alloying depth in application of protective heat- and radiation-resistant coatings; optimize the surface condition in terms of its roughness, mesostructure, micro-grain structure and material amorphization; and create the favorable compressive stress field and increase the surface material density. Repetition of these operations on a damaged layer provides recovery of the radiation resistance of the surface material at a level of an original material being affected.
  • the symptom of corrosion cracking includes corrosion cracks.
  • the mechanisms of corrosion cracking include: adsorption of solution anions on movable dislocations and other structural imperfections which reduces the surface energy and facilitates the breakdown of atomic bonding of metals; occurrence of crack nucleation as a result of a wedging action of surface-active substances in adsorption thereof in microcrevices on the metal surface.
  • a high crack development rate in this case is caused by the accelerated anodic dissolution of the metal at the crack base, where the stressed-deformed state is generally determined by a tensile stress concentration.
  • Corrosion cracking occurs most often in chemical plants, nuclear power engineering, and pipeline transportation (tanks, pipelines, pumping facilities, reactors).
  • the method of protection against corrosion cracking in accordance with the present invention provides creation of a compensation protective barrier against the formation of corrosion cracks in the original condition of a material and in recovery of the properties thereof by using the PSUI mechanism to: optimize the quality, adhesion or to increase the alloying depth of protective coatings applied to potentially or actually damaged surface, as well as to induce favorable compressive stresses into the surface in strengthening or modification thereof to a predetermined depth in optimal or specified condition of the mesostructure; modify the structure and create the stressed-deformed state of the material structure that makes impossible absorption of solution anions on movable dislocations and other structural imperfections that reduce the surface energy and weaken atomic bonds; optimize the surface mesostructure and prevent crack nucleation as a result of a wedging action of surface-active substances in adsorption thereof in microcrevices on the metal surface; create a compressive stress field on the surface with optimal mesostructure, the magnitude and depth of which is sufficient for protection against high crack propagation rate caused by accelerated anodic dissolution of a metal at the
  • the symptoms of hydrogen embrittlement include reduction in strength properties and brittle cracks.
  • the mechanisms of hydrogen embrittlement include: penetration of atomic hydrogen in voids, pores and other lattice defects; hydrogen transformation into molecular gas that creates high pressure; adsorption of atomic hydrogen on surfaces of a component and internal defects with formation of chemical compounds with metal and impurities; and reducing the surface energy and the brittle fracture resistance of a metal.
  • Hydrogen embrittlement occurs most often in metallurgical and engineering plants, pipelines (welded structures, galvanic plants), petrochemical plants (reactors), and aviation (skin).
  • the method of protection against hydrogen embrittlement in accordance with the present invention provides using the PSUI mechanism to: strengthen the surface alloying quality, adhesion strength and density of galvanic coatings; create a compressive stress field on the surface with optimal mesostructure, the magnitude and depth of which is sufficient for protection against reduction in strength properties and formation of brittle cracks that may be caused by penetration of atomic hydrogen in voids, pores and other lattice defects; hydrogen transformation into molecular gas that creates high interfragmentary pressure; adsorption of atomic hydrogen on surfaces of a material and internal defects with formation of chemical compounds with metal and impurities that reduce the surface energy of a metal and the brittle fracture resistance.
  • liquid-metal embrittlement Another type of degradation is liquid-metal embrittlement.
  • the symptoms of liquid-metal embrittlement include reducing strength properties and brittle cracks.
  • the physics of liquid-metal embrittlement includes: adsorption penetration of the molten metal in the solid metal pre-failure zone; and reduction in surface energy and metal rupture resistance in the damaged area. Liquid-metal embrittlement occurs most often in metallurgical plants (galvanic manufacture).
  • the method of prevention or “healing” against liquid-metal embrittlement in accordance with the present invention provides using PSUI to create an optimal mesostructure and compressive stress field on a surface, the magnitude and depth of which is sufficient for protection against the strength properties reduction, formation of brittle cracks, adsorption penetration of the molten metal in a solid metal pre-failure zone, reduction in surface energy and metal rupture resistance.
  • the symptom of erosion includes surface relief change.
  • the physics of erosion include detaching solid particles from the body surface being affected as a result of the body contact with a moving liquid, gaseous environment or particles entrained thereby as a result of the impact of solid particles with the surface being affected. Erosion occurs most often in pipeline transportation (pipes, pumping facilities), aviation (turbines), sea transport (propellers), rockets and missiles (skin).
  • the method of prevention or recovery of eroded surfaces in accordance with the present invention provides using PSUI to create an optimum density, roughness, mesostructure and compressive stress field at the surface, the magnitude and depth of which is sufficient for protection against the detachment of solid particles from the body surface as a result of the body contact with a moving liquid, gaseous environment or particles entrained thereby or as a result of the impact of solid particles upon the surface being affected.
  • the symptoms of creep include formation of microcracks and pores (microvoids) at grain boundaries and substructure formation.
  • the mechanisms of creep include: gliding and slip (dislocation diagram); twinning; bending of slip planes; lamellation; rotation and relative movement of grains; rotation and relative shift of mosaic blocks; poligonization; diffusion plasticity; recrystallization mechanism; and combining defects and structural damage at micro and macro levels. Creep occurs most often in heat and nuclear power plants, petrochemical industry, and aviation (structures, reactor bodies and turbine blades operating at high temperature).
  • the method of preventing and “healing” creep in accordance with the present invention provides using PSUI to attain an optimal density, mesostructure condition and grain in a packing size and the field of compressive macrostress and microstress at and under the surface, the magnitude and depth of which is sufficient to protect against formation of microcracks and pores (microvoids) at grain boundaries and substructure, gliding and slip (based on dislocation diagram), twinning, bending of slip planes, lamellation, rotation and relative movement of gains, rotation and relative shift of mosaic blocks, polygonization, diffusion plasticity, recrystallization, and combining defects and structural damage at micro and macro levels.
  • microstructural degradation Another type of degradation is microstructural degradation.
  • the symptom of microstructural degradation includes reduction in strength properties of a material.
  • the mechanisms of microstructural degradation include absorption of molecules from the environment by micro-surfaces developing in a deformed body (Rebinder effect) and stabilizing the unfavorable metal phase condition in time at the expense of transforming unstable phases without a considerable change in microstructure (aging).
  • Microstructural degradation occurs most often in power plants, refineries (frame structures), pipelines, sea transport, and aviation (body, skin).
  • the method of preventing and “healing” microstructural degradation in accordance with the present invention is based on using PSUI in creating optimum density of a material, mesostructure on the material surface, and normalizing plastic deformations and compressive stress field at the surface, the magnitude and depth of which is sufficient to prevent reduction in material strength properties caused by microstructural degradation that may include absorption of molecules from the environment by micro-surfaces developing in a deformed body (Rebinder effect); and/or stabilizing the unfavorable metal phase condition in time at the expense of transforming unstable phases without a considerable change in microstructure (aging).
  • radiation embrittlement Another type of degradation is radiation embrittlement.
  • a symptom of radiation embrittlement includes brittle cracking with an abrupt increase in yield strength.
  • the physics of radiation embrittlement include a neutron stream shifting the atoms or producing a shift cascade in a metal lattice depending on the amount of the energy the neutron transfers to the metal atom which results in the volumes with high vacancy concentration, which are surrounded along the periphery by zones with increased density of interstitial atoms. Radiation embrittlement occurs most often in nuclear power engineering (reactors), space systems, and military facilities (missile body skin).
  • the method of preventing or “healing” radiation embrittlement in accordance with the present invention provides using PSUI to attain the optimal density and mesostructure of the treated material through normalization of plastic deformations and compressive stress field on and under the surface, the magnitude and depth of which is sufficient to prevent the formation, in the case of an abrupt increase in yield strength of brittle cracks caused by atomic shift or a shift cascade (under neutron stream) in a metal lattice depending on the amount of the energy the neutron transfers to the metal atom and thereafter the formation of high concentration of vacancies surrounded along the periphery by zones with increased density of interstitial atoms.
  • exfoliation Another type of degradation is exfoliation.
  • the symptoms of exfoliation include surface corrosion exfoliation of a metal with formation of stress concentrators and loss of strength.
  • the physics of exfoliation include synergetic effect of corrosion and hydrogen embrittlement. Exfoliation occurs most often in aviation.
  • the method of preventing or suppressing ongoing corrosion exfoliation in accordance with the present invention is based on using PSUI with a level and time parameters corresponding to the experimentally found requirements for attaining the optimum density of a treated material with a guaranteed integrity of its mesostructure, and for the conditions of formation and normalization of local point heating and the rate of heat rejection from this plastic deformation region, plastic deformations themselves and a compressive stress field on and under the treated surface, the magnitude and depth of which is sufficient to:
  • FIGS. 52-53 show microhardness distribution and FIG. 53 shows residual stress distribution.
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; A—30 ⁇ m; Pressure—21 kg; Indenter—6.35 ⁇ 25 mm, R5.5 mm; Dia.—419 mm; Rot.—190 RPM; Pass 1: Feed—0.8 mm/min.; Pass 2: Feed—0.4 mm/min.
  • This material effect is attained by introduction of compressive stresses of high level, an increase in microhardness of a surface layer, and protection of mesostructure against service and process-induced damages.
  • FIGS. 54-56 Another material effect in cast iron by UIT in accordance with the invention is increased corrosion strength, in particular, of water cast iron pipes ANSI/AWWA C151/A21.51-96 made of cast iron of VCh45-5 type.
  • the outcome is shown in FIGS. 54-56 . More particularly, FIG. 54 shows a structure of an untreated specimen at a depth of 100 ⁇ m, FIG. 55 shows a structure of a UIT treated specimen at the depth of 100 ⁇ m and FIG. 56 shows a comparison of specimens treated and not treated by UIT and tested in tap water.
  • the UIT conditions for this material effect are preferably as follows: f—44 kHz; A—18 ⁇ m; Pressure—5 kg; Indenter—5 ⁇ 25 mm, R5 mm; Dia.—230 mm; Rot.—16 RPM; Feed—0.25 mm/min.
  • This material effect is attained by modification of the surface layer structure by intense normalized plastic deformation thereof, creation of the compressive stress region, and suppression of surface defects that initiate mesostructural damage during service.
  • a material effect attained is increased fatigue resistance of welded specimens in Weldox420 steel.
  • the outcome is shown in FIG. 57 .
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; P—up to 900 W; A—30 ⁇ m; Pressure—5 kg; Ultrasonic impact duration—1.2-2 msec.
  • This material effect is attained by introduction of compressive stresses of high level, stress concentration reduction, ultrasonic plastic deformation and structural modification of the treated material in the stress concentration area.
  • the preferable relationship has been experimentally established between the conditions of ultrasonic oscillations, the pressure and indenter sizes that ensure protection of mesostructure against process-induced and operational damage during service and preparation of a surface with the use of PSUI.
  • Another material effect attained in steel is increased fatigue resistance of welded specimens in Weldox700 steel.
  • the outcome is shown in FIG. 58 .
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; P—up to 900 W; A—30 ⁇ m; Pressure—5 kg; Ultrasonic impact duration—0.8-1.2 msec.
  • This material effect is attained by introduction of compressive stresses of high level, stress concentration reduction, ultrasonic plastic deformation and structural modification of the treated material in the stress concentration area.
  • the relationship has been experimentally established between the conditions of ultrasonic oscillations, the pressure and indenter sizes that ensure protection of mesostructure against process-induced and operational damage during service and preparation of a surface with the use of PSUI.
  • Another material effect attained in steel is increased corrosion-fatigue strength of 45Mn17Al3 steel.
  • the outcome is shown in FIG. 59 .
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; P—up to 900 W; A—30 ⁇ m; Pressure—5 kg; Ultrasonic impact duration—1.5-2 msec.
  • This material effect is attained by introduction of compressive stresses of high level into the treated surface and treated material and modification of their structure.
  • the relationship has been experimentally established between the conditions of ultrasonic oscillations, the pressure and indenter sizes that ensure protection of mesostructure during service and treatment of a surface with the use of the ultrasonic impact in accordance with the invention.
  • Another material effect attained in steel is increased impact strength of bridge steel 10CrSiNiCu.
  • the outcome is shown in FIG. 60 .
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; P—up to 900 W; A—30 ⁇ m; Pressure—5 kg; Ultrasonic impact duration—1.2-1.7 msec.
  • This material effect is attained by arrangement of a block structure at nanolevel and creation of regions of compressive stresses sufficient to retard mesostructural damage during effect upon the treated material by quasistatic and dynamic loads initiated by the ultrasonic impact normalized as defined by the task and thereafter by operation forces.
  • Another material effect attained in steel is a grain refinement in high-strength steels SUJ2 and S33C.
  • the outcome is shown in FIG. 61 .
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; A—25, 30 and 33 ⁇ m; NI80; Pressure—20 kg; Indenter—6.35 ⁇ 25 mm; Dia.—5 mm; Rot.—500 RPM; Ultrasonic impact duration—1.5-1.6 msec.
  • This material effect is attained by intense ultrasonic plastic deformation of the treated material and arrangement of microstructure at nanolevel and suppression of mesostructural damage.
  • FIGS. 62-63 Another material effect attained in steel is obtaining a “white layer” in 10Mn2VNb steel welded joint of a main pipeline and in specimens of high-strength steel SUJ2.
  • the outcome is shown in FIGS. 62-63 . More particularly, FIG. 62 shows a welded joint of 10Mn2VNb steel and FIG. 63 shows a specimen of SUJ2 steel.
  • the UIT conditions to attain this material effect are preferably as follows:
  • FIGS. 64-65 Another material effect in steel is attained by the effect of UIT on weld metal crystallization in welding carbon ship building steel 10CrSiNiCu which includes: (1) the dendritic structure in the untreated weld (before UIT) being much coarser than that in the treated weld (after UIT); (2) the grain structure, preferably with finer grain, prevailing in the UIT treated weld; and (3) dendrites in the untreated weld before UIT being longer and wider in the thicker intergranular layer than after UIT.
  • FIGS. 64-65 More particularly, FIG. 64 shows welding without UIT and FIG. 65 shows welding with UIT.
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; A—30 ⁇ m; Pressure—20 kg; Indenter—6.35 ⁇ 25 mm; Ultrasonic impact duration—1.5-2 msec.
  • This material effect is attained by intensification of diffusion processes and metal recrystallization under the action of ultrasonic wave, acoustic flows, sound pressure and cavitation, which are initiated by indenter ultrasonic oscillations synchronously with carrier oscillations of the ultrasonic oscillating system during ultrasonic impact.
  • UIT Another material effect of affecting the structure and condition of a material is attained by UIT of sintered powder steel.
  • This provides strengthened mechanical properties of steel specimens containing 0.4% C, 0.85% Mo, the remainder Fe, including: (1) up to 4.9% increase in density; and (2) up to 32% increase in strength.
  • the structural condition of the sintered specimens before UIT and after UIT is shown in FIGS. 66-67 , respectively.
  • the UIT conditions to attain this are preferably as follows: f—27 kHz; A—28 ⁇ m; NI64; Pressure—17 kg; Indenter—6.35 ⁇ 25 mm; Feed—400 mm/min.; Cross feed—0.5 mm/travel; Static pressing at a level of 0.5 YS; Ultrasonic impact duration—1.2-2 msec. This material effect is attained by intense ultrasonic plastic deformation of the surface material and activation therethrough of diffusion processes caused by ultrasonic wave during ultrasonic impact.
  • a material effect attained in aluminum alloys by UIT of the invention is the fatigue limit of specimens made of 6061 T6 alloy increased by 21% and the fatigue limit of the structure, which is equivalent to the type of a welded joint, increased by 32%.
  • the outcome is shown in FIG. 68 .
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; P—up to 900 W; A—up to 30 ⁇ m; Treatment speed—1.2 sec./cm per 2 passes, i.e., 0.6 sec./cm per pass for lap welds; Ultrasonic impact duration—1.2-1.7 msec.
  • This material effect is attained by introduction of compressive stresses of high level, stress concentration reduction, and creation of a physical barrier against mesostructural defect formation in the region of directed plastic deformation and compressive stresses corresponding to the level of defects.
  • FIGS. 69-70 Another material effect attained in aluminum alloys is increased high-cycle fatigue strength in particular of welds in aluminum alloy AA5083 (or AlMg4.5Mn) was about 80% for 8 mm lap joints and specimens with longitudinal attachments.
  • the outcome is shown in FIGS. 69-70 . More particularly, FIG. 69 shows S-N curves for 8 mm specimens with longitudinal attachments and FIG. 70 shows S-N curves for 8 mm specimens of lap joints.
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; P—up to 900 W; A—up to 30 ⁇ m; Ultrasonic impact duration—1.2-1.7 msec.
  • This material effect is attained by introduction of compressive stresses of high level, stress concentration reduction, and suppression of possible mesostructural damages by means of ultrasonic recrystallization in solid solution and activation of ultrasonic diffusion at grain boundaries during ultrasonic impact in accordance with the invention.
  • Another material effect attained in aluminum alloys is suppression of near-surface, specifically casting porosity at a depth of up to 2.5 mm and as a result of this life extension of cast wheels, specifically automobile wheels, made of alloys AlSi7Mg, AlSi9Mg and AlSi11Mg.
  • the outcome is shown in FIGS. 71-72 .
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; Feed—400 mm/min.; Cross feed—0.5 mm/travel; Pressure—15 kg; A—30 pm; Pass 1: Indenter—6.35 ⁇ 25 mm, R5.5 mm; Pass 2: ⁇ —9.05 ⁇ 25 mm, R10 mm; Ultrasonic impact duration—1.2-1.7 msec.
  • This material effect is attained by intense plastic deformation of the treated material near-surface layer, ultrasonic diffusion at defect boundaries, closed under ultrasonic impact, in the form of pores or discontinuities in a material and suppression of mesostructural defects in the region of normalized plastic deformation and compressive stresses, corresponding to the level of plastic deformations, under normalized ultrasonic impact of the invention and effects accompanying its influence on the structure, which are caused, in particularly, by reduced deformation resistance during propagation of the ultrasonic stress wave in the material being deformed by the ultrasonic impact.
  • FIGS. 73-74 show impact strength on specimens with a strengthened notch and FIG. 74 shows impact strength on specimens cut out from a strengthened wheel.
  • the UIT and ultrasonic impact machining (UIM) conditions made it possible to fix the impact strength in the region of intense plastic deformation caused by impact loading at the level of original material.
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; Feed—400 mm/min.; Pressure—15 kg; Pin—9.05 ⁇ 25 mm, R0.25 mm; Wedge 44° ; Condition 1: A—10 ⁇ m; Condition 2: A—20 ⁇ m; Condition 3: A—30 ⁇ m; Ultrasonic impact duration—1.2-1.7 msec.
  • UIT conditions are: f—27 kHz; Indenter—6.35 ⁇ 25 mm, R25 mm; UIT conditions: Pass 1: A—20 ⁇ m and Pass 2: A—12 ⁇ m; UIM conditions: V—18 m/min.; Feed—0.5 mm/rev.; Indenter—6.35 ⁇ 33 mm, R25 mm; Pass 1: Pressure—15 kg and A—22 ⁇ m; Pass 2: Pressure—7 kg and A—12 ⁇ m; Ultrasonic impact duration—1.2-1.7 msec.
  • a Charpy Test is a pendulum-type single-blow impact test in which the specimen, which is usually notched, is supported at both ends as a simple beam and broken at the notch, a dynamic stress concentrator, by an impact of a falling pendulum.
  • the energy absorbed is taken as a measure of impact strength or notch toughness calculated by the subsequent rise of the pendulum (following the impact upon the specimen being broken).
  • the Charpy value is directly affected by the condition of the notch mesostructure, which according to the invention is controlled by normalizing plastic deformation during the action of the ultrasonic impact of the present invention and ultrasonic stress waves initiated thereby.
  • FIGS. 75-77 Another material effect attained in aluminum alloys by UIT in accordance with the present invention is specifically precipitation of silicon inclusions from solid solution of AlSi 11 Mg alloy, which are alloying inclusions and increase the material strength.
  • This effect is shown in FIGS. 75-77 . More particularly, FIG. 75 shows an untreated specimen structure; FIG. 76 shows silicon precipitates on a UIT treated specimen and FIG. 77 shows microhardness distribution in depth of untreated specimens and UIM specimens, which clearly demonstrates the increase of, in particular, microstrength of the treated surface and treated material at the depth of at least 2 mm due to precipitation of silicon inclusions in the layer.
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; V—18 m/min.; Feed—0.5 mm/rev.; Indenter—6.35 ⁇ 25 mm, R25 mm; Pass 1: Press—15 kg and A—22 ⁇ m; Pass 2: Press—7 kg and A—12 ⁇ m; Ultrasonic impact duration—1.2-1.7 msec.
  • This material effect is attained by UIM in accordance with the present invention by strengthening a surface layer due to structural changes occurring therein. In the surface layer, a more solid eutectic structure ( ⁇ +Si)+Si forms out of two-phase condition of the original structure ( ⁇ +eutectic ( ⁇ +Si)+Si). This process is also accompanied by migration of silicon inclusions to the surface under ultrasonic impacts and substantially reflects the objective ability of Al—Si alloys to be strengthened due to silicon precipitation in the near-surface layer.
  • Another material effect attained in aluminum alloys by UIT/UIM in accordance with the invention is a recovery of properties of 2024-T351 alloy after corrosion exfoliation.
  • the yield strength of exfoliated specimens increased by 33% (19% increase as against the untreated non-exfoliated material), the ultimate strength increase by 24% (as against the untreated non-exfoliated material, after UIT/UIM an increase is up to typical strength of the material within measuring accuracy).
  • the outcome is shown in FIGS. 78-79 .
  • the UIT conditions to attain this material effect are preferably as follows: f—36 kHz; Indenter—5 ⁇ 17 mm, R25 mm; A—18 ⁇ m; NI64; Pressure—3 kg; Feed—400 mm/min.; Cross feed—0.5 mm/travel; Ultrasonic impact duration—1.0-1.3 msec. This material effect is attained by ultrasonic impact diffusion at grain boundaries.
  • FIG. 80 shows the effect of UIT in accordance with the invention on fatigue resistance of specimens with different degree of corrosion.
  • the UIT conditions to attain this material effect are preferably as follows: F—36 kHz; Indenter—5 ⁇ 17 mm, R25 mm; A—20 ⁇ m; NI64; Press—3 kg; Feed—400 mm/min; Cross feed—0.5 mm/travel; Ultrasonic impact duration—1.0-1.3 msec.
  • UIT of the invention changes the crack nucleation mechanism.
  • cracks nucleate from intergranular cracking on the interface of the corrosion region and substrate; and for lightly corroded specimens with UIT of these portions in accordance with the invention, cracks do not nucleate. This effect is explained by mechanical closing of the grain boundaries followed by ultrasonic diffusion therebetween in the area of intergranular corrosive damage under intense ultrasonic plastic deformation.
  • FIG. 81 shows a structure in a surface layer before UIT treatment
  • FIG. 82 shows a finer grain structure refined by UIT.
  • the UIT conditions to attain this material effect are preferably as follows: f—36 kHz; Indenter—5 ⁇ 17 mm, R25 mm; A—15 ⁇ m; NI64; Press—3 kg; Feed—1000 mm/min.; Cross feed—0.5 mm/travel; Ultrasonic impact duration—0.9-1.2 msec.
  • This material effect of grain refinement occurs due to: formation of high dislocation density and twinning structure because of additional deformation; formation of microband structure; subdivision of microband structure into submicron grains; and further breakdown of the subgrains to be equiaxed.
  • Another material effect attained in aluminum alloys by UIT in accordance with the invention is precipitate migration and occurrence of microbands 10-15 nm wide. This accompanies the process of subfinegrain structure self-arrangement and increases the resistance of the mesostructure to mechanical and corrosive damage in the surface layer at nanolevel.
  • two effects that occur due to UIT of the invention are an increase in microhardness in the surface layer and hence an increase in static strength of the material, and creation of conditions for fatigue strength improvement through the reduction of distribution density of precipitates, i.e., structural stress concentrators, as well as an increase in structural homogeneity in the surface layer. This effect is shown in FIGS. 83-85 .
  • FIG. 83 shows microhardness distribution
  • FIG. 84 shows a surface layer structure before UIT treatment of the invention
  • FIG. 85 shows microbands in a UIT specimen.
  • EDS energy dispersive spectroscopy
  • the UIT conditions to attain this material effect are preferably as follows: f—36 kHz; Pin—5 ⁇ 17 mm, R25 mm; A—18 ⁇ m; NI64; Pressure—3 kg; Feed—400 mm/min.; Cross feed—0.5 mm/travel; Ultrasonic impact duration—1.0-1.3 msec.
  • This material effect is attained by a geometric dynamic recrystallization process in which the high energy and high temperature may achieve a critical level and hence cause the precipices to migrate. In any case, this effect is accompanied by a normalized action of the ultrasonic impact, local heating, heat removal, distribution of a normalized ultrasonic stress wave and, as a result thereof, normalization of metal plastic deformation.
  • a material effect attained in bronze by UIT in accordance with the invention is an increase in corrosion-fatigue strength, in particular of Cu 3 bronze propellers (BrAl 9 Fe 4 Ni 4 ).
  • the outcome is shown in FIGS. 86-87 . More particularly, FIG. 86 shows corrosion damage on an untreated sample surface and FIG. 87 shows a surface of a sample after UIT.
  • the UIT conditions to attain this material effect are preferably as follows: f—27 kHz; P—900 W; A—up to 30 ⁇ m; Pins—3 ⁇ 20 mm, R3 mm.
  • This material effect is attained by introduction of compressive stresses of high level, modification of the surface layer structure, ultrasonic diffusion at boundary closing of structural defects such as pores, protection against damages and suppression of mesostructural damages at micro and macro levels.
  • the material effects described above are attained by controlling ultrasonic impact parameters during its soft and force phases.
  • the major criterion of setting ultrasonic impact parameters is a specific engineering task that governs the requirements to the depth of controlling thereof.
  • the ultrasonic impact parameters are set based on experimental or expert data.
  • the depth of controlling ultrasonic impact parameters specifically a resultant velocity at the onset of impact, impact energy, repetition rate and time of impact, amplitude and phase of impact, is defined by a specific task based on experimental or expert data, wherein these parameters are set with a scatter from 5% to random values based on specific technical requirements and practical results.
  • any of the above described types or symptoms of degradation can be prevented or suppressed by the described engineering solution on the material either individually or in combination to provide at least one desired material effect to achieve any desired technical effect or task.
  • degradation based on corrosion cracking can be addressed individually to achieve one technical effect or can be addressed in combination, for example, with thermal cracking and/or erosion to achieve a further technical effect.
  • different data elements are interchangeable to achieve different results or technical effects for different tasks.

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US11/342,846 2005-09-23 2006-01-31 Method of metal performance improvement and protection against degradation and suppression thereof by ultrasonic impact Abandoned US20070068605A1 (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US11/342,846 US20070068605A1 (en) 2005-09-23 2006-01-31 Method of metal performance improvement and protection against degradation and suppression thereof by ultrasonic impact
CN2006800439116A CN101558174B (zh) 2005-09-23 2006-09-22 通过超声冲击改进金属性能和防止及抑制劣化的方法
PCT/US2006/037154 WO2007038378A2 (fr) 2005-09-23 2006-09-22 Procede d'amelioration du rendement du metal et protection contre la degradation et sa suppression par impact ultrasonore
KR1020087009584A KR101362019B1 (ko) 2005-09-23 2006-09-22 초음파 충격에 의한 금속 성능 개선과 금속의 열화로부터의보호 및 열화의 억제를 위한 방법
JP2008532465A JP5682993B2 (ja) 2005-09-23 2006-09-22 超音波衝撃による、金属性能の改善ならびに劣化からの保護およびその抑制の方法
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TWI336730B (en) 2011-02-01
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