WO1992013111A1

WO1992013111A1 - Aluminium alloys, substrates coated with same and their applications

Info

Publication number: WO1992013111A1
Application number: PCT/FR1992/000030
Authority: WO
Inventors: Jean-Marie Dubois; Antoine Pianelli
Original assignee: Centre National De La Recherche Scientifique
Priority date: 1991-01-18
Filing date: 1992-01-15
Publication date: 1992-08-06
Also published as: ES2110492T3; EP0521138A1; JP3244178B2; AU1271792A; DE69223180T2; EP0521138B1; AU648876B2; JPH05505649A; FR2671808B1; DE69223180D1; FR2671808A1

Abstract

Alloys, the essential constituent of which is aluminium, metal deposits using on said alloys, substrates coated with same and their application. The alloys of the present invention are characterized by having the following atomic composition (I): Ala?Cub?Cob'?(B, C)c?Md?Ne?If?, a + b + b' + c + d + e + f = 100 number of atoms, a 50, 0 b < 14, 0 b' 22, 0 < b + b' 30, 0 c 5, 8 d 30, 0 e 4, f 2, M being one or more elements selected from Fe, Cr, Mn, Ni, Ru, Os, Mo, V, Mg, Zn, Pd; N being one or more elements selected from W, Ti, Zr, Hf, Rh, Nb, Ta, Y, Si, Ge, the rare earths; I being the impurities inevitably formed during processing; and in that they contain at least 30 % in mass of one or more quasicrystalline phases.

Description

The present invention relates to alloys, the essential constituent of which is aluminum, the substrates coated with aluminum alloys, and their applications.

'5 these alloys and the applications of these alloys, for example * for the constitution of thermal protection elements.

Various metals or metal alloys, for example aluminum alloys, have hitherto found numerous applications because of their advantageous properties and in particular their mechanical properties, their good thermal conductivity, their lightness, their low cost. . Thus, for example, cooking utensils and appliances are known, anti-friction bearings, chassis or apparatus supports, various parts obtained by molding. However, most of these metals or metal alloys have drawbacks for certain applications, linked to their insufficient hardness and resistance to wear, and to their low resistance to corrosion, in particular in an alkaline medium. Various attempts have been made to obtain improved aluminum alloys. Thus, European patent 100287 describes a family of amorphous or microcrystalline alloys having improved hardness, usable as reinforcing elements of other materials or for obtaining surface coatings improving resistance to corrosion or to wear. However, a large number of the alloys described in this patent are not stable at temperatures above 200 ° C., and during a heat treatment, in particular the treatment to which they are subjected when deposited on a substrate, they change structure: return to the microcrystalline state in the case of essentially amorphous alloys, grain magnification for essential alloys-

11 microcrystalline which initially have a grain size of less than one micron. This change in structure is

35 talline or morphological induces a change in the physical characteristics of the material which essentially affects its density. This results in the appearance of micro-cracks, hence a brittleness, which adversely affects the mechanical stability of the materials.

Another family of alloys has been described in EP 356287. These alloys have improved properties. However, their copper content is relatively high.

Thermal stability is an essential property for an alloy to be used as a thermal barrier.

Thermal barriers are assemblies of one or more materials intended to limit the heat transfer to or from parts and components of equipment in many domestic or industrial devices. For example there may be mentioned the use ^'of thermal barriers in the heating or cooking devices, irons at the attachment of the hot part of the carcass and thermal insulation; in cars, at several points such as the turbocharger, the exhaust pipe, the insulation of the passenger compartment, etc .; in aeronautics, for example on the rear of compressors and reactors.

Thermal barriers are sometimes used in isolation in the form of a screen, but very often they are directly associated with the heat source or with the part to be protected for reasons of mechanical strength. Thus, mica sheets, ceramic plates, etc. are used in household utensils, adapting them by screwing or gluing, or sheets of agglomerated glass wool supported by a metal sheet. A particularly advantageous method for adding a thermal barrier to a part, in particular to a metallic part, consists in depositing on a substrate the material constituting the barrier in the form of a layer of thickness determined by a thermal spraying technique such as plasma spraying. for example.

Very often, it is recommended to combine the thermal barrier with other materials also deposited in layers by thermal spraying. These other materials can be intended to ensure the protection of the barrier vis-à-vis external aggressions such as for example mechanical shocks, a corrosive medium, etc. or can serve as a sub-layer for bonding to the substrate.

The most frequently used material in aeronautics to form thermal barriers is yttria zirconia which withstands very high temperatures. The deposition of zirconia is carried out by plasma spraying according to a conventional technique from powder of the material. Zirconia has a low thermal diffusivity (o. = 10 ~ ⁶ m ² / s). However, it has a relatively high specific mass d, which is a drawback for certain applications; in addition, some of its mechanical properties, such as hardness, resistance to wear and abrasion are low. Other materials are used as a thermal barrier. Mention may be made of alumina which has a specific mass lower than that of zirconia, a diffusivity and a specific heat greater than that of zirconia, but whose mechanical properties are not satisfactory. Mention may also be made of stainless steels and certain refractory steels which offer thermal insulation properties, but which have a high specific mass.

The object of the present invention is to provide a family of alloys having high hardness and thermal stability, improved ductility and resistance to corrosion. The present invention thus relates to a new family of alloys, the essential constituent of which is aluminum.

The invention also relates to the metallic coatings obtained from these alloys. Another object of the invention consists of the substrates coated with said alloys.

Finally, another object is constituted by the applications of said alloys.

The alloys of the present invention are characterized in that:

- they have the following atomic composition (I):

Al _a CU _b Cθ _{b '} (B, C) _c M _d N _e I _f (I) in which: a + b + b '+ c + d + e + f = 100 in number of atoms a> 50 0 <b <14 0 <b ¹ <22

0 <b + b '<30 0 <c ≤ 5 8 ≤ d ≤ 30 0 ≤ e ≤ 4 f <2

M represents one or more elements chosen from Fe, Cr, Mn, Ni, Ru, Os, Mo, V, Mg, Zn, Pd;

N represents one or more elements chosen from W, Ti, Zr, Hf, Rh, Nb, Ta, Y, Si, Ge, rare earths; I represents the inevitable processing impurities;

- And that they contain at least 30% by mass of one or more quasicrystalline phases.

In the present text, the expression "quasi-crystal-line phase" includes: 1) the phases having rotation symmetries normally incompatible with translation symmetry, that is to say symmetries of axis of rotation of order 5, 8, 10 and 12, these symmetries being revealed by the diffraction of the radiation. As an example, we can cite the icosahedral phase I of point group m3 5 (cf. D. Shechtman, I. Blech, D. Gratias, J.. Cahn, Metallic Phase w ± th Long-Range Orientational Order and No Translational Symmetry, Physical Revie Letters, Vol. 53, No. 20, 1984, pages 1951-1953) and the decagonal phase D of point group 10 / mmm (cf. L. Benders y, Quasicrystal with One Dimensional Translational Symmetry and a Tenfold Rotation. Axis, Physical Review Letters, Vol. 55, n ° 14, 1985, pages 1461-1463). The diffraction pattern of X-rays d ^r a true decagonal phase was published in "approach to the diffraction structure of membered Quasicrystals, JM Dubois, C. Janot, J. Pannetier, A. Pianelli, Physics Letters 117-8 (1986 ) 421- 2) the approximate phases or approximate compounds which are true crystals insofar as their crystallographic structure remains compatible with the symmetry of transla¬ tion, but which present, in the electron diffraction plate, diffraction figures including the symmetry is close to the axes of rotation 5, 8, 10 or 12. Some of these approximate phases had been identified in compounds of the prior art. Others have been demonstrated in certain alloys of the present invention. Among these phases, one can cite by way of example the orthorhombic phase 0ι, characteristic of an alloy of the prior art having the atomic composition Al65Cu ₂ oFeιoCrs, the mesh parameters of which are: a ₀ d> = 2.366 , b ₀ d) = 1.267, c ₀ <* ι> = 3.252 in nanometers. This orthorhombic phase 0 * ι is said to be approximate to the decagonal phase. It is so close to it that it is not possible to distinguish its X-ray diffraction pattern from that of the decagonal phase.

We can also cite the rhombohedral phase of parameters at _R = 3.208 nm, a = 36 °, present in the alloys of composition close to Al64Cu ₂ 4Fei2 in number of atoms (M. Audier and P. Guyot, Microcrystalline AlFeCu Phase of Pseudo Icoshadral Symmetry, in Quasicrystals, eds. MV Jaric and S. Lundqvist, World Scientific, Singapore, 1989).

This phase is an approximate phase of the icosahedral phase.

We can also cite orthorhombic phases 0 ₂ and O ₃ with respective parameters a _o ** ² - ¹ = 3.83; b _o <*> = 0.41; c ₀ <2> = 5.26 and ao ** ³ - ¹ = 3.25; bot ³ - * = 0.41; Co "* ³ - * = 9.8 in nanometers present in an alloy of composition Al63C *, 7 _# 5Coi7 _f 5Si2 in number of atoms or also the orthorhombic phase O4 with parameters a ₀ << *) = 1.46; b _o '*' **. ¹ = 1.23; c ₀ ⁽ .-> r = 1.24 in nanometers which is formed in the alloy of composition Al63CU8Fei2Cri ₂ in number of atoms of the present invention. The approximants orthorhom¬ biques are described for example in C. Dong, JM Dubois, J. Materials Science, 2_6 (1991), 1647.

We can also cite a phase C, with a cubic structure, very often observed in coexistence with the approximate phases. mantis or quasicrystalline true. This phase, which is formed in certain Al-Cu-Fe and Al-Cu-Fe-Cr alloys, consists of a super-structure, by chemical effect of the alloying elements compared to the aluminum sites, of a phase Cs-Cl type structure and network parameter a * ι = 0.297 n.

A diffraction diagram of this cubic phase has been published (C. Dong, JM Dubois, M. de Boissieu, C. Janot; Neutron diffraction study of the peritectic growth of the Alg ₅ CU ₂ oFei ₅ icosahedral quasicrystal; J. Phys. Condensed Matter, 2 (1990), 6339-6360) for a sample of pure cubic phase and of composition Al _ό sCu∑oFe-is in number of atoms.

One can also cite a phase H of hexagonal structure which derives directly from phase C as demonstrated by the epitaxy relations observed by electron microscopy between crystals of phases C and H and the simple relations which connect the parameters of the crystal lattices, namely u = 3 a * - /? (to within 4.5%) and c _H = 3 fi? ai / 2 (to within 2.5%). This phase is isotype of a hexagonal phase, noted AlMn, discovered in Al-Mn alloys containing 40% by weight of Mn [MA Taylor, Intermetallic phases in the Aluminum-Manganese Binary System, Acta Metallurgica 8 (1960) 256 ].

The cubic phase, its superstructures and the phases derived therefrom, constitute a class of approximate phases of the quasicrystalline phases of neighboring compositions. Among the alloys of the present invention, mention may be made of those, hereinafter designated by (II), which have the above-mentioned atomic composition (I) in which 0 <b <5, 0 <b '<22 and / or 0 < c ≤ 5, and M represents Mn + Fe + Cr or Fe + Cr. These alloys (II) are more particularly intended for the coating of cooking utensils.

Another particularly interesting family, designated below by (III), presents the above atomic composition (I) in which 15 <d <30 and M represents at least Fe + Cr, with an atomic ratio Fe / Cr <2 These alloys (III) have a particularly high resistance to oxidation. In addition, among the alloys (III) one can distinguish a family of alloys (IV) particularly resistant to corrosion:

- in weakly acidic medium (5 <pH <7) if b> 6, b '<7 and e> 0 with N chosen from Ti, Zr, Rh and Nb in strongly alkaline medium (up to pH = 14) if b ≤ 2, b ¹ > 7 and e> 0.

Another family of alloys (V) of interest by ^" the fact that they offer improved resistance to grain growth up to 700 ° C. presents the composition of the alloys (I) with 0 <e ≤ 1, N being chosen among W, Ti, Zr, Rh, Nb, Hf and

Your.

Another family of alloys (VI), having improved hardness, presents the composition of the alloys (I), with b <5 and b ¹ > 5, preferably b <2 and b '> 7.

Finally, the alloys (VII) having composition (I) and which exhibit improved ductility are those for which c> 0, preferably 0 <c ≤ 1, and / or 7 ≤ b ¹ ≤ 14.

The alloys of the present invention are distinguished from the alloys of the prior art, and in particular those of EP 356 287 by their copper content which is lower, or even zero. Alloys are therefore less sensitive to corrosion in an acid medium. In addition, the low copper content is more favorable for obtaining improved ductility by adding other elements such as B or C. In the alloys of the present invention, the copper can be replaced in whole or in part by cobalt. These alloys are therefore particularly advantageous with regard to hardness, ductility and resistance to corrosion both in an alkaline medium and in an acid medium in the range of intermediate pHs (5 <pH <7). The combination of these different properties offers the alloys of the present invention a wide range of applications.

The alloys of the present invention can for example be used as an anti-wear or reference surface coating or for the production of metal-metal or metal-ceramic joints. They are also suitable for all uses involving food contact. The alloys of the invention, preferably those of the group

(VII), can also be used for anti-shock surfaces.

For electrical or electrotechnical applications, or for high frequency heating, the alloys according to the invention of groups (III) and (V) are preferably used.

To produce surfaces resistant to oxidation, the alloys of group (III) will preferably be used, whereas those of groups (III) and (IV) are particularly suitable for surfaces resistant to corrosion. The alloys of groups (III), (IV) and (VII) are particularly suitable for the production of anti-cavitation or anti-erosion surfaces.

The materials of the present invention, and more particularly those of group (V), can be used to constitute thermal protection elements of a substrate, in the form of a thermal barrier or in the form of an undercoat of attachment for thermal barriers made of conventional materials. They have good thermal insulation properties, good mechanical properties, a low specific mass, good resistance to corrosion, especially to oxidation, and great ease of use.

The materials of the present invention which can be used for producing thermal protection elements according to the present invention have values of thermal diffusivity or gold close to 10 ~ ⁶ m ² / s which are very comparable to the thermal diffusivity of zirconia . Given the lower specific gravity d of these materials, the thermal conductivity λ = αdCp in the vicinity of room temperature does not differ significantly from that of zirconia. The quasicrystalline alloys of the present invention are therefore suitable substitutes for the replacement of many thermal barrier materials, and in particular of zirconia, with respect to which they have advantages of low specific mass, excellent mechanical properties in this which relates to hardness, improved resistance to wear, abrasion, scratching, as well as corrosion. The diffusivity of the materials constituting the thermal protection elements of the present invention is reduced when the porosity of the materials increases. The porosity of a quasi-crystalline alloy can be increased by an appropriate heat treatment.

The materials constituting the thermal protection elements of the present invention may contain a small proportion of heat conducting particles, for example metallic aluminum crystals. The thermal conduction of the material will be dominated by the conduction properties of the matrix as long as the particles do not coalesce, that is to say as long as their volume proportion remains below the percolation threshold. For approximately spherical particles with a weakly distributed radius, this threshold is around 20%. This condition implies that the material constituting the thermal protection element contains at least 80% by volume of quasi-crystalline phases as defined above. Preferably, therefore, materials containing at least 80% of quasi-crystalline phase are used for their application as a thermal barrier.

At temperatures below about 700 ° C, the thermal protection elements can be used as thermal barriers. Such temperature conditions correspond to most domestic or automotive applications. In addition, they have a great ability to resist the stresses due to the expansion of the support and their expansion coefficient is intermediate between that of metal alloys and that of insulating oxides. Preferably, for temperatures above about 600 "C, the quasicrystalline alloys constituting the thermal barriers can contain stabilizing elements chosen from W, Zr, Ti, Rh, Nb, Hf and Ta. The content of stabilizing element is less than or equal 2% by number of atoms.

The thermal barriers of the present invention can be multi-layer barriers having an alternation of layers of materials which are good conductors of heat and layers of materials which are poor conductors which are alloys. almost crystalline. Such structures constitute, for example, abradable thermal barriers.

For applications in which temperatures reach values greater than about 600 ° C., the thermal protection elements of the present invention can be used as a bonding undercoat for a layer serving as a thermal barrier and constituted by a material. of the prior art such as zirconia. In these temperature ranges, the materials constituting the thermal protection elements of the present invention become super¬ plastic. They therefore correspond well to the conditions of use required for the production of a bonding sub-layer while being capable of participating themselves in the isolation of the substrate. Thus, the thermal protection elements of the present invention can be used up to a few tens of degrees from the melting point of the material from which they are made. This limit is around 950 ° C to 1200 ° C depending on the composition.

The alloys according to the invention can be obtained by conventional metallurgical production processes, that is to say which comprise a slow cooling phase (ie ΔT / t less than a few hundred degrees). For example, ingots can be obtained by melting separate metallic elements or pre-alloys in a graphite crucible brazed under a protective gas blanket (argon, nitrogen), a blanket flux used in conventional metallurgy ¬ ration, or in a crucible kept under vacuum. It is also possible to use refractory ceramic or copper crucibles cooled by high frequency current heating. The preparation of the powders necessary for the metallization process can be carried out for example by mechanical grinding or by ato isation of the liquid alloy in a jet of argon according to a conventional technique. The alloying and atomizing operations can be carried out in sequence without requiring the casting of intermediate ingots. The alloys thus produced can be deposited in thin form, generally up to a few tens of micrometers, but also in thick form, up to several millimeters, by any metallization technique, including those which have already been mentioned.

The alloys of the present invention can be used in the form of a surface coating by deposition from a pre-prepared ingot, or of ingots of the separate elements, taken as targets in a sputtering reactor, or also by vapor phase deposition. produced ^" by vacuum melting of the solid material. Other methods, for example those which employ sintering of agglomerated powder, can also be used. The coatings can also be obtained by thermal spraying, for example using an oxy-gas torch, a super-sonic torch or a plasma torch The thermal spray technique is particularly interesting for the development of thermal protection elements.

The present invention will be explained in more detail with reference to the following nonlimiting examples.

The alloys obtained were characterized in the raw state by their X-ray diffraction diagram with a wavelength λ = 0.17889 nm (cobalt anticathode), supplemented when necessary by diagrams electron diffraction recorded on a Jeol 200 CX electron microscope. Some alloys have been subjected to temperature maintenance under secondary vacuum or in air in order to assess their thermal stability and their ability to resist oxidation. The morphology of the phases and the grain size obtained in the raw state of preparation were analyzed by optical micrography using an Olympus microscope.

The hardness of the alloys was determined using the WOLPERT V-Testor 2 durometer under loads of 30 and 400 grams.

An estimate of the ductility of certain alloys was obtained by measuring the length of the cracks formed from the angles of the cavity under load of 400 grams. An average value of this length, as well as the hardness, was evaluated from at least 10 different fingerprints distributed on the sample. Another estimate of the ductility is based on the amplitude of the deformation produced before rupture during a compression test applied to a cylindrical specimen of 4.8 mm in diameter and 10 mm in height machined with perfectly parallel faces perpendicular to the cylinder axis. An INSTROM brand traction / compression machine was used.

Finally, the coefficient of friction of a 100C6 steel ball on a substrate coated with an alloy of "the present invention was measured using a tribological tester of the pion / disc type and brand CSEM.

The electrical resistivity of the samples was measured at room temperature on cylindrical specimens 20 mm long and 4.8 mm in diameter. The conventional method known as 4 points was used, with a constant measuring current of 10 A. The voltage across the internal electrodes was measured with a high precision nanovoltmeter. A measurement was made as a function of the temperature using a specifically adapted oven. The melting temperatures of some alloys were determined on heating with a speed of 5 ° C / min by Differential Thermal Analysis on a SETARAM 2000C device.

The crystallographic structure of the alloys was defined by analysis of their X-ray diffraction diagram and their electron diffraction diagrams.

Example 1 Development of Quasicrystalline Alloys A series of alloys was produced by melting pure elements in a high frequency field under an argon atmosphere in a cooled copper crucible. The total mass thus produced was between 50 g and 100 g of alloy. The melting temperature, which depends on the composition of the alloy, has always been found in the temperature range between 950 and 1200 ^a C. During the maintenance of fusion of the alloy, a cylindrical test tube full of 10 mm + 0.5 mm in diameter and a few centimeters in height was formed by aspiration of the molten metal in a quartz tube. The the cooling rate of this sample was close to 250 ° C per second. This sample was then cut with a diamond saw to shape the metallography and hardness specimens used in the examples below. Part of the test piece was fragmented for thermal stability tests and a crushed powder fraction for X-ray diffraction analysis of each alloy. A similar assembly was used to obtain the 4.8 mm diameter cylindrical samples intended for electrical resistivity. The cooling rate of the specimen was then close to 1000 ° C per second.

Table 1 below gives the quasicrystalline phase content of the alloys according to the invention obtained, as well as the melting temperature of some of them. The X-ray diffraction patterns and the electron diffraction patterns were recorded for the quasicrystalline alloys listed in Table 1. Their study made it possible to determine the crystallographic nature of the phases present. This is how, for example, alloys 2, 5, 7, 8, 9, 19, 22 mainly have the O * phase. and the alloy 1 ma mainly phase C. The alloy 3 mainly contains phase H. The alloy 6 consists essentially of phase H, as well as a small fraction of phase C. The other alloys contain varying proportions of phases C, 0 * ι, O ₃ , O4 (and H for 23).

TABLE 1

U

TABLE 1 (continued)

A bath of one hundred (100) kilograms of an alloy producing a mass fraction of more than 95% of quasicrystalline phase has been developed. The nominal composition of the alloy was Al ₆ 7Cu9 _f 5Fei ₂ Cr * n ₍ 5 in number of atoms (alloy 39). tion was made from industrial metallic components, namely aluminum A5, a Cu-Al-Fe alloy containing 19.5% Al by weight, 58.5% Cu by weight and 21.5 % Fe by weight. These elements and alloys were introduced cold into a graphite crucible brazed with alumina. Their merger was carried out under a hedging flow which was maintained until the end of the operation. A high frequency generator of 125 k was used. After fusion of this charge and homogenization of its temperature at 1140 "C, pure iron in bars of 8 mm in diameter then Al-Cr briquettes containing 74% by weight of Chromium and 14% by weight of flux to reach the nominal composition of the alloy. After homogenization, casting was carried out in ingot molds of 2 kg of the entire melt. Two samples, respectively in the middle of the casting and at the end, were analyzed. wet and gave two very similar compositions of Al66,8CU9,4Fei2,2Crιι _# 5 no, ι in number of atoms.The rate of impurities, carbon and sulfur, was found less than 0.1% at. The X-ray diffraction examination of several ingots of samples, reduced to powder, shows diffraction diagrams corresponding to an O * - phase, approximating the true decagonal phase.

The specific heat of the alloy was determined in the temperature range 20-80 "C with a SETARAM scanning calorimeter. The thermal diffusivity of a pellet of this alloy 15 mm thick and 32 mm in diameter was deduced from the temperature / time curve measured on one face of the patch, knowing that the opposite face, previously blackened, was irradiated by a laser flash of calibrated power and shape. The thermal conductivity is deduced from the two previous measurements, knowing the specific gravity of the alloy which has been measured by the Archimedes method by immersion in butyl phthalate maintained at 30 "C (+ 0.1 ° C) and found equal to 4.02 g / cm ³ . Comparative Example 3

Elaboration of alloys of the prior art By way of comparison, a series of alloys known from the prior art was prepared according to the method of example 1. These compositions are collated in table 2 below. The alloys contained at most 30% by mass of quasi-crystalline phase, with the exception of that whose atomic copper content was greater than 18%.

TABLE 2

Example 4

Thermal stability The thermal stability of some alloys of the present invention has been evaluated. The selected alloys were subjected to maintenance at different temperatures for periods ranging from a few hours to several tens of hours. Fragments extracted by breaking the ingots prepared according to Example 1 were placed in quartz ampoules sealed under secondary vacuum. The volume of these fragments was of the order of 0.25 cm ³ . The ampoules were placed in an oven previously heated to the treatment temperature. At the end of the treatment, they were cooled under vacuum to ambient temperature by natural convection in air or at a controlled speed. The fragments were then ground for X-ray diffraction examination. Electron diffraction examinations were also carried out. The experimental conditions of the heat treatments are summarized in table 3 below.

TABLE 3

The structural development of the alloys during isothermal treatment of the present example was assessed by comparison with the X-ray diffraction diagrams recorded very before and after the heat treatment respectively. It is remarkable to note that these diagrams do not present any major modification neither in the number of diffraction lines nor in their relative intensities. However, there is a refinement of the diffraction lines which is due to the well-known phenomenon of grain enlargement at high temperature.

The alloys of the present invention are thermally stable in the sense that their structure, as it is charac¬ terized by the appropriate diffraction figures, does not change essentially during isothermal heat treatments at temperatures which can reach the melting temperature of the alloys. In other words, the mass fraction of quasicrystalline phase present in the raw state of production does not decrease during temperature maintenance.

Example 5 Oxidation resistance Samples in fragments identical to those described in Example 4 were subjected to heat treatments in an oven open to air, under conditions summarized in Table 4 below.

TABLE 4

The comparison between the diffraction diagrams of the samples before treatment and those recorded at the end of the thermal air treatments shows that the samples have not undergone any alteration. Specifically, no trace of grain wholesale- quenched, is detectable from the diffraction line widths that remain identical to those of crude 1'état characteristics diagrams ^development.

Example 6 Morphology and Grain Size The alloys of the present invention, produced according to the method of Example 1, are polycrystalline materials whose morphology has been studied by optical microscopy according to a conventional metallography technique. For this, the 10 mm diameter pellets (produced according to the method of Example 1) were finely polished and then attacked with an appropriate metallographic reagent. The metallographic images were photographed with an Olympus optical microscope, working in white light. The grain size observed is between a few micrometers and a few tens of micrometers. The same characterization method was applied to the samples treated with air in the temperature range 400 "C to 500 ° C as described in Table 4 of the example above. give in. On the metallographic images thus obtained, it has been found that the alloys have not undergone grain enlargement at the end of these heat treatments. It follows that the polycrystalline morphology of these materials, which determines many thermomechanical properties, in particular the macroscopic hardness (H ₄ oo), the coefficients of friction, the elastic limit, the resilience, is not sensitive to temperature maintenance can reach at least 500 "C for at least several tens of hours, including in the presence of air. Example 7

Hardness and ductility at room temperature The Vickers hardnesses of the alloys of the present invention and of certain alloys of the prior art were measured at room temperature on fragments of alloys produced according to the method of Example 1, coated in a resin for metallographic use, then finely polished. Two loads of the microdurometer, respectively 30g and 400g, were used. The results are given in Table 5 below. The Vickers hardnesses observed for the alloys of the present invention are particularly high in comparison with the Vickers hardnesses under load of 400 grams recorded for the alloys of the prior art prepared as in Example 3 (sample 41 to 46). The presence of cobalt in the alloys of the present invention considerably increases the hardness observed since certain values exceed HV00 = 800.

In general, the ductility of alloys with high hardness is relatively low. However, it is surprisingly found that the alloys of the present invention containing cobalt have a higher ductility. For the alloys of the present invention not containing cobalt, it is possible to improve the ductility by means of additions, for example of boron or carbon. To simply assess the effect of such additions on the ductility of certain alloys, the average length of the cracks that form from the angles of the Vickers cavities under load 2 D of 400 grams was measured. The shorter the length, the more ductile the alloy. Some results are reported in Table 5.

TABLE 5

In addition, a compression test was carried out with alloy 2 of Example 1, which does not contain boron, and alloy 19, modified by adding 3.3 atomic% of boron. The test was carried out at ambient temperature, under increasing load, on cylindrical specimens with a diameter of 4.8 mm and 10 mm in height. The faces of the cylinder, on which the load is applied, have been very carefully machined from so as to be perfectly parallel to each other and perpendicular to the axis of the cylinder. From the deformation - compressive stress curves which were recorded during the deformation of test specimens of alloys 2 and 19 (such as elaborates according to the method of example 1), it was found that the addition boron doubles the deformation obtained at break, which reaches about 2%, and the limit at break, which exceeds 1000 MPa.

EXAMPLE 8 Electrical Resistivity at Room Temperature

Resistivity measurements were carried out for alloys according to the invention, and, for comparison, for compositions of the prior art. In all cases, cylindrical test pieces prepared according to the procedure of Example 1 were used.

The results obtained are collated in Table 6 below.

The compositions 41 to 46 and 40 are alloys of the prior art, the others are alloys according to the invention. The compositions of the prior art have an electrical resistivity at room temperature which is between a few μΩ cm and a few tens of μΩ cm. There is, however, an exception with the alloy 42 of composition AlβsCris in number of atoms which has a resistivity of 300 μΩ cm. This value is to be compared with the presence of a rate of quasicrystalline phase fairly close, although lower, of 30% by mass. This state is however metastable and has only been achieved thanks to the high cooling rate which characterizes the method of preparation of the present test pieces. TABLE 6

The characteristic values of the electrical resistivity of the alloys of the present invention are between 300 and 600 μΩ cm. Such high values mean the quasicrystalline alloys of the present invention for any application where this property must be taken advantage of, such as, for example, Joule heating, resistors with high heat dissipation, electromagnetic coupling, possibly high frequency.

In addition, an alloy representative of the family (III) has a low temperature coefficient of electrical resistivity (1 / p dp / dT). The relative variation of the electrical resistivity with the temperature of a test tube of alloy 2 was measured. This test tube was prepared from a tape 0.1 mm thick and 1.2 mm wide. produced by quenching the liquid alloy on a copper drum, the surface of which scrolled at a speed of 12 m / s (technique, known as melt spinning). The ingot brought to the liquid state had been prepared according to the method of example 1. The test piece was heated at a constant speed of 5 ° C./minute and kept in contact with four platinum wires according to the so-called measurement method. in four points. The difference between potential electrodes was 20 mm and the potential measurement carried out with a precision nanovoltmeter. A constant current of 10 A flowed through the test tube through the other two electrodes. The measuring device was kept under a protective argon flow in a suitable oven. It was found that the variation in resistance is linear, which demonstrates that no transformation of the sample takes place during the measurement or during the following heating cycle, in confirmation of the great thermal stability of the alloys (example 4). The temperature coefficient deduced from the curve (l / ρ (20 ° C)) (p (T) -p (20 ° C)) / ΔT is -3.10 - ***. This low value distinguishes the alloy for applications where it is preferable to keep the characteristics of the material within a narrow range as a function of the temperature, such as for example heating by electromagnetic induction.

Example 9 Corrosion resistance The dissolution of certain alloys of the present invention in different media was measured as well as that of an alloy of the prior art.

The samples tested are:

- alloy No. 40 of the prior art with 18.5% Cu

- alloy 2 of the invention with 9% Cu - alloy 3 of the invention with 10% Co, 0% Cu

- alloy No. 6 of the invention with 18% Co, 0% Cu.

To measure the dissolution rate, a test tube 10 mm in diameter and 3 mm thick, prepared according to the procedure of Example 1, was immersed for 30 h in a corrosive solution, at different temperatures. The solution was stirred for the duration of the immersion and kept at temperature by a thermostatically controlled bath. After 30 hours, the weight loss of each test piece was determined.

The results are collated in Table 7 below. The quantities given represent the weight loss of the sample in gm-2h "i. ND means" not detected ". TABLE 7

It is well known that the addition of copper decreases the corrosion resistance of aluminum alloys (chapter 7 of Aluminum, Vol.I, d. K.R. Van Horn, American Society for Metals). In dilute acidic medium, for example, aluminum alloys have a high dissolution rate which usually decreases with increasing acid content. Close to the 100% acid concentration, this dissolving rate again increases very sharply. Conversely, on the alkaline side, the behavior of the aluminum alloys is satisfactory until the pH rises above pH = 12. The passivating alumina film which protects them can then go into solution and the aluminum alloys are usually very little resistant to corrosion in a strongly alkaline medium.

The above tests show that the present invention provides alloys which have excellent corrosion resistance in an acid medium (No. 2, having a Cu content greater than 5 atomic%), or in a strongly alkaline medium (No. 3 and 6, having a cobalt content greater than 5 atomic%).

Thus, the quasicrystalline alloys of the present invention combine several properties which designate them very particularly for many applications in the form of surface coatings: high hardness, low but not negligible ductility, thermal stability, high resistance to corrosion. The following example will show that these alloys retain these properties after they have been used as a surface coating. They then have a coefficient of friction remarkably weak which enriches the range of interesting properties already mentioned.

Example 10 Use of an Alloy of the Present Invention for the Production of a Surface Deposit

An ingot of two kilograms of the alloy produced according to Example 2 was reduced to powder by grinding using a mill with carbide steel concentric rollers. The ^" powder thus obtained was sieved so as to retain only the fraction of grains whose size was between 25 μm minimum and 80 μm maximum. A deposit of 0.5 mm thick was then produced by spraying this powder onto a mild steel plate previously sandblasted. This spraying was carried out by means of a Metco flame torch fed by a mixture dosed with 63% hydrogen and 27% oxygen. The operation was carried out under a protective atmosphere of 30% hydrogenated nitrogen so as to prevent any oxidation of the sample After removal of the surface roughness by mechanical polishing, an examination by X-ray diffraction revealed that the alloy deposited consisted of at least 95% icosahedral phase. The specimen, consisting of the steel substrate provided with its quasicrystalline coating, was then divided into two parts by cutting and one of these parts was subjected to a heat treatment at 500 ° C. in air as indicated in example 4. A study of the X-ray diffraction diagram carried out on the treated sample does not reveal any major modification of the structure after 28 hours of maintenance and confirms the very high thermal stability of the alloy, including following the surface metallization operation. Table 8 below summarizes the results of the hardness measurements carried out, as in Example 7, before and after heat treatment. The value measured on the ingot before reduction to powder is also given. TABLE 8

In addition, the coefficient of friction of a Brinell ball, made of tool steel 100C6, on the deposit of this example, was measured using a tribological tester of the pin-disc type of CSEM brand. A normal force F _n - 5N was applied to the wiper normally at the plane of the deposit. The force of resistance to displacement of the wiper F _t (N), measured (in newtons) tangentially to the displacement, gives the coefficient of friction μ = F _t (N) / F _n , under constant normal force, which is reported in Table 8. It should be noted that the values in Table 8 are comparable, or even significantly better than the values used for other materials used in tribological applications.

Example 11 Thermal diffusivity at room temperature. The thermal diffusivity, the specific mass d and the specific heat Cp were determined in the vicinity of room temperature for several samples prepared according to Example 1 and one sample prepared according to Example 2. The samples prepared according to the method of 1 ' Example 1 are pellets 10 mm in diameter and 3 mm thick. The sample of Example 2 is a pellet 32 mm in diameter and 15 mm thick.

The opposite faces of each pellet have been polished mechanically under water, taking great care to guarantee their parallelism. The structural state of the test pieces was determined by X-ray diffraction and by electron microscopy. All selected samples contained at least 90% quasicrystalline phase volume according to the definition given above.

The thermal conductivity is given by the product λ = αdCp. The thermal diffusivity has been determined using a laboratory device combining the laser flash method with an Hg-Cd-Te semiconductor detector. The laser was used to supply pulses of power between 20 J and 30 J with a duration of 5.10 ^"4 s, to heat the front face of the specimen and the semiconductor thermometer was used to detect the thermal response on the opposite side of the specimen. The thermal diffusivity was deduced from the experiments according to the method described in "A. Degiovanni, High Te p. - High Pressure, 17 (1985) 683.

The specific heat of the alloy was determined in the temperature range 20-80 ° C with a SETARAM scanning calorimeter.

The thermal conductivity λ is deduced from the two previous measurements, knowing the specific mass of the alloy which has been measured by the Archimedes method by immersion in butyl phthalate maintained at 30 ° C (+ 0.1 ° C ).

The values obtained are given in table 9. This table contains, for comparison, the values relating to some materials of the prior art (samples 5 to 13), some of which are known as thermal barrier (samples 5 to 8 ).

In Table 9, the acronyms in the last column have the meanings given above.

These results show that, at room temperature, the thermal conductivity of the quasicrystalline alloys constituting the protective elements of the present invention is considerably lower than that of metallic materials (aluminum metal or quadratic Al 2 Cu), given by way of comparison. It is two orders of magnitude less than that of aluminum and an order of magnitude to that of stainless steel usually considered as a good thermal insulator. In addition, it is lower than that of alumina and quite comparable to that of zirconia doped with Y ₂ ° ₃ 'considered as the archetype of thermal insulators in 1'industrie.

By way of comparison, the thermal diffusivity of the alloys 90, 100, 110, 120 and 130 was determined. These alloys, which form defined aluminum compounds, have compositions close to those of the quasi-crystalline alloys which can be used for the protective elements of the present invention. However, they do not have the quasi-crystalline structure defined above. In all cases, their thermal diffusivity is greater than 5.10 " ⁶ m ² / s, that is to say much greater than that of the alloys selected for the present invention.

Example 12

Thermal diffusivity as a function of temperature

The values of a were recorded as a function of the temperature up to 900 ° C.

The measurement of the thermal diffusivity was carried out according to the method of Example 11. Each test tube was placed under a stream of purified argon in the center of an oven heated by the Joule effect; the temperature rise rate, programmed by computer, varied linearly at the rate of 5 ° C / min. All the samples according to the present invention show an approximately linear increase in o. with temperature. The value of o; determined at 700 ° C is close to twice that measured at room temperature. Likewise, the specific heat increases with temperature and reaches from 800 to 900 J / kgK at 700 ° C. The specific mass decreases on the order of 1 to 2% as indicated by thermal expansion or neutron diffraction measurements. Consequently, the thermal conductivity remains below 12 W / mK, that is to say the thermal conductivity of stainless steels which are used for certain thermal insulation applications. Figures 1, 2 and 3 respectively represent the evolution of a as a function of the temperature for the alloys 28, 31 and 33. The measurements recorded during heating are represented by black squares, those recorded during cooling by white squares.

Example 13

The variation in the thermal expansion of the alloy 2 was measured. The thermal expansion curve is app ^'araître that the coefficient of expansion depends very little on the tempera- ture and is 9.10 ^-6 / ° C, the value close to that of stainless steels.

Example 14 The superplastic behavior of certain alloys likely to constitute the thermal protection elements of the present invention was studied. Cylindrical test pieces 4 mm in diameter and 10 mm in length, with strictly parallel faces, were produced according to the same method as those of Example 1 with alloys 34 and 35. These test pieces were subjected mechanical compression tests on an INSTROM machine. Tests were carried out up to a load of 250 MPa, at a speed of movement of the beam of 50 μm / min, the temperature being kept constant between 600 and 850 ° C. The two alloys exhibit a superplastic behavior from 600 "C. Example 15

Development of thermal protection elements according to the invention and according to the prior art.

A first series of test pieces has been produced. The substrate was a massive copper cylinder having a diameter of 30 mm and a height of 80 mm and the coating was applied with a plasma torch according to a conventional technique. The C0 test tube is the uncoated copper cylinder. The specimen Cl was coated over its entire surface with a layer of 1 mm thick of the alloy 2 and the specimen C2 was coated with a layer of 2 mm thick of the alloy 2. The C5 test tube comprises a layer of alloy 2 constituting the thermal protection element of the present invention serving as a bonding layer and a layer of yttria zirconia. The C3 and C4 test pieces used for comparison respectively comprise a layer of yttria-containing zirconia and a layer of alumina. Another series of test pieces was produced with, as support, a stainless steel tube having a length of 50 cm, a diameter of 40 mm, a wall thickness of 1 mm (test pieces A0 to A2). In each case, the support tube is coated at one of its ends over a length of 30 cm. In the latter case, the deposits were made with an oxy-gas torch. Table 10 below gives the nature and thickness of the layers for the different test pieces. The precision on the final thicknesses of the deposits was + 0.3 mm. All the test pieces were fitted with very low inertia Chromel - Alumel thermocouples. FIG. 4 represents a test tube of the copper cylinder 1 type comprising a coating 2 and provided with a central thermocouple 3 and a lateral thermo¬ couple 4, both being inserted up to half the length of the cylinder . FIG. 5 represents a hollow tube 5 in which a flow of hot air 6 is passed and which is provided with three thermocouples designated respectively by TI, T2 and T3, the first two being inside the tube and placed respectively at beginning of the coated area and at the end of the coated area, and the third being on the outer surface of the coating. Example 16

Use of protective elements as protection against a flame. The test pieces C0, Cl, C2, C3, C4 and C5 were placed on their base on a refractory brick. Successive heat pulses lasting 10 s were applied to each specimen at 60 s intervals and the response of the thermocouples was recorded. These pulses were produced by the flame of a torch, placed at a constant distance from the specimen and oriented opposite the thermocouple close to the surface. The flow of combustion gases was carefully controlled and kept constant throughout the experiment. Two series of experiments were carried out: one with tests vettes initially at 20 ° C and the other with test tubes initially at 650 ° C.

The CO to C5 test tubes make it possible to define three parameters which summarize the results of the experiment, namely the maximum temperature difference P between the two thermo¬ couples, ΔT / Δt the rate of temperature rise of the lateral thermo¬ couple 4 during the pulse and the temperature increment ΔT produced in the center of the test tube (thermocouple 3). These data are shown in Table 10. It was found that the zirconia layer of the C3 specimen did not resist more than three pulses and was cracked from the first pulse. The C2 sample did not start to crack until the sixth pulse and the C1 sample withstood more than 50 pulses. These results show that the protective elements of the present invention, used as a thermal barrier, have performances at least equivalent to those of zirconia.

Example 17 Use of the protective elements according to the invention as a thermal barrier underlay.

In the C5 specimen, the thermal protection element of the present invention constitutes an undercoat. It was found that the zirconia layer of the C3 specimen did not resist more than three heat pulses and was cracked from the first pulse. For the C5 test tube, also subjected to a series of thermal pulses, the surface temperature of the zirconia deposit, measured by a third thermocouple placed in contact with the deposit at the end of the tests, stabilized at 1200 ° C. . The experiment focused on 50 pulses and the C5 test-tube resisted without apparent damage, although the coeffi¬ cient of copper expansion is close to twice that of the quasi-crystalline alloy, which would imply significant shear stresses at the substrate / deposition interface, if the underlay material does not become plastic. The thermal protection elements of the present invention are therefore well suited to the production of bonding sub-layers, in particular for thermal barriers. TABLE 10

EXAMPLE 18 Application of a thermal protection element of the present invention to the insulation of a reactor. Test specimens A0, A1 and A2 were used to assess the ability of the alloys of the invention to thermally insulate a device. The test pieces were each provided with 3 thermocouples TI, T2 and T3 as shown in FIG. 5. A current of hot air at constant flow rate was sent through the stainless steel tube constituting the substrate of each test piece. The inlet air temperature, measured using the TI thermocouple, was 300 + 2 "C. The surface temperature, measured using the T3 thermocouple, was recorded as a function of the time from the start of the hot air generator The thermocouple T2 made it possible to verify that the transient conditions for establishing the hot air flow were identical for all the measurements.

Figures 6 and 7 show the evolution of the surface temperature of each of the test pieces A0, Al and A2 as a function of time. The surface temperature of the AO specimen (without coating) exceeds at equilibrium that of the A2 specimen by 3

35 ° C approximately and that of the A1 specimen 27 ° C. The thermal protection elements of the present invention give interesting results with regard to thermal insulation.

Claims

1. Alloys, the essential constituent of which is aluminum, characterized in that:

- they have the following atomic composition: Al _a CUbCθb “(B, C) cMdN _e If (I) a + b + b '+ c + d + e + f = 100 in number of atoms a> 50 0 <b <14 0 ≤ b '≤ 22 0 <b + b'<30

0 ≤ c ≤ 5 8 ≤ d <30

0 ≤ e <4 f <2 M represents one or more elements chosen from Fe, Cr, Mn, Ni, Ru, Os, Mo, V, Mg, Zn, Pd;

N represents one or more elements chosen from W, Ti, Zr, Hf, Rh, Nb, Ta, Y, Si, Ge, rare earths;

1 represents the inevitable processing impurities; - And they contain at least 30% by mass of one or more quasicrystalline phases.

2. Alloys according to claim 1, characterized in that they have the atomic composition (I) with 0 <b <5, 0 <b '<22 and / or 0 <c <5, M representing Mn + Fe + Cr or Fe + Cr.

3. Alloys according to claim 1, characterized in that they have the atomic composition (I) with 15 <d ≤ 30, M representing at least Fe + Cr, with an atomic ratio Fe / Cr <2.

4. Alloys according to claim 3, characterized in that b> 6, b '<7 and e> 0 and N is chosen from Ti, Zr, Rh and

Nb.

5. Alloys according to claim 3, characterized in that b <2, b '> 7 and e> _. 0.

6. Alloys according to claim 1, characterized in that 0 <e ≤ 1, N being chosen from W, Ti, Zr, Rh, Nb, Hf and

Your.

7. Alloys according to claim 1, characterized in that b <5 and b '5.

8. Alloys according to claim 7, characterized in that b <2 and b ¹ > 7.

9. Alloys according to claim 1, characterized in that 0 <c <1 and / or 7 <b '<14.

10. Alloys according to any one of claims 1 to 9, characterized in that they are obtained in the form of a solid part.

11. Alloys according to any one of claims 1 to 9, characterized in that they are obtained in the form of a deposit on a substrate.

12. Substrates coated with an alloy according to one of the claims 1 to 9.

13. Application of an alloy according to any one of claims 1 to 9, to the development of anti-wear and / or anti-friction surfaces, anti-shock surfaces, reference surfaces, anti-cavitation surfaces or anti-erosion, surface resistant to oxidation or corrosion.

14. Application of an alloy according to any one of claims 1 to 9, in the preparation of metal-metal joints or metal-ceramic joints.

15. Application of an alloy according to any one of claims 1 to 9, to the coating of utensils for food contact.

16. Electrotechnical applications of the alloys according to any one of claims 1 to 9.

17. Application according to claim 16 for the production of heating elements by electromagnetic induction.

18. Application of an alloy according to any one of claims 1 to 9, to the production of thermal protection elements of a substrate.

19. Application according to claim 18, characterized in that the thermal protection element consists of a quasicrystalline material consisting essentially of said alloy, deposited on the substrate.

20. Application according to claim 19, characterized in that said quasicrystalline material is deposited on the substrate by thermal spraying.

21. Application according to claim 18, characterized in that said quasicrystalline material comprises at least 80% by volume of at least one quasi-crystalline phase.

22. Application according to claim 18, characterized in that said quasicrystalline material has a porosity greater than 10%.

23. Application according to claim 18, characterized in that the thermal protection element constitutes a thermal barrier at temperatures below 800 "C.

24. Application according to claim 23, characterized in that said quasicrystalline material also contains stabilizing elements at a content of less than 2% by number of atoms, chosen from W, Zr, Ti, Rh, Nb, Hf and Ta.

25. Application according to claim 18, characterized in that the thermal protection element is used in the form of an intermediate bonding layer between a support and a thermal barrier, the surface temperature of said barrier possibly being able to exceed 800 °. vs.

26. Application according to claim 25, characterized in that the thermal protection element is constituted by an alternation of layers of quasi-crystalline material and layers of materials which are good conductors of heat.