+

US20170342527A1 - Cobalt-based super alloy - Google Patents

Cobalt-based super alloy Download PDF

Info

Publication number
US20170342527A1
US20170342527A1 US15/500,992 US201515500992A US2017342527A1 US 20170342527 A1 US20170342527 A1 US 20170342527A1 US 201515500992 A US201515500992 A US 201515500992A US 2017342527 A1 US2017342527 A1 US 2017342527A1
Authority
US
United States
Prior art keywords
weight
cobalt
alloys
temperature
phase
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US15/500,992
Inventor
Alexander Bauer
Mathias GOEKEN
Lisa FREUND
Steffen NEUMEIER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Friedrich Alexander Universitaet Erlangen Nuernberg
Original Assignee
Friedrich Alexander Universitaet Erlangen Nuernberg
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Friedrich Alexander Universitaet Erlangen Nuernberg filed Critical Friedrich Alexander Universitaet Erlangen Nuernberg
Assigned to FRIEDRICH-ALEXANDER-UNIVERSITAET ERLANGEN-NUERNBERG reassignment FRIEDRICH-ALEXANDER-UNIVERSITAET ERLANGEN-NUERNBERG ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BAUER, ALEXANDER, FREUND, Lisa, GOEKEN, MATHIAS, Neumeier, Steffen
Publication of US20170342527A1 publication Critical patent/US20170342527A1/en
Abandoned legal-status Critical Current

Links

Images

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/07—Alloys based on nickel or cobalt based on cobalt

Definitions

  • the invention relates to polycrystalline, precipitation-hardened and oxidation-resistant ⁇ / ⁇ ′ cobalt-based superalloys for high-temperature applications.
  • the mechanical properties of the cobalt-based superalloys indicated are superior to those of conventional, carbide-hardened cobalt alloys. Up to a temperature of 800° C., similar hot strengths as those of nickel-based ⁇ / ⁇ ′ forging alloys are achieved, and at temperatures above 800° C. even higher hot strengths than those of nickel-based ⁇ / ⁇ ′ forging alloys are achieved.
  • the creep strengths are likewise significantly higher.
  • Similar proportions of the ⁇ ′ precipitate phase are achieved despite a lower solvus temperature. Owing to the large temperature range between solidus and solvus temperature, the precipitation-hardened ⁇ / ⁇ ′ cobalt-based superalloys are particularly suitable as polycrystalline forging alloys.
  • Cobalt-based and in particular ⁇ / ⁇ ′ nickel-based superalloys are essential materials for many components in jet engines of commercial aircraft or in stationary gas turbines for power conversion. New materials which have a greater heat resistance, longer life and lower production and processing costs make it possible to increase the efficiency of these turbines, lower the costs and reduce the consumption of fossil fuel.
  • ⁇ / ⁇ ′ cobalt-based superalloys generally have a very high solidus temperature in the temperature range from 1300° C. to 1450° C. combined with a relatively low ⁇ ′ solvus temperature in the temperature range from 900° C. to 1150° C. Despite the relatively low ⁇ ′ solvus temperature, very high ⁇ ′ proportions by volume of over 75% can be realized at temperatures up to 900° C. (see, for example, Bauer et al., Microstructure and creep strength of different ⁇ / ⁇ ′-strengthened Co-base superalloy variants, Scripta Materialia 63 (2010) 1197-1200).
  • the ternary ⁇ / ⁇ ′ cobalt-based superalloy Co-9Al-9W (reported in atom%) has, for example, a relatively high proportion by volume of ⁇ ′ precipitates of 58% despite a ⁇ ′ solvus temperature of only about 975° C. Owing to the large temperature range between solidus temperature and ⁇ ′ solvus temperature (forging window), the comparatively low ⁇ ′ solvus temperatures and the high ⁇ ′ proportion by volume at use temperatures, the ⁇ / ⁇ ′ cobalt-based superalloys are thus particularly suitable as forging alloys.
  • Nickel-based superalloys have either a low ⁇ ′ solvus temperature below 1100° C., associated with a low ⁇ ′ proportion by volume at use temperatures of up to 700° C. (e.g. Waspaloy: ⁇ ′ solvus temperature: 1038° C. Semiatin et al., Deformation behavior of Waspaloy at hot-working temperatures, Scripta Materialia 50 (2004) 625-629); ⁇ ′ proportion by volume at use temperature: 25% (ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys, Ed. Davies et al, ASM International, Materials Park, Ohio 44073, USA)) or a high ⁇ ′ proportion by volume at 700° C.
  • ⁇ ′ solvus temperature e.g. Udimet 720Li: ⁇ ′ solvus temperature: 1142° C.; ⁇ ′ proportion by volume at use temperature: 45% (Gu et al., Development of Ni—Co base alloys for high-temperature disk applications, Superalloys 2008, Ed. Roger C. Reed et al., The Minerals, Metals & Materials Society, Warrendale Pa., USA)
  • the alloys are either forgable but have a low strength or they still have a relatively high proportion of the precipitate phase at forging temperatures of from 1000° C. to 1150° C. and are thus deformable only with difficulty or not at all and can be processed only by a powder-metallurgical route. This significantly increases costs.
  • cobalt-based alloys can have a higher hot gas corrosion resistance than nickel-based alloys since a liquid Co-sulfur phase can appear only at 877° C., while a liquid Ni—S phase is formed at as low as 637° C. (see Bürgel, Maier, Niendorf, Handbuch Hochtemperaturtechnik, 4 th revised edition 2011, Vieweg+Teubner Verlag, Springer crampmedien Wiesbaden GmbH 2011, or ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys, Ed. Davies et al, ASM International, Materials Park, Ohio 44073, USA). An increased hot gas corrosion resistance can thus lead to a lengthening of the life.
  • a good oxidation resistance in combination with good mechanical properties is, however, essential for these new ⁇ / ⁇ ′ cobalt-based superalloys to be able to be used in future as high-temperature material.
  • a cobalt-based superalloy comprising 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0-9% by weight of Ta, 0-8% by weight of Ti, 0.1-1% by weight of Si, 0-0.5% by weight of B, 0-0.5% by weight of C, 0-2% by weight of Hf, 0-0.1% by weight of Zr, 0-8% by weight of Fe, 0-6% by weight of Nb, 0-7% by weight of Mo, 0-4% by weight of Ge and a balance of unavoidable impurities.
  • the cobalt-based superalloy comprises 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0-9% by weight of Ta, 0-8% by weight of Ti, 0.1-1% by weight of Si, 0-0.5% by weight of B, 0-0.5% by weight of C, from 0 to ⁇ 2% by weight of Hf, from 0 to ⁇ 0.1% by weight of Zr, from 0 to ⁇ 8% by weight of Fe, from 0 to ⁇ 6% by weight of Nb, from 0 to ⁇ 7% by weight of Mo, from 0 to ⁇ 4% by weight of Ge and a balance of unavoidable impurities.
  • the cobalt-based superalloy advantageously comprises 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0.2-9% by weight of Ta, 0.2-8% by weight of Ti, 0.1-1% by weight of Si, ⁇ 0.5% by weight of B, ⁇ 0.5% by weight of C, 0-2% by weight of Hf, 0-0.1% by weight of Zr, 0-8% by weight of Fe, 0-6% by weight of Nb, 0-7% by weight of Mo, 0-4% by weight of Ge and a balance of unavoidable impurities.
  • the cobalt-based superalloy comprises 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0.2-9% by weight of Ta, 0.2-8% by weight of Ti, 0.1-1% by weight of Si, ⁇ 0.5% by weight of B, ⁇ 0.5% by weight of C, from 0 to ⁇ 2% by weight of Hf, from 0 to ⁇ 0.1% by weight of Zr, from 0 to ⁇ 8% by weight of Fe, from 0 to ⁇ 6% by weight of Nb, from 0 to ⁇ 7% by weight of Mo, from 0 to ⁇ 4% by weight of Ge and a balance of unavoidable impurities.
  • the cobalt-based superalloy which in particular comprises a composition as mentioned above, is advantageously characterized by an intermetallic ⁇ ′ phase having the composition (Co,Ni) 3 (Al, W, Ti, Ta) where at least one of the elements shown in parentheses from each set of parentheses is present in each case.
  • the intermetallic ⁇ ′ phase (precipitate phase) is advantageously present in a proportion by volume of more than 35%, preferably more than 45%.
  • Co as base element forms, among other elements, the face-centered cubic y matrix phase and is an important constituent of the hardening ⁇ ′-(Co,Ni) 3 (Al, W, Ti, Ta) precipitate phase. Co also lowers the stacking fault energy.
  • Ni (nickel) 28-40% by weight
  • the alloy element Cr In order to attain a sufficient corrosion and oxidation resistance, the alloy element Cr should be added in the range indicated. In addition, Cr acts as mixed crystal hardener.
  • Al forms the ⁇ ′ precipitate phase (Co,Ni) 3 (Al, W, Ti, Ta), which contributes significantly to the increasing strength. Furthermore, Al increases the oxidation resistance. Relatively high proportions of Al in the indicated composition range can lead to formation of further intermetallic phases such as CoAl which can inhibit grain growth in forging alloys. This makes it possible to achieve smaller grain sizes and thus higher strengths.
  • W forms the ⁇ ′ precipitate phase Co 3 (Al,W), which contributes significantly to the increasing strength and, as slowly diffusing element, increases the creep strength. Higher contents lead to an excessively high density and further undesirable intermetallic phases can be formed.
  • Si is a critical element and signicantly improves the oxidation resistance. However, excessively large amounts of Si can lead to further undesirable intermetallic phases.
  • B acts as grain boundary strengthening alloy element and improves the oxidation properties. Excessively high concentrations lead to an excessively high proportion of borides. B is preferably present in an amount of more than 0.01% by weight.
  • C acts as grain boundary strengthening alloy element.
  • C forms carbides.
  • C is preferably present in an amount of more than 0.01% by weight.
  • Ta (tantalum): 0.2-9% by weight
  • Ta contributes to the formation of the ⁇ ′ precipitate phase, increases the ⁇ ′ solvus temperature and the ⁇ / ⁇ ′ lattice mismatching. Ta hardens the ⁇ ′ precipitate phase and leads to an increasing strength.
  • the two elements Ta and Ti are necessary particularly when high hot strengths at 800° C. are required.
  • Ti contributes to the formation of the ⁇ ′ precipitate phase, increases the ⁇ ′ solvus temperature and the ⁇ / ⁇ ′ lattice mismatching. Ti hardens the ⁇ ′ precipitate phase and leads to an increasing strength.
  • the two elements Ta and Ti are necessary particularly when high hot strengths at 800° C. are required. Ti can replace W to a substantial extent and in this way reduces the density significantly.
  • Hf stabilizes the ⁇ ′ precipitate phase.
  • Hf is preferably present in an amount of more than 0.2% by weight.
  • Zr serves to increase the grain boundary strength and is able to stabilize the ⁇ ′ precipitate phase.
  • Zr is preferably present in an amount of more than 0.01% by weight.
  • Fe lowers the ⁇ ′ solvus temperature and can be used for setting this, particularly in the case of forging alloys. Fe is also an inexpensive element and can improve the weldability. Excessively high concentrations destabilize the ⁇ / ⁇ ′ microstructure. Fe is preferably present in an amount of more than 0.1% by weight.
  • Nb contributes to the formation of the ⁇ ′ precipitate phase, leads to an increase in strength and increases the ⁇ ′ solvus temperature. Relatively high concentrations within the concentration range indicated can lead to formation of further intermetallic phases which can inhibit grain growth in forging alloys. Smaller grain sizes and thus higher strengths can be achieved as a result. Nb is preferably present in an amount of more than 0.1% by weight.
  • Mo serves as mixed crystal hardening element and can partly replace W and thus decreases the density. Relatively high concentrations lead to formation of further intermetallic phases which can inhibit grain growth in forging alloys. Smaller grain sizes and thus higher strengths can be achieved as a result. Mo is preferably present in an amount of more than 0.1% by weight.
  • Ge forms the ⁇ ′ precipitate phase Co 3 (Al,Ge,W), lowers the ⁇ ′ solvus temperature and can be used for setting this, particularly in the case of forging alloys.
  • Ge is preferably present in an amount of more than 0.1% by weight.
  • FIG. 1 a graph of the relationship between the proportion of precipitates at use temperature and the solvus temperature of the ⁇ ′ phase of ⁇ / ⁇ ′ nickel-based superalloys compared to working examples of the invention
  • FIG. 2 the microstructure of illustrative alloys of the invention
  • FIG. 3 an EBSD measurement to determine the grain size and the twin density of an illustrative alloy of the invention
  • FIG. 4 a graph of the yield point as a function of temperature for illustrative alloys of the invention
  • FIG. 5 a graph of the creep strength of an illustrative alloy of the invention compared to nickel-based superalloys
  • FIG. 6 images of the microstructure of the ternary alloy Co9Al9W compared to an illustrative alloy of the invention
  • FIG. 7 the element distribution in the oxide layer of an illustrative alloy of the invention
  • FIG. 8 scanning electron micrographs of an illustrative alloy of the invention
  • FIG. 9 scanning electron micrographs and transmission electron micrographs of an illustrative alloy of the invention.
  • FIG. 10 a graph of the yield point as a function of temperature for a further illustrative alloy of the invention.
  • compositions of some working examples of the ⁇ / ⁇ ′ cobalt-based superalloys of the invention hereinafter referred to as CoWAlloy0 and CoWAlloy1 and CoWAlloy2, and also some reference alloys are indicated in table 1 below.
  • CoWAlloy0 and CoWAlloy1 and CoWAlloy2 are indicated in table 1 below.
  • Table 1 the properties of working examples of the invention are described in more detail below with the aid of the figures and studies.
  • the alloys which have been developed and are described here have, compared to nickel-based forging alloys, the important advantage that high proportions by volume of precipitates of more than 45% (CoWAlloy0) can be achieved at 750° C. despite the relatively low ⁇ ′ solvus temperatures of about 1050° C. (CoWAlloy0), 1070° C. (CoWAlloy1) and 1030° C. (CoWAlloy2).
  • FIG. 1 shows the relationship between the proportion of precipitates at use temperature and the solvus temperature of the ⁇ ′ phase of ⁇ / ⁇ ′ nickel-based superalloys and the ⁇ / ⁇ ′ cobalt-based superalloy CoWAlloy0 reported here.
  • ⁇ ′ solvus temperatures Despite high proportions by volume of precipitates, easier deformation at typical forging temperatures of from 1000° C. to 1150° C. is made possible by the relatively low ⁇ ′ solvus temperatures.
  • FIG. 2 shows, in different resolutions, the microstructure of the ⁇ / ⁇ ′ cobalt-based superalloys CoWAlloy1 a) and c) and also CoWAlloy2 b) and d) in the heat-treated state.
  • FIG. 3 shows an EBSD (“electron backscattering diffraction”) measurement to determine the grain size and twin density of the ⁇ / ⁇ ′ cobalt-based superalloy CoWAlloy2 described here.
  • the twin density of the alloy CoWAlloy2 determined by means of EBSD is, at 55%, significantly higher than that of the nickel-based superalloy Udimet 720Li of only 33%. This is attributable to the lower stacking fault energy of the cobalt-based superalloys.
  • FIG. 4 shows the yield point as a function of temperature of the alloys CoWAlloy1 and CoWAlloy2 reported here compared to the nickel-based alloys Waspaloy and Udimet 720Li and to the cobalt alloy Mar-M509.
  • the yield strengths determined by means of compressive tests are, at room temperature, 1110 MPa (CoWAlloy1) and 995 MPa (CoWAlloy2) and thus in the region of the yield strengths of Waspaloy (1010 MPa) and Udimet (1155 MPa), and at 800° C. sometimes achieve significantly higher values (880 MPa (CoWAlloy1) compared to Waspaloy (680 MPa) and Udimet 720Li (about 800 MPa)).
  • FIG. 5 shows the creep strength of the ⁇ / ⁇ ′ cobalt-based superalloy CoWAlloy2 compared to the polycrystalline ⁇ / ⁇ ′ nickel-based superalloys Waspaloy and Udimet 720Li at 700° C. Accordingly, the alloy CoWAlloy2 also has, at 700° C., a significantly higher creep strength than the nickel-based alloys Waspaloy and Udimet 720Li.
  • FIG. 6 shows images of the microstructure of the oxide layers on the ternary alloy Co9Al9W (a) and the abovementioned alloy CoWAlloy2 (b).
  • the oxide layer thickness after heat treatment at 900° C. for 50 hours is a factor of at least 10 smaller in the case of the alloy CoWAlloy2 than for the ternary alloy Co9Al9W (cf. a with b).
  • the alloy CoWAlloy2 FIG. 6 b
  • the alloy CoWAlloy2 has a significantly better oxidation resistance.
  • FIG. 7 shows the element distributions in the various oxide layers of the alloy CoWAlloy2 after heat treatment at 900° C. for 50 hours, determined by energy-dispersive X-ray spectroscopy EDS in a scanning electron microscope SEM.
  • the relatively good oxidation properties are due to the protective oxide layers rich in Al, Si and Cr.
  • the cobalt-based superalloys of the invention are characterized, in particular, in that they are based on the element cobalt, in that they are hardened by means of the intermetallic ⁇ ′ phase (Co,Ni) 3 (Al, W, Ti, Ta), in that they have better mechanical properties than conventional, carbide-hardened cobalt-based superalloys, in that they have higher strengths than comparable, polycrystalline ⁇ / ⁇ ′ nickel-based superalloys at temperatures above 800° C., in that they have higher creep strengths than comparable, polycrystalline ⁇ / ⁇ ′ nickel-based superalloys at temperatures of 700° C., in that they have better oxidation properties than previous ⁇ / ⁇ ′ cobalt-based superalloys and/or in that, at comparatively low ⁇ ′ solvus temperatures, they have high ⁇ ′ proportions by volume at use temperatures of up to 850° C. and thus can be used as forging alloy.
  • a ⁇ / ⁇ ′ cobalt-based superalloy having an addition of molybdenum (CoWAlloy3) will be reported.
  • the composition is shown in table 2 again together with the further above-described illustrative alloys CoWAlloy0, CoWAlloy1 and CoWAlloy2.
  • the content of Mo has been changed at the expense of Co.
  • Mo serves, as described above, as mixed crystal hardening element and can partly replace W, as a result of which the density is decreased.
  • Mo leads, in particular, to formation of further “grain boundary pinning” intermetallic phases which can restrict grain growth in forging alloys.
  • a relatively low solvus temperature of about 1050° C. combined with a relatively high solidus temperature which is advantageous for processing, in particular by casting and forging, since these two temperatures span the window for processing and heat treatment, is expected for CoWAlloy3.
  • the alloy CoWAlloy3 was subjected to an intermediate heat treatment at 1100° C. for one hour after a homogenizing heat treatment at 1250° C. for 3 hours and subsequently hot rolled. The diameter in a number of random samples was reduced here from 40 mm to 15 mm. A recrystallization heat treatment was subsequently carried out in order to obtain a homogeneous, fine-grain microstructure.
  • the simultaneous precipitation of the ⁇ phase allows targeted variation of the grain size by appropriate selection of the heat treatment parameters.
  • FIG. 8 shows scanning electron micrographs of the microstructure of CoWAlloy3 after recrystallization for 4 hours at (a) 1000° C. and (b) 1100° C.
  • the phase having white contrast which is predominantly present at the grain boundaries is the W- and Mo-containing ⁇ phase. It is clear that the proportion of p phase decreases significantly and at the same time the grain size increases significantly at higher recrystallization temperature. Recrystallization at 1000° C. leads to a proportion of ⁇ phase of about 3.2% and a median grain size of about 5 ⁇ m.
  • the CoWAlloy2 which has undergone the same heat treatment has a median of about 8 ⁇ m, which demonstrates the grain boundary pinning effect of the p phase.
  • a further, two-stage heat treatment (900° C., 4 h+750° C., 16 h) leads to uniform precipitation of ⁇ ′ phase in the Co mixed crystal.
  • FIG. 9 shows that the ⁇ / ⁇ ′ microstructure after a two-stage heat treatment (900° C., 4 h+750° C., 16 h) is depicted: (a) scanning electron micrograph with primary and secondary ⁇ ′ particles, (b) dark-field transmission electron micrograph with secondary and tertiary ⁇ ′ particles.
  • the ⁇ ′ particles are, as in the case of the comparative alloy CoWAlloy2, round, which indicates low lattice mismatching.
  • the particle diameter is about 65 nm and thus likewise in the range of the comparative alloy.
  • One noticeable difference is the ⁇ ′ proportion, which is about 37% and thus lower than in the case of CoWAlloy2.
  • the reason for this can be presumed to be the formation of a ⁇ phase Co 7 (W,Mo) 6 , which reduces the W content available for ⁇ ′ formation in the Co mixed crystal.
  • this somewhat lower phase content does not have an adverse effect on the high-temperature strength.
  • FIG. 10 shows the yield stress versus temperature of the Mo-containing alloy CoWAlloy3 with grain boundary pinning ⁇ phase compared to CoWAlloy2.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Powder Metallurgy (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)

Abstract

A cobalt-based superalloy includes the following: 32-45 wt.-% Co, 28-40 wt.-% Ni, 10-15 wt.-% Cr, 2.5-5.5 wt.-% Al, 6.5-16 wt.-% W, 0-9 wt.-% Ta, 0-8 wt.-% Ti, 0.1-1 wt.-% Si, 0-0.5 wt.-% B, 0-0.5 wt.-% C, 0-2 wt.-% Hf, 0-0.1 wt.-% Zr, 0-8 wt.-% Fe, 0-6 wt.-% Nb, 0-7 wt.-% Mo, 0-4 wt.-% Ge and a remainder of unavoidable impurities.

Description

  • The invention relates to polycrystalline, precipitation-hardened and oxidation-resistant γ/γ′ cobalt-based superalloys for high-temperature applications. The mechanical properties of the cobalt-based superalloys indicated are superior to those of conventional, carbide-hardened cobalt alloys. Up to a temperature of 800° C., similar hot strengths as those of nickel-based γ/γ′ forging alloys are achieved, and at temperatures above 800° C. even higher hot strengths than those of nickel-based γ/γ′ forging alloys are achieved. The creep strengths are likewise significantly higher. Compared to γ/γ′ nickel-based superalloys, similar proportions of the γ′ precipitate phase are achieved despite a lower solvus temperature. Owing to the large temperature range between solidus and solvus temperature, the precipitation-hardened γ/γ′ cobalt-based superalloys are particularly suitable as polycrystalline forging alloys.
  • Cobalt-based and in particular γ/γ′ nickel-based superalloys are essential materials for many components in jet engines of commercial aircraft or in stationary gas turbines for power conversion. New materials which have a greater heat resistance, longer life and lower production and processing costs make it possible to increase the efficiency of these turbines, lower the costs and reduce the consumption of fossil fuel.
  • Conventional cobalt-based superalloys are used as high-temperature materials in aircraft engines and stationary gas turbines because of their high melting point, their high wear resistance, their good weldability and in particular because of their excellent hot-gas corrosion and sulfidation resistance (see, for example, Bürgel, Maier, Niendorf, Handbuch Hochtemperaturwerkstofftechnik, 4th revised edition 2011, Vieweg+Teubner Verlag, Springer Fachmedien Wiesbaden GmbH 2011).
  • However, since they are mixed crystal- and carbide-hardened, they are used only for components which are subject to relatively low stresses or are static, e.g. guide blades, because of their lower high-temperature strength compared to the precipitation-hardened γ/γ′ nickel-based superalloys. These are thus not used as materials for rotor blades or turbine disks. With the discovery of the intermetallic γ′ phase Co3 (Al, W) having an L12 crystal structure in the ternary Co—Al—W system in 2006, it is now also possible to produce higher-strength, precipitation-hardened, two-phase γ/γ′ superalloys based on cobalt (γ: face-centered cubic cobalt mixed crystal) having the same microstructure as the γ/γ′ nickel-based superalloys which have been used for decades, as is described, for example, in Sato et al., Cobalt-Base High-Temperature Alloys, Science 312 (2006) 90-91. These have significant advantages compared to the polycrystalline γ/γ′ nickel-based superalloys.
  • γ/γ′ cobalt-based superalloys generally have a very high solidus temperature in the temperature range from 1300° C. to 1450° C. combined with a relatively low γ′ solvus temperature in the temperature range from 900° C. to 1150° C. Despite the relatively low γ′ solvus temperature, very high γ′ proportions by volume of over 75% can be realized at temperatures up to 900° C. (see, for example, Bauer et al., Microstructure and creep strength of different γ/γ′-strengthened Co-base superalloy variants, Scripta Materialia 63 (2010) 1197-1200). The ternary γ/γ′ cobalt-based superalloy Co-9Al-9W (reported in atom%) has, for example, a relatively high proportion by volume of γ′ precipitates of 58% despite a γ′ solvus temperature of only about 975° C. Owing to the large temperature range between solidus temperature and γ′ solvus temperature (forging window), the comparatively low γ′ solvus temperatures and the high γ′ proportion by volume at use temperatures, the γ/γ′ cobalt-based superalloys are thus particularly suitable as forging alloys. Nickel-based superalloys, on the other hand, have either a low γ′ solvus temperature below 1100° C., associated with a low γ′ proportion by volume at use temperatures of up to 700° C. (e.g. Waspaloy: γ′ solvus temperature: 1038° C. Semiatin et al., Deformation behavior of Waspaloy at hot-working temperatures, Scripta Materialia 50 (2004) 625-629); γ′ proportion by volume at use temperature: 25% (ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys, Ed. Davies et al, ASM International, Materials Park, Ohio 44073, USA)) or a high γ′ proportion by volume at 700° C. combined with a significantly higher γ′ solvus temperature (e.g. Udimet 720Li: γ′ solvus temperature: 1142° C.; γ′ proportion by volume at use temperature: 45% (Gu et al., Development of Ni—Co base alloys for high-temperature disk applications, Superalloys 2008, Ed. Roger C. Reed et al., The Minerals, Metals & Materials Society, Warrendale Pa., USA)). As a result, the alloys are either forgable but have a low strength or they still have a relatively high proportion of the precipitate phase at forging temperatures of from 1000° C. to 1150° C. and are thus deformable only with difficulty or not at all and can be processed only by a powder-metallurgical route. This significantly increases costs.
  • Furthermore, it is known that cobalt-based alloys can have a higher hot gas corrosion resistance than nickel-based alloys since a liquid Co-sulfur phase can appear only at 877° C., while a liquid Ni—S phase is formed at as low as 637° C. (see Bürgel, Maier, Niendorf, Handbuch Hochtemperaturwerkstofftechnik, 4th revised edition 2011, Vieweg+Teubner Verlag, Springer Fachmedien Wiesbaden GmbH 2011, or ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys, Ed. Davies et al, ASM International, Materials Park, Ohio 44073, USA). An increased hot gas corrosion resistance can thus lead to a lengthening of the life. In addition, although pure cobalt displays a lower corrosion resistance than pure nickel in sulfuric acid, according to the literature only 10% by weight of chromium in cobalt is necessary for passivation, while in the case of nickel 14% by weight of chromium is required (see, for example, ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys, Ed. Davies et al, ASM International, Materials Park, Ohio 44073, USA).
  • In addition, it has been able to be shown over past years that the stacking fault energy decreases with increased Co content in nickel-based forging alloys having a γ/γ′ microstructure and the twin density in the material increases as a result, which leads to an additional hardening effect in the polycrystalline forging alloys and higher hot strengths can thus be achieved (see, for example, Yuan et al., A new method to strengthen turbine disc superalloys at service temperatures Scripta Mat. 66 (2012) 884-889). It is to be expected that cobalt-based forging alloys have an even higher twin density, so that this hardening effect can be increased further.
  • Despite increased research activity in the field of this new class of materials made up of the γ/γ′ cobalt-based superalloys, usually only simple alloys having relatively few alloy elements and an unsatisfactory oxidation resistance have been developed and examined to date (e.g. Titus et al., Creep and directional coarsening in single crystals of new γ-γ′ cobalt-base alloys, Scripta Mat. 66 (2012) 574-577, US 2011/0268989 A1, US 2010/0291406 A1, EP 2251446 A1, CA 2620606 A1, EP 1925683 A1, US 2008/0185078 A1, EP 2163656 A1, US 2011/0062214 A1, EP 2 298 486 A2).
  • A good oxidation resistance in combination with good mechanical properties is, however, essential for these new γ/γ′ cobalt-based superalloys to be able to be used in future as high-temperature material.
  • It is an object of the invention to develop polycrystalline, higher-strength, precipitation-hardened γ/γ′ cobalt-based superalloys which have very good oxidation properties and can be processed by means of various forming processes such as forging.
  • This object is achieved according to the invention by a cobalt-based superalloy comprising 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0-9% by weight of Ta, 0-8% by weight of Ti, 0.1-1% by weight of Si, 0-0.5% by weight of B, 0-0.5% by weight of C, 0-2% by weight of Hf, 0-0.1% by weight of Zr, 0-8% by weight of Fe, 0-6% by weight of Nb, 0-7% by weight of Mo, 0-4% by weight of Ge and a balance of unavoidable impurities.
  • In an advantageous variant, the cobalt-based superalloy comprises 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0-9% by weight of Ta, 0-8% by weight of Ti, 0.1-1% by weight of Si, 0-0.5% by weight of B, 0-0.5% by weight of C, from 0 to <2% by weight of Hf, from 0 to <0.1% by weight of Zr, from 0 to <8% by weight of Fe, from 0 to <6% by weight of Nb, from 0 to <7% by weight of Mo, from 0 to <4% by weight of Ge and a balance of unavoidable impurities.
  • In a further embodiment, the cobalt-based superalloy advantageously comprises 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0.2-9% by weight of Ta, 0.2-8% by weight of Ti, 0.1-1% by weight of Si, <0.5% by weight of B, <0.5% by weight of C, 0-2% by weight of Hf, 0-0.1% by weight of Zr, 0-8% by weight of Fe, 0-6% by weight of Nb, 0-7% by weight of Mo, 0-4% by weight of Ge and a balance of unavoidable impurities.
  • In a further preferred embodiment, the cobalt-based superalloy comprises 32-45% by weight of Co, 28-40% by weight of Ni, 10-15% by weight of Cr, 2.5-5.5% by weight of Al, 6.5-16% by weight of W, 0.2-9% by weight of Ta, 0.2-8% by weight of Ti, 0.1-1% by weight of Si, <0.5% by weight of B, <0.5% by weight of C, from 0 to <2% by weight of Hf, from 0 to <0.1% by weight of Zr, from 0 to <8% by weight of Fe, from 0 to <6% by weight of Nb, from 0 to <7% by weight of Mo, from 0 to <4% by weight of Ge and a balance of unavoidable impurities.
  • The cobalt-based superalloy, which in particular comprises a composition as mentioned above, is advantageously characterized by an intermetallic γ′ phase having the composition (Co,Ni)3(Al, W, Ti, Ta) where at least one of the elements shown in parentheses from each set of parentheses is present in each case. The intermetallic γ′ phase (precipitate phase) is advantageously present in a proportion by volume of more than 35%, preferably more than 45%.
  • These oxidation-resistant, precipitation-hardened cobalt-based superalloys characterized by their composition are made up of many alloy elements. The reasons for the chosen concentration ranges of the alloy elements and their significant modes of action are described below:
  • Necessary Alloy Elements:
  • Co (cobalt): 32-45% by weight
  • Co as base element forms, among other elements, the face-centered cubic y matrix phase and is an important constituent of the hardening γ′-(Co,Ni)3(Al, W, Ti, Ta) precipitate phase. Co also lowers the stacking fault energy.
  • Ni (nickel): 28-40% by weight
  • Ni in the range indicated widens the γ/γ′ two-phase region to a sufficient extent, so that further alloy elements, in particular Cr, can be added in a sufficient amount. Proportions of Cr above about 4% by weight destabilize the two-phase γ/γ′ microstructure in ternary Co—Al—W alloys, and further undesirable intermetallic phases are formed. Ni shifts the maximum possible concentration of Cr to higher concentrations. Furthermore, the γ′ solvus temperature can be increased by means of Ni.
  • Cr (chromium): 10-15% by weight
  • In order to attain a sufficient corrosion and oxidation resistance, the alloy element Cr should be added in the range indicated. In addition, Cr acts as mixed crystal hardener.
  • Al (aluminum): 2.5-5.5% by weight
  • Al forms the γ′ precipitate phase (Co,Ni)3(Al, W, Ti, Ta), which contributes significantly to the increasing strength. Furthermore, Al increases the oxidation resistance. Relatively high proportions of Al in the indicated composition range can lead to formation of further intermetallic phases such as CoAl which can inhibit grain growth in forging alloys. This makes it possible to achieve smaller grain sizes and thus higher strengths.
  • W (tungsten): 6.5-16% by weight
  • W forms the γ′ precipitate phase Co3(Al,W), which contributes significantly to the increasing strength and, as slowly diffusing element, increases the creep strength. Higher contents lead to an excessively high density and further undesirable intermetallic phases can be formed.
  • Si (silicon): 0.1-1% by weight
  • Si is a critical element and signicantly improves the oxidation resistance. However, excessively large amounts of Si can lead to further undesirable intermetallic phases.
  • B (boron): <0.5% by weight
  • B acts as grain boundary strengthening alloy element and improves the oxidation properties. Excessively high concentrations lead to an excessively high proportion of borides. B is preferably present in an amount of more than 0.01% by weight.
  • C (carbon): <0.5% by weight
  • C acts as grain boundary strengthening alloy element. In addition, C forms carbides. C is preferably present in an amount of more than 0.01% by weight.
  • Required for High Hot Strengths:
  • Ta (tantalum): 0.2-9% by weight
  • Ta contributes to the formation of the γ′ precipitate phase, increases the γ′ solvus temperature and the γ/γ′ lattice mismatching. Ta hardens the γ′ precipitate phase and leads to an increasing strength. The two elements Ta and Ti are necessary particularly when high hot strengths at 800° C. are required.
  • Ti (titanium): 0.2-8% by weight
  • Ti contributes to the formation of the γ′ precipitate phase, increases the γ′ solvus temperature and the γ/γ′ lattice mismatching. Ti hardens the γ′ precipitate phase and leads to an increasing strength. The two elements Ta and Ti are necessary particularly when high hot strengths at 800° C. are required. Ti can replace W to a substantial extent and in this way reduces the density significantly.
  • Optional Alloy Elements:
  • Hf (hafnium): <2% by weight
  • Hf stabilizes the γ′ precipitate phase. Hf is preferably present in an amount of more than 0.2% by weight.
  • Zr (zirconium): <0.1% by weight
  • Zr serves to increase the grain boundary strength and is able to stabilize the γ′ precipitate phase. Zr is preferably present in an amount of more than 0.01% by weight.
  • Fe (iron): <8% by weight
  • Fe lowers the γ′ solvus temperature and can be used for setting this, particularly in the case of forging alloys. Fe is also an inexpensive element and can improve the weldability. Excessively high concentrations destabilize the γ/γ′ microstructure. Fe is preferably present in an amount of more than 0.1% by weight.
  • Nb (niobium): <6% by weight
  • Nb contributes to the formation of the γ′ precipitate phase, leads to an increase in strength and increases the γ′ solvus temperature. Relatively high concentrations within the concentration range indicated can lead to formation of further intermetallic phases which can inhibit grain growth in forging alloys. Smaller grain sizes and thus higher strengths can be achieved as a result. Nb is preferably present in an amount of more than 0.1% by weight.
  • Mo (molybdenum): <7% by weight
  • Mo serves as mixed crystal hardening element and can partly replace W and thus decreases the density. Relatively high concentrations lead to formation of further intermetallic phases which can inhibit grain growth in forging alloys. Smaller grain sizes and thus higher strengths can be achieved as a result. Mo is preferably present in an amount of more than 0.1% by weight.
  • Ge (germanium): <4% by weight
  • Ge forms the γ′ precipitate phase Co3(Al,Ge,W), lowers the γ′ solvus temperature and can be used for setting this, particularly in the case of forging alloys. Ge is preferably present in an amount of more than 0.1% by weight.
  • Working examples of the invention will be explained in more detail with the aid of a drawing and the following information. The drawing shows:
  • FIG. 1 a graph of the relationship between the proportion of precipitates at use temperature and the solvus temperature of the γ′ phase of γ/γ′ nickel-based superalloys compared to working examples of the invention,
  • FIG. 2 the microstructure of illustrative alloys of the invention,
  • FIG. 3 an EBSD measurement to determine the grain size and the twin density of an illustrative alloy of the invention,
  • FIG. 4 a graph of the yield point as a function of temperature for illustrative alloys of the invention,
  • FIG. 5 a graph of the creep strength of an illustrative alloy of the invention compared to nickel-based superalloys,
  • FIG. 6 images of the microstructure of the ternary alloy Co9Al9W compared to an illustrative alloy of the invention,
  • FIG. 7 the element distribution in the oxide layer of an illustrative alloy of the invention,
  • FIG. 8 scanning electron micrographs of an illustrative alloy of the invention,
  • FIG. 9 scanning electron micrographs and transmission electron micrographs of an illustrative alloy of the invention and
  • FIG. 10 a graph of the yield point as a function of temperature for a further illustrative alloy of the invention.
    •
  • The compositions of some working examples of the γ/γ′ cobalt-based superalloys of the invention, hereinafter referred to as CoWAlloy0 and CoWAlloy1 and CoWAlloy2, and also some reference alloys are indicated in table 1 below. Likewise, the properties of working examples of the invention are described in more detail below with the aid of the figures and studies.
  • TABLE 1
    Compositions of the γ/γ′ cobalt-based superalloys CoWAlloy0,
    CoWAlloy1 and CoWAlloy2 described here and also some polycrystalline,
    cobalt- and nickel-based reference alloys (figures in % by weight).
    Co Ni Al Cr W Ta Ti Hf Zr Si B C
    Co-based
    CoWAlloy
    0 39.8 28.8 2.7 12.8 9.0 4.4 2.0 0.3 0.02 0.2 0.014 0.016
    CoWAlloy 1 40.6 30.6 2.7 10.2 9.0 4.4 2.0 0.3 0.02 0.2 0.014 0.016
    CoWAlloy 2 39.2 30.5 4.0 10.1 14.9 0.6 0.2 0.3 0.02 0.2 0.014 0.016
    Co9Al9W Bal. — 3.6 — 24.6 — — — — — 0.06 —
    MarM 509 Bal. 10 — 24 7 3.5 0.2 — 0.5 — — 0.6
    Ni-based
    Waspaloy 13.5 Bal. 1.3 19.5 4.3 — 3.0 — — — 0.006 0.08
    Udimet 720Li 15.0 Bal. 2.5 16.0 3.0 — 5.0 — 0.05 — 0.018 0.025
  • Microstructure and Mechanical Properties:
  • The alloys which have been developed and are described here have, compared to nickel-based forging alloys, the important advantage that high proportions by volume of precipitates of more than 45% (CoWAlloy0) can be achieved at 750° C. despite the relatively low γ′ solvus temperatures of about 1050° C. (CoWAlloy0), 1070° C. (CoWAlloy1) and 1030° C. (CoWAlloy2). To illustrate this, FIG. 1 shows the relationship between the proportion of precipitates at use temperature and the solvus temperature of the γ′ phase of γ/γ′ nickel-based superalloys and the γ/γ′ cobalt-based superalloy CoWAlloy0 reported here. Despite high proportions by volume of precipitates, easier deformation at typical forging temperatures of from 1000° C. to 1150° C. is made possible by the relatively low γ′ solvus temperatures.
  • After hot rolling at a rolled material temperature of 1100° C. and subsequent heat treatment at 1050° C./4 h+900° C./8 h (CoWAlloy1) or 1000° C./4 h+900° C./4 h+750° C./16 h (CoWAlloy2), average grain sizes of from about 8 to 15 μm and a typical γ/γ′ microstructure can be set. This can be seen directly from FIG. 2. Here, FIG. 2 shows, in different resolutions, the microstructure of the γ/γ′ cobalt-based superalloys CoWAlloy1 a) and c) and also CoWAlloy2 b) and d) in the heat-treated state.
  • FIG. 3 shows an EBSD (“electron backscattering diffraction”) measurement to determine the grain size and twin density of the γ/γ′ cobalt-based superalloy CoWAlloy2 described here. The twin density of the alloy CoWAlloy2 determined by means of EBSD is, at 55%, significantly higher than that of the nickel-based superalloy Udimet 720Li of only 33%. This is attributable to the lower stacking fault energy of the cobalt-based superalloys.
  • FIG. 4 shows the yield point as a function of temperature of the alloys CoWAlloy1 and CoWAlloy2 reported here compared to the nickel-based alloys Waspaloy and Udimet 720Li and to the cobalt alloy Mar-M509. The yield strengths determined by means of compressive tests are, at room temperature, 1110 MPa (CoWAlloy1) and 995 MPa (CoWAlloy2) and thus in the region of the yield strengths of Waspaloy (1010 MPa) and Udimet (1155 MPa), and at 800° C. sometimes achieve significantly higher values (880 MPa (CoWAlloy1) compared to Waspaloy (680 MPa) and Udimet 720Li (about 800 MPa)).
  • FIG. 5 shows the creep strength of the γ/γ′ cobalt-based superalloy CoWAlloy2 compared to the polycrystalline γ/γ′ nickel-based superalloys Waspaloy and Udimet 720Li at 700° C. Accordingly, the alloy CoWAlloy2 also has, at 700° C., a significantly higher creep strength than the nickel-based alloys Waspaloy and Udimet 720Li.
  • Oxidation and Corrosion Behavior:
  • The oxidation behavior can be assessed by means of the oxide layer thicknesses formed at 900° C. in 50 hours. For this purpose, FIG. 6 shows images of the microstructure of the oxide layers on the ternary alloy Co9Al9W (a) and the abovementioned alloy CoWAlloy2 (b). The oxide layer thickness after heat treatment at 900° C. for 50 hours is a factor of at least 10 smaller in the case of the alloy CoWAlloy2 than for the ternary alloy Co9Al9W (cf. a with b). Compared to the ternary γ/γ′ cobalt-based superalloy Co9Al9W (FIG. 6a ), the alloy CoWAlloy2 (FIG. 6b ), for example, has a significantly better oxidation resistance.
  • FIG. 7 shows the element distributions in the various oxide layers of the alloy CoWAlloy2 after heat treatment at 900° C. for 50 hours, determined by energy-dispersive X-ray spectroscopy EDS in a scanning electron microscope SEM. The relatively good oxidation properties are due to the protective oxide layers rich in Al, Si and Cr.
  • The cobalt-based superalloys of the invention are characterized, in particular, in that they are based on the element cobalt, in that they are hardened by means of the intermetallic γ′ phase (Co,Ni)3(Al, W, Ti, Ta), in that they have better mechanical properties than conventional, carbide-hardened cobalt-based superalloys, in that they have higher strengths than comparable, polycrystalline γ/γ′ nickel-based superalloys at temperatures above 800° C., in that they have higher creep strengths than comparable, polycrystalline γ/γ′ nickel-based superalloys at temperatures of 700° C., in that they have better oxidation properties than previous γ/γ′ cobalt-based superalloys and/or in that, at comparatively low γ′ solvus temperatures, they have high γ′ proportions by volume at use temperatures of up to 850° C. and thus can be used as forging alloy.
  • As further working example of the invention, a γ/γ′ cobalt-based superalloy having an addition of molybdenum (CoWAlloy3) will be reported. The composition is shown in table 2 again together with the further above-described illustrative alloys CoWAlloy0, CoWAlloy1 and CoWAlloy2. Compared to CoWAlloy2, the content of Mo has been changed at the expense of Co. Mo serves, as described above, as mixed crystal hardening element and can partly replace W, as a result of which the density is decreased. Mo leads, in particular, to formation of further “grain boundary pinning” intermetallic phases which can restrict grain growth in forging alloys.
  • TABLE 2
    Compositions of the γ/γ′ cobalt-based superalloy CoWAlloy3 together
    with CoWAlloy0, CoWAlloy1 and CoWAlloy2 (figures in % by weight)
    Co-based Co Ni Al Cr W Ta Ti Hf Zr Si B C Mo
    CoWAlloy0 39.8 28.8 2.7 12.8 9.0 4.4 2.0 0.3 0.02 0.2 0.014 0.016
    CoWAlloy1 40.6 30.6 2.7 10.2 9.0 4.4 2.0 0.3 0.02 0.2 0.014 0.016
    CoWAlloy2 39.2 30.5 4.0 10.1 14.9 0.6 0.2 0.3 0.02 0.2 0.014 0.016
    CoWAlloy3 37.9 30.3 4.0 10.1 14.9 0.6 0.2 0.3 0.02 0.2 0.014 0.016 1.55
  • Microstructure and Properties:
  • As in the case of the above-described CrWAlloy alloys 0, 1, 2, a relatively low solvus temperature of about 1050° C. combined with a relatively high solidus temperature, which is advantageous for processing, in particular by casting and forging, since these two temperatures span the window for processing and heat treatment, is expected for CoWAlloy3. The alloy CoWAlloy3 was subjected to an intermediate heat treatment at 1100° C. for one hour after a homogenizing heat treatment at 1250° C. for 3 hours and subsequently hot rolled. The diameter in a number of random samples was reduced here from 40 mm to 15 mm. A recrystallization heat treatment was subsequently carried out in order to obtain a homogeneous, fine-grain microstructure. The simultaneous precipitation of the μ phase allows targeted variation of the grain size by appropriate selection of the heat treatment parameters.
  • FIG. 8 shows scanning electron micrographs of the microstructure of CoWAlloy3 after recrystallization for 4 hours at (a) 1000° C. and (b) 1100° C. The phase having white contrast which is predominantly present at the grain boundaries is the W- and Mo-containing μ phase. It is clear that the proportion of p phase decreases significantly and at the same time the grain size increases significantly at higher recrystallization temperature. Recrystallization at 1000° C. leads to a proportion of μ phase of about 3.2% and a median grain size of about 5 μm. The CoWAlloy2 which has undergone the same heat treatment has a median of about 8 μm, which demonstrates the grain boundary pinning effect of the p phase. A further, two-stage heat treatment (900° C., 4 h+750° C., 16 h) leads to uniform precipitation of γ′ phase in the Co mixed crystal. This is shown by FIG. 9 in which the γ/γ′ microstructure after a two-stage heat treatment (900° C., 4 h+750° C., 16 h) is depicted: (a) scanning electron micrograph with primary and secondary γ′ particles, (b) dark-field transmission electron micrograph with secondary and tertiary γ′ particles.
  • The γ′ particles are, as in the case of the comparative alloy CoWAlloy2, round, which indicates low lattice mismatching. The particle diameter is about 65 nm and thus likewise in the range of the comparative alloy. One noticeable difference is the γ′ proportion, which is about 37% and thus lower than in the case of CoWAlloy2. The reason for this can be presumed to be the formation of a μ phase Co7(W,Mo)6, which reduces the W content available for γ′ formation in the Co mixed crystal. However, this somewhat lower phase content does not have an adverse effect on the high-temperature strength. To illustrate this, FIG. 10 shows the yield stress versus temperature of the Mo-containing alloy CoWAlloy3 with grain boundary pinning μ phase compared to CoWAlloy2.

Claims (8)

1-5 (canceled)
6. A cobalt-based superalloy, comprising:
32-45% by weight of Co;
28-40% by weight of Ni;
10-15% by weight of Cr;
2.5-5.5% by weight of Al;
6.5-16% by weight of W;
0-9% by weight of Ta;
0-8% by weight of Ti;
0.1-1% by weight of Si;
0-0.5% by weight of B;
0-0.5% by weight of C;
0-2% by weight of Hf;
0-0.1% by weight of Zr;
0-8% by weight of Fe;
0-6% by weight of Nb;
0-7% by weight of Mo;
0-4% by weight of Ge; and
a remainder of unavoidable impurities.
7. The cobalt-based superalloy according to claim 6, which comprises:
from 0 to <2% by weight of Hf;
from 0 to <0.1% by weight of Zr;
from 0 to <8% by weight of Fe;
from 0 to <6% by weight of Nb;
from 0 to <7% by weight of Mo;
from 0 to <4% by weight of Ge.
8. The cobalt-based superalloy according to claim 6, comprising an intermetallic γ′ phase (Co,Ni)3(Al, W, Ti, Ta).
9. A cobalt-based superalloy, comprising:
32-45% by weight of Co;
28-40% by weight of Ni;
10-15% by weight of Cr;
2.5-5.5% by weight of Al;
6.5-16% by weight of W;
0.2-9% by weight of Ta;
0.2-8% by weight of Ti;
0.1-1% by weight of Si;
an amount of <0.5% by weight of B;
an amount of <0.5% by weight of C;
0-2% by weight of Hf;
0-0.1% by weight of Zr;
0-8% by weight of Fe;
0-6% by weight of Nb;
0-7% by weight of Mo;
0-4% by weight of Ge; and
a remainder of unavoidable impurities.
10. The cobalt-based superalloy according to claim 9, comprising an intermetallic γ′ phase (Co,Ni)3(Al, W, Ti, Ta).
11. A cobalt-based superalloy, comprising:
32-45% by weight of Co;
28-40% by weight of Ni;
10-15% by weight of Cr;
2.5-5.5% by weight of Al;
6.5-16% by weight of W;
0.2-9% by weight of Ta;
0.2-8% by weight of Ti;
0.1-1% by weight of Si;
an amount of <0.5% by weight of B;
an amount <0.5% by weight of C;
from 0 to <2% by weight of Hf;
from 0 to <0.1% by weight of Zr;
from 0 to <8% by weight of Fe;
from 0 to <6% by weight of Nb; from 0 to <7% by weight of Mo;
from 0 to <4% by weight of Ge; and
a remainder of unavoidable impurities.
12. The cobalt-based superalloy according to claim 11, comprising an intermetallic γ′ phase (Co,Ni)3(Al, W, Ti, Ta).
US15/500,992 2014-08-01 2015-07-31 Cobalt-based super alloy Abandoned US20170342527A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE102014011249 2014-08-01
DE102014011249.7 2014-08-01
PCT/EP2015/067697 WO2016016437A2 (en) 2014-08-01 2015-07-31 Cobalt-based super alloy

Publications (1)

Publication Number Publication Date
US20170342527A1 true US20170342527A1 (en) 2017-11-30

Family

ID=53836558

Family Applications (1)

Application Number Title Priority Date Filing Date
US15/500,992 Abandoned US20170342527A1 (en) 2014-08-01 2015-07-31 Cobalt-based super alloy

Country Status (3)

Country Link
US (1) US20170342527A1 (en)
EP (1) EP3175008B1 (en)
WO (1) WO2016016437A2 (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190003017A1 (en) * 2016-01-08 2019-01-03 Siemens Aktiengesellschaft Gamma, gamma' cobalt based alloys for additive manufacturing methods or soldering, welding, powder and component
US20200048738A1 (en) * 2017-04-21 2020-02-13 Oerlikon Surface Solutions Ag, Pfaffikon Superalloy target
CN115233074A (en) * 2022-07-12 2022-10-25 北京科技大学 Cobalt-nickel-based high-temperature alloy for gas turbine moving blade and preparation method thereof
US20230151475A1 (en) * 2021-11-17 2023-05-18 Shenyang Aerospace University Plastic cocrni-based medium-entropy alloy with 2.0 gpa-level ultra-high yield strength and preparation method thereof
US11725263B2 (en) 2018-04-04 2023-08-15 The Regents Of The University Of California High temperature oxidation resistant co-based gamma/gamma prime alloys DMREF-Co

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3612656B1 (en) * 2017-04-21 2024-08-07 CRS Holdings, LLC Precipitation hardenable cobalt-nickel base superalloy and article made thereform
DE102018208737A1 (en) * 2018-06-04 2019-12-05 Siemens Aktiengesellschaft Y, Y` hardened cobalt-nickel base alloy, powder, component and process
DE102018208736A1 (en) * 2018-06-04 2019-12-05 Siemens Aktiengesellschaft Y, Y 'hardened cobalt-nickel base alloy, powder, component and process
DE102020203436A1 (en) 2020-03-18 2021-09-23 Siemens Aktiengesellschaft Cobalt-based alloy, powder mixture, process and component
CN113684398B (en) * 2021-08-26 2022-05-13 大连理工大学 900℃ Microstructure Stable Cubic γ' Nanoparticle Coherent Precipitation Strengthened Superalloy and Preparation Method
US11913093B2 (en) * 2022-07-11 2024-02-27 Liburdi Engineering Limited High gamma prime nickel based welding material

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2383356A1 (en) * 2010-04-29 2011-11-02 General Electric Company Cobalt-Nickel Superalloys, and Related Articles
EP2532762A1 (en) * 2011-06-09 2012-12-12 General Electric Company Aumina-forming cobalt-nickel base alloy and method of making an article therefrom
EP2532763A1 (en) * 2011-06-10 2012-12-12 Shenzhen Sun Xing Light Alloys Materials Co., Ltd. Application of aluminum-zirconium-titanium-carbon intermediate alloy in deformation process of magnesium and magnesium alloys
US20150010428A1 (en) * 2013-07-04 2015-01-08 Rolls-Royce Plc Alloy
US10094004B2 (en) * 2014-12-10 2018-10-09 Rolls-Royce Plc Alloy

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB0719195D0 (en) * 2007-10-02 2007-11-14 Rolls Royce Plc A nickel base superalloy
JP5201334B2 (en) * 2008-03-19 2013-06-05 大同特殊鋼株式会社 Co-based alloy

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2383356A1 (en) * 2010-04-29 2011-11-02 General Electric Company Cobalt-Nickel Superalloys, and Related Articles
EP2532762A1 (en) * 2011-06-09 2012-12-12 General Electric Company Aumina-forming cobalt-nickel base alloy and method of making an article therefrom
EP2532763A1 (en) * 2011-06-10 2012-12-12 Shenzhen Sun Xing Light Alloys Materials Co., Ltd. Application of aluminum-zirconium-titanium-carbon intermediate alloy in deformation process of magnesium and magnesium alloys
US20150010428A1 (en) * 2013-07-04 2015-01-08 Rolls-Royce Plc Alloy
US10094004B2 (en) * 2014-12-10 2018-10-09 Rolls-Royce Plc Alloy

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190003017A1 (en) * 2016-01-08 2019-01-03 Siemens Aktiengesellschaft Gamma, gamma' cobalt based alloys for additive manufacturing methods or soldering, welding, powder and component
US11180830B2 (en) * 2016-01-08 2021-11-23 Siemens Energy Global GmbH & Co. KG γ, γ′ cobalt based alloys for additive manufacturing methods or soldering, welding, powder and component
US20200048738A1 (en) * 2017-04-21 2020-02-13 Oerlikon Surface Solutions Ag, Pfaffikon Superalloy target
US11866805B2 (en) * 2017-04-21 2024-01-09 Oerlikon Surface Solutions Ag, Pfaffikon Superalloy target
US11725263B2 (en) 2018-04-04 2023-08-15 The Regents Of The University Of California High temperature oxidation resistant co-based gamma/gamma prime alloys DMREF-Co
US20230151475A1 (en) * 2021-11-17 2023-05-18 Shenyang Aerospace University Plastic cocrni-based medium-entropy alloy with 2.0 gpa-level ultra-high yield strength and preparation method thereof
CN115233074A (en) * 2022-07-12 2022-10-25 北京科技大学 Cobalt-nickel-based high-temperature alloy for gas turbine moving blade and preparation method thereof

Also Published As

Publication number Publication date
EP3175008B1 (en) 2018-10-17
EP3175008A2 (en) 2017-06-07
WO2016016437A3 (en) 2016-04-07
WO2016016437A2 (en) 2016-02-04

Similar Documents

Publication Publication Date Title
US20170342527A1 (en) Cobalt-based super alloy
JP5177559B2 (en) Ni-based single crystal superalloy
JP5696995B2 (en) Heat resistant superalloy
JP6839401B1 (en) Manufacturing method of Ni-based super heat-resistant alloy and Ni-based super heat-resistant alloy
JP5278936B2 (en) Heat resistant superalloy
EP2826877B1 (en) Hot-forgeable Nickel-based superalloy excellent in high temperature strength
JP2778705B2 (en) Ni-based super heat-resistant alloy and method for producing the same
JP3814662B2 (en) Ni-based single crystal superalloy
JP5467307B2 (en) Ni-based single crystal superalloy and alloy member obtained therefrom
US8764919B2 (en) High-temperature-resistant cobalt-base superalloy
CN101087894A (en) A Ni based alloy, a component, a gas turbine arrangement and use of pd in connection with such an alloy
WO2007091576A1 (en) Iridium-based alloy with high heat resistance and high strength and process for producing the same
CN103114225B (en) A kind of High-strength hot-corrosion-resistnickel-base nickel-base monocrystal high-temperature alloy
JP5323162B2 (en) Polycrystalline nickel-based superalloy with excellent mechanical properties at high temperatures
US20180057920A1 (en) Grain refinement in in706 using laves phase precipitation
WO2006104059A1 (en) COBALT-FREE Ni BASE SUPERALLOY
CN107828989A (en) A Co-Al-W-Based Superalloy Based on the Cluster Plus Connecting Atom Model
JP5645054B2 (en) Nickel-base heat-resistant superalloys and heat-resistant superalloy components containing annealing twins
JP6419102B2 (en) Ni-base superalloy and method for producing Ni-base superalloy
JP5595495B2 (en) Nickel-base superalloy
JP2012193453A (en) Single crystal nickel-based super heat resistant alloy with improved creep property
JP2002097537A (en) Co-Ni base heat-resistant alloy and method for producing the same
WO2005064027A1 (en) Nickel-based super-heat-resistant alloy and gas turbine component using same
JP4543380B2 (en) Fuel cell stack fastening bolt alloy
JP6176665B2 (en) Ni-Fe base alloy and method for producing Ni-Fe base alloy material

Legal Events

Date Code Title Description
AS Assignment

Owner name: FRIEDRICH-ALEXANDER-UNIVERSITAET ERLANGEN-NUERNBER

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BAUER, ALEXANDER;GOEKEN, MATHIAS;FREUND, LISA;AND OTHERS;SIGNING DATES FROM 20170210 TO 20170212;REEL/FRAME:041927/0124

STPP Information on status: patent application and granting procedure in general

Free format text: DOCKETED NEW CASE - READY FOR EXAMINATION

STPP Information on status: patent application and granting procedure in general

Free format text: NON FINAL ACTION MAILED

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION

点击 这是indexloc提供的php浏览器服务，不要输入任何密码和下载