Patent Application
20170051382
The present application claims priority under 35 U.S.C. §119 of European Patent Application No. 15181489.4, filed Aug. 19, 2015, the entire disclosure of which is expressly incorporated by reference herein.
1. Field of the Invention
The invention relates to a nickel-based alloy, in particular a nickel-based superalloy, for high-temperature applications, preferably for use in turbomachines, such as aeroengines, and also to a corresponding component of a turbomachine, in particular an aeroengine, made of such a nickel-based alloy.
A nickel-based alloy is taken to mean a material which comprises nickel in the main constituent. A particular embodiment of nickel-based alloys are nickel-based superalloys, which are taken to mean alloys that are usable at high temperatures up to virtually the melting point thereof owing to their special composition and structure development. The expression nickel-based alloy, as used hereinafter, therefore also comprises the expression nickel-based superalloy.
2. Discussion of Background Information
Nickel-based superalloys, owing to the high-temperature stability thereof, are used in high-temperature applications, e.g. in the construction of stationary gas turbines or aeroengines. High-temperature application is taken to mean in this case an application in which the usage temperature of a component produced from the alloy is in a temperature range above half the inciting temperature of the alloy.
The nickel-based superalloys owe their good high-temperature properties and in particular their outstanding high-temperature stability to a specific structure development which is characterized by a γ matrix and the γ′-precipitates incorporated therein. The cubic face-centered α phase of the matrix consists of the main constituent nickel and also elements such as cobalt, chromium, molybdenum, rhenium and tungsten which are alloyed together to form nickel-based superalloys. Such alloy constituents such as tungsten, rhenium and molybdenum achieve a mixed-crystal solidification of the γ matrix that gives the alloy strength in addition to the precipitation hardening with the γ′-precipitates.
The alloy constituents rhenium, tungsten and molybdenum, in addition to the mixed-crystal solidification of the γ matrix, additionally generate a stabilization of the γ′-precipitates and counteract their coarsening, which would lead to a fall in creep strength.
However, in the alloying of refractory metals such as rhenium, tungsten and molybdenum, there is the problem that what are termed topologically close-packed (TCP) phases form in that are brittle and can lead to crack formation.
The γ′-precipitate phases likewise usually have a cubic face-centered structure with the composition Ni3(Al,Ti,Ta,Nb).
In addition, the strength of nickel-based superalloys can be increased by the formation of carbides that stabilize the grain boundaries and therefore make a contribution to creep strength.
Correspondingly, it is of critical importance for the property profile of nickel-based superalloys in high-temperature applications how the composition is selected with respect to the refractory metals cobalt, chromium, molybdenum, rhenium and tungsten as mixed-crystal formers and also the fractions of aluminum, tantalum and titanium as constituents of the γ′-precipitates. In order to obtain an optimum nickel-based superalloy for high-temperature applications with high service temperatures close to the melting point of the alloy with high creep resistance and specific gravity as low as possible, and also good processability, the optimum composition of the alloy elements is correspondingly important.
A multiplicity of nickel-based superalloys of differing compositions are already known, as disclosed, for example, in the documents EP 0 663 462 A1 and EP 2 128 284 A1, the entire disclosures of which are incorporated by reference herein. Whereas in EP 0 663 462 A1 the focus is on two groups of alloy elements, more precisely firstly the group having molybdenum, chromium and niobium and secondly the group having aluminum, titanium and tungsten, being present in a defined total quantitative fraction in the application, EP 2 128 284 A1 proposes a nickel-based superalloy in which the fractions of the elements tungsten, chromium, molybdenum and rhenium in % by weight, which in each case are weighted with an individual factor, in total shall not exceed a defined value.
In EP 0 663 462 A1 it is described, in addition, how, by addition of ruthenium, the distribution of other alloy constituents can be shifted between γ matrix and γ′-precipitates, in such a manner that the formation of TCP phases can be influenced.
Nevertheless, in the known nickel-based superalloys, in production by casting, casting segregation of the diffusion-inert elements, such as rhenium and tungsten, occurs, which counteracts a homogeneous property profile of the alloy. Correspondingly, to achieve a higher degree of homogenization, complex solution annealing cycles must be carried out.
Furthermore, in the known nickel-based superalloys at correspondingly high temperatures, nevertheless, brittle TCP phases form that can impair the strength of corresponding components.
Furthermore, it is desirable to increase the strength of such nickel-based superalloys by corresponding refractory metals such as tungsten and molybdenum being present at a fraction as small as possible in the γ′-precipitates, but instead contributing to the mixed-crystal solidification of the γ matrix, in such a manner that it is necessary to avoid that, owing to certain alloy constituents such as, e.g., ruthenium, an unfavorable distribution of the alloy constituents such as, e.g., the chemical elements contributing to the mixed-crystal hardening, is established between γ matrix and γ′-precipitates.
In view of the foregoing, it would be advantageous to have available an optimized nickel-based superalloy in which the above-described problems of cast segregation and also the avoidance of the formation of TCP phases is improved and at the same time the mechanical properties with respect to high-temperature strength and creep resistance are improved. However, here the density of the alloy shall be kept as low as possible and good and simple production and also processability of the alloy are to be ensured.
The present invention provides a nickel-based alloy for high-temperature applications, in particular for use in kinetic flow engines (hubomachines). The alloy has a chemical composition which comprises, in % by weight: Al from 3.7 to 7.0, Co from 10 to 20, Cr from 2.1 to 7.2, Mo from 1.1 to 3.0, Re from 5.7 to 9.2, Ru from 3.1 to 8.5, Ta from 4.1 to 11.9, Ti from 0 to 3.3, W from 2.1 to 4.9, C from 0 to 0.05, Si from 0 to 0.1, Mn from 0 to 0.05, P from 0 to 0.015, S from 0 to 0.001, B from 0 to 0.003, Cu from 0 to 0.05, Fe from 0 to 0.15, Hf from 0 to 0.15, Zr from 0 to 0.015, Y from 0 to 0.001, remainder nickel and unavoidable impurities. Further, the ratio of the fractions of Ta to Al in percent by weight is from 1 to 2, and the ratio of the fractions of Co to W in percent by weight is from 2 to 5.
In one aspect of the alloy, the ratio of the fractions of Co to W in percent by weight may be less than or equal to 4 and/or the ratio of the fractions of W to Mo in percent by weight may be from 1 to 4 and/or the ratio of the fractions of Co to Re in percent by weight may be from 1 to 2.
In another aspect, the alloy may comprise in percent by weight: from 5.0 to 7.0% Al and/or from 10.5 to 15.0% Co and/or from 4.0 to 6.0% Cr and/or from 1.1 to 2.5% Mo and/or from 5.5 to 7.0% Re and/or from 3.1 to 5.5% Ru and/or from 5.0 to 9.0% Ta and/or from 0 to 2.0% Ti and/or from 3.0 to 4.5% W. For example, the alloy may comprise, in percent by weight: from 5.5 to 6.0% Al and/or from 11.0 to 12.0% Co and/or from 4.5 to 5.5% Cr and/or from 1.1 to 2.0% Mo and/or from 5.7 to 6.5% Re and/or from 3.3 to 5.0% Ru and/or from 5.5 to 8.0% Ta and/or from 0.5 to 2.0% Ti, e.g., from 1.1 to 1.7% Ti, and/or from 3.5 to 4.5% W.
In yet another aspect, the density of the alloy may be not higher than 9.09 g/cm3, e.g., not higher than 8.94 g/cm3, not higher than 8.85 g/cm3, or not higher than 8.80 g/cm3.
In a still further aspect, the alloy may comprise a γ matrix and γ′-precipitates, the fraction of W and/or Mo in the γ matrix being greater than that in the γ′-precipitates.
The present invention also provides a component of a turbomachine, in particular an aeroengine, which comprises the alloy as set forth above (including the various aspects thereof). For example, the alloy may be thimed as a single crystal or may be fowled by directed solidification.
As set forth above, the present invention proposes providing an optimized composition of a nickel-based alloy, in particular with respect to the alloy elements cobalt, rhenium, tungsten, tantalum, aluminum and titanium, since these alloy elements considerably influence the structure—and microstructure—development, and also the corresponding mechanical properties of the alloy.
Accordingly, it is proposed to provide a nickel-based superalloy having a chemical composition which comprises, based on the total weight of the alloy, 3.7 to 7.0% by weight of Al, 10 to 20% by weight of Co, 2.1 to 7.2% by weight of Cr, 1.1 to 3.0% by weight of Mo, 5.7 to 9.2% by weight of Re, 3.1 to 8.5% by weight of Ru, 4.1 to 11.9% by weight of Ta, 0 to 3.3% by weight of Ti, 2.1 to 4.9% by weight of W, 0 to 0.05% by weight of C, 0 to 0.1% by weight of Si, 0 to 0.05% by weight of Mn, 0 to 0.015% by weight of P, 0 to 0.001% by weight of S, 0 to 0.003% by weight of B, 0 to 0.05% by weight of Cu, 0 to 0.15% by weight of Fe, 0 to 0.15% by weight of Hf, 0 to 0.015% by weight of Zr, 0 to 0.001% by weight of Y and the remainder nickel, and also unavoidable impurities.
The nickel fraction of the alloy is the main constituent of the alloy, that is to say the constituent which has the highest fraction in % by weight or at. % of the alloy. It is understood that the corresponding alloy is always only present at 100%, and so no addition of the limiting values of the stated fraction ranges can proceed in such a manner that the composition of the alloy would make less or more than 100%, or nickel would not make the corresponding greatest fraction. Rather, when an alloy element is used at a high fraction, a corresponding reduction of other alloy elements must be performed with a lower fraction corresponding to the details.
The nickel-based alloy is distinguished, in particular, in that the fraction of tantalum is always greater than or equal to the fraction of aluminum, in such a manner that the ratio of the fractions of tantalum to aluminum in % by weight is greater than or equal to 1, that is to say c(Ta)/c(Al)≧1. Furthermore, the ratio of tantalum to aluminum in % by weight is to be less than or equal to 2. This is because it has been found that an improved distribution of tungsten and molybdenum between the γ matrix and the γ′-precipitates is achievable thereby, in such a manner that the fraction of tungsten and/or molybdenum in the γ matrix is greater than in the γ′-precipitates.
In addition, in the case of the nickel-based superalloy of the present invention, the ratio of the fractions of cobalt to tungsten in % by weight is selected to be greater than or equal to 2 and less than or equal to 5, since by increasing the cobalt content an improvement of the segregation behavior, i.e. a lower cast segregation and a higher degree of homogenization, are achievable, in such a manner that shorter and/or simpler solution annealing cycles can be employed. In combination with the higher tungsten fraction in the γ matrix by the established ratio of tantalum to aluminum, either the strength can be increased or, with the mixed-crystal solidification remaining the same, in total the tungsten content can be reduced, which, in particular, also acts advantageously on the density of the alloy.
In particular, the ratio of the fractions of cobalt to tungsten in % by weight can be less than or equal to 4.
In addition to the ratio of tantalum to aluminum and of cobalt to tungsten, the nickel-based alloy can be established in such a manner that the ratio of the fractions of tungsten to molybdenum in % by weight is greater than or equal to 1 and less than or equal to 4. Also this makes it possible to achieve the targets of avoiding cast segregation, avoiding the formation of TCP phases and also improved distribution of tungsten and molybdenum between the γ matrix and the γ′-precipitates.
For this purpose, the ratio of the fractions of cobalt to rhenium in % by weight can also be selected to be greater than or equal to 1 and less than or equal to 2.
The alloy constituents aluminum, cobalt, chromium, molybdenum, rhenium, ruthenium, tantalum, titanium and/or tungsten that are important for the mechanical properties can be co-alloyed, in particular at from 5.0 to 7.0%, in particular from 5.5 to 6.0% Al and/or from 10.5 to 15.0%, in particular from 11.0 to 12.0% Co and/or from 4.0 to 6.0%, in particular from 4.5 to 5.5% Cr and/or from 1.1 to 2.5%, in particular from 1.1 to 2.0% Mo and/or from 5.5 to 7.0%, in particular from 5.7 to 6.5% Re and/or from 3.1 to 5.5%, in particular from 3.3 to 5.0% Ru and/or from 5.0 to 9.0%, in particular from 5.5 to 8.0% Ta and/or from 0 to 2.0%, in particular from 0.5 to 2.0%, preferably from 1.1 to 1.7% Ti and/or from 3.0 to 4.5%, in particular from 3.5 to 4.5% W.
A corresponding alloy can have a density ≦8.94 g per cm3, in particular ≦8.85 g per cm3 and preferably ≦8.8 g per cm3.
The nickel-based alloy of the present invention can be used not only in single-crystal form but also in directed solidification form, wherein, in particular for high-temperature applications in aeroengine construction, mono-crystalline components are used.
The following table shows the composition of four alloys according to the invention with respect to the main constituents aluminum, cobalt, chromium, molybdenum, rhenium, ruthenium, tantalum, titanium, tungsten, with the remainder nickel, in % by weight, wherein further constituents such as carbon, silicon, manganese, phosphorus, sulfur, boron, copper, iron, hafnium, zirconium and yttrium can be present at an overall fraction of less than 0.7% by weight.
The corresponding alloys have the properties stated in the following table.
The MCH index designates the mixed-crystal index according to E. Fleischmann, Einfluss der Mischkristallhärtung der Matrix auf die Kriechbeständigkeit einkristalliner Nickelbasis—Superlegierungen [Effect of mixed-crystal hardening of the matrix on the creep resistance of single-crystal nickel-based superalloys], Dissertation University of Bayreuth, 2013, in which weighted element contents of Re, W and Mo in the matrix are detected in % by weight (MCH Index=1.6 Re+W+Mo). An MCH index as high as possible is advantageous for forming a creep-resistant and high-temperature-stable alloy. The fraction of the alloy elements in the matrix can be determined by measurements by means of an atomic probe or transmission-electron microscope.
Although the present invention has been described in detail with reference to the exemplary embodiments, the invention is not restricted to these exemplary embodiments, but rather modifications are possible in such a manner that individual features can be modified within the stated scope of protection of the accompanying claims. The disclosure includes all combinations of the individual features presented.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15181489.4 | Aug 2015 | EP | regional |
