Nickel-based superalloy, single-crystal blade and turbomachine

Abstract

The invention relates to a nickel-based superalloy comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 9.5% tantalum, 0 to 1.50% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0 to 2.50% rhenium, 0.05 to 0.15% hafnium, 0.70 to 4.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities. The invention also relates to a single-crystal blade comprising such an alloy and a turbomachine comprising such a blade.

Claims

1. A nickel-based superalloy comprising, in weight percent, 5.0 to 6.0% aluminum, 6.0 to 9.5% tantalum, 0 to 1.50% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0 to 2.50% rhenium, 0.05 to 0.15% hafnium, 0.70 to 4.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

2. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 9.5% tantalum, 0 to 1.50% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0 to 2.50% rhenium, 0.05 to 0.15% hafnium, 1.70 to 4.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

3. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 7.0% tantalum, 0 to 1.50% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0 to 2.50% rhenium, 0.05 to 0.15% hafnium, 1.70 to 4.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

4. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 8.5 to 9.5% tantalum, 0 to 1.50% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0 to 1.50% rhenium, 0.05 to 0.15% hafnium, 1.70 to 3.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

5. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 9.5% tantalum, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.05 to 0.15% hafnium, 2.70 to 4.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

6. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 9.5% tantalum, 0.50 to 1.50% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.05 to 0.15% hafnium, 2.70 to 4.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

7. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 9.5% tantalum, 0.80 to 1.20% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0 to 2.50% rhenium, 0.05 to 0.15% hafnium, 0.70 to 3.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

8. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 9.5% tantalum, 0 to 1.50% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0 to 2.50% rhenium, 0.05 to 0.15% hafnium, 0.70 to 4.30% platinum, 0.10% silicon, the remainder being nickel and unavoidable impurities.

9. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 7.0% tantalum, 0.80 to 1.20% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.05 to 0.15% hafnium, 2.70 to 3.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

10. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 7.0% tantalum, 0.80 to 1.20% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.70 to 1.30% rhenium, 0.05 to 0.15% hafnium, 1.70 to 2.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

11. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 7.0% tantalum, 0.80 to 1.20% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 1.70 to 2.30% rhenium, 0.05 to 0.15% hafnium, 0.70 to 1.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

12. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 6.0 to 7.0% tantalum, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.05 to 0.15% hafnium, 3.70 to 4.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

13. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 8.5 to 9.5% tantalum, 0.80 to 1.20% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.70 to 2.30% rhenium, 0.05 to 0.15% hafnium, 1.70 to 2.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

14. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 8.5 to 9.5% tantalum, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.05 to 0.15% hafnium, 2.70 to 3.30% platinum, 0 to 0.15% silicon, the remainder being nickel and unavoidable impurities.

15. The superalloy as claimed in claim 1, comprising, in percentages by mass, 5.0 to 6.0% aluminum, 8.5 to 9.5% tantalum, 0.80 to 1.20% titanium, 8.0 to 10.0% cobalt, 6.0 to 7.0% chromium, 0.30 to 0.90% molybdenum, 5.5 to 6.5% tungsten, 0.05 to 0.15% hafnium, 2.70 to 3.30% platinum, 0.10% silicon, the remainder being nickel and unavoidable impurities.

16. A single-crystal blade for a turbomachine comprising a superalloy as claimed in claim 1.

17. The blade as claimed in claim 16, comprising a protective coating comprising a metallic bond coat deposited on the superalloy and a ceramic thermal barrier deposited on the metallic bond coat.

18. The blade as claimed in claim 16, having a structure oriented in a <001> crystallographic direction.

19. A turbomachine comprising a blade as claimed in claim 16.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the subject matter of the present disclosure will be apparent from the following description of embodiments, given by way of non-limiting examples, with reference to the appended figures, wherein:

(2) FIG. 1 is a schematic longitudinal section view of a turbomachine;

(3) FIG. 2 is a graph representing the change in the γ′ phase volume fraction as a function of temperature.

(4) FIG. 3 is a graph representing the no-freckles parameter (NFP) for different superalloys;

(5) FIG. 4 is a graph representing the γ′ phase volume fraction at different temperatures and for different superalloys;

(6) FIG. 5 is a graph representing yield strength at 0.2% as a function of temperature for two superalloys;

(7) FIG. 6 is a graph representing tensile strength as a function of temperature for the two superalloys of FIG. 5;

(8) FIG. 7 is a graph representing mass gain as a function of time at 1000° C. for three superalloys;

(9) FIG. 8 is a micrograph representing the microstructure of a superalloy.

(10) In all the figures, common elements are identified by identical numerical references.

DETAILED DESCRIPTION

(11) Nickel-based superalloys are intended for the manufacture of single-crystal blades by a process of directed solidification in a thermal gradient. The use of a monocrystalline seed or grain selector at the beginning of solidification makes it possible to obtain this monocrystalline structure. The structure is oriented, for example, in a<001> crystallographic direction which is the orientation that generally confers the optimum mechanical properties on superalloys.

(12) Solidified single-crystal nickel-based superalloys have a dendritic structure and consist of γ′ Ni.sub.3(Al, Ti, Ta) precipitates dispersed in a γ matrix of face-centered cubic structure, a nickel-based solid solution. These γ′ phase precipitates are heterogeneously distributed in the volume of the single crystal due to chemical segregations resulting from the solidification process. In addition, γ/γ′ eutectic phases are present in the inter-dendritic regions and are preferred crack initiation sites. These γ/γ′ eutectic phases are formed at the end of solidification. Moreover, the γ/γ′ eutectic phases are formed to the detriment of the fine precipitates (size lower than one micrometer) of the γ′ hardening phase. These γ′ phase precipitates constitute the main source of hardening of nickel-based superalloys. Also, the presence of residual γ/γ′ eutectic phases does not allow optimization of the hot creep resistance of the nickel-based superalloy.

(13) It has indeed been shown that the mechanical properties of superalloys, in particular the creep resistance, were optimal when the precipitation of the γ′ precipitates was ordered, i.e. the γ′ phase precipitates were aligned in a regular way, with a size ranging from 300 to 500 nm, and when the totality of the γ/γ′ eutectic phases was put back into solution.

(14) Raw solidified nickel-based superalloys are therefore heat-treated to obtain the desired distribution of the different phases. The first heat treatment is a homogenization treatment of the microstructure which aims to dissolve the γ′ phase precipitates and to eliminate the γ/γ′ eutectic phases or to significantly reduce their volume fraction. This treatment is carried out at a temperature higher than the solvus temperature of the γ′ phase and lower than the starting melting temperature of the superalloy (T.sub.solidus). A quenching is then carried out at the end of this first heat treatment to obtain a fine and homogeneous dispersion of the γ′ precipitates. Tempering heat treatments are then carried out in two stages, at temperatures below the solvus temperature of the γ′ phase. In a first step, to grow the γ′ precipitates to the desired size, then in a second step, to grow the volume fraction of this phase to about 70% at room temperature.

(15) FIG. 1 shows a vertical cross-section of a bypass turbofan engine 10 in a vertical plane through its main axis A. The turbofan engine 10 comprises, from upstream to downstream according to the flow of air, a fan 12, a low-pressure compressor 14, a high-pressure compressor 16, a combustor 18, a high-pressure turbine 20, and a low-pressure turbine 22.

(16) The high-pressure turbine 20 comprises a plurality of moving blades 20A rotating with the rotor and rectifiers 20B (stationary blades) mounted on the stator. The stator of the turbine 20 comprises a plurality of stator rings 24 arranged opposite to the moving blades 20A of the turbine 20.

(17) These properties thus make these superalloys interesting candidates for the manufacture of single-crystal parts for the hot parts of turbojet engines.

(18) A moving blade 20A or a rectifier 20B for turbomachinery comprising a superalloy as defined above can therefore be manufactured.

(19) Alternatively, a moving blade 20A or rectifier 20B for a turbomachine comprising a superalloy as defined above coated with a protective coating comprising a metallic bond coat.

(20) A turbomachine can in particular be a turbojet engine such as a turbofan engine 10. A turbomachine may also be a single-flow turbojet engine, a turboprop engine or a turboshaft engine.

EXAMPLES

(21) Eight single-crystal nickel-based superalloys of the present disclosure (Ex 1 to Ex 8) were studied and compared with five commercial single-crystal superalloys: René N5 (Ex 9), CMSX-4 (Ex 10), CMSX-4 Plus Mod C (Ex 11), Rene N6 (Ex 12), CMSX-10 K (Ex 13) and an experimental superalloy containing platinum (Ex 14), cited in the publication J. S. Van Sluytman, C. J. Moceri, and T. M. Pollock, “A Pt-modified Ni-base superalloy with high temperature precipitate stability,” Mater. Sci. Eng. A, vol. 639, pp. 747-754, July 2015. The chemical composition of each of the single-crystal superalloys is given in Table 1, the composition Ex 7 further comprising 0.03% by mass carbon, Ex 13 further comprising 0.10% by mass niobium (Nb), Ex 12 further comprising 0.05% by mass carbon (C) and 0.004% by mass boron (B), and Ex 14 further comprising 0.02% by mass carbon, 0.015% by mass boron and 0.02% by mass zircon. All these superalloys are nickel-based superalloys, i.e. the remainder to 100% of the compositions shown consists of nickel and unavoidable impurities.

(22) Superalloys Ex 1 to Ex 8 show a change in the volume fraction of the γ′ phase as a function of temperature according to curve B of FIG. 2, while Ex 9 to Ex 14 superalloys show a change in the volume fraction of the γ′ phase as a function of temperature according to curve A of FIG. 2.

(23) TABLE-US-00001 TABLE 1 Al Ta Ti Co Cr Mo W Re Hf Pt Si Ex 1 5.6 6.5 1.00 9.0 6.5 0.60 6.0 0 0.10 3.00 0 Ex 2 5.6 6.5 1.00 9.0 6.5 0.60 6.0 1.00 0.10 2.00 0 Ex 3 5.6 6.5 1.00 9.0 6.5 0.60 6.0 2.00 0.10 1.00 0 Ex 4 5.6 6.5 0 9.0 6.5 0.60 6.0 0 0.10 4.00 0 Ex 5 5.6 9.0 1.00 9.0 6.5 0.60 6.0 1.00 0.10 2.00 0 Ex 6 5.6 9.0 0 9.0 6.5 0.60 6.0 0 0.10 3.00 0 Ex 7 5.6 6.5 1.00 9.0 6.5 0.60 6.0 1.00 0.10 2.00 0 Ex 8 5.6 9.0 1.00 9.0 6.5 0.60 6.0 0 0.10 3.00 0.01 Ex 9 6.2 6.0 0 8.0 7.0 2.00 5.0 3.00 0.20 0 0 Ex 10 5.6 6.5 1.00 9.0 6.5 0.60 6.0 3.00 0.10 0 0 Ex 11 5.7 8.0 0.85 10.0 3.50 0.60 6.0 4.40 0.10 0 0 Ex 12 6.0 7.5 0 12.2 4.40 1.10 5.7 5.3 0.15 0 0 Ex 13 5.7 8.0 0.20 3.00 2.00 0.40 5.0 6.0 0.03 0 0 Ex 14 5.8 5.8 0.40 0 6.2 1.50 2.90 3.00 0.30 7.8 0.20

(24) Density

(25) The density at room temperature of each superalloy was estimated using a modified version of the Hull formula (F. C. Hull, Metal Progress, November 1969, pp 139-140). The density is expressed in g.Math.cm.sup.−3 (gram per cubic centimeter). This empirical equation was proposed by Hull. The empirical equation is based on the law of mixtures and includes corrective terms derived from a linear regression analysis of experimental data (chemical compositions and measured densities) for 235 superalloys and stainless steels. This Hull formula has been modified, in particular to take account of elements such as rhenium and ruthenium. The modified Hull formula given by P. Carondans “High gamma prime solvus New Generation Nickel-Based Superalloys for Single Crystal Turbine Blade Applications”, 2000, pp 737-746 is as follows:
d=8.29604−0.00435 wt % Co−0.0164 wt % (Cr+Mo)+0.06274 wt % W+0.0593 wt % (Re+Pt)+0.01811 wt % Ru−0.06595 wt % Al−0.0236 wt % Ti+0.05441 wt % Ta  (1)

(26) where wt % Co, wt % (Cr+Mo), . . . , wt % Ta are the percentages by mass of the elements Co, (Cr+Mo), . . . , Ta.

(27) where d is the density of the superalloy expressed in g/cm.sup.3.

(28) For example, the density of superalloy Ex 5 is estimated at 8.81 g/cm.sup.3 and the measured value is 8.83 g/cm.sup.3. The density is measured with a helium pycnometer. The above modified Hull formula is therefore a good match for the measured density of the superalloys.

(29) The densities calculated for the alloys of the invention and for the reference alloys are less than 8.90 g/cm.sup.3, preferably less than 8.85 g/cm.sup.3 (see Table 2).

(30) Table 2 shows different parameters for superalloys Ex 1 to Ex 12.

(31) TABLE-US-00002 TABLE 2 Estimated δ′ at δ′ at density (1) Cost 25° C. 1100° (g/cm.sup.3) NFP SRZ(%)].sup.1/2 (euros/kg) (%) C. (%) Ex 1 8.67 1.08 −29.91 1019.28 0.248 −0.065 Ex 2 8.67 0.90 −25.72 721.98 0.250 −0.136 Ex 3 8.67 0.77 −21.54 424.68 0.274 −0.207 Ex 4 8.76 1.16 −29.61 1329.38 0.363 0.047 Ex 5 8.81 1.24 −26.05 724.84 0.257 −0.205 Ex 6 8.83 1.58 −30.36 1012.07 0.313 −0.007 Ex 7 8.67 0.90 −25.72 721.98 0.251 −0.130 Ex 8 8.81 1.49 −30.30 1022.14 0.152 −0.141 Ex 9 8.58 0.85 −21.95 118.34 0.182 −0.274 Ex 10 8.67 0.67 −17.36 127.38 0.279 −0.222 Ex 11 8.90 0.68 3.70 160.20 0.363 0.005 Ex 12 8.87 0.69 1.35 167.13 0.331 −0.205 Ex 13 8.98 0.67 15.56 170.94 0.256 −0.185 Ex 14 8.96 1.05 −15.64 2612.21 0.262 −0.134

(32) No-Freckles Parameter (NFP)
NFP=[% Ta+1.5% Hf+0.5% Mo−0.5%% Ti)]/[% W+1.2% Re)].  (2)

(33) where % Cr, % Ni, . . . % X are the contents, expressed in percentages by mass, of the superalloy elements Cr, Ni, . . . , X.

(34) The NFP is used to quantify the sensitivity to the formation of freckles during the directed solidification of the component (document U.S. Pat. No. 5,888,451). To prevent the formation of freckles, the NFP must be greater than or equal to 0.7.

(35) As can be seen in Table 2 and FIG. 3, superalloys Ex 1 to Ex 8 all have an NFP greater than or equal to 0.7, while commercial superalloys Ex 10 to Ex 13 have an NFP less than 0.7.

(36) Sensitivity to the Formation of SRZ

(37) To estimate the sensitivity of rhenium-containing nickel-based superalloys to the formation of SRZ, Walston (document U.S. Pat. No. 5,270,123) established the following equation:
SRZ (%)].sup.1/2=13.88 (% Re)+4.10 (% W)−7.07 (% Cr)−2.94 (% Mo)−0.33 (% Co)+12.13  (3)

(38) where SRZ (%) is the linear percentage of SRZ in the superalloy under the coating and where the concentrations of the alloying elements are in atomic percent.

(39) This equation (3) was obtained by multiple linear regression analysis from observations made after aging for 400 hours at 1093° C. (degrees centigrade) of samples of various alloys with compositions close to composition Ex 12 under a NiPtAl coating.

(40) The higher the value of the parameter [SRZ (%)].sup.1/2, the more sensitive the superalloy is to SRZ formation. Thus, as can be seen in Table 2, for the superalloys Ex 1 to Ex 8, the values of the parameter [SRZ (%)].sup.1/2 are all negative and these superalloys therefore have a low sensitivity to SRZ formation under a NitPtAl coating, as does the commercial superalloy Ex 12, which is known for its low sensitivity to SRZ formation, and the superalloys Ex 9, Ex 10 and Ex 14. By way of example, the commercial superalloy Ex 13, which is known to be very sensitive to the formation of SRZ under a NiPtAl coating, has a relatively high [SRZ (%)].sup.1/2 parameter value.

(41) Cost of the Alloys

(42) The cost per kilogram of superalloys Ex 1 to Ex 14 is calculated on the basis of the composition of the superalloy and the costs of each compound (updated February 2018). This cost is given by way of illustration.

(43) Crystalline Parameter Difference δ′

(44) The crystalline parameter difference between phases γ and γ′, also called ‘Mismatch’ δ′ is expressed in percent. This parameter varies as a function of temperature due to the different thermal expansion coefficients of these two phases. It is considered to influence the mechanical properties and in particular the creep properties. When δ′ is negative, or even weakly positive, the stability of the microstructure at the given temperature is promoted.

(45) Phase γ′ Solvus Temperature

(46) The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the solvus temperature of the γ′ phase at equilibrium.

(47) As can be seen in Table 3, superalloys Ex 1 to Ex 8 have a γ′ solvus temperature similar to those of superalloys Ex 9 to Ex 14.

(48) Solidus and Liquidus Temperature

(49) The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the solidus and liquidus temperatures of superalloys Ex 1 to Ex 14.

(50) Phase γ′ Volume Fraction

(51) The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the volume fraction (volume percent) of phase γ′ at equilibrium in superalloys Ex 1 to Ex 14 at 950° C., 1050° C. and 1200° C.

(52) As can be seen in Table 3 and FIG. 4, superalloys Ex 1 to Ex 8 contain phase γ′ volume fractions greater than or comparable to the phase γ′ volume fractions of commercial superalloys Ex 9 to Ex 14.

(53) Thus, the combination of a high γ′ solvus temperature and high γ′ phase volume fractions for superalloys Ex 1 to Ex 8 is favorable for good creep resistance at high and very high temperatures, for example at 1200° C. This resistance should therefore be higher than the creep strength of commercial superalloys Ex 9 to Ex 12 and close to that of commercial superalloy Ex 11.

(54) TABLE-US-00003 TABLE 3 Transformation γ′ phase temperature (° C.) volume fraction (% vol) Solvus Solidus Liquidus 950° C. 1050° C. 1200° C. Ex 1 1262 1317 1380 59 50 20 Ex 2 1266 1316 1383 60 50 21 Ex 3 1271 1315 1385 60 51 23 Ex 4 1244 1354 1398 52 41 11.5 Ex 5 1294 1292 1366 64 56 30 Ex 6 1284 1337 1386 57 48 23 Ex 7 1266 1316 1383 60 50 21 Ex 8 1292 1292 1365 63 55 29 Ex 9 1306 1300 1392 63 53 29 Ex 10 1270 1310 1385 58 48 25 Ex 11 1320 1330 1400 63 57 36 Ex 12 1283 1319 1404 60 51 24 Ex 13 1373 1381 1428 65 60 46 Ex 14 1337 1343 1386 69 49 40

(55) Volume Fraction of TCP Type σ

(56) The ThermoCalc software (nickel database) based on the CALPHAD method was used to calculate the volume fraction (in volume percent) of phase σ at equilibrium in superalloys Ex 1 to Ex 14 at 950° C. and 1050° C. (see table 4).

(57) The calculated volume fractions of the σ phase are relatively low, reflecting a low sensitivity to TCP precipitation.

(58) Mass Concentration of Chromium Dissolved in the γ Matrix

(59) The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the chromium content (in percent by mass) in the γ phase at equilibrium in superalloys Ex 1 to Ex 14 at 950° C. 1200° C.

(60) As can be seen in Table 4, the chromium concentrations in the γ phase are higher or similar for superalloys Ex 1 to Ex 8, compared with the chromium concentrations in the γ phase for commercial superalloys Ex 9 to Ex 13, which is favorable to better corrosion and hot oxidation resistance.

(61) TABLE-US-00004 TABLE 4 Volume fraction Chromium content in of TCP the γ phase (in % by type σ (in % vol) mass) 950° C. 1050° C. 950° C. 1200° C. Ex 1 0 0 12.3 7.5 Ex 2 0 0 12.4 7.6 Ex 3 0 0 12.5 7.7 Ex 4 0 0 10.7 7.0 Ex 5 0 0 14.0 8.3 Ex 6 0 0 12.1 7.7 Ex 7 0 0 12.4 7.6 Ex 8 0 0 13.9 8.2 Ex 9 0.3 0 13.3 8.6 Ex 10 0.7 0 10.9 7.8 Ex 11 1.2 0.5 6.4 4.8 Ex 12 1.0 0.3 7.1 5.3 Ex 13 0.9 0.4 3.4 2.8 Ex 14 0.07 0 12.1 8.4

(62) Mechanical Properties

(63) FIG. 5 represents the change in yield strength at 0.2% (in MPa) as a function of temperature (in ° C.) for superalloy Ex 5 and superalloy Ex 11 at 650° C., 760° C. and 950° C.

(64) FIG. 6 represents the change in tensile strength at break (in MPa) as a function of temperature (in ° C.) for superalloy Ex 5 and superalloy Ex 11 at 650° C., 760° C. and 950° C.

(65) The 0.2% yield strength and the tensile strength are measured according to standards ISO 6892-1 at room temperature and ISO 6892-2 for temperatures greater than room temperature.

(66) As can be seen in FIG. 5, superalloy Ex 5 has a yield strength of 0.2% and a tensile strength similar to that of superalloy Ex 11.

(67) Oxidation Property

(68) The oxidation properties of superalloys Ex 5, Ex 9 and Ex 10 are shown in FIG. 7. The mass gain (in g/m.sup.2) as a function of time (in hours) of the superalloys was measured at 1000° C. As shown in FIG. 7, it can be seen that superalloy Ex 5 has a lower mass gain than superalloys Ex 9 and Ex 10 after less than 10 hours of testing at 1000° C.

(69) The test is carried out on pellets of the studied material with a diameter of 14 mm and a thickness of 1.2 to 1.4 mm. The oxidation test, also called thermogravimetric analysis test, is carried out under a constant flow of synthetic air (21% O.sub.2+79% N.sub.2), with a thermobalance compensated for the variation of Archimedes' principle. Thus, the mass gain is measured continuously, at the temperature of the test. Note that the sample holders have been previously stabilized so that they do not react with the samples and do not oxidize.

(70) Microstructure

(71) FIG. 8 shows a microstructure of superalloy Ex 5 after solution annealing and tempering by scanning electron microscopy at 5000× magnification. The microstructure shown is typical of an optimal microstructure for the mechanical properties of nickel-based superalloys, showing a microstructure with γ/γ′ phases. In FIG. 8, the γ′ precipitates are the dark gray cubes.

(72) Although the present disclosure has been described with reference to a specific example of a specific embodiment, it is obvious that various modifications and changes can be made to these examples without going beyond the general scope of the invention as defined by the claims. Furthermore, individual features of the different embodiments referred to can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.