NICKEL-BASED SUPERALLOY, SINGLE-CRYSTAL BLADE AND TURBOMACHINE

Abstract

The invention relates to a nickel-based superalloy comprising, in percentages by mass, 4.0 to 5.5% rhenium, 1.0 to 3.0 ruthenium, 2.0 to 14.0% cobalt, 0.3 to 1.0% molybdenum, 3.0 to 5.0% chromium, 2.5 to 4.0% tungsten, 4.5 to 6.5% aluminum, 0.50 to 1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance being nickel and unavoidable impurities.

The invention also relates to a single-crystal blade (20A, 20B) comprising such an alloy and a turbomachine (10) comprising such a blade (20A, 20B).

Claims

1. A nickel-based superalloy comprising, in percentages by mass, 4.0 to 5.5% rhenium, 1.0 to 3.0% ruthenium, 2.0 to 14.0% cobalt, 0.30 to 1.00% molybdenum, 3.0 to 5.0% chromium, 2.5 to less than 4.0% tungsten, 4.5 to 6.5% aluminum, 0.50 to 1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance being nickel and unavoidable impurities.

2. (canceled)

3. The superalloy according to claim 1, comprising, in percentages by mass, 4.0 to 5.5% rhenium, 1.0 to 3.0% ruthenium, 3.0 to 13.0% cobalt, 0.40 to 1.00% molybdenum, 3.0 to 4.5% chromium, 2.5 to less than 4.0% tungsten, 4.5 to 6.5% aluminum, 0.50 to 1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance being nickel and unavoidable impurities.

4. The superalloy according to claim 1, comprising, in percentages by mass, 4.0 to 5.0% rhenium, 1.0 to 3.0% ruthenium, 11.0 to 13.0% cobalt, 0.40 to 1.00% molybdenum, 3.0 to 4.5% chromium, 2.5 to less than 4.0% tungsten, 4.5 to 6.5% aluminum, 0.50 to 1.50% titanium, 8.0 to 9.0% tantalum, 0.15 to 0.30% hafnium, 0.05 to 0.15% silicon, the balance being nickel and unavoidable impurities.

5-10. (canceled)

11. A single-crystal blade for a turbomachine comprising a superalloy according to claim 1.

12. The single-crystal blade according to claim 11, comprising a protective coating comprising a metallic bond coat deposited on the superalloy and a ceramic thermal barrier deposited on the metallic bond coat.

13. (canceled)

14. A turbomachine comprising a single-crystal blade according to claim 11.

15. The superalloy according to claim 1, wherein the superalloy has a density less than or equal to 9.00 g/cm.sup.3.

16. The superalloy according to claim 1, wherein a volume percentage of γ′ phase precipitates in the superalloy is greater than or equal to 50%.

17. The single-crystal blade according to claim 12, wherein the metallic bond coat includes an MCrAlY type alloy or a nickel aluminide type alloy.

18. The superalloy according to claim 1, wherein the superalloy has a no-freckles parameter greater than or equal to 0.91.

19. The superalloy according to claim 1, wherein the superalloy has a gamma prime resistance greater than or equal to 0.376.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Other features and advantages of the invention will be apparent from the following description of embodiments of the invention, given by way of non-limiting examples, with reference to the single appended figure wherein:

[0055] FIG. 1 is a schematic longitudinal section view of a turbomachine;

[0056] FIG. 2 is a graph representing the no-freckles parameter (NFP) for different superalloys;

[0057] FIG. 3 is a graph representing the γ′ phase volume fraction at different temperatures and for different superalloys.

DETAILED DESCRIPTION OF THE INVENTION

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] These properties thus make these superalloys interesting candidates for the manufacture of single-crystal parts for the hot parts of turbojet engines.

[0065] A moving blade 20A or a rectifier 20B for turbomachinery comprising a superalloy as defined above can therefore be manufactured.

[0066] 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.

[0067] 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

[0068] Six nickel-based single-crystal superalloys of the present disclosure (Ex 1 to Ex 6) were studied and compared with six commercial single-crystal superalloys CMSX-4 (Ex 7), CMSX-4PlusC (Ex 8), René N6 (Ex 9), CMSX-10 (Ex 10), MC-NG (Ex 11) and TMS-138 (Ex 12). The chemical composition of each of the single-crystal superalloys is given in Table 1, the composition Ex 9 further comprising 0.05% by mass carbon (C) and 0.004% by mass boron (B), the composition Ex 10 further comprising 0.10% by mass niobium (Nb). All these superalloys are nickel-based superalloys, i.e. the balance to 100% of the compositions shown consists of nickel and unavoidable impurities.

TABLE-US-00001 TABLE 1 Re Ru Co Mo Cr W Al Ti Ta Hf Si Ex 1 5.0 2.0 4.0 0.50 4.0 3.0 5.4 1.00 8.5 0.25 0.10 Ex 2 5.0 2.0 4.0 0.50 4.0 3.5 5.4 0.90 8.5 0.25 0.10 Ex 3 4.4 2.0 4.0 0.70 4.0 3.0 5.4 1.00 8.5 0.25 0.10 Ex 4 4.4 2.0 12.0 0.70 4.0 3.0 5.4 1.00 8.5 0.25 0.10 Ex 5 5.0 2.0 4.0 0.50 3.5 3.5 5.4 0.90 8.5 0.25 0.10 Ex 6 4.4 2.0 12.0 0.70 3.5 3.5 5.4 0.90 8.5 0.25 0.10 Ex 7 3.0 0.0 9.6 0.60 6.6 6.4 5.6 1.00 6.5 0.10 0.00 Ex 8 4.8 0.0 10.0 0.60 3.5 6.0 5.7 0.85 8.0 0.10 0.00 Ex 9 5.3 0.0 12.2 1.10 4.4 5.7 6.0 0.00 7.5 0.15 0.00 Ex 10 6.0 0.0 3.0 0.40 2.0 5.0 5.7 0.20 8.0 0.03 0.00 Ex 11 4.0 4.0 0.0 1.00 4.0 5.0 6.0 0.50 5.0 0.10 0.10 Ex 12 4.9 2.0 5.9 2.9 2.9 5.9 5.9 0.00 5.6 0.10 0.00

Density

[0069] The room temperature density of each superalloy was estimated using a modified version of the Hull formula (F. C. Hull, Metal Progress, November 1969, pp 139-140). 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 is as follows:

D=27.68×[D.sub.1+0.14037−0.00137% Cr−0.00139% Ni−0.00142% Co−0.00140% Fe−0.00186% Mo−0.00125% W−0.00134% V−0.00119% Nb−0.00113% Ta+0.0004% Ti+0.00388% C+0.0000187 (% Mo).sup.2−0.0000506 (% Co)×(% Ti)−0.00096% Re−0.001131% Ru]  (1)

[0070] where D.sub.1=100/[(% Cr/D.sub.Cr) (% Ni/D.sub.Ni)+ . . . +(% X/D.sub.x)]

[0071] where D.sub.Cr, D.sub.Ni, . . . , D.sub.X are the densities of the elements Cr, Ni, . . . , X expressed in lb/in.sup.3 (pounds per cubic inch) and D is the density of the superalloy expressed in g/cm.sup.3.

[0072] where % Cr, % Ni, . . . % X are the contents, expressed in percentages by mass, of the superalloy elements Cr, Ni, . . . , X.

[0073] The calculated densities for the alloys in the presentation and for the reference alloys are less than 9.00 g/cm.sup.3 (see Table 2).

[0074] The comparison between the estimated and measured densities (see Table 2) is used to validate the modified Hull model (equation (1)). The estimated and measured densities are consistent.

[0075] Table 2 shows various parameters for super alloys Ex 1 to Ex 12.

TABLE-US-00002 TABLE 2 Estimated Measured density (1) density (g/cm.sup.3) (g/cm.sup.3) NFP RGP Md Ex 1 8.89 — 0.96 0.380 0.98 Ex 2 — — 0.91 0.376 — Ex 3 8.85 — 1.05 0.380 0.98 Ex 4 8.83 — 1.05 0.380 0.98 Ex 5 8.91 8.8  0.91 0.376 0.98 Ex 6 8.86 — 1.00 0.376 0.98 Ex 7 8.71 — 0.65 0.358 0.99 Ex 8 8.91 — 0.68 0.371 0.99 Ex 9 8.87 — 0.69 0.256 0.98 Ex 10 8.99 — 0.67 0.299 0.96 Ex 11 8.75 8.75 0.55 0.232 0.97 Ex 12 8.88 — 0.61 0.215 0.97

No-Freckles Parameter (NFP)

[0076]
NFP=[% Ta+1.5% Hf+0.5% Mo−0.5% % Ti)]/[% W+1.2% Re)]  (2)

[0077] where % Cr, % Ni, . . . % X are the contents, expressed in percentages by mass, of the superalloy elements Cr, Ni, . . . , X.

[0078] The NFP is used to quantify the sensitivity to the formation of freckles during directed solidification of the workpiece (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.

[0079] As can be seen in Table 2 and FIG. 2, all Ex 1 to Ex 6 superalloys have an NFP greater than or equal to 0.7, whereas Ex 7 to Ex 12 commercial superalloys have an NFP less than 0.7.

Gamma Prime Resistance (GPR)

[0080] The intrinsic mechanical strength of the γ′ phase increases with the content of elements substituting for aluminum in the Ni.sub.3Al compound, such as titanium, tantalum and part of tungsten. The γ′ phase compound can therefore be written as Ni.sub.3(Al, Ti, Ta, W). The parameter GPR is used to estimate the level of hardening of the γ′ phase:

GPR=[C.sub.Ti+C.sub.Ta+(C.sub.W/2)]/C.sub.Al   (3)

[0081] (4) where C.sub.Ti, C.sub.Ta, C.sub.W and C.sub.Al are the concentrations, expressed in atomic percent, of the elements Ti, Ta, W and Al, respectively, in the superalloy.

[0082] A higher GPR parameter is conducive to better mechanical strength of the superalloy. It can be seen from Table 2 that the GPR parameter calculated for super alloys Ex 1 to Ex 6 is higher than the GPR parameter calculated for commercial super alloys Ex 7 to Ex 12.

Sensitivity to the Formation of TPC (Md d)

[0083] The parameter Md is defined as follows:

Md=Σ.sub.i=1.sup.nX.sub.i(Md).sub.i   (5)

[0084] where X.sub.i is the fraction of element i in the superalloy expressed in atomic percent, (Md).sub.i is the value of the parameter Md for element i.

[0085] Table 3 shows the Md values for the different elements of the superalloys.

TABLE-US-00003 TABLE 3 Element Md Element Md Ti 2.271 Hf 3.02 Cr 1.142 Ta 2.224 Co 0.777 W 1.655 Ni 0.717 Re 1.267 Nb 2.117 Al 1.9 Mo 1.55 Si 1.9 Ru 1.006

[0086] Sensitivity to TCP formation is determined by the parameter Md d, according to the New PHACOMP method which was developed by Morinaga et al. (Morinaga et al., New PHACOMP and its application to alloy design, Superalloys 1984, edited by M Gell et al., The Metallurgical Society of AIME, Warrendale, Pa., USA (1984) pp. 523-532). According to this model, the sensitivity of superalloys to the formation of TCP increases with the value of the parameter Md.

[0087] As can be seen in Table 2, the superalloys Ex 1 to Ex 12 have values of the parameter Md approximately equal. These superalloys therefore exhibit similar sensitivities to the formation of TCP, sensitivities which are relatively low.

Phase γ′ Solvus Temperature

[0088] ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the solvus temperature of the γ′ phase at equilibrium.

[0089] As can be seen from Table 4, Ex 1 to Ex 6 superalloys have a high γ′ solvus temperature comparable to the γ′ solvus temperature of Ex 7 to Ex 12 commercial superalloys.

Phase γ′ Volume Fraction

[0090] 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 12 at 950° C., 1050° C. and 1200° C.

[0091] As can be seen in Table 4 and FIG. 3, Ex 1 to Ex 6 superalloys contain higher or comparable phase γ′ volume fractions than the phase γ′ volume fractions of commercially available Ex 7 to Ex 12 superalloys.

[0092] Thus, the combination of high γ′ solvus temperature and high phase γ′ volume fractions for the super alloys Ex 1 to Ex 6 is favorable for good creep resistance at high and very high temperatures, for example at 1200° C. This resistance must therefore be higher than the creep resistance of commercial superalloys Ex 7 to Ex 12.

TABLE-US-00004 TABLE 4 T.sub.solvus γ′ Phase γ′ volume fraction (% vol) (° C.) 950° C. 1050° C. 1200° C. Ex 1 1338 67.0 62.0 46.0 Ex 2 1335 67.6 62.4 45.9 Ex 3 1337 66.6 61.1 43.2 Ex 4 1276 60.0 51.2 22.7 Ex 5 1344 65.0 60.0 46.0 Ex 6 1295 58.0 50.0 38.0 Ex 7 1290 58.0 48.0 25.0 Ex 8 1320 63.0 57.0 36.0 Ex 9 1283 60.0 51.0 24.0 Ex 10 1374 65.0 60.0 46.0 Ex 11 1348 68.0 62.0 45.0 Ex 12 1321 67.0 58.0 35.0

Volume Fraction of TCP type σ

[0093] The ThermoCalc software (Ni25 database) based on the CALPHAD method was used to calculate the volume fraction (in volume percent) of equilibrium phase σ in superalloys Ex 1 to Ex 12 at 950° C. and 1050° C. (see Table 5).

[0094] The calculated volume fractions of the phase a are zero at 950° C. for Ex 3, Ex 4 and Ex 6 superalloys, and relatively low for Ex 1 and Ex 5 superalloys, reflecting a low sensitivity to TCP precipitation. These results therefore corroborate the results obtained with the New PHACOMP method (parameter Md).

Mass Concentration of Chromium Dissolved in the γ Matrix

[0095] 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 12 at 950° C., 1050° C. and 1200° C.

[0096] As can be seen in Table 5, the chromium concentrations in the γ phase for super alloys Ex 1 to Ex 6 are comparable to the chromium concentrations in the γ phase for commercial superalloys Ex 7 to Ex 12, which is favorable for good corrosion and hot oxidation resistance.

TABLE-US-00005 TABLE 5 Volume fraction of TCP Chromium content in the γ phase type σ (in % vol) (in % by mass) 950° C. 1050° C. 950° C. 1050° C. 1200° C. Ex 1 0.4 0.00 8.80 7.80 6.00 Ex 2 0.00 0.00 11.30 9.90 7.30 Ex 3 0.0 0.00 8.50 7.60 5.80 Ex 4 0.0 0.00 8.10 5.50 4.80 Ex 5 0.7 0.05 8.70 7.90 6.30 Ex 6 0.0 0.00 8.10 7.00 5.20 Ex 7 0.7 0.00 12.80 10.90 7.84 Ex 8 1.2 0.50 7.40 6.43 4.82 Ex 9 1.0 0.25 8.37 7.10 5.25 Ex 10 0.9 0.40 3.62 3.36 2.77 Ex 11 0.8 0.20 7.83 7.10 5.70 Ex 12 0.4 0.60 5.60 4.80 3.70

Very High Temperature Creep Property

[0097] Creep tests were carried out on the superalloys Ex 2, Ex 7, Ex 9 and Ex 10. Creep tests were carried out at 1200° C. and 80 MPa according to the NF EN ISO 204 standard of August 2009 (Guide U125_J).

[0098] The results of creep tests in which the superalloys were loaded (80 MPa) at 1200° C. are shown in Table 6. The results represent the time in hours (h) at specimen failure.

TABLE-US-00006 TABLE 6 Time to break (hour) Ex 2 63 Ex 7 7 Ex 9 9 Ex 10 59

[0099] The Ex 2 superalloy exhibits better creep behavior than the Ex 7 and Ex 9 superalloys. Ex 10 superalloy also has good creep properties.

Cyclic Oxidation Property at 1150° C.

[0100] Superalloys shall be thermally cycled as described in INS-TTH-001 and INS-TTH-002: Oxidative Cycling Test Method (Mass Loss Test and Thermal Barrier).

[0101] A specimen of the superalloy under test (pin having a diameter of 20 mm and a height of 1 mm) is subjected to thermal cycling, each cycle of which comprises a rise to 1150° C. in less than 15 min (minutes), a 60 min stop at 1150° C. and turbine-cooling of the specimen for 15 min.

[0102] The thermal cycle is repeated until a loss in mass of the test piece equal to 20 mg/cm.sup.2 (milligrams per square centimeter) is observed.

[0103] The service life of the superalloys tested is shown in Table 7.

TABLE-US-00007 TABLE 7 Service life (hours) Ex 2 >1700 Ex 7 ~230 Ex 8 ~480 Ex 10 ~100

[0104] It can be seen that the Ex 2 superalloy has a much longer service life than the Ex 7, Ex 8 and Ex 9 superalloys. It should be noted that the oxidation properties of the Ex 10 superalloy are much poorer than those of the Ex 2 superalloy.

Microstructural Stability

[0105] After aging for 300 hours at 1050° C., no TCP phase is observed for the Ex 2 superalloy by scanning electron microscopy image analysis.

Sensitivity to Foundry Defect Formation

[0106] After forming by the lost-wax process and directional solidification in the Bidgman furnace, no defects resulting from the casting process, particularly of the “freckles” type, were observed in the Ex 2 superalloy. The “freckles” type defects are observed after immersion of the specimen in a solution based on HNO.sub.3/H.sub.2SO.sub.4.

[0107] 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. In addition, individual features of the different embodiments referred to may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.