The fourth-generation nickel-based single-crystal superalloy designed based on improving the intermediate and high-temperature creep properties

Abstract

The present invention discloses a fourth-generation nickel-based single-crystal superalloy based on intermediate and high-temperature creep properties, characterized in that, by weight percentage, the chemical composition of the alloy is as follows: chromium 2 wt.% - 4 wt.%, cobalt 3 wt.% - 7 wt.%, molybdenum 1 wt.% - 5 wt.%, tungsten 6.5 wt.% - 8 wt.%, tantalum 6 wt.% - 8 wt.%, aluminum 4 wt.% - 7.5 wt.%, hafnium 0.05 wt.% - 0.25 wt.%, rhenium 2 wt.% - 6 wt.%, ruthenium 1 wt.% - 3 wt.%, yttrium 0 wt.% - 0.02 wt.%, and the balance is nickel; and by weight percentage, 0.17 < molybdenum / tungsten < 0.7, 8.5 wt.% < molybdenum + tungsten < 12 wt.%. Based on the synergistic regulation of key strengthening elements, the present invention develops a nickel-based single-crystal superalloy with excellent tissue stability. The intermediate and high-temperature properties of this alloy are superior to those of some commercially available fourth-generation nickel-based single-crystal superalloys, and it is suitable for the preparation of hot-end components such as aeroengine turbine blades.

Description

Technical Field

[0001] The present invention belongs to the technical field of nickel-based single-crystal superalloys, and particularly relates to a fourth-generation nickel-based single-crystal superalloy based on medium- and high-temperature creep properties, which has excellent high-temperature tissue stability and excellent medium- and high-temperature creep properties, and is suitable for the manufacture of advanced aero-engines. Background Art

[0002] To improve the thrust-to-weight ratio of aero-engines, the inlet temperature at the front end of the high-pressure turbine of new aero-engines has been continuously rising, and the highest inlet temperature of advanced aero-engines can reach about 2200K. This poses high temperature resistance requirements and mechanical property requirements for the materials of the turbine blades at the intake end of aero-engines. Nickel-based single-crystal superalloys are widely used in the manufacture of aero-engine turbine blades due to their excellent high-temperature mechanical properties. To meet the performance requirements of aero-engines, it is necessary to further develop high-performance nickel-based single-crystal superalloys to improve the blade strength and engine performance. At the same time, due to the differences in service temperatures and stress conditions in different regions of the turbine blades, it is also crucial to develop nickel-based single-crystal superalloys with excellent mechanical properties under different conditions.

[0003] Currently, the sixth-generation nickel-based single-crystal superalloys have been developed internationally. With the continuous increase in the alloy generation, the high-temperature mechanical properties of the alloys have been continuously optimized. To achieve a better strengthening effect, higher contents of heavy elements, such as rhenium, molybdenum, and tungsten, are often required in high-generation alloys. Among them, rhenium has a significant effect on improving the high-temperature properties of nickel-based single-crystal superalloys. From the second-generation single-crystal alloy to the fifth-generation single-crystal superalloy, the rhenium content has increased from 2wt.% to about 6wt.%. To maintain tissue stability, about 2wt.% of ruthenium element has been added since the fourth-generation single-crystal alloy, and the ruthenium content has risen to about 5wt.% in the fifth-generation alloy. Since the prices of rhenium and ruthenium elements are relatively high, and the addition of rhenium significantly increases the density of the alloy, which is not conducive to the service of the alloy, it is necessary to limit the further increase in the contents of rhenium and ruthenium elements in the development of new alloys. Molybdenum and tungsten elements, as typical strengthening elements, have significantly lower prices than rhenium, and molybdenum has a lower density, so molybdenum and tungsten have received extensive attention. Therefore, exploring the optimal contents and ratios of molybdenum and tungsten is also crucial for the development of new alloys.

[0004] During the process of long-term service at high temperatures, heavy elements represented by rhenium promote the precipitation of the topologically close-packed phase (TCP phase). The precipitation of the TCP phase consumes a large amount of key strengthening elements and causes local stress concentration, which damages the high-temperature mechanical properties of the alloy. Therefore, it is necessary to adjust the alloy element design to prepare an alloy with high tissue stability and maintain excellent medium- and high-temperature mechanical properties. Summary of the Invention

[0005] The object of the present invention is to design a fourth-generation nickel-based single-crystal superalloy with excellent intermediate and high-temperature creep properties in view of the current requirements for high-performance aero-engines.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows: A fourth-generation nickel-based single-crystal superalloy based on intermediate and high-temperature creep properties, characterized in that, by weight percentage, the chemical composition of the alloy is as follows:

[0007] Chromium 2 wt.% - 4 wt.%, cobalt 3 wt.% - 7 wt.%, molybdenum 1 wt.% - 5 wt.%, tungsten 6.5 wt.% - 8 wt.%, tantalum 6 wt.% - 8 wt.%, aluminum 4 wt.% - 7.5 wt.%, hafnium 0.05 wt.% - 0.25 wt.%, rhenium 2 wt.% - 6 wt.%, ruthenium 1 wt.% - 3 wt.%, yttrium 0 wt.% - 0.02 wt.%, and the balance is nickel;

[0008] And by weight percentage, 0.17 < molybdenum / tungsten < 0.7, 8.5 wt.% < molybdenum + tungsten < 12 wt.%.

[0009] Further, by weight percentage, the chemical composition of the alloy is as follows: chromium 2 wt.% - 4 wt.%, cobalt 4 wt.% - 6.5 wt.%, molybdenum 1 wt.% - 4.5 wt.%, tungsten 6.5 wt.% - 7 wt.%, tantalum 6 wt.% - 7 wt.%, aluminum 4 wt.% - 6 wt.%, hafnium 0.05 wt.% - 0.25 wt.%, rhenium 3 wt.% - 5.5 wt.%, ruthenium 2 wt.% - 3 wt.%, yttrium 0 wt.% - 0.02 wt.%, and the balance is nickel.

[0010] Further, the effective diffusion coefficient of the elements of the alloy at 1100 °C is 2.3 - 4.5×10 -19 m 2 / s.

[0011] The nickel-based single-crystal superalloy of the present invention is mainly composed of a matrix phase γ phase and a strengthening phase γ' phase. Among them, the γ' phase mainly plays a role in precipitation strengthening, and the contents of Al and Ta are used to maintain the content and volume fraction of the γ' phase. Al and Ta can also maintain the oxidation resistance and corrosion resistance of the alloy. The present invention controls the Al content to be 4 wt.% - 7.5 wt.%, and the Ta content to be 6 wt.% - 8 wt.%.

[0012] The Cr element is often used to improve the oxidation resistance and hot corrosion resistance of the alloy. However, the addition of an excessive amount of Cr element will accelerate the precipitation of the TCP phase and destroy the tissue stability. Therefore, the Cr content is controlled at 2 wt.% - 4 wt.%.

[0013] Co and Ru can be used as organizational stability elements to inhibit the precipitation of TCP phase. However, the addition of Co will significantly reduce the solid solution temperature of γ' phase and the content of γ' phase under high-temperature service. Therefore, the Co content is controlled at 3wt.% - 7wt.%. Adding too much Ru element will significantly increase the cost of the alloy. Therefore, in this invention, the Ru content is not further increased on the basis of the existing fourth-generation single crystal, and the Ru element content is controlled at 1wt.% - 3wt.%.

[0014] Mo, W, and Re are the main solid solution strengthening elements. Among them, Re and Mo are mainly distributed in the γ phase, significantly increasing the mismatch degree between the γ and γ' phases and stabilizing the dislocation network of the misfit at the phase interface, thereby improving the creep resistance. W has no significant distribution trend between the two phases and has a strong solid solution strengthening effect on both phases. At the same time, Mo, W, and Re are all TCP phase-forming elements. Therefore, the W content is controlled at 6wt.% - 8wt.%, the Mo content is controlled at 1wt.% - 5wt.%, and the Re content is controlled at 2wt.% - 6wt.%. Due to the high cost and density of Re, in this invention, the Re content is not further increased on the basis of the existing fourth-generation single crystal. Therefore, in this invention, by coordinating and controlling the relationship between the Mo and W contents, the total content of Mo and W is limited to between 8.5wt.% and 12wt.%. While ensuring the strengthening effect, the precipitation of TCP phase is delayed to a certain extent, improving the organizational stability of the alloy. At the same time, adding a large amount of Mo will reduce the solidus line and the solid solution temperature of the γ' phase, while W is the opposite. In order to facilitate the design of the heat treatment system and maintain a certain content of the precipitation strengthening phase γ' phase at high temperature, the mass percentage of Mo and W is limited to 0.17 < Mo / W < 0.7.

[0015] The Hf element helps to improve the corrosion resistance of the alloy at high temperature. However, adding too much Hf will reduce the primary melting temperature of the alloy; the addition of Y can react with the remaining oxygen, sulfur, phosphorus and other elements in the alloy to form a purification effect. However, adding too much Y will react with the crucible to form impurities. Therefore, in this invention, the Hf content is controlled at 0.05wt.% - 0.25wt.%, and the Y content is controlled at 0wt.% - 0.02wt.%.

[0016] During the high-temperature creep process, the diffusion process of elements in the alloy is closely related to the creep performance. At medium and low temperatures, the element diffusion is effectively inhibited and has little effect on the creep performance. The larger the effective diffusion coefficient of the element, the faster the climb of dislocations at high temperature, the faster the degradation of the two-phase structure and the change of element dendritic segregation, which is less conducive to maintaining the creep resistance. Therefore, by adjusting the elements, the effective diffusion coefficient of the alloy at 1100°C is 2.3 - 4.5*10 -19 m 2 / s.

[0017] The beneficial effects of the present invention are as follows: 1) effectively restricting the diffusion of elements at a high temperature of 1100 °C, and improving the creep life at 1100 °C; 2) by adjusting the content ratio and total amount of Mo and W, on the basis of the same levels of the contents of Re and Ru in the fourth-generation alloy, the creep life at medium and high temperatures is superior to that of some commercial third- and fourth-generation nickel-based single-crystal superalloys, and it is applicable to the preparation of hot-end components such as turbine blades of aeroengines; 3) the alloy provided by the present invention is based on the synergistic regulation of key strengthening elements and has good tissue stability at medium and high temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the cross-sectional microstructure of Example 1 in the present invention after being exposed at 1100 °C for 500 h.

[0019] Figure 2 It is the comparison of the effective diffusion coefficients of elements of Example 1-5 in the present invention with those of some commercial alloys at 1100 °C.

[0020] Figure 3 It is the cross-sectional microstructure of Example 1 in the present invention after being exposed at 900 °C for 1010 h. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following examples further illustrate the present invention, but do not limit the present invention. All other examples obtained by those of ordinary skill in the art based on the examples in the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0022] Requirements for the specific preparation method: Use a vacuum induction furnace for melting, first cast into a master alloy meeting the composition requirements, and then prepare single-crystal test bars by the spiral grain selection method. Appropriate heat treatment is required before performance testing.

[0023] Example 1

[0024] A nickel-based single-crystal superalloy with excellent medium and high temperature creep performance. By mass percentage, the chemical composition components of the alloy include: chromium (Cr) 3.2 wt.%, cobalt (Co) 6.5 wt.%, molybdenum (Mo) 2.2 wt.%, tungsten (W) 6.8 wt.%, tantalum (Ta) 6.3 wt.%, aluminum (Al) 4.7 wt.%, hafnium (Hf) 0.1 wt.%, rhenium (Re) 5.3 wt.%, ruthenium (Ru) 2.6 wt.%, yttrium (Y) 0.01 wt.%, and the balance is nickel (Ni). And the mass fraction relationship between molybdenum and tungsten in the alloy is Mo / W = 0.32, and the mass percentage of Mo + W is 9 wt.%, denoted as A1.

[0025] After heat treatment, the alloy has a creep rupture life of up to 492.6 hours under the condition of 1100 °C / 137 MPa, and the effective diffusion coefficient of elements at high temperature is only 4.21×10 -19 m 2 / s. Under the condition of 900 °C / 392 MPa, the creep rupture life can reach 1228.7 hours. The creep rupture life at medium and high temperatures is significantly higher than that of the third-generation single crystal CMSX-10 and TMS-138.

[0026] After the alloy is fully heat treated and exposed at 1100 °C for 500 hours, very few TCP phases precipitate, and the area fraction is only 3.6%. Its microstructure is as Figure 1 shown. When exposed at 900 °C for more than 1000 h, no precipitation of TCP phase is observed either. Its microstructure is as Figure 3 shown.

[0027] Example 2

[0028] A nickel-based single crystal superalloy with excellent medium and high temperature creep rupture properties. By mass percentage, the chemical composition of the alloy includes: chromium (Cr) 3.1 wt.%, cobalt (Co) 6.2 wt.%, molybdenum (Mo) 3.2 wt.%, tungsten (W) 6.6 wt.%, tantalum (Ta) 6.3 wt.%, aluminum (Al) 4.5 wt.%, hafnium (Hf) 0.1 wt.%, rhenium (Re) 5.1 wt.%, ruthenium (Ru) 2.6 wt.%, yttrium (Y) 0.005 wt.%, and the balance is nickel (Ni). And the mass fraction relationship between molybdenum and tungsten in the alloy is Mo / W = 0.48, and the mass percentage of Mo + W is 9.8 wt.%, denoted as A2.

[0029] After heat treatment, the alloy has a creep rupture life of up to 511.6 hours under the condition of 1100 °C / 137 MPa, and the effective diffusion coefficient of elements at high temperature is only 3.47×10 -19 m 2 / s. Under the condition of 900 °C / 392 MPa, the creep rupture life can reach 985.6 hours. The high temperature life is significantly higher than that of the third-generation single crystal CMSX-10 and the fourth-generation single crystal TMS-138, and the medium temperature life is basically the same as that of TMS-138.

[0030] Example 3

[0031] A nickel-based single-crystal superalloy with excellent intermediate and high-temperature creep properties. By mass percentage, the chemical composition of the alloy includes: chromium (Cr) 2.6 wt.%, cobalt (Co) 6.5 wt.%, molybdenum (Mo) 4.4 wt.%, tungsten (W) 6.8 wt.%, tantalum (Ta) 6.0 wt.%, aluminum (Al) 4.5 wt.%, hafnium (Hf) 0.1 wt.%, rhenium (Re) 4.5 wt.%, ruthenium (Ru) 2.8 wt.%, and the balance is nickel (Ni). And the mass fraction relationship between molybdenum and tungsten in the alloy is Mo / W = 0.65, and the mass percentage of Mo + W is 11.2 wt.%, denoted as A3.

[0032] After heat treatment, the alloy has a creep life of up to 450.3 hours under the creep conditions of 1100 °C / 137 MPa, and the effective diffusion coefficient of elements at high temperature is only 4.32×10 -19 m 2 / s. Under the creep conditions of 900 °C / 392 MPa, the alloy has a creep life of up to 903.3 hours. Its high-temperature life is higher than that of the third-generation single-crystal CMSX-10 and the fourth-generation single-crystal TMS-138, and its intermediate-temperature life is basically the same as that of TMS-138.

[0033] Example 4

[0034] A nickel-based single-crystal superalloy with excellent intermediate and high-temperature creep properties. By mass percentage, the chemical composition of the alloy includes: chromium (Cr) 2.8 wt.%, cobalt (Co) 6.4 wt.%, molybdenum (Mo) 2.2 wt.%, tungsten (W) 7.0 wt.%, tantalum (Ta) 6.0 wt.%, aluminum (Al) 5.5 wt.%, hafnium (Hf) 0.1 wt.%, rhenium (Re) 5.5 wt.%, ruthenium (Ru) 2.7 wt.%, and the balance is nickel (Ni). And the mass fraction relationship between molybdenum and tungsten in the alloy is Mo / W = 0.31, and the mass percentage of Mo + W is 9.2 wt.%. Under the creep conditions of 1100 °C / 137 MPa, the alloy has a creep life of 519.4 h; under 900 °C / 392 MPa, the creep life reaches 1044.5 h. The effective diffusion coefficient at 1100 °C is 3.36×10 -19 m 2 / s.

[0035] Example 5

[0036] A nickel-based single crystal superalloy with excellent intermediate and high temperature creep properties. By mass percentage, the chemical composition of the alloy includes: chromium (Cr) 3.5 wt.%, cobalt (Co) 5.9 wt.%, molybdenum (Mo) 4.3 wt.%, tungsten (W) 6.8 wt.%, tantalum (Ta) 6.2 wt.%, aluminum (Al) 5.4 wt.%, hafnium (Hf) 0.1 wt.%, rhenium (Re) 4.7 wt.%, ruthenium (Ru) 2.9 wt.%, yttrium (Y) 0.003 wt.%, and the balance is nickel (Ni). And the mass fraction relationship between molybdenum and tungsten in the alloy is Mo / W = 0.63, and the mass percentage of Mo + W is 11.1 wt.%. Under the creep conditions of 1100 °C / 137 MPa, the life of the alloy reaches 421.7 h; at 900 °C / 392 MPa, the life reaches 859.5 h. The effective diffusion coefficient at 1100 °C is 2.55*10 -19 m 2 / s.

[0037] Comparative Example 1

[0038] The third-generation nickel-based single crystal superalloy CMSX-10. By mass percentage, its composition includes: chromium (Cr) 6.5 wt.%, cobalt (Co) 9.0 wt.%, molybdenum (Mo) 0.5 wt.%, tungsten (W) 6.0 wt.%, tantalum (Ta) 6.5 wt.%, aluminum (Al) 5.6 wt.%, hafnium (Hf) 0.1 wt.%, rhenium (Re) 3.0 wt.%, titanium (Ti) 1.0 wt.%, and the balance is nickel (Ni). The mass fraction relationship between molybdenum and tungsten in the alloy is Mo / W = 0.083, and the mass percentage of Mo + W is 6.5 wt.%. The creep life of this alloy at 1100 °C and 900 °C is significantly lower than that of Examples 1-3.

[0039] Comparative Example 2

[0040] The fourth-generation nickel-based single crystal superalloy TMS-138. By mass percentage, its chemical composition includes: chromium (Cr) 3.2 wt.%, cobalt (Co) 5.8 wt%, tungsten (W) 5.9 wt%, molybdenum (Mo) 2.9 wt%, rhenium (Re) 5.0 wt.%, aluminum (Al) 5.8 wt.%, tantalum (Ta) 5.6 wt.%, hafnium (Hf) 0.1 wt.%, ruthenium (Ru) 2.0 wt.%, and the balance is nickel (Ni). The mass fraction relationship between molybdenum and tungsten in the alloy is Mo / W = 0.25, Mo + W = 13.9%, and its elemental effective diffusion coefficient is close to that of Examples 1-3. However, compared with the examples, the W content of this alloy is lower, the strengthening effect is relatively weak, and the creep life at 1100 °C is also significantly lower than that of Examples 1-3.

[0041] Table 1 Endurance life under different conditions in the embodiments of the present invention and endurance life of comparative alloy 1100°C / 137 MPa and 900°C / 392 MPa

[0042]

[0043] The above specific embodiments are used to explain the present invention rather than limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A fourth-generation nickel-based single-crystal superalloy designed based on enhancing medium- and high-temperature creep properties, characterized in that, By weight percentage, the chemical composition of the alloy is as follows: Chromium 2 wt.% - 4 wt.%, cobalt 3 wt.% - 7 wt.%, molybdenum 1 wt.% - 5 wt.%, tungsten 6.5 wt.% - 8 wt.%, tantalum 6 wt.% - 8 wt.%, aluminum 4 wt.% - 7.5 wt.%, hafnium 0.05 wt.% - 0.25 wt.%, rhenium 2 wt.% - 6 wt.%, ruthenium 1 wt.% - 3 wt.%, yttrium 0 wt.% - 0.02 wt.%, the balance being nickel; And by weight percentage, 0.17 < molybdenum / tungsten < 0.63, 8.5 wt.% < molybdenum + tungsten < 11.1 wt.%.

2. The fourth-generation nickel-based single-crystal superalloy designed based on improving intermediate and high-temperature creep properties according to claim 1, characterized in that, By weight percentage, the chemical composition of the alloy is as follows: Chromium 2 wt.% - 4 wt.%, cobalt 4 wt.% - 6.5 wt.%, molybdenum 1 wt.% - 4.5 wt.%, tungsten 6.5 wt.% - 7 wt.%, tantalum 6 wt.% - 7 wt.%, aluminum 4 wt.% - 6 wt.%, hafnium 0.05 wt.% - 0.25 wt.%, rhenium 3 wt.% - 5.5 wt.%, ruthenium 2 wt.% - 3 wt.%, yttrium 0 wt.% - 0.02 wt.%, the balance being nickel; and by weight percentage, 0.17 < molybdenum / tungsten < 0.63, 8.5 wt.% < molybdenum + tungsten < 11.1 wt.%.

3. The fourth-generation nickel-based single-crystal superalloy designed based on improving intermediate and high-temperature creep properties according to claim 1, characterized in that: The effective diffusion coefficient of the elements in the alloy at 1100 °C is 2.3×10 -19 -4.5×10 -19 m 2 / s.

Images