Gamma '-phase reinforced cobalt-nickel-based superalloy and preparation method thereof

Abstract

The invention discloses a gamma '-phase reinforced cobalt-nickel-based high-temperature alloy and a preparation method thereof, and belongs to the field of high-temperature alloys, and the alloy comprises the following chemical components in percentage by mass: 4.5-5.0% of Al, 1-2% of Ti, 16-19% of Ta, 32-32.5% of Ni, 4.5-5.5% of Cr, 0-3.2% of Mo, 0-0.02% of B, 0-0.02% of C and the balance of Co. The preparation method adopts a vacuum arc furnace smelting and solid solution heat treatment combined two-stage aging process. The alloy obtained through the method has a gamma / gamma'two-phase structure, the gamma 'phase is of a cubic morphology, has an L12 crystal structure, the volume fraction is larger than 75%, and the gamma' phase is evenly distributed in a gamma matrix with an A1 structure. The gamma / gamma'two-phase structure of the alloy stably exists at the temperature of 900-1100 DEG C, secondary phase precipitation is avoided, the alloy has excellent gamma 'phase dissolution temperature and high-temperature yield strength, the density is small, and the alloy has high potential application value in the field of high-temperature structural materials.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy technology, specifically relating to a γ′ phase-strengthened cobalt-nickel-based high-temperature alloy and its preparation method. Background Technology

[0002] High-temperature alloys, due to their excellent high-temperature strength, oxidation resistance, and hot corrosion resistance, have become key materials for hot-end components of aero-engines and industrial gas turbines. With the continuous improvement of engine thrust and thermal efficiency, the temperature resistance of nickel-based alloys has approached its limit (structural instability occurs above 1100℃), while cobalt-based alloys with higher melting points are considered a key direction for breaking through the temperature barrier. However, traditional cobalt-based high-temperature alloys (such as Co-Cr-Mo systems) rely on solid solution strengthening and carbide strengthening, and their high-temperature strength (especially above 800℃) is significantly lower than that of nickel-based alloys. The fundamental reason is the lack of a γ′ phase strengthening mechanism similar to the L12 structure in nickel-based alloys.

[0003] In 2006, Sato's research group first discovered the γ′-Co3(Al,W) ordered phase in the Co-Al-W ternary system, a breakthrough that provided a new pathway for γ′ phase strengthening in cobalt-based alloys. Studies confirmed that this system exhibits creep resistance comparable to the first-generation nickel-based single-crystal alloy René N4 at 900℃, demonstrating excellent development prospects and high research value. However, this series of alloys suffers from drawbacks such as low γ′ phase dissolution temperature, poor microstructural stability, and high alloy density. Existing research on cobalt-based superalloys has struggled to simultaneously overcome these shortcomings, as evidenced by:

[0004] (a) Attempts to increase the dissolution temperature of the γ′ phase (e.g., by adding Ta / Nb) are usually accompanied by a further increase in density (>9.5 g / cm³). 3 );

[0005] (b) A density-reducing approach (e.g., reducing the W content) may result in a sharp drop in the volume fraction of the γ′ phase (<50%) or a decrease in the dissolution temperature;

[0006] (c) Increasing the strength requires increasing the γ′ phase fraction, but this can easily lead to the precipitation of harmful topologically close-packed phases (such as μ phase), which can worsen the stability of the tissue.

[0007] Against this backdrop, the present invention develops a novel cobalt-nickel-based superalloy that combines a high γ′ phase dissolution temperature, high-temperature structural stability, high-temperature strength, and low alloy density. It is expected to make up for the current shortcomings in this research field and has high potential application value in the field of high-temperature structural materials. Summary of the Invention

[0008] To address the mutually exclusive problem of the "performance triangle" in the existing cobalt-based alloys, this invention provides a γ′ phase-strengthened cobalt-nickel-based superalloy and its preparation method, enabling the cobalt-based superalloy to simultaneously meet the requirements of γ′ phase dissolution temperature >1250℃, density ≤8.5 g / cm³, and compressive yield strength >850 MPa at 800℃. The preparation method employs a three-stage heat treatment process: (1) solution treatment at 1270-1300℃ for 12-24h (to eliminate segregation); (2) two-stage aging: first-stage aging at 1000-1100℃ for 4h (to promote γ′ phase nucleation); (3) second-stage aging at 800-900℃ for 16h (to regulate the size and distribution of the γ′ phase). Simultaneously, air cooling is used throughout the process, avoiding complex temperature control and significantly reducing costs. The obtained cobalt-nickel-based superalloy can form a stable γ / γ′ two-phase structure at 900-1100℃, without secondary phase precipitation. The γ′ phase has a cubic morphology and a volume fraction greater than 75%.

[0009] This invention is achieved through the following technical solution:

[0010] A γ′ phase-strengthened cobalt-nickel-based superalloy comprises the following components by mass percentage: Al 4.5-5.0%, Ti 1-2%, Ta 16-19%, Ni 32-32.5%, Cr 4.5-5.5%, Mo 0-3.2%, B 0-0.02%, C 0-0.02%, with the balance being Co.

[0011] Furthermore, the amounts of each component are as follows: Al 4.7-5.0%, Ti 1.5-2.0%, Ta 17-19%, Ni 32.2-32.5%, Cr 5-5.5%, Mo 0-3.2%, B 0.01-0.02%, C 0.01-0.02%, with the balance being Co.

[0012] Furthermore, the amounts of each component are as follows: Al 4.8-5.0%, Ti 1.5-1.8%, Ta 17.5-19%, Ni 32.3-32.5%, Cr 5-5.5%, Mo 0-2%, B 0.01-0.02%, C 0.01-0.02%, with the balance being Co.

[0013] Furthermore, the above alloy has a γ′ phase dissolution temperature ≥1260℃, a density ≤8.5g / cm³, and a compressive yield strength ≥880MPa at 800℃.

[0014] Furthermore, the alloy contains a volume fraction >75% of L12 structure γ′ phase, which has a cubic morphology and is uniformly distributed in the γ matrix. After the alloy is heat-treated at 900-1100℃ for 100 hours, no topological close-packed phase precipitation was observed under a scanning electron microscope.

[0015] The preparation method of the above alloy includes the following steps:

[0016] S1. Weigh each elemental metal according to the component ratio;

[0017] S2. Vacuum arc melting: Place each elemental metal from step S1 into a vacuum arc melting furnace and melt it under a current of 280-350A and an Ar atmosphere. After complete liquefaction, hold it at the temperature for 30-60 seconds, cool and solidify, and repeat the melting process to obtain cobalt-based high-temperature alloy ingots.

[0018] S3. Solution treatment: The cobalt-based superalloy ingot obtained in step S2 is kept at a solution temperature of 1250-1300℃ for 12-24 hours and then air-cooled.

[0019] S4. Two-level time limit:

[0020] Level 1 aging: 1000-1100℃ for 2-6 hours (4 hours preferred), air cooling;

[0021] Secondary aging: Hold at 800-900℃ for 12-20 hours (preferably 16 hours), then air cool to obtain the γ′ phase reinforced CoNi-based high-temperature alloy.

[0022] Furthermore, in step S2, the melting process is repeated 6-15 times and the alloy is flipped 8-12 times to ensure the uniformity of the alloy.

[0023] Furthermore, in step S3, the solution temperature is 1250-1270℃.

[0024] Furthermore, in step S4, the preferred temperature for the first-stage aging is 1000-1050℃, and the preferred temperature for the second-stage aging is 800-850℃.

[0025] The beneficial effects of this invention are as follows:

[0026] (1) The alloy of the present invention has good stability and forms a stable two-phase structure of γ / γ′. Under long-term service conditions of 900-1150℃: the volume fraction of γ′ phase (L12 structure) is >75%, which is significantly higher than that of traditional cobalt-based alloys (60-70%); the γ′ phase has a uniform cubic morphology (size 200-500nm) and no secondary phase precipitation, which completely avoids the risk of embrittlement caused by topological close-packed phases (such as μ phase).

[0027] (2) The alloy of the present invention has excellent high-temperature performance. Its γ′ phase dissolution temperature reaches 1260.6℃, which is more than 160℃ higher than that of typical Co-Al-W based alloys (≤1100℃), and even surpasses some commercial nickel-based alloys (such as Inconel 713C at 1240℃), approaching the third-generation nickel-based single crystal alloys (around 1300℃), providing a cobalt-based high-temperature alloy solution for the operating conditions of aero-engines >1100℃.

[0028] (3) The alloy of this invention achieves a breakthrough in the synergistic effect of low density and high strength, with a density of only 8.45-8.53 g / cm³. 3 Compared to traditional cobalt-based alloys (>9.3 g / cm³), 3 The concentration of [aluminum content] was significantly reduced, compared to second-generation nickel-based single-crystal alloys (8.6-8.7 g / cm³). 3 It is comparable to other cobalt-based alloys; its compressive yield strength at 800℃ is as high as 890 MPa, which is significantly higher than that of similar cobalt-based alloys (not exceeding 800 MPa) and surpasses that of the classic nickel-based alloy Inconel 713C. Attached Figure Description

[0029] Figure 1 The image shows a typical microstructure of the alloy obtained in Example 1 after aging heat treatment for 20 hours.

[0030] Figure 2 The phase transformation temperature diagram of alloy 1 obtained in Example 1 after DSC is shown.

[0031] Figure 3 This is a comparative graph showing the dissolution temperature and yield strength (800℃) of the γ′ phase of the alloy obtained in Example 1 with those of the high-temperature alloy in the literature. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0033] Example 1

[0034] Alloy 1 contains the following components by mass percentage: Co 38.96%, Al 4.8%, Ti 1.5%, Ta 17.5%, Ni 32.2%, Cr 5%, B 0.02%, and C 0.02%.

[0035] The preparation method of the above alloy includes the following steps:

[0036] (1) Weigh each elemental metal according to the above composition ratio;

[0037] (2) Place the above-mentioned elemental metals in a vacuum arc melting furnace and melt them under a current of 350A and an Ar atmosphere. After complete liquefaction, keep them at the temperature for 60 seconds, cool and solidify, and repeat the melting process 12 times to obtain cobalt-based high-temperature alloy ingots.

[0038] (3) The above cobalt-based high-temperature alloy ingots were kept at a solution temperature of 1270℃ for 24 hours and then air-cooled;

[0039] (4) Two-level time limit:

[0040] Level 1 aging: 1050℃ for 4 hours, air cooling;

[0041] Secondary aging: Hold at 800℃ for 16 hours, then air cool to obtain alloy products.

[0042] Comparative Example 1

[0043] Alloy 2 contains the following components by mass percentage: Co 38.86%, Al 4.8%, Ti 1.5%, Ta 11.7%, Ni 32.2%, Cr 5%, B 0.02%, C 0.02%, W 5.9%.

[0044] Comparative Example 1 was prepared by adding W, using the same method as Example 1.

[0045] Comparative Example 2

[0046] Alloy 3 contains the following components by mass percentage: Co 39.06%, Al 4.9%, Ti 1.6%, Ta 12.0%, Ni 33.2%, Cr 5.2%, Mo 4.0%, B 0.02%, C 0.02%, W 0%.

[0047] Comparative Example 1 had a larger amount of Mo added, and the preparation method was the same as in Example 1.

[0048] The compositions of the above alloys are shown in Table 1.

[0049] Table 1. Mass percentage of alloy components in this invention.

[0050]

[0051] The density of each alloy was tested using the Archimedes' displacement method. The densities of the alloys are shown in Table 2.

[0052] Table 2. Density comparison between the alloy of this invention and second-generation nickel-based single-crystal superalloys

[0053]

[0054] As shown in Table 2, the density of Alloy 1 (Example 1) obtained by the present invention is lower than that of Co-Al-W based superalloy (Alloy 2) and alloy with higher Mo content (Alloy 3), and is comparable to the average level of second-generation nickel-based single crystal superalloys (DD6, Rene N5, and CMSX-4 are typical commercial grades of second-generation nickel-based single crystal superalloys).

[0055] After heat treatment, the alloy (alloy 1) obtained in Example 1 of this invention was polished, and then its microstructure was obtained under a scanning electron microscope (e.g., ...). Figure 1As shown in the figure, the matrix (γ phase) exhibits a continuous gray contrast, and the precipitated phase (γ′ phase) is uniformly distributed in the matrix, exhibiting an approximately cubic morphology with a size ranging from 200 to 500 nm. Clear grain boundaries are visible, with no obvious precipitate aggregation and no visible secondary phases (no topologically close-packed phases (such as μ phase) or other harmful precipitates are observed). The uniform contrast indicates that the γ′ phase is evenly distributed without obvious segregation or coarsening. This microstructure demonstrates that the alloy possesses a good γ / γ′ two-phase structure and structural stability.

[0056] DSC testing revealed that the γ′ dissolution temperature of the alloy (Alloy 1) obtained in Example 1 of this invention was 1260.6℃, significantly higher than the γ′ phase dissolution temperature of most currently commercially available high-temperature alloys (e.g., Figure 2 (As shown). Furthermore, as... Figure 3 As shown, the experimentally measured compressive yield strength of Alloy 1 at 800℃ was 890 MPa, while the yield strength was only 680 MPa when W was present in the alloy (Alloy 2). Furthermore, excessive Mo content in the alloy also negatively impacted the yield strength, resulting in a yield strength of only 600 MPa (Alloy 3). Comparative Example 3

[0057] The alloy composition is the same as in Example 1, and the preparation method is the same as in Example 1, except that only aging treatment at 1050℃ for 20 hours is performed (single-stage aging).

[0058] Experimental results show that the compressive yield strength of this alloy at 800℃ is 708MPa, which is 20.5% lower than that of alloy 1 (890MPa) obtained in Example 1.

[0059] Example 2

[0060] The alloy contains the following components by mass percentage: Co 42.0%, Al 4.5%, Ti 1.0%, Ta 16.0%, Ni 32.0%, Cr 4.5%, Mo 0%, B 0%, C 0%.

[0061] The preparation method of the above alloy includes the following steps:

[0062] (1) Weigh each elemental metal according to the above composition ratio;

[0063] (2) Place the above-mentioned elemental metals in a vacuum arc melting furnace and melt them under a current of 280A and an Ar atmosphere. After complete liquefaction, keep them at the temperature for 30 seconds, cool and solidify, and repeat the melting process 6 times to obtain cobalt-based high-temperature alloy ingots.

[0064] (3) The above cobalt-based high-temperature alloy ingots were kept at a solution temperature of 1250℃ for 12 hours and then air-cooled;

[0065] (4) Two-level time limit:

[0066] Level 1 aging: 1000℃ for 2 hours, then air-cooled;

[0067] Secondary aging: Hold at 800℃ for 12 hours, then air cool to obtain alloy products.

[0068] Performance test results: γ′ phase dissolution temperature 1265℃, density 8.42 g / cm³ 3 The compressive yield strength at 800℃ is 865 MPa.

[0069] Example 3

[0070] The alloy contains the following components by mass percentage: Co 32.76%, Al 5.0%, Ti 2.0%, Ta 19.0%, Ni 32.5%, Cr 5.5%, Mo 3.2%, B 0.02%, and C 0.02%.

[0071] The preparation method of the above alloy includes the following steps:

[0072] (1) Weigh each elemental metal according to the above composition ratio;

[0073] (2) Place the above-mentioned elemental metals in a vacuum arc melting furnace and melt them under a current of 350A and an Ar atmosphere. After complete liquefaction, keep them at the temperature for 60 seconds, cool and solidify, and repeat the melting process 15 times to obtain cobalt-based high-temperature alloy ingots.

[0074] (3) The above cobalt-based high-temperature alloy ingots were kept at a solution temperature of 1300℃ for 24 hours and then air-cooled;

[0075] (4) Two-level time limit:

[0076] Level 1 aging: 1100℃ for 6 hours, air cooling;

[0077] Secondary aging: Hold at 900℃ for 20 hours, then air cool to obtain alloy products.

[0078] Performance test results: γ′ phase dissolution temperature 1258℃, density 8.56 g / cm³ 3 The compressive yield strength at 800℃ is 900 MPa.

[0079] Example 4

[0080] The alloy contains the following components by mass percentage: Co 37.18%, Al 4.7%, Ti 1.8%, Ta 17.0%, Ni 32.3%, Cr 5.0%, Mo 2.0%, B 0.01%, and C 0.01%.

[0081] The preparation method of the above alloy includes the following steps:

[0082] (1) Weigh each elemental metal according to the above composition ratio;

[0083] (2) Place the above-mentioned elemental metals in a vacuum arc melting furnace and melt them under a current of 300A and an Ar atmosphere. After complete liquefaction, keep them at the temperature for 40 seconds, cool and solidify, and repeat the melting process 8 times to obtain cobalt-based high-temperature alloy ingots.

[0084] (3) The above cobalt-based high-temperature alloy ingots were kept at a solution temperature of 1250℃ for 12 hours and then air-cooled;

[0085] (4) Two-level time limit:

[0086] Level 1 aging: 1000℃ for 2 hours, then air-cooled;

[0087] Secondary aging: Hold at 800℃ for 12 hours, then air cool to obtain alloy products.

[0088] Performance test results: γ′ phase dissolution temperature 1262℃, density 8.49 g / cm³ 3 The compressive yield strength at 800℃ is 875 MPa.

Claims

1. A γ′ phase-strengthened cobalt-nickel-based superalloy, characterized in that, It contains the following components by mass percentage: Al 4.5-5.0%, Ti 1-2%, Ta 16-19%, Ni 32-32.5%, Cr 4.5-5.5%, Mo 0-3.2%, B 0-0.02%, C 0-0.02%, with the balance being Co.

2. The γ′ phase-strengthened cobalt-nickel-based superalloy according to claim 1, characterized in that, It contains the following components by mass percentage: Al 4.7-5.0%, Ti 1.5-2.0%, Ta 17-19%, Ni 32.2-32.5%, Cr 5-5.5%, Mo 0-3.2%, B 0.01-0.02%, C 0.01-0.02%, with the balance being Co.

3. The γ′ phase-strengthened cobalt-nickel-based superalloy according to claim 1, characterized in that, It contains the following components by mass percentage: Al 4.8-5.0%, Ti 1.5-1.8%, Ta 17.5-19%, Ni 32.3-32.5%, Cr 5-5.5%, Mo 0-2%, B 0.01-0.02%, C 0.01-0.02%, with the balance being Co.

4. The γ′ phase strengthened cobalt-nickel-based superalloy as described in any one of claims 1 to 3, characterized in that, The alloy has a γ′ phase dissolution temperature ≥1250℃ and a density ≤8.5g / cm³. 3 The compressive yield strength at 800℃ is ≥880MPa.

5. The γ′ phase strengthened cobalt-nickel-based superalloy as described in any one of claims 1 to 3, characterized in that, The alloy contains a volume fraction >75% of γ′ phase, which has an L12 crystal structure, a cubic morphology, and is uniformly distributed in the γ matrix. After the alloy is heat-treated at 900-1100℃ for 100 hours, no topological close-packed phase precipitation is observed under a scanning electron microscope.

6. The method for preparing the alloy according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Weigh each elemental metal according to the component ratio; S2. Vacuum arc melting: The weighed elemental metals are placed in a vacuum arc melting furnace and melted under a current of 280-350A and an Ar atmosphere. After complete liquefaction, the metals are held at the temperature for 30-60 seconds, cooled and solidified, and the melting is repeated to obtain cobalt-based high-temperature alloy ingots. S3. Solution treatment: The cobalt-based superalloy ingot obtained in step S2 is kept at a solution temperature of 1250-1300℃ for 12-24 hours and then air-cooled. S4. Two-level time limit: Level 1 aging: 1000-1100℃ for 2-6 hours, air cooling; Secondary aging: Hold at 800-900℃ for 12-20 hours, then air cool to obtain the product γ′ phase strengthened cobalt-nickel-based high-temperature alloy.

7. The preparation method according to claim 6, characterized in that, In step S2, the melting process is repeated 6 to 15 times.

8. The preparation method according to claim 6, characterized in that, In step S3, the solution temperature is 1250-1270℃.

9. The preparation method according to claim 6, characterized in that, In step S4, the temperature for the first-stage aging is 1000-1050℃, and the temperature for the second-stage aging is 800-850℃.

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