High-performance low-cost directional solidification column crystal high-temperature alloy

Abstract

The invention discloses a high-performance low-cost directional solidification column crystal high-temperature alloy which comprises the following components in percentage by mass: 1.5 to 3.5 percent of Cr, 8.0 to 12.0 percent of Co, 2.0 to 4.5 percent of Mo, 10.0 to 13.0 percent of W, 0.5 to 2.0 percent of Ti, 4.0 to 7.0 percent of Al, 2.5 to 4.5 percent of Ta, 0.02 to 0.15 percent of Hf, 0.30 to 0.60 percent of Nb and the balance of Ni. The mass fraction ratio of Al to Ti is larger than or equal to 2.5, the total mass fraction of Ti and Al is 5.0-7.5%, and the total mass fraction of Mo and W is 13.0-17.0%. According to the high-performance low-cost directional solidification column crystal high-temperature alloy, the elements such as Mo and W are used for forming solid solution strengthening, and the high-content gamma '(Ni3 (Ti, Al)) precipitated phase is used for strengthening the inside of the crystal; the grain boundary does not contain C, B and other grain boundary strengthening elements, the bending grain boundary formed in the high-temperature service process of the alloy is utilized for strengthening the grain boundary, and the excellent high-temperature creep property of the alloy is guaranteed; the low cost of the alloy is ensured by removing Re, Ru and other elements in the alloy.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy technology, and in particular relates to a high-performance, low-cost directionally solidified columnar high-temperature alloy. Background Technology

[0002] Gas turbines are widely used in distributed energy, surface ships, long-distance ground pipeline pressurization, and industrial power generation. With the in-depth development of natural gas resources, increasing requirements for low-carbon emissions, and continuous advancements in power systems and transportation technologies, next-generation gas turbines are rapidly developing towards higher power capacity and thermal efficiency. This places higher demands on the performance of their core hot-end component—the high-pressure turbine blade. Due to their lower manufacturing and processing costs and higher yield compared to single-crystal alloys, directionally solidified columnar superalloys have become an ideal choice for large-size gas turbine blades. Therefore, there is an urgent need to develop high-performance directionally solidified columnar superalloys that can meet the temperature resistance requirements of high-parameter gas turbine blades.

[0003] Directional solidification superalloys have undergone several generations of development. Early alloys (such as GTD 111) used equiaxed crystal compositions, containing no precious elements such as Re and Ru, with Mo + W content less than 12% and the Al to Ti ratio less than 2.0. However, starting with second-generation alloys, the main method for strengthening alloys was to add precious metals such as Re and Ru to improve performance, significantly increasing costs. Second-generation alloys (such as PWA 1426 and CM 186LC) added approximately 3 wt.% Re to enhance performance. The third-generation (such as TMD-103) and fourth-generation (such as TMD-107 and TMD-111) alloys developed in this century offer even stronger performance, but significantly increase the content of expensive elements (approximately 5 wt.% Re in the third generation and 2-6 wt.% Ru in the fourth generation). Although these high-performance alloys (especially the TMD series) adapt to directional solidification processes by adding grain boundary strengthening elements, their high Re and Ru content leads to a dramatic increase in raw material costs. This cost structure is uneconomical for large-sized gas turbine blades, severely limiting their large-scale application.

[0004] Therefore, for the development of high-parameter gas turbines, it is necessary to develop new high-performance directionally solidified columnar superalloys that can meet the performance requirements such as long-term creep under extreme service conditions, while not containing precious metal elements such as Re and Ru, thereby significantly reducing the cost of high-performance directionally solidified columnar superalloys. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a high-performance, low-cost directionally solidified columnar superalloy, which has excellent high-temperature creep properties and good microstructure stability, and reduces costs.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A high-performance, low-cost directionally solidified columnar superalloy, characterized in that, by mass percentage, it comprises: Cr: 1.5–3.5%, Co: 8.0–12.0%, Mo: 2.0–4.5%, W: 10.0–13.0%, Ti: 0.5–2.0%, Al: 4.0–7.0%, Ta: 2.5–4.5%, Hf: 0.02–0.15%, Nb: 0.30–0.60%, with the balance being Ni; the mass fraction ratio of Al to Ti is ≥2.5, the total mass fraction of Ti + Al is 5.0–7.5%, and the total mass fraction of Mo + W is 13.0–17.0%.

[0008] A further improvement of the present invention is that, by mass percentage, it comprises: Cr: 1.5–3.2%, Co: 9.0–12.0%, Mo: 2.0–4.0%, W: 10.5–12.5%, Ti: 0.5–1.5%, Al: 4.0–6.5%, Ta: 3.0–4.5%, Hf: 0.02–0.10%, Nb: 0.40–0.60%, with the balance being Ni; the mass fraction ratio of Al to Ti is ≥2.8, the total mass fraction of Ti + Al is 5.0–7.0%, and the total mass fraction of Mo + W is 13.0–16.0%.

[0009] Furthermore, after heat treatment, the volume fraction of the intragranular γ′ strengthening phase in the alloy is not less than 70%.

[0010] Furthermore, the alloy exhibits a creep rupture life of over 360 hours at 1040℃ / 137MPa and a creep rupture life of over 80 hours at 1100℃ / 137MPa.

[0011] The selection of the role and composition range of alloying elements in this invention is based on the following criteria:

[0012] The high-performance, low-cost directional solidification columnar superalloy of the present invention has a γ phase matrix, which enhances the solid solution strengthening effect of elements such as Mo and W, and strengthens the intragranular structure by utilizing the γ′(Ni3(Ti, Al)) precipitate phase. The alloy also strengthens the grain boundaries by promoting the formation of flexural grain boundaries under the synergistic effect of temperature and stress fields during high-temperature service, thus ensuring the excellent high-temperature creep performance of the alloy.

[0013] W and Mo are important solid solution strengthening elements with large atomic radii. They can improve the lattice mismatch between the γ and γ′ phases in the alloy, form a high-density phase interface dislocation network to hinder the shearing of the γ′ phase, and act as solute atoms to impede dislocation movement, thus improving the high-temperature creep performance of the alloy. However, excessively high W and Mo contents can easily lead to the formation of harmful phases such as the TCP phase, causing severe segregation during alloy smelting. Therefore, this invention controls the total mass percentage of W and Mo to be between 13.0% and 17.0%.

[0014] Ti and Al combine with the Ni matrix to form a reinforcing phase γ′, and the volume fraction of the γ′ phase increases with the Ti+Al content. Increasing the γ′ phase content increases the γ / γ′ phase interface area, enhancing the ability to hinder dislocation migration and improving the alloy's strength. However, excessive Ti content can form the harmful η phase, reducing the alloy's strength. Excessive Al content can form a large amount of blocky eutectic, which cannot be eliminated by solution heat treatment, further reducing the alloy's strength. Therefore, to maximize the alloy's creep life and suppress η phase precipitation, the mass fraction ratio of Al to Ti should be controlled at ≥2.5, and the total mass percentage of Ti and Al should be between 5.0% and 7.5%.

[0015] C, B, and Zr are important grain boundary strengthening elements that can form carbide precipitates at grain boundaries to pin them and inhibit grain boundary slip. These elements are often added to columnar alloys to strengthen grain boundaries. However, the precipitation of carbide phases reduces the content of strengthening elements in the alloy, which is detrimental to the creep life of the alloy. Therefore, in order to further improve the creep life of the alloy at high temperatures, this invention removes grain boundary strengthening elements such as C, B, and Zr from the alloy and strengthens the grain boundaries by inducing the formation of bent grain boundaries through coarsening of the grain boundary γ′ phase during creep loading, thereby improving creep resistance.

[0016] Ta is an important precipitation strengthening element, capable of forming a large elastic stress field that hinders dislocation movement. It can increase the volume fraction of the γ′ phase in the alloy, raise the alloy diffusion activation energy, and inhibit the aggregation, growth, and dissolution of γ′. However, excessively high Ta levels can reduce the solidification temperature range of the alloy and increase the eutectic size and volume fraction. Therefore, this invention controls the mass percentage of Ta to be between 2.5% and 4.5%.

[0017] Cr is an important element for resisting high-temperature oxidation and corrosion. In high-temperature environments, it will form dense Cr2O3 oxide with oxygen, which will prevent further oxidation of the alloy and improve its oxidation resistance. However, Cr will promote the precipitation of the harmful TCP phase, which is not conducive to the high-temperature creep performance of the alloy. Al, Ta and other elements also have certain anti-oxidation effects. Therefore, the mass percentage of Cr is controlled at 1.5 to 3.5% in this invention.

[0018] Co plays a crucial role in suppressing segregation in nickel-based superalloys. Similar to Ru, it alters the segregation coefficients of other elements, lowers the lattice constant of the γ phase to increase the interfacial energy between the TCP and γ phases, thereby promoting the diffusion of TCP phase-forming elements and further suppressing TCP phase precipitation in the alloy. Therefore, this invention controls the mass percentage of Co to be between 8.0% and 12.0%.

[0019] Hf can improve the casting performance of nickel-based superalloys, enhancing melt flow and suppressing the formation of casting defects. Furthermore, Hf enhances the adhesion and durability of the protective oxide film on blade materials, thus improving the high-temperature mechanical properties of the alloy. However, excessive Hf can lower the initial melting temperature and reduce the heat treatment window of the alloy; therefore, this invention controls the mass percentage of Hf to be between 0.02% and 0.15%.

[0020] Nitrogen (Nb) is an important strengthening element in nickel-based superalloys, enhancing precipitation strengthening by increasing the volume fraction and thermal stability of the γ′ phase. Furthermore, Nb improves the alloy's resistance to intergranular corrosion, making it suitable for harsh environments such as marine and aerospace applications. However, excessive Nb can disrupt the formation of the protective oxide layer; therefore, this invention controls the Nb mass percentage to be between 0.30% and 0.60%.

[0021] Re (re) has a significant solid solution strengthening effect on alloys, while Ru (ru) has an effect on suppressing segregation. However, introducing these two expensive elements into the alloy will increase the cost several times over. Therefore, in order to obtain low-cost oriented columnar superalloys, this alloy does not contain Re or Ru, unlike other high-performance oriented columnar superalloys.

[0022] This invention employs a combination of solid solution strengthening, precipitation strengthening, and bending grain boundary strengthening to ensure that the alloy has good high-temperature creep properties. Increasing the content of Mo and W elements improves the solid solution strengthening effect, while increasing the content of Al and Ti elements maximizes the precipitation strengthening effect. In order to reduce the cost of the alloy, elements such as Re and Ru are removed from the alloy.

[0023] This invention, while ensuring the alloy's excellent high-temperature creep performance and good microstructural stability, achieves a cost significantly lower than alloys with similar performance. The alloy exhibits a creep rupture life exceeding 360 hours at 1040℃ / 137MPa and exceeding 80 hours at 1100℃ / 137MPa, making it suitable for applications in turbine blades for gas turbines and aero-engines. Attached Figure Description

[0024] Figure 1 This shows the intragranular γ / γ′ phase morphology of the alloy after heat treatment in this invention.

[0025] Figure 2 The image shows the γ / γ′ phase morphology of the heat-treated alloy in this invention after being exposed to heat at 1040℃ for 500 hours.

[0026] Figure 3 This shows the grain boundary morphology of the alloy after heat treatment in this invention.

[0027] Figure 4 This shows the grain boundary morphology of the alloy after creep loading in this invention. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0029] A high-performance, low-cost directionally solidified columnar superalloy, comprising, by mass percentage: Cr: 1.5–3.5%, Co: 8.0–12.0%, Mo: 2.0–4.5%, W: 10.0–13.0%, Ti: 0.5–2.0%, Al: 4.0–7.0%, Ta: 2.5–4.5%, Hf: 0.02–0.15%, Nb: 0.30–0.60%, with the balance being Ni; the mass fraction ratio of Al to Ti is ≥2.5, the total mass fraction of Ti + Al is 5.0–7.5%, and the total mass fraction of Mo + W is 13.0–17.0%.

[0030] Preferably, a high-performance, low-cost directionally solidified columnar superalloy comprises, by mass percentage: Cr: 1.5–3.2%, Co: 9.0–12.0%, Mo: 2.0–4.0%, W: 10.5–12.5%, Ti: 0.5–1.5%, Al: 4.0–6.5%, Ta: 3.0–4.5%, Hf: 0.02–0.10%, Nb: 0.4–0.60%, with the balance being Ni; the mass fraction ratio of Al to Ti is ≥2.8, the total mass fraction of Ti + Al is 5.0–7.0%, and the total mass fraction of Mo + W is 13.0–16.0%.

[0031] After the alloy that meets the above conditions is smelted into a master alloy, it is remelted and then directionally solidified to prepare a directional columnar crystal alloy. For the cast alloy, conventional heat treatment processes can be used, such as, but not limited to, 1300℃ / 4h / air cooling + 1100℃ / 4h / air cooling + 870℃ / 16h / air cooling, to obtain a high-performance, low-cost directional solidified columnar crystal high-temperature alloy.

[0032] The following are specific embodiments and comparative examples:

[0033] Example 1

[0034] A high-performance, low-cost directionally solidified columnar superalloy, comprising, by mass percentage: Cr: 2.72%, Co: 9.84%, Mo: 3.37%, W: 11.03%, Ti: 1.50%, Al: 5.41%, Ta: 3.98%, Hf: 0.10%, Nb: 0.52%, with the balance being Ni; the mass fraction ratio of Al to Ti is 3.6, the total mass fraction of Ti + Al is 6.91%, and the total mass fraction of Mo + W is 14.40%.

[0035] Example 2

[0036] A high-performance, low-cost directionally solidified columnar superalloy, comprising, by mass percentage: Cr: 1.69%, Co: 9.61%, Mo: 2.35%, W: 10.91%, Ti: 1.29%, Al: 5.59%, Ta: 4.24%, Hf: 0.07%, Nb: 0.58%, with the balance being Ni; the mass fraction ratio of Al to Ti is 3.0, the total mass fraction of Ti + Al is 6.88%, and the total mass fraction of Mo + W is 13.26%.

[0037] Example 3

[0038] A high-performance, low-cost directionally solidified columnar superalloy, comprising, by mass percentage: Cr: 3.15%, Co: 9.14%, Mo: 3.71%, W: 12.25%, Ti: 0.81%, Al: 4.69%, Ta: 3.08%, Hf: 0.09%, Nb: 0.43%, with the balance being Ni; the mass fraction ratio of Al to Ti is 5.8, the total mass fraction of Ti + Al is 5.50%, and the total mass fraction of Mo + W is 15.96%.

[0039] Comparative Example 1

[0040] A directionally solidified columnar superalloy, comprising, by mass percentage: Cr: 2.0%, Co: 9.0%, Mo: 2.0%, W: 10.0%, Ti: 2.0%, Al: 6.0%, Ta: 4.0%, Hf: 0.10%, Nb: 0.50%, C: 0.0%, B: 0.0%, with the balance being Ni; the mass fraction ratio of Al to Ti is 3.0, the total mass fraction of Ti + Al is 8.0%, and the total mass fraction of Mo + W is 12.0%.

[0041] Comparative Example 2

[0042] A directionally solidified columnar superalloy, alloy designation GTD 111, comprises, by mass percentage: Cr: 14.0%, Co: 9.5%, Mo: 1.5%, W: 3.8%, Ti: 5.0%, Al: 3.0%, Ta: 3.0%, Hf: 0.15%, Nb: 0.0%, C: 0.1%, B: 0.01%, with the balance being Ni; the mass fraction ratio of Al to Ti is 0.6, the total mass fraction of Ti + Al is 6.0%, and the total mass fraction of Mo + W is 5.3%.

[0043] Comparative Example 3

[0044] A second-generation single-crystal high-temperature alloy, alloy designation René N5, comprises, by mass percentage: Cr: 7.0%, Co: 7.5%, Mo: 1.5%, W: 5.0%, Ti: 0.0%, Al: 6.2%, Ta: 6.5%, Hf: 0.15%, Nb: 0.0%, Re: 3.0%, with the balance being Ni; the total mass fraction of Ti + Al is 6.2%, and the total mass fraction of Mo + W is 6.5%.

[0045] The creep life of the alloys in the three examples and the first comparative example was tested at 1040℃ / 137MPa and 1100℃ / 137MPa. The cost of the six alloys was calculated based on the current raw material prices. The results are shown in Table 1.

[0046] Table 1 shows the creep life and estimated cost of the embodiments and comparative examples of the present invention.

[0047]

[0048] As shown in the results of Comparative Example 1 in Table 1, the present invention significantly improves the creep life of the alloy by optimizing the Mo + W and Al + Ti alloy compositions. Comparative Examples 2 and 3 show that the cost of the alloy of the present invention is comparable to that of the existing GTD 111 alloy for gas turbines, and far lower than the raw material price of René N5, a second-generation single-crystal high-temperature alloy for gas turbines. However, its creep life is significantly higher than that of the GTD 111 alloy, and also higher than that of the high-cost single-crystal high-temperature alloy René N5 with added Re, indicating that the alloy has a significant cost-performance advantage.

[0049] Figure 1 The image shows the intragranular γ / γ′ phase morphology of the alloy after heat treatment in Example 1. The γ′ phase area fraction is close to 75%, and the γ phase channel width is approximately 40 nm. Figure 2 The tissue of the heat-treated sample from Example 1, after being exposed to heat at 1040°C for 500 hours, showed no precipitation of harmful phases such as TCP phase and η phase, and exhibited good tissue stability. Figure 3 The grain boundaries in the heat-treated sample of Example 1, Figure 4 The grain boundary morphology of the heat-treated sample in Example 1 after persistent fracture at 1040℃ / 137MPa is shown. During the persistent loading process, the grain boundaries are transformed from straight grain boundaries in the heat-treated state to curved grain boundaries.

[0050] This invention is a high-performance, low-cost directionally solidified columnar superalloy developed to meet the material requirements of next-generation heavy-duty gas turbines. Compared with typical directionally solidified columnar superalloys, this alloy has significantly different strengthening design concepts and compositional characteristics. The alloy employs a combination of solid solution strengthening, precipitation strengthening, and bending grain boundary strengthening to ensure excellent high-temperature creep performance. Increasing the Mo + W content further enhances the solid solution strengthening effect, controlling the mass percentage of Al and Ti elements suppresses the precipitation of the η phase, and increasing the Al + Ti content maximizes the precipitation strengthening effect. To reduce alloy cost, elements such as Re and Ru are removed from the alloy. While ensuring excellent high-temperature creep performance and good microstructural stability, the alloy has a cost far lower than alloys with similar performance. The alloy exhibits a creep life exceeding 360 hours at 1040℃ / 137MPa and exceeding 80 hours at 1100℃ / 137MPa.

[0051] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A high-performance, low-cost, directionally solidified columnar superalloy, characterized in that: The composition by mass percentage includes Cr: 1.5–3.5%, Co: 8.0–12.0%, Mo: 2.0–4.5%, W: 10.0–13.0%, Ti: 0.5–2.0%, Al: 4.0–7.0%, Ta: 2.5–4.5%, Hf: 0.02–0.15%, Nb: 0.30–0.60%, with the balance being Ni; the mass fraction ratio of Al to Ti is ≥2.5, the total mass fraction of Ti + Al is 5.0–7.5%, and the total mass fraction of Mo + W is 13.0–17.0%.

2. The high-performance, low-cost, directionally solidified columnar superalloy according to claim 1, characterized in that: The composition by mass percentage includes Cr: 1.5–3.2%, Co: 9.0–12.0%, Mo: 2.0–4.0%, W: 10.5–12.5%, Ti: 0.5–1.5%, Al: 4.0–6.5%, Ta: 3.0–4.55%, Hf: 0.02–0.10%, Nb: 0.4–0.60%, with the balance being Ni; the mass fraction ratio of Al to Ti is ≥2.8, the total mass fraction of Ti + Al is 5.0–7.0%, and the total mass fraction of Mo + W is 13.0–16.0%.

3. The high-performance, low-cost, directionally solidified columnar superalloy according to claim 1, characterized in that: After heat treatment, the volume fraction of the γ′ strengthening phase within the crystals of the alloy is not less than 70%.

4. The high-performance, low-cost, directionally solidified columnar superalloy according to claim 1, characterized in that: The alloy has a creep rupture life of more than 360 hours at 1040℃ / 137MPa and a creep rupture life of more than 80 hours at 1100℃ / 137MPa.

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