Rhenium-free nickel-based single-crystal high-temperature alloy and preparation method thereof

Abstract

The invention discloses a rhenium-free nickel-based single-crystal high-temperature alloy and a preparation method thereof, and relates to the technical field of high-temperature alloys. According to the high-temperature alloy provided by the invention, by finely regulating and controlling the proportion of strengthening elements such as Al, Ti, Ta and W and synergistically exerting the auxiliary effects of elements such as Cr, Co, C and Hf, after an expensive rhenium (Re) element and a molybdenum (Mo) element which is easy to promote generation of a harmful phase are thoroughly abandoned, collaborative optimization of high strength, high structure stability, excellent oxidation resistance and good casting performance is successfully realized. The rhenium-free nickel-based single crystal superalloy provided by the invention has high performance, high stability, excellent oxidation resistance and hot corrosion resistance and good castability, and provides an ideal material solution for low-cost and high-reliability manufacturing of high-temperature parts of heavy duty gas turbines.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy technology, and in particular to a rhenium-free nickel-based single-crystal high-temperature alloy and its preparation method. Background Technology

[0002] Single-crystal superalloys, with their excellent comprehensive mechanical properties, have become the preferred material for aero-engine blades. As the inlet temperature of gas turbines continues to increase, in order to meet the market demand for higher efficiency and power, these alloys are gradually being used by domestic and foreign manufacturers in the manufacture of heavy-duty gas turbine blades, which places more stringent requirements on their high-temperature strength, creep rupture life, and microstructure stability.

[0003] In traditional high-performance single-crystal superalloys, the addition of the key element rhenium (Re) is typically used to improve the alloy's temperature resistance and creep resistance. However, Re is a rare metal, scarce and expensive, resulting in high costs. To reduce manufacturing costs, conserve strategic resources, and promote self-sufficiency in materials, research institutions both domestically and internationally are actively working to develop high-performance single-crystal superalloys that do not contain any rhenium, and have made a series of advances.

[0004] Currently, several representative rhenium-free superalloys have been developed. For example, the MD2 alloy successfully developed by the French National Aeronautics and Space Agency (ONERA) has achieved comprehensive performance levels comparable to second-generation rhenium-containing single-crystal alloys; General Electric (GE) has developed the rhenium-free Rene N500 by optimizing the composition of the classic Rene N5 alloy; in addition, Cannon-Muskegon has also launched the rhenium-free derivative alloy CMSX-7 by adjusting the CMSX-4 system. These achievements have initially demonstrated that competitive mechanical properties can still be obtained through scientific composition design without relying on rhenium.

[0005] Nevertheless, existing rhenium-free single-crystal superalloys still face a series of severe challenges in their large-scale engineering applications, especially in meeting the requirements of long-term, high-temperature, and high-load service in heavy-duty gas turbines: their topological close-packed (TCP) phase precipitation temperature is relatively high, and their microstructure stability is difficult to meet the requirements of gas turbine blades for long-term service at high temperatures; at the same time, their high alloy density results in poor casting processability, which is not conducive to the preparation and reliable operation of large turbine blades. In addition, their high-temperature oxidation resistance needs further verification and improvement.

[0006] Therefore, to truly promote the large-scale application of rhenium-free single-crystal superalloys in high-temperature components of next-generation heavy-duty gas turbines, it is still necessary to further optimize the alloy composition, improve the microstructure stability and casting processability while maintaining high strength and good oxidation resistance, and effectively reduce density, so as to meet the comprehensive performance requirements of large-sized blades of heavy-duty gas turbines in high-temperature and long-term service environments. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a rhenium-free single crystal high-temperature alloy with high strength and good oxidation resistance.

[0008] To address the above problems, the present invention proposes the following technical solution:

[0009] In a first aspect, the present invention provides a rhenium-free nickel-based single-crystal superalloy, comprising the following components by mass percentage:

[0010] 6-7% Al, 9-11% Co, 9-10% Cr, 0.1-0.2% Hf, 5-7% Ta, 0-1% Ti, 7-9% W, 0.03-0.06% C, balance Ni.

[0011] The further technical solution is that, by mass percentage, it includes the following components:

[0012] 6-7% Al, 10-11% Co, 9-10% Cr, 0.1-0.2% Hf, 6-7% Ta, 0.5-1% Ti, 7.5-8.5% W, 0.03-0.05% C, balance Ni.

[0013] The formulation of the rhenium-free nickel-based single-crystal superalloy of this invention optimizes the following elements to achieve high-temperature strength and oxidation resistance under rhenium (Re)-free conditions: Al and Ti, as the main forming elements of the γ' phase [Ni3(Al,Ti)], jointly provide core precipitation strengthening, with Ti also contributing additionally to the alloy's resistance to hot corrosion. Without adding Re, the content of Ta is increased to leverage its dual effects of solid solution strengthening and precipitation strengthening, partially compensating for the strengthening loss. W, as an important solid solution strengthening element, is also appropriately increased in content. To ensure microstructure stability, the contents of Ta and W are strictly controlled (below 7% and 9%, respectively), and Mo, which easily promotes the precipitation of harmful topologically close-packed phases (TCP), is completely eliminated, effectively preventing the large-scale formation of TCP phases. Regarding oxidation resistance, Cr is set at a high level, synergistically providing reliable oxidation protection with Al. Furthermore, Hf and Ta together improve the alloy's casting properties; the addition of Co helps reduce stacking fault energy, thereby improving creep performance; while C reduces porosity and provides second-phase strengthening by forming carbides.

[0014] Secondly, the present invention provides a method for preparing the rhenium-free nickel-based single-crystal superalloy, comprising the following steps:

[0015] S1. Preparation of master alloy: The raw materials are prepared according to the target alloy composition, and the purity of the metal raw materials used is not less than 99.99%. The master alloy ingot is obtained by vacuum induction melting process.

[0016] S2. Single crystal preparation: The master alloy ingot is directionally solidified to prepare a single crystal casting with

[001] orientation;

[0017] S3. Heat treatment: The single crystal casting is subjected to solution heat treatment and multi-stage aging heat treatment in sequence.

[0018] The further technical solution is that in the master alloy ingot prepared in step S1, the content of each of O, N and S elements is less than 5 ppm and the total content is less than 10 ppm, and the total content of trace impurity elements is less than 100 ppm.

[0019] A further technical solution is that, in step S2, the directional solidification adopts the spiral crystal selection method, and the process parameters are: casting temperature 1510-1530℃, heat preservation zone temperature 1560-1580℃, and pulling speed 3-4mm / min.

[0020] A further technical solution is that, in step S3, the solution heat treatment is a segmented heating and holding process, specifically including: heating to 1260-1280℃ at a rate of 5-10℃ / min and holding for 1-2 hours; then heating to 1290-1305℃ at a rate of 0.1-1℃ / min and holding for 1-2 hours; then heating to 1305-1310℃ at a rate of 0.1-1℃ / min and holding for 1-2 hours, followed by gas quenching.

[0021] A further technical solution is that, in step S3, the multi-stage aging heat treatment includes:

[0022] Level 1 aging: Heat to 1110-1130℃ at a rate of 10-15℃ / min, hold for 2-6 hours, and then quench in air.

[0023] Secondary aging: Heat to 1070-1090℃ at 10-15℃ / min, hold for 2-6 hours, and then quench in air;

[0024] Level 3 aging: Heat to 890-910℃ at a rate of 10-15℃ / min, hold for 4-8 hours, and then quench in air.

[0025] The further technical solution is that the single crystal casting prepared in step S2 meets the following quality requirements: the primary dendrite spacing is less than 300 μm, there are no freckle defects, no impurities, the primary orientation deviates from the

[001] direction by an angle of less than 13°, and the small-angle grain boundary is less than 8°.

[0026] A further technical solution is that the trace impurity elements include one or more of Pb, Bi, Te, Tl, Se, Ag, Sb, Au, As, In, Th, Cd, Hg, Sn, Ga, K, Ge, Zn, Ba, Be, Br, Ca, Cs, Ce, Cl, Ho, I, Ir, La, Li, Lu, Pt, Mg, Nd, Os, Pd, Pr, Ru, Sr, Tm, Y, Er, Rh, Rb, Yb, and U.

[0027] Thirdly, the present invention provides a heavy-duty gas turbine blade, the heavy-duty gas turbine blade being made of the rhenium-free nickel-based single-crystal high-temperature alloy described in the first aspect.

[0028] Compared with the prior art, the technical effects achieved by the present invention include:

[0029] The rhenium-free nickel-based single-crystal superalloy provided by this invention achieves synergistic optimization of high strength, high microstructure stability, excellent oxidation resistance and good casting performance by finely controlling the proportion of strengthening elements such as Al, Ti, Ta and W, and synergistically leveraging the auxiliary effects of elements such as Cr, Co, C and Hf, after completely eliminating expensive rhenium (Re) and molybdenum (Mo) which easily promotes harmful phases.

[0030] The alloy of this invention exhibits an oxidation rate as low as 0.0041 g / (m³) in a cyclic oxidation test at 1100 °C for 100 h. 2 •h), reaching the level of complete antioxidant properties, and significantly superior to Rene N5 alloy with 3% Re added (0.0137g / (m 2 The alloy exhibits excellent oxidation resistance. Furthermore, the TCP phase precipitation temperature of this invention is as high as 916℃, and the TCP phase content is significantly lower than that of typical alloys of the same type after long-term exposure at 950℃, ensuring the structural stability and reliability during long-term high-temperature service. In addition, through optimization of elements such as Hf and Ta, the eutectic range of the alloy is narrowed, and the as-cast microstructure is refined. The porosity after casting is less than 0.09%, and remains below 0.09% after heat treatment, completely avoiding common casting defects such as freckles and impurities, demonstrating excellent casting process window and forming quality. Most importantly, without any Re content, the room temperature and high-temperature tensile strength of the alloy of this invention meet the service requirements of heavy-duty gas turbine blades, achieving a significant reduction in raw material costs while ensuring key mechanical properties.

[0031] In summary, the rhenium-free nickel-based single-crystal superalloy provided by this invention combines high performance, high stability, excellent oxidation and hot corrosion resistance, and good castability, providing an ideal material solution for the low-cost and high-reliability manufacturing of high-temperature components for heavy-duty gas turbines. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 Density data for alloys in the embodiments and comparative examples of this invention;

[0034] Figure 2 The paste-like region and heat treatment window of the alloys in the embodiments and comparative examples of the present invention;

[0035] Figure 3 Microstructure diagrams of the alloy in the as-cast and heat-treated states according to embodiments of the present invention;

[0036] Figure 4 The precipitation temperature of TCP harmful phase and the proportion of TCP phase at 950°C of the alloys in the embodiments and comparative examples of the present invention;

[0037] Figure 5 The images show the average oxidation rate of the alloys in the embodiments and comparative examples at 1100℃ / 100h and the sample photographs at 100h. Detailed Implementation

[0038] 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 embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0040] It should also be understood that the terminology used in this specification of embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. As used in this specification of embodiments of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0041] This invention provides a rhenium-free nickel-based single-crystal superalloy and its preparation method. The specific chemical composition of the alloy is shown in Table 1, and single-crystal preparation is carried out accordingly. For ease of performance comparison, Table 1 also lists the alloy composition of the embodiments of this invention, as well as the corresponding chemical compositions of typical Re-free second-generation nickel-based single-crystal superalloys Rene N500, CMSX-7, and MD2, and the traditional second-generation single-crystal alloy Rene N5, which serve as comparative examples.

[0042] Table 1. Alloy composition (wt.%) of the examples and comparative examples

[0043]

[0044] The preparation method of the rhenium-free nickel-based single-crystal superalloy of this invention is as follows:

[0045] Based on the alloy composition in Table 1, metal elements with a purity of over 99.99% were used for batching. After baking, the raw materials were melted in a vacuum induction melting furnace to prepare a high-purity master alloy ingot. The vacuum degree was controlled at 10 during the melting process. -2 Pa. The specific melting process is as follows: the melting temperature is controlled by the heating power. Co, Cr, Mo, W, and Ni are added first, and the power is gradually increased to 15.5 kW. After melting, the power is reduced to 0 kW and then increased back to 10.2 kW before adding Al. The power is then gradually reduced to 0 kW to melt Al. The melting furnace power is then increased to 10.2 kW before adding Ta, and the power is gradually reduced to 0 kW to melt Ta. The melting furnace power is then increased to 10.2 kW before adding Ti and Hf, and the power is gradually reduced to 0 kW to melt them all. After the master alloy is cast, the refining temperature is controlled at 1510-1550℃ during the melting process.

[0046] The composition of the master alloy was determined by ICP (inductively coupled plasma atomic absorption spectrometry) and X-ray fluorescence spectrometry (XRF). The impurity contents of O, N, and S were all less than 5 ppm and the total content was less than 10 ppm. The total content of impurities such as Pb, Bi, Te, Tl, Se, Ag, Sb, Au, As, In, Th, Cd, Hg, Sn, Ga, K, Ge, Zn, Ba, Be, Br, Ca, Cs, Ce, Cl, Ho, I, Ir, La, Li, Lu, Pt, Mg, Nd, Os, Pd, Pr, Ru, Sr, Tm, Y, Er, Rh, Rb, Yb, and U did not exceed 100 ppm.

[0047] After removing the riser and surface oxide scale from the prepared master alloy ingot, and ensuring it meets the chemical composition requirements, the master alloy was used in a directional solidification furnace to prepare single crystal castings using the spiral crystal selection method. The single crystal growth direction was

[001] , the casting temperature was 1520℃, the holding temperature was 1570℃, the pulling rate was 4mm / min, and the prepared single crystal specimen had a primary dendrite spacing of 250μm, no freckles, no impurities, no bands, a primary orientation deviation of <10°, and a small-angle grain boundary of <8°.

[0048] Single-crystal castings were subjected to solution heat treatment and multi-stage aging heat treatment sequentially to obtain single-crystal superalloy samples. The specific heat treatment process is as follows:

[0049] (1) Solution heat treatment: The segmented heating heat treatment process is adopted. The solution treatment regime is to heat to 1270℃ at a heating rate of 10℃ / min and hold for 1h, then heat to 1290℃, 1300℃, 1305℃ and 1310℃ at a rate of 0.1℃ / min, hold for 2h, and then quench in air.

[0050] (2) First-level aging heat treatment: Heat to 1120℃ at a heating rate of 10℃ / min, hold for 4 hours, and then cool by air quenching.

[0051] (3) Secondary aging heat treatment: Heat to 1080℃ at a heating rate of 10℃ / min and hold for 4 hours, then air quench and cool.

[0052] (4) Three-stage aging heat treatment: Heat to 900℃ at a heating rate of 10℃ / min and hold for 4 hours, then air quench and cool.

[0053] The single-crystal superalloy samples prepared in the embodiments of the present invention were characterized and tested, and the relevant data were compared with those of comparative examples reported in the literature. The specific contents and results are as follows:

[0054] The alloy densities of the examples and comparative examples were calculated using JMatPro software, and the results are as follows: Figure 1 As shown. The density of the alloy in this embodiment of the invention is comparable to Rene N5 and MD2, but lower than CMSX-7. The lower density helps to reduce the centrifugal force on the blades and turbine disk during gas turbine operation, further reducing failures caused by excessive stress.

[0055] The temperature range of the paste region (i.e., the temperature interval between the solidus and liquidus lines) and the heat treatment window (i.e., the solution treatment temperature range) of the examples and comparative examples were calculated using JMatPro software. The results are shown in […]. Figure 2It can be seen that the width of the paste-like region (46°C) of the alloy in this embodiment is comparable to that of comparative example MD2 (41°C), and significantly narrower than that of comparative alloys Rene N5 (61°C), Rene N500 (58°C), and CMSX-7 (57°C). The heat treatment window of the alloy in this embodiment is 55°C, which is significantly larger than that of the comparative alloys (Rene N5, Rene N500, and CMSX-7, which have heat treatment windows of 48°C, 31°C, and 15°C, respectively). The narrower paste-like region is beneficial for reducing solidification segregation, while the wider heat treatment window improves process tolerance and facilitates homogenization solution treatment.

[0056] The microstructure of the alloys in the examples, both in the as-cast and heat-treated states, was observed using a metallographic microscope. The photographs are shown below. Figure 3 As shown, the porosity in the heat-treated state is 0.08% (0.05% in the as-cast state), which is lower than the results reported in the literature for other Re-free alloys (above 0.9%). In the example alloy, the eutectic content decreased from 4.1% in the as-cast state to 0.1% after heat treatment, essentially eliminating the eutectic.

[0057] Based on thermodynamic simulations, the initial precipitation temperature of the topologically close-packed (TCP) phase in the alloy and the volume fraction of the TCP phase at 950℃ are shown in the following results: Figure 4 As shown, the initial precipitation temperature of the TCP phase in the alloy of this invention is only 916°C, lower than that of the comparative alloy; and at 950°C, the volume fraction of the TCP phase is significantly lower than that of the comparative alloy. This indicates that the alloy of this invention has better microstructural stability, and the tendency of TCP phase precipitation is significantly suppressed, which is beneficial for long-term high-temperature service.

[0058] Tensile properties at room temperature and high temperature were tested using a mechanical testing machine. Antioxidant properties were evaluated using the static oxidation weight gain method. Specific data are listed in Table 2. Oxidation kinetic curves and photographs of the specimens at 100 hours are shown in the table below. Figure 5 .

[0059] Table 2 Tensile properties of the examples and comparative examples at room temperature and 980°C.

[0060]

[0061] It can be seen that the room temperature properties of the alloy in this embodiment are at the same level as CMSX-7, and the tensile strength at 980℃ is higher than 700MPa; furthermore, the oxidation rate of the alloy in this embodiment is as low as 0.0041g / (m 2 •h), reaching the level of complete antioxidant properties, and significantly superior to Rene N5 alloy with 3% Re added (0.0137g / (m 2 ·h)). From Figure 5 The photos also show that the Rene N5 alloy showed obvious oxidation after 100 hours of testing.

[0062] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0063] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A rhenium-free nickel-based single-crystal superalloy, characterized in that, By mass percentage, it includes the following components: 6-7% Al, 9-11% Co, 9-10% Cr, 0.1-0.2% Hf, 5-7% Ta, 0-1% Ti, 7-9% W, 0.03-0.06% C, balance Ni.

2. The rhenium-free nickel-based single-crystal superalloy according to claim 1, characterized in that, By mass percentage, it includes the following components: 6-7% Al, 10-11% Co, 9-10% Cr, 0.1-0.2% Hf, 6-7% Ta, 0.5-1% Ti, 7.5-8.5% W, 0.03-0.05% C, balance Ni.

3. A method for preparing a rhenium-free nickel-based single-crystal superalloy according to claim 1 or 2, characterized in that, Includes the following steps: S1. Preparation of master alloy: The raw materials are prepared according to the target alloy composition, and the purity of the metal raw materials used is not less than 99.99%. The master alloy ingot is obtained by vacuum induction melting process. S2. Single crystal preparation: The master alloy ingot is directionally solidified to prepare a single crystal casting with [001] orientation; S3. Heat treatment: The single crystal casting is subjected to solution heat treatment and multi-stage aging heat treatment in sequence.

4. The preparation method according to claim 3, characterized in that, In the master alloy ingot prepared in step S1, the contents of O, N and S elements are each less than 5 ppm and the total content is less than 10 ppm, and the total content of trace impurity elements is less than 100 ppm.

5. The preparation method according to claim 3, characterized in that, In step S2, the directional solidification adopts the spiral crystal selection method, and the process parameters are: casting temperature 1510-1530℃, heat preservation zone temperature 1560-1580℃, and pulling speed 3-4mm / min.

6. The preparation method according to claim 3, characterized in that, In step S3, the solution heat treatment is a segmented heating and holding process, specifically including: heating to 1260-1280℃ at a rate of 5-10℃ / min and holding for 1-2 hours; then heating to 1290-1305℃ at a rate of 0.1-1℃ / min and holding for 1-2 hours; then heating to 1305-1310℃ at a rate of 0.1-1℃ / min and holding for 1-2 hours, followed by gas quenching.

7. The preparation method according to claim 3, characterized in that, In step S3, the multi-stage aging heat treatment includes: Level 1 aging: Heat to 1110-1130℃ at a rate of 10-15℃ / min, hold for 2-6 hours, and then quench in air. Secondary aging: Heat to 1070-1090℃ at 10-15℃ / min, hold for 2-6 hours, and then quench in air; Level 3 aging: Heat to 890-910℃ at a rate of 10-15℃ / min, hold for 4-8 hours, and then quench in air.

8. The preparation method according to claim 3, characterized in that, The single crystal casting prepared in step S2 meets the following quality requirements: the primary dendrite spacing is less than 300 μm, there are no freckle defects, no impurities, the primary orientation deviates from the [001] direction by an angle of less than 13°, and the small-angle grain boundary is less than 8°.

9. The preparation method according to claim 4, characterized in that, The trace impurity elements include one or more of the following: Pb, Bi, Te, Tl, Se, Ag, Sb, Au, As, In, Th, Cd, Hg, Sn, Ga, K, Ge, Zn, Ba, Be, Br, Ca, Cs, Ce, Cl, Ho, I, Ir, La, Li, Lu, Pt, Mg, Nd, Os, Pd, Pr, Ru, Sr, Tm, Y, Er, Rh, Rb, Yb, and U.

10. A heavy-duty gas turbine blade, characterized in that, The heavy-duty gas turbine blades are made of the rhenium-free nickel-based single-crystal high-temperature alloy as described in claim 1 or 2.

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