A continuous heating heat treatment process for a second generation nickel-based single crystal superalloy

Abstract

The application discloses a continuous temperature rising heat treatment process of a second-generation nickel-based single crystal high-temperature alloy, and optimizes an industrial traditional heat treatment system by adopting a multi-stage stepwise temperature rising method in a low-temperature section and a slow continuous temperature rising method in a high-temperature section, improves a peak heat treatment temperature, and effectively reduces segregation of difficult-to-dissolve elements such as Re and W. Meanwhile, the continuous temperature rising process in the high-temperature section can effectively avoid an initial melting phenomenon caused by the improved peak heat treatment temperature, improves a heat treatment structure, and thus improves mechanical properties and a yield of products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat treatment of second-generation nickel-based single-crystal superalloys, and particularly relates to a continuous heating heat treatment process for a second-generation nickel-based single-crystal superalloy. BACKGROUND

[0002] High-temperature alloys refer to a kind of metal materials taking iron, nickel and cobalt as the base and capable of working at a high temperature of 600 DEG C or above and under the action of a certain stress for a long time, and have good high-temperature strength, creep resistance and organizational stability. Single-crystal high-temperature alloys reduce the use of grain boundary strengthening elements, and their comprehensive performance is also greatly improved, and are widely used in advanced aero-engine and gas turbine blades. The second-generation single-crystal high-temperature alloy greatly improves the temperature resistance and high-temperature creep performance by adding 2-3 wt.% of Re element. At present, China has made important progress in the research and development of second-generation nickel-based single-crystal high-temperature alloy materials. The nickel-based single-crystal high-temperature alloy obtained by directional solidification technology usually has a large number of coarse γ / γ' eutectic in the microstructure, which destroys the integrity of the single crystal, easily causes stress concentration and affects the mechanical properties of the alloy. In addition, there is element segregation in the interdendritic region, and the size and distribution of the main strengthening phase γ' phase are also very uneven, so the industrial multi-stage solid solution treatment process is usually adopted to eliminate eutectic and reduce element segregation, and a multi-step aging treatment process is adopted to control the cubic degree of γ' phase and improve the microstructure of the alloy.

[0003] With the development of nickel-based single-crystal high-temperature alloys, the content of refractory elements in the alloy is continuously increased, the types and proportions of added elements are large, especially after the second generation of single-crystal high-temperature alloys, with the introduction of Re, the instability of the alloy system is increased, the mutual diffusion coefficient of each element in the alloy is significantly improved, and the element segregation of the alloy is aggravated. The increase of segregation makes the interdendritic region prone to incipient melting, and TCP phase is more likely to precipitate during service, which endangers the mechanical properties of the alloy, and the traditional heat treatment process in industry is difficult to meet the growing requirements for microstructure and performance, and needs to be improved.

[0004] The segregation of the refractory elements will cause the occurrence of the primary melting phenomenon, which greatly narrows the heat treatment window. However, the diffusion coefficient of the refractory elements is several orders of magnitude higher than that of other elements, and the time and temperature required for homogenization process are greatly increased. The peak heat treatment temperature of the traditional second-generation single crystal superalloy cannot reach this temperature condition, and long-term solid solution treatment will also lead to the increase of solid solution micropores. At the same time, Ta element has been proved to have uphill diffusion behavior in the second-generation nickel-based single crystal superalloy, and different heat treatment processes will also affect the shape, size, proportion, mismatch relationship of γ' phase, eutectic phase, and matrix channel width, etc. These factors greatly increase the difficulty of solid solution treatment. Therefore, in the field of nickel-based single crystal superalloy, how to improve the element segregation and avoid the occurrence of primary melting phenomenon at the same time, and optimize the heat treatment organization, specific solutions are urgently needed.

[0005] Through literature retrieval of the prior art, it is found that the document "Designing homogenization-solution heat treatments for single crystal superalloys" published by S.R. Hegde, R.M. Kearsey, et al. in Materials Science and Engineering: A, first discovered that compared with the traditional stepwise heating solid solution treatment, continuous heating solid solution treatment at a lower heating rate in a certain temperature range can reduce the tendency of primary melting and reduce residual interdendritic precipitation, but the specific temperature range and temperature gradient are not discussed in the document.

[0006] The document "Investigation on a ramp solution heat treatment for a third generation nickel-based single crystal superalloy" published by Yanbin Zhang, Lin Liu, et al. in Journal of Alloys and Compounds, carried out continuous heating heat treatment for third-generation and above high-Re nickel-based single crystal superalloy. However, the inventors verified that this direct continuous heating heat treatment method is not suitable for low Re content second-generation nickel-based single crystal superalloy.

[0007] The patent with publication number CN 104561867 A optimizes the original process of the related alloy, but only simply increases the original solid solution temperature of the alloy, and the effect of improving segregation and optimizing organization is limited.

[0008] The patent with publication number CN 113528993 A relates to a heat treatment method for third-generation nickel-based single-crystal superalloys, which effectively reduces the segregation level of difficult-to-dissolve elements, but there are a large number of solid solution cavities in the alloy, and primary melting easily occurs. SUMMARY

[0009] In order to reduce element segregation, improve the service performance of the product, and avoid the occurrence of primary melting, and improve the heat treatment structure of the alloy, the present application proposes a solid solution treatment method for second-generation nickel-based single-crystal superalloys.

[0010] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0011] A continuous heating heat treatment process for second-generation nickel-based single-crystal superalloys is provided, comprising:

[0012] The second-generation nickel-based single-crystal superalloy test bar is placed in a heat treatment furnace; in the heat treatment furnace, the second-generation nickel-based single-crystal superalloy test bar is raised from room temperature to 1280℃ and held for 60min; after the holding is completed, it is raised to 1290℃ and held for 120min; after the holding is completed, it is raised to 1300℃ and held for 180min; after the holding is completed, it is raised to 1305℃ and held for 180min; after the holding is completed, it is raised to 1310℃ and slowly raised to 1315℃ at a heating rate of 1℃ / h, and after the temperature is reached, the furnace is opened and the second-generation nickel-based single-crystal superalloy test bar is taken out and air-cooled to room temperature to obtain a second-generation nickel-based single-crystal superalloy test bar after solid solution treatment.

[0013] As a further description of the present application, the heat treatment process further comprises:

[0014] The second-generation nickel-based single-crystal superalloy test bar after the solid solution treatment is placed in the heat treatment furnace; in the heat treatment furnace, the second-generation nickel-based single-crystal superalloy test bar is raised from room temperature to 1140℃ and held for 240min; after the holding is completed, the furnace is opened and the second-generation nickel-based single-crystal superalloy test bar is taken out and air-cooled to room temperature to obtain a second-generation nickel-based single-crystal superalloy test bar after a first aging treatment.

[0015] As a further description of the present application, the heat treatment process further comprises:

[0016] The second-generation nickel-based single-crystal superalloy test bar after the first aging treatment is placed in the heat treatment furnace; in the heat treatment furnace, the second-generation nickel-based single-crystal superalloy test bar is raised from room temperature to 870℃ and held for 960min; after the holding is completed, the furnace is opened and the second-generation nickel-based single-crystal superalloy test bar is taken out and air-cooled to room temperature to obtain a second-generation nickel-based single-crystal superalloy test bar after a second aging treatment.

[0017] As a further illustration of the present application, the second generation nickel-based single crystal superalloy has a composition comprising, by weight percentage: Al: 5.45%-5.75%; Co: 9.3%-10.0%; Cr: 6.2%-6.6%; Hf: 0.07%-0.12%; Mo: 0.5%-0.7%; Re: 2.8%-3.2%; Ta: 6.3%-6.7%; Ti: 0.7%-1.2%; W: 6.2%-6.6%.

[0018] As a further illustration of the present application, the heat treatment process is performed under vacuum condition and inert gas is introduced.

[0019] As a further illustration of the present application, the heat treatment process has a temperature rising rate of 9-10℃ / min below 1000℃ and 2-3℃ / min above 1000℃.

[0020] As a further illustration of the present application, the second generation nickel-based single crystal superalloy test bar needs to be removed of surface oxidation before being placed in the heat treatment furnace for heat treatment.

[0021] The purpose of the present application is to improve a second generation nickel-based single crystal superalloy heat treatment process, aiming to further reduce the element segregation level while avoiding the initial melting of the alloy during solution treatment, optimizing the product microstructure, and improving the mechanical properties and yield of the product.

[0022] In the present application, the purpose of adopting the step-by-step holding process in the temperature range of 1280℃-1305℃ is to make the elements in the alloy initially diffuse, improve the homogenization degree, and thus gradually increase the initial melting temperature of the alloy.

[0023] In the present application, the purpose of adopting the continuous temperature rising process in the temperature range of 1310℃-1315℃ is to reduce the tendency of initial melting of the alloy at high temperature, further improve the upper limit temperature of the heat treatment window, and thus greatly reduce the element segregation degree.

[0024] By comparing the microstructure of the traditional step-by-step temperature rising process with the same peak temperature and heat treatment time Figure 3 and the microstructure after solution treatment using the present application Figure 2 It can be seen that the microstructure after traditional solution treatment Figure 3 has a large amount of initial melting eutectic, while the microstructure after solution treatment using the present application Figure 2 does not have initial melting. This shows that the solution treatment method of the present application can effectively avoid the occurrence of initial melting.

[0025] By comparing the microstructure of the continuous temperature rising process with the same peak temperature and heat treatment time Figure 4 and the microstructure after solution treatment using the present application Figure 2It can be seen that after continuous heating Figure 4 There are a large number of coarse globular eutectic, and the degree of γ' phase cubic is poor, and there is coarsening and secondary γ' phase precipitation behavior, and the solid solution treatment of the present application Figure 2 The above phenomenon does not occur. It is proved that the improved method of the present application can effectively improve the heat treatment structure of the alloy, and successfully realize the application of continuous heating idea to the second generation of nickel-based single crystal high-temperature alloy.

[0026] By comparing Figure 5 It can be seen from the element segregation coefficient of the process of the present application and the existing industrial process that the process of the present application significantly improves the element segregation, and generally improves the homogenization degree of each element in the alloy.

[0027] The present application adopts a process different from the gradual increase of solid solution treatment temperature in the traditional multi-step solid solution treatment process, and adopts a heat treatment method of stepwise heating at low temperature and continuous heating at high temperature.

[0028] Compared with the prior art, the present application has the following beneficial technical effects:

[0029] (1) The upper limit temperature of the heat treatment window of the alloy is increased from 1300 DEG C to 1315 DEG C, the diffusion of each element in the alloy is more sufficient, the element segregation degree is greatly reduced, the homogenization degree of the structure is better, and the mechanical properties of the alloy are more excellent.

[0030] (2) The process provided by the present application can effectively avoid the generation of initial melting structure, and can effectively promote the dissolution of the coarse γ' phase and γ / γ' phase in the solid solution process, the γ' phase precipitated after aging is small and uniform, the cubic degree is high, there is no directional coarsening phenomenon and secondary γ' phase precipitation, and the structure and performance are good.

[0031] (3) The heat treatment method of the present application is easy to operate and realize, under the condition of not changing the composition, the nickel-based single crystal high-temperature alloy obtained by the present application not only has low element segregation degree, but also has excellent heat treatment structure, excellent comprehensive performance and yield, and has good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0033] Figure 1 is a schematic diagram of the heat treatment method of the second generation of nickel-based single crystal high-temperature alloy according to the embodiments of the present application.

[0034] Figure 2 is a schematic diagram of the microstructure of the second generation nickel-based single crystal superalloy after solution treatment according to the embodiments of the present application, wherein (a) is a microstructure structure diagram, and (b) is a γ' phase structure diagram;

[0035] Figure 3 is a schematic diagram of the microstructure of the conventional stepwise heating according to the comparison of the present application with the same peak temperature and heat treatment time, wherein (a) is a microstructure structure diagram, and (b) is a γ' phase structure diagram, and the solution treatment system is: 1280℃ / 1h+1290℃ / 2h+1300℃ / 3h+1305℃ / 3h+1310℃ / 3h+1315℃ / 2h;

[0036] Figure 4 is a schematic diagram of the microstructure of the continuous heating according to the comparison of the present application with the same peak temperature and heat treatment time, wherein (a) is a microstructure structure diagram, and (b) is a γ' phase structure diagram, and the solution treatment system is: 1280℃-5h-1300℃-6h-1310℃-5h-1315℃;

[0037] Figure 5 is a diagram of the element segregation coefficient distribution (dendrite stem / dendrite interdendrite, wt%) under the process of the present application and the existing industrial process, wherein the solution treatment system of the industrial conventional process is: 1280℃ / 1h+1290℃ / 2h+1300℃ / 6h. DETAILED DESCRIPTION

[0038] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application will be described in detail below in combination with the drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0040] The present application is a heat treatment method of a second generation nickel-based single crystal superalloy, and the following embodiments are described according to the drawings:

[0041] Embodiment 1

[0042] The second generation nickel-based single crystal superalloy used in this embodiment is CMSX-4 alloy, and the actual composition is tested as follows: Al: 5.7%; Co: 9.7%; Cr: 6.4%; Hf: 0.1%; Mo: 0.6%; Re: 3.0%; Ta: 6.4%; Ti: 0.9%; W: 6.4%.

[0043] (1) The CMSX-4 alloy cast bar is prepared by using a vacuum induction furnace to smelt a master alloy and using directional solidification technology.

[0044] (2) The sample with a proper size is obtained by wire cutting, and the surface oxide is removed by mechanical polishing.

[0045] (3) The vacuum packaging treatment is performed by using a quartz tube vacuum packaging machine, and high-purity argon is filled at the same time.

[0046] (4) The CMSX-4 alloy test bar is placed in a KSL-1400X-A2 box-type heat treatment furnace; in the heat treatment furnace, the CMSX-4 alloy test bar is raised from room temperature to 1280℃ and kept for 60 min; after the heat preservation is completed, the temperature is raised to 1290℃ and kept for 120 min; after the heat preservation is completed, the temperature is raised to 1300℃ and kept for 180 min; after the heat preservation is completed, the temperature is raised to 1305℃ and kept for 180 min; after the heat preservation is completed, the temperature is raised to 1310℃ and slowly raised to 1315℃ at a temperature rising rate of 1℃ / h, and the furnace is opened after the temperature is reached, and the CMSX-4 alloy test bar is air-cooled to room temperature to obtain a CMSX-4 alloy test bar subjected to solid solution treatment. The temperature rising rate is 10℃ / min below 1000℃, and the temperature rising rate is 3℃ / min above 1000℃.

[0047] (5) The oxide on the surface of the CMSX-4 alloy test bar after solid solution treatment is cleaned, and the vacuum packaging treatment is performed again by using a quartz tube vacuum packaging machine, and high-purity argon is filled at the same time.

[0048] (6) The CMSX-4 alloy test bar subjected to solid solution treatment is placed in a KSL-1400X-A2 box-type heat treatment furnace; in the heat treatment furnace, the CMSX-4 alloy test bar is raised from room temperature to 1140℃ and kept for 240 min; after the heat preservation is completed, the furnace is opened and taken out, and the CMSX-4 test bar is air-cooled to room temperature to obtain a CMSX-4 alloy test bar subjected to primary aging treatment. The temperature rising rate is 10℃ / min below 1000℃, and the temperature rising rate is 3℃ / min above 1000℃.

[0049] (7) The CMSX-4 test bar subjected to primary aging treatment is placed in a KSL-1400X-A2 box-type heat treatment furnace; in the heat treatment furnace, the CMSX-4 alloy test bar is raised from room temperature to 870℃ and kept for 960 min; after the heat preservation is completed, the furnace is opened and taken out, and the CMSX-4 alloy test bar is air-cooled to room temperature to obtain a CMSX-4 alloy test bar subjected to secondary aging treatment, wherein the temperature rising rate is 10℃ / min.

[0050] The microstructure obtained after the heat treatment is as shown in Figure 2as shown.

[0051] In this embodiment, by comparing the microstructure of traditional stepwise heating with the same peak temperature and heat treatment time Figure 3 and the microstructure after solution treatment using the present application Figure 2 It can be seen that the microstructure after traditional solution treatment Figure 3 There is a large amount of primary melting eutectic, while the microstructure after solution treatment using the present application Figure 2 There is no primary melting. It shows that the solution treatment method of the present application can effectively avoid the occurrence of primary melting.

[0052] By comparing the microstructure of continuous heating with the same peak temperature and heat treatment time Figure 4 and the microstructure after solution treatment using the present application Figure 2 It can be seen that the microstructure after continuous heating Figure 4 There is a large amount of coarse globular eutectic, and the degree of γ' phase is poor, and there is coarsening and secondary γ' phase precipitation behavior, while the microstructure after solution treatment using the present application Figure 2 There is no above phenomenon. It shows that the improved method of the present application can effectively improve the heat treatment microstructure of the alloy, and successfully realize the application of continuous heating idea in the second generation of nickel-based single crystal high-temperature alloy.

[0053] Figure 5 The element segregation coefficient distribution diagram (dendrite stem / dendrite interdendritic, wt%) under the present embodiment and the existing industrial process,

[0054] Compared with the existing process, the segregation of refractory elements is improved, especially in this process. The segregation coefficient of Re element decreases from 2.10 to 1.45; the segregation coefficient of W element decreases from 1.25 to 1.13; the segregation coefficient of Ta element increases from 0.67 to 0.95; the segregation coefficient of Ti element increases from 0.66 to 0.91 (the closer the segregation coefficient is to 1, the higher the uniformity of the element is).

[0055] In summary, compared with the existing process, the process in the present application increases the peak heat treatment temperature while reducing the occurrence of primary melting tendency, thereby effectively improving the element segregation level and effectively improving the high temperature performance and yield of the product, and has good application prospect.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A continuous heating heat treatment process for second-generation nickel-based single-crystal superalloys, characterized in that, The composition of the second-generation nickel-based single-crystal superalloy, by weight percentage, includes: Al: 5.45%~5.75%; Co: 9.3%-10.0%; Cr: 6.2%-6.6%; Hf: 0.07%-0.12%; Mo: 0.5%-0.7%; Re: 2.8%-3.2%; Ta: 6.3%-6.7%; Ti: 0.7%-1.2%; W: 6.2%-6.6%. The heat treatment process includes: placing a second-generation nickel-based single-crystal superalloy test rod in a heat treatment furnace; raising the temperature of the second-generation nickel-based single-crystal superalloy test rod from room temperature to 1280°C and holding it for 60 minutes; raising the temperature to 1290°C and holding it for 120 minutes; raising the temperature to 1300°C and holding it for 180 minutes; raising the temperature to 1305°C and holding it for 180 minutes; raising the temperature to 1310°C and slowly raising it to 1315°C at a heating rate of 1°C / h; opening the furnace after reaching the desired temperature and removing the test rod; and air-cooling the second-generation nickel-based single-crystal superalloy test rod to room temperature to obtain a solution-treated second-generation nickel-based single-crystal superalloy test rod. The heating rate of the heat treatment process is as follows: below 1000℃, the heating rate is 9-10℃ / min; above 1000℃, the heating rate is 2-3℃ / min.

2. The continuous heating heat treatment process for the second-generation nickel-based single-crystal superalloy according to claim 1, characterized in that, The heat treatment process further includes: The second-generation nickel-based single-crystal superalloy test bar, after solution treatment, was placed in the heat treatment furnace. In the heat treatment furnace, the second-generation nickel-based single-crystal superalloy test bar was heated from room temperature to 1140°C and held for 240 minutes. After the holding period, the furnace was opened and the test bar was taken out and air-cooled to room temperature to obtain a second-generation nickel-based single-crystal superalloy test bar with one aging treatment.

3. The continuous heating heat treatment process for the second-generation nickel-based single-crystal superalloy according to claim 2, characterized in that, The heat treatment process further includes: The second-generation nickel-based single-crystal superalloy test rod, after undergoing the first aging treatment, was placed in a heat treatment furnace. In the heat treatment furnace, the second-generation nickel-based single-crystal superalloy test rod was heated from room temperature to 870°C and held for 960 minutes. After the holding period, the furnace was opened and the test rod was removed. The second-generation nickel-based single-crystal superalloy test rod was then air-cooled to room temperature to obtain the second-generation nickel-based single-crystal superalloy test rod after the second aging treatment.

4. The continuous heating heat treatment process for the second-generation nickel-based single-crystal superalloy according to claim 1, characterized in that, The heat treatment process is carried out under vacuum conditions and an inert gas is introduced.

5. The continuous heating heat treatment process for the second-generation nickel-based single-crystal superalloy according to any one of claims 1-3, characterized in that, Before each heat treatment in the heat treatment furnace, the surface oxide scale of the second-generation nickel-based single-crystal high-temperature alloy test bar needs to be removed.

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