A sub-solid solution recovery heat treatment method for repairing creep damage of nickel-based single crystal alloy

Abstract

The application discloses a sub-solid solution recovery heat treatment method for repairing creep damage of a nickel-based single crystal alloy, and belongs to the field of single crystal high-temperature alloy repair and remanufacturing. The recovery heat treatment system comprises two steps of sub-solid solution treatment and aging treatment. The method can effectively recover the structure and performance of the single crystal alloy, the gamma prime phase in the dendrite trunk region is uniformly distributed in the form of coherent cubes, and the volume fraction is recovered to more than 98% of the original state; the irregular large-size gamma prime phase and the small-size near-cubic gamma prime phase coexist in the interdendritic region, and the volume fraction is recovered to 85-90% of the original state; and the creep performance of the damaged alloy at the end of the second stage of creep and before the end of the second stage of creep can be recovered to meet the alloy delivery standard state. The method is simple, reliable and highly applicable, can meet engineering application, and has a wide prospect in the life extension of single crystal alloy turbine blades.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy preparation, specifically relating to the repair and remanufacturing of single-crystal high-temperature alloys. Background Technology

[0002] Recovery heat treatment is a crucial step in the turbine blade repair and remanufacturing process. Its main purpose is to promote the dissolution and re-precipitation of the damaged γ' phase in the alloy through high-temperature heat treatment, restoring the alloy's microstructure to a near-original state and thus restoring its mechanical properties. Therefore, recovery heat treatment is of great significance for improving the service safety and economy of turbine blades.

[0003] Currently, recovery heat treatment regimes for single-crystal alloys generally consist of two parts: high-temperature solution treatment and aging treatment. The solution temperature is typically set near the complete dissolution temperature of the γ' phase, while the aging temperature is usually directly referenced from the alloy's standard heat treatment aging regime. Regarding the recovery heat treatment of single-crystal superalloys, Ruttert et al. (Ruttert B, Horst O, Lopez-Galilea I, et al. Rejuvenation of Single-Crystal Ni-Base Superalloy Turbine Blades: Unlimited Service Life?[J]. Metallurgical and MaterialsTransactions A, 2018, 49: 4262-4273.) successfully restored the microstructure and creep properties of creep-damaged second-generation single-crystal ERBO / 1 using a recovery heat treatment at 1300℃ (above the complete dissolution temperature of the alloy's γ' phase) combined with two-stage aging. However, this method only shows good recovery effects for microstructures with slight damage before the minimum creep rate point; the recovery effect is poor for more severe damage.

[0004] ZL202410784840.5 discloses a multi-stage solution recovery heat treatment method for single-crystal superalloys with rhenium content of 1.5–6.0 wt%. This method requires first setting the solution initiation temperature within the range of 1250–1300 °C, then determining the alloy solidus temperature and determining the solution termination temperature within the range of 40–60 °C below the solidus temperature. Subsequently, six different temperatures are selected within the temperature range (initial solution temperature to termination solution temperature) for multi-stage solution treatment. The solution treatment process is complex and the total solution treatment time is as long as 20–30 hours, making it inconvenient for engineering applications.

[0005] ZL202310146396.X discloses a method for developing recovery heat treatment processes for third- and fourth-generation single-crystal alloys. The principle is to design recovery heat treatments at different temperatures based on the porosity or creep strain of the single-crystal alloy sample. However, this method is very complex in practice. It not only requires predicting creep strain based on porosity but also pre-treating at different temperatures and analyzing the microstructure and residual stress after each pre-treatment temperature to further determine the recovery heat treatment regime. This requires users to have extensive relevant experience. Furthermore, the amount of creep deformation is difficult to measure for single-crystal blades actually in service.

[0006] ZL202311564018.X discloses a recovery heat treatment method for second-generation nickel-based single-crystal superalloys. This method can effectively improve the creep performance of the alloy by using a full solution recovery heat treatment above the complete dissolution temperature of the alloy's γ' phase. However, actual service blades may have welded repair zones of dissimilar metals and welds connecting components, and the melting points of these areas are usually lower than the alloy bulk. Furthermore, high-temperature full solution heat treatment is not conducive to recrystallization control of single-crystal blades. Therefore, this method has many limitations in engineering applications.

[0007] In summary, developing a subsolution recovery heat treatment method that can effectively restore creep damage in second-generation nickel-based single-crystal superalloys, with a simple process flow, is easy to apply in industry, and has a solution temperature lower than the complete dissolution temperature of the γ' phase, is of great engineering significance for the repair and service life extension of second-generation nickel-based single-crystal turbine blades. Summary of the Invention

[0008] The purpose of this invention is to provide a subsolution recovery heat treatment method for repairing creep damage in nickel-based single-crystal alloys. This method, through subsolution and two-stage aging heat treatment, partially restores the microstructure of single crystals in various damaged states at the end of the second stage of creep and before. It can be used to repair creep damage in second-generation nickel-based single-crystal high-temperature alloys used in aero-engine turbine blades, restoring their creep performance to meet the alloy's factory standard condition.

[0009] A subsolution recovery heat treatment method for repairing creep damage in nickel-based single-crystal alloys specifically includes the following steps:

[0010] 1) Determine the solution treatment temperature T1 for recovery heat treatment based on the complete dissolution temperature T0 of the γ' phase of the single crystal alloy to be repaired.

[0011] 2) Perform subsolution treatment on the single crystal alloy to be repaired. The specific parameters are as follows: under vacuum or protective atmosphere, heat from room temperature to 900~1100℃ at 10~15℃ / min, then heat to T1 at 5~10℃ / min, hold for 2~4h and then cool to room temperature. The cooling rate is controlled as air cooling rate.

[0012] 3) Perform first-level aging treatment on the alloy after step 2): hold at 1115~1125℃ for 4~6 hours under vacuum or protective atmosphere, and then air cool to room temperature.

[0013] 4) Perform a secondary aging treatment on the alloy after step 2): Under vacuum or protective atmosphere, hold at 865~875℃ for 32~36h and then air cool to room temperature. The microstructure and creep properties of the creep-damaged single crystal alloy are restored.

[0014] Furthermore, in step 1), T1 is 10~20℃ lower than the complete dissolution temperature T0 of the γ' phase of the single crystal alloy.

[0015] Furthermore, in step 4), the microstructure of the single-crystal alloy in the creep-damaged state is restored after a recovery heat treatment. The γ' phase in the dendritic trunk region is uniformly distributed in a coherent cubic shape, and its volume fraction is restored to more than 98% of the original state. The large-sized irregular morphology γ' phase and the small-sized near-cubic γ' phase coexist in the interdendritic region, and their volume fraction is restored to 85-90% of the original state.

[0016] Furthermore, in step 4), the recovery of the creep performance of the single-crystal alloy in the creep-damaged state means restoring the creep performance of the damaged alloy at the end of the second creep stage and earlier to a state that meets the alloy's factory standards.

[0017] Furthermore, the recovery heat treatment time is no later than the end of the second stage of creep.

[0018] Furthermore, this method is applicable to a second-generation nickel-based single-crystal superalloy containing 1.6–2.4% rhenium by mass.

[0019] Compared with existing recovery heat treatment methods, the most significant feature of this invention is that it employs a subsolution recovery heat treatment with a solution temperature lower than that of the γ' phase, thereby reducing the peak temperature of the recovery heat treatment. This effectively avoids the risk of initial melting in low-melting-point regions such as the interdiffusion zone and secondary reaction zone of the single-crystal turbine blade coating, the weld repair zone, and the risk of recrystallization after the blade has been in service.

[0020] Furthermore, this method features simple process steps, a short flow rate, and eliminates the need for hot isostatic pressing, resulting in lower process costs. The advantage of this invention is that after the aforementioned recovery heat treatment, the creep performance of the creep-damaged single-crystal alloy can be restored to a state meeting the alloy's factory standards, satisfying engineering applications and showing broad prospects for extending the service life of single-crystal alloy turbine blades. Attached Figure Description

[0021] Figure 1 The original dendritic trunk and interdendritic microstructure of the second-generation nickel-based single-crystal superalloys in Examples 1-3 of this invention.

[0022] Figure 2 The microstructure of dendritic trunk and interdendritic space in the longitudinal section of the alloy in Example 1 of this invention after creeping at 1100℃ / 12MPa for 200h is shown.

[0023] Figure 3 The microstructure of the dendritic trunk and interdendritic space of the longitudinal section of the alloy in Example 1 of this invention after creeping at 1100℃ / 12MPa for 200h and then undergoing recovery heat treatment.

[0024] Figure 4 The microstructure of the dendritic trunk and interdendritic space of the longitudinal section of the alloy in Example 2 of this invention after creeping at 1100℃ / 50MPa for 250h is shown.

[0025] Figure 5 The microstructure of the dendritic trunk and interdendritic space of the longitudinal section of the alloy in Example 2 of this invention after creeping at 1100℃ / 50MPa for 250h and then undergoing recovery heat treatment.

[0026] Figure 6 The microstructure of the dendritic trunk and interdendritic space of the longitudinal section of the alloy in Example 3 of this invention after creeping at 980℃ / 200MPa for 250h is shown.

[0027] Figure 7 The microstructure of the longitudinal section of the alloy in Example 3 of this invention, after creeping at 980℃ / 200MPa for 250h and then undergoing recovery heat treatment, is the dendritic trunk and interdendritic microstructure.

[0028] Figure 8 The damaged state of the alloys in Examples 1-3 of this invention and the creep life at 980℃ / 250MPa after recovery heat treatment are shown. Detailed Implementation

[0029] The following examples will further illustrate the present invention so that those skilled in the art can better understand its advantages and features.

[0030] Example 1

[0031] This embodiment uses DD6 nickel-based single-crystal superalloy used in turbine rotor blades of a certain type of aero-engine as the object of restoration. The original microstructure of this alloy consists of a cubic, uniformly sized γ' phase, such as... Figure 1 As shown, the volume fractions of the dendritic trunk and interdendritic γ' phase in the original alloy are 69% and 70%, respectively. The complete dissolution temperature (T0) of the γ' phase in this alloy was obtained by DSC testing as 1297℃. The "Chinese High-Temperature Alloy Handbook" specifies that the factory standard for the creep performance of this alloy is a creep life ≥100h under conditions of 980℃ / 250MPa.

[0032] After undergoing creep damage at 1100℃ / 12MPa / 200h, the microstructure of this alloy has been severely degraded, such as... Figure 2As shown, in the longitudinal section, the γ' phase has formed a raft structure in some parts, while in others it remains cubic. At this point, the alloy is in the early stage of the second creep stage.

[0033] The above-mentioned damaged alloy is restored using the recovery heat treatment method provided by this invention. The specific steps are as follows:

[0034] Subsolid treatment: Under vacuum, the temperature is increased from room temperature to (1000±3)℃ at 15℃ / min, then increased to (1280±3)℃ at 5℃ / min, held for 2 hours and then cooled to room temperature. The cooling rate is controlled as air cooling rate.

[0035] First-level aging treatment: Under vacuum, keep at (1120±3)℃ for 4 hours, then cool to room temperature, with the cooling rate controlled as air cooling rate.

[0036] Secondary aging treatment: Under vacuum, the temperature is maintained at (870±3)℃ for 32 hours, and then cooled to room temperature. The cooling rate is controlled to be the air cooling rate.

[0037] After the above-mentioned recovery heat treatment, the dendritic trunk microstructure of the damaged alloy was restored to near its original state, and the γ' phase re-emerged cubically, with a volume fraction of approximately 69%. The interdendritic microstructure was partially restored, with small-sized cubic γ' phases coexisting with larger, less regularly morphologically irregular γ' phases, and a volume fraction of approximately 60%. Figure 3 As shown.

[0038] In this example, the creep life at 980℃ / 250MPa of the alloy in the damaged state and after recovery heat treatment are as follows: Figure 8 As shown in the figure, after creep damage at 1100℃ / 12MPa / 200h, the creep life of the alloy at 980℃ / 250MPa is approximately 87h, which no longer meets the specified factory performance standards for this alloy grade. After recovery heat treatment, the creep life of the alloy is restored to approximately 181h, and the creep performance is significantly recovered.

[0039] Example 2

[0040] This embodiment uses a second-generation nickel-based single-crystal high-temperature alloy for turbine rotor blades of a certain type of aero-engine as the object of restoration. Its chemical composition, γ' phase complete dissolution temperature, and original microstructure are the same as in Example 1.

[0041] After undergoing creep damage at 1100℃ / 50MPa / 250h, the microstructure of this alloy has been severely degraded, such as... Figure 4 As shown, the γ' phase in the longitudinal section has formed a well-developed raft structure, indicating that the alloy is in the middle of the second stage of creep.

[0042] The above-mentioned damaged alloy is restored using the recovery heat treatment method provided by this invention. The specific steps are as follows:

[0043] Subsolid treatment: Under vacuum, the temperature is increased from room temperature to (1000±3)℃ at 15℃ / min, then increased to (1280±3)℃ at 5℃ / min, held for 2 hours and then cooled to room temperature. The cooling rate is controlled as air cooling rate.

[0044] First-level aging treatment: Under vacuum, keep at (1120±3)℃ for 4 hours, then cool to room temperature, with the cooling rate controlled as air cooling rate.

[0045] Secondary aging treatment: Under vacuum, the temperature is maintained at (870±3)℃ for 32 hours, and then cooled to room temperature. The cooling rate is controlled to be the air cooling rate.

[0046] After the above-mentioned recovery heat treatment, the dendritic trunk microstructure of the damaged alloy was restored to near its original state, and the γ' phase re-emerged cubically, with a volume fraction of approximately 68%. The interdendritic microstructure was partially restored, with small-sized cubic γ' phases coexisting with larger, less regularly morphologically irregular γ' phases, and a volume fraction of approximately 61%. Figure 5 As shown.

[0047] In this example, the creep life at 980℃ / 250MPa of the alloy in the damaged state and after recovery heat treatment are as follows: Figure 8 As shown in the figure, after creep damage at 1100℃ / 50MPa / 250h, the creep life of the alloy at 980℃ / 250MPa is about 55h, which no longer meets the specified factory performance standards for this grade of alloy. After recovery heat treatment, the creep life of the alloy is restored to about 151h, and the creep performance is significantly restored.

[0048] Example 3

[0049] This embodiment uses a second-generation nickel-based single-crystal high-temperature alloy for turbine rotor blades of a certain type of aero-engine as the object of restoration. Its chemical composition, γ' phase complete dissolution temperature, and original microstructure are the same as in Example 1.

[0050] After undergoing creep damage at 980℃ / 200MPa / 250h, the microstructure of this alloy has been severely degraded, such as... Figure 6 As shown, the γ' phase in the longitudinal section has undergone severe topological inversion, indicating that the alloy is in the late stage of the second creep stage.

[0051] The above-mentioned damaged alloy is restored using the recovery heat treatment method provided by this invention. The specific steps are as follows:

[0052] Subsolid treatment: Under vacuum, the temperature is increased from room temperature to (1000±3)℃ at 15℃ / min, then increased to (1280±3)℃ at 5℃ / min, held for 2 hours and then cooled to room temperature. The cooling rate is controlled as air cooling rate.

[0053] First-level aging treatment: Under vacuum, keep at (1120±3)℃ for 4 hours, then cool to room temperature, with the cooling rate controlled as air cooling rate.

[0054] Secondary aging treatment: Under vacuum, the temperature is maintained at (870±3)℃ for 32 hours, and then cooled to room temperature. The cooling rate is controlled to be the air cooling rate.

[0055] After the above-mentioned recovery heat treatment, the dendritic trunk microstructure of the damaged alloy was restored to near its original state, and the γ' phase re-emerged cubically, with a volume fraction of approximately 69%. The interdendritic microstructure was partially restored, with small-sized cubic γ' phases coexisting with larger, less regularly morphologically irregular γ' phases, and a volume fraction of approximately 62%. Figure 7 As shown.

[0056] In this example, the creep life at 980℃ / 250MPa of the alloy in the damaged state and after recovery heat treatment are as follows: Figure 8 As shown in the figure, after creep damage at 980℃ / 200MPa / 250h, the creep life of the alloy at 980℃ / 250MPa is approximately 61h, which no longer meets the specified factory performance standards for this alloy grade. After recovery heat treatment, the creep life of the alloy is restored to approximately 129h, and the creep performance is significantly recovered.

[0057] The above description is only a preferred embodiment of the present invention, but the present invention is not limited thereto. Any equivalent substitutions, improvements, etc. made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A sub-solid solution recovery heat treatment method for repairing creep damage in a nickel-based single crystal alloy, characterized by, For a second-generation nickel-based single-crystal superalloy DD6 containing 1.6~2.4% rhenium by mass, the recovery heat treatment is applicable to the creep-damaged alloy at or before the end of the second creep stage, and the recovery heat treatment time is no later than the end of the second creep stage, specifically including the following steps: 1 ) according to the monocrystalline alloy to be repaired the phase complete dissolution temperature T0, the recovery heat treatment solid solution temperature T1, the phase complete dissolution temperature T0 is 1297℃, T1 is lower than the monocrystalline alloy the phase complete dissolution temperature T0 is 10~20℃; 2) Perform subsolution treatment on the single crystal alloy to be repaired. The specific parameters are: under vacuum or protective atmosphere, heat from room temperature to 900~1100℃ at 10~15℃ / min, then heat to T1 at 5~10℃ / min, hold for 2~4h and then cool to room temperature. The cooling rate is controlled as air cooling rate. 3) Perform first-level aging treatment on the alloy after step 2): hold at 1115~1125℃ for 4~6 hours under vacuum or protective atmosphere, and then air cool to room temperature; 4) Perform a secondary aging treatment on the alloy after step 3): Under vacuum or protective atmosphere, hold at 865~875℃ for 32~36h and then air cool to room temperature. The microstructure and creep properties of the creep-damaged single crystal alloy are restored.

2. The subsolvus heat treatment method of claim 1, wherein Step 4) The microstructure of the creep damage state single crystal alloy is recovered to be that the dendrite trunk region The phase is uniformly distributed in a coherent cubic shape, and the volume fraction is recovered to more than 98% of the original state; the interdendritic region has large-size irregular morphology The phase and small-size near-cubic The phase coexists, and the volume fraction is recovered to 85-90% of the original state.

3. The subsolvus recovery heat treatment method of claim 1, wherein the first temperature is between 700°C and 750°C. Step 4) The creep performance of the single crystal alloy in the creep-damaged state is restored to the state that meets the alloy's factory standards at the end of the second stage of creep and before.

4. The subsolvus recovery heat treatment method of any one of claims 1-3, characterized in that, The DD6 nickel-based single crystal superalloy has a factory standard creep life of ≥100h under 980℃ / 250MPa conditions, and after recovery heat treatment, the creep life is restored to the state that meets the factory standard.

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