A method of recovery heat treatment of a second generation nickel-based single crystal superalloy

Abstract

The application relates to a recovery heat treatment method of a second-generation nickel-based single-crystal high-temperature alloy, which comprises the following steps: in vacuum or a protective atmosphere, heating the nickel-based single-crystal high-temperature alloy to be repaired to 1280-1300 DEG C, keeping the temperature for 4-6 hours, continuously heating to 1300-1320 DEG C, keeping the temperature for 2-4 hours, continuously heating to 1320-1350 DEG C, keeping the temperature for 2-4 hours, and cooling to obtain a nickel-based single-crystal high-temperature alloy after three-stage solid solution treatment; and performing a set two-step aging treatment on the nickel-based single-crystal high-temperature alloy after the three-stage solid solution treatment, and cooling to obtain a repaired nickel-based single-crystal high-temperature alloy. Through the above multi-stage solid solution heat treatment, the gamma prime phase and harmful phases generated by the persistent damage are dissolved into the gamma matrix to form a gamma single-phase structure; then through the above aging treatment, the gamma prime phase is precipitated from the gamma phase in the form of interface coherence to form a regularly arranged cubic structure, the alloy structure is restored to the initial morphology before the persistent damage, the creep performance of the alloy is basically restored, the service life of the alloy is prolonged, and the cost is saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of repair of nickel-based single crystal superalloys, and particularly relates to a recovery heat treatment method for a second-generation nickel-based single crystal superalloy. BACKGROUND

[0002] Nickel-based single crystal superalloy turbine blades are one of the key components of advanced aero-engines, and are usually served in a complex environment of high temperature and high pressure, and are subjected to corrosion and erosion of high-temperature gas and complex mechanical load, and the service environment is harsh. Therefore, the nickel-based single crystal superalloy turbine blades will inevitably produce degradation of organization and performance during service, and even failure and fracture. According to statistics, turbine blade failure accounts for more than 40% of the total failure of aero-engines, and therefore, the turbine blades need to be repaired or replaced regularly. However, with the development of advanced aero-engines, the generation of nickel-based single crystal superalloys is getting higher and higher, and the production process is more and more complex and the content of refractory elements is increasing, which makes the cost higher and higher. Therefore, people pay more and more attention to the performance recovery of turbine blades through repair treatment.

[0003] The recovery heat treatment technology mainly re-dissolves and precipitates the strengthening phase in the alloy by heat treatment at different temperatures and times, so that the alloy organization after service is basically or completely restored to the initial morphology, so as to achieve the purpose of performance recovery. For the actual service nickel-based single crystal superalloy turbine blades, the damage of the blade body is usually more serious, and the damage type is similar to the high-temperature low-stress creep damage of the alloy. However, compared with the equiaxed casting alloy and the directionally solidified casting alloy, the composition of the nickel-based single crystal superalloy is more complex, and the research on the recovery heat treatment of the nickel-based single crystal superalloy is still limited.

[0004] The second generation single crystal superalloy is the most widely used single crystal alloy at present, and the research on the rejuvenation heat treatment process thereof is very important. Among them, the first related technology (Effects of rejuvenation heat treatment on microstructure and creep property of a Ni-based single crystal superalloy published by K.J. Tan, X.G. Wang, et al. in Journal of Materials Science & Technology) carries out rejuvenation heat treatment on the second generation nickel-based single crystal superalloy, and the rejuvenation heat treatment system is solution treatment (holding at a temperature of 1290℃ for 2h), air cooling + primary aging treatment (holding at a temperature of 1100℃ for 4h, holding at a temperature of 1050℃ for 4h), air cooling + secondary aging treatment (holding at a temperature of 900℃ for 4h), and air cooling. However, the method of the rejuvenation heat treatment will cause the formation of a poor layer of γ' phase, a transition layer and a recrystallization organization damage zone on the surface of the alloy, which is not conducive to the performance of the alloy after the rejuvenation heat treatment. The second related technology (CN115584455 B) proposes a rejuvenation heat treatment process for a nickel-based single crystal superalloy. However, the technology is only suitable for the repair of single crystal alloys with a creep strain of ≤2.5%, and has limited repair effect on single crystal alloys with a larger creep strain. At the same time, the rejuvenation heat treatment needs to determine the initial solution temperature and the final solution temperature through DSC, and the experimental process is complex and time-consuming. During the rejuvenation heat treatment process, the γ' phase will be coarsened, which makes it difficult to restore the alloy to the state before failure.

[0005] In summary, there is an urgent need for a rejuvenation heat treatment method for the second generation nickel-based single crystal superalloy, which can repair the second generation nickel-based single crystal superalloy, restore the microstructure to the original morphology, and basically restore the creep performance of the alloy, prolong the service life of the alloy, and save costs. SUMMARY

[0006] Therefore, the present application provides a rejuvenation heat treatment method for a second generation nickel-based single crystal superalloy, which mainly aims to repair the second generation nickel-based single crystal superalloy, restore the microstructure to the original morphology, and basically restore the creep performance of the alloy.

[0007] To achieve the above-mentioned purpose, the present application mainly provides the following technical solutions:

[0008] On the one hand, the embodiment of the present application provides a rejuvenation heat treatment method for a second generation nickel-based single crystal superalloy, which is carried out under the condition of vacuum or protective atmosphere, and the following steps are carried out:

[0009] The first solid solution treatment: the nickel-based single crystal superalloy to be repaired is heated to a first temperature at a first set rate, and is kept at the first temperature for 4-6 hours; wherein the first temperature is 1280-1300℃;

[0010] The second solid solution treatment: the temperature of the nickel-based single crystal superalloy after the first solid solution treatment is heated to a second temperature at a second set rate from the first temperature, and is kept at the second temperature for 2-4 hours; wherein the second temperature is 1300-1320℃, and the second temperature is higher than the first temperature;

[0011] The third solid solution treatment: the temperature of the nickel-based single crystal superalloy to be repaired after the second solid solution treatment is heated to a third temperature at a third set rate from the second temperature, and is kept at the third temperature for 2-4 hours, and after cooling, the nickel-based single crystal superalloy after the third solid solution treatment is obtained; wherein the third temperature is 1320-1350℃, and the third temperature is higher than the second temperature;

[0012] The first aging treatment: the nickel-based single crystal superalloy after the third solid solution treatment is heated to 1100-1150℃, and is subjected to the first aging treatment, and after cooling, the nickel-based single crystal superalloy after the first aging treatment is obtained;

[0013] The second aging treatment: the nickel-based single crystal superalloy after the first aging treatment is heated to 840-880℃, and is subjected to the second aging treatment, and after cooling, the repaired nickel-based single crystal superalloy is obtained.

[0014] Preferably, the first set rate is 20-25℃ / min; and / or the second set rate is 3-5℃ / min; and / or the third set rate is 3-5℃ / min.

[0015] Preferably, in the step of the first aging treatment: the time of the first aging treatment is 4-8 hours; and / or the heating rate of the nickel-based single crystal superalloy after the third solid solution treatment to 1100-1150℃ is 20-25℃ / min.

[0016] Preferably, in the step of the second aging treatment: the time of the second aging treatment is 20-24 hours; and / or the heating rate of the nickel-based single crystal superalloy after the first aging treatment to 840-880℃ is 20-25℃ / min.

[0017] Preferably, the nickel-based single crystal superalloy after the third solid solution treatment is a γ single-phase structure; preferably, the forming elements of γ and γ' phases in the nickel-based single crystal superalloy after the third solid solution treatment are uniformly distributed, thereby inhibiting the phenomenon of composition segregation.

[0018] Preferably, after the first aging treatment and the second aging treatment, the gamma prime phase is arranged in a regular cubic structure in a form of a phase interface coherent; and / or the first aging treatment is used for regulating the size of the gamma prime phase, and the edge length of the gamma prime phase is controlled to be 300-400 nm; and / or the second aging treatment is used for regulating the morphology of the gamma prime phase, so that the gamma prime phase evolves into a uniform cubic shape, and the gamma / gamma prime phase interface exists in a coherent state, and the alloy is restored to the state before failure.

[0019] Preferably, the primary solid solution treatment, the secondary solid solution treatment, the tertiary solid solution treatment, the first aging treatment and the second aging treatment are all carried out in a vacuum muffle furnace.

[0020] Preferably, in the tertiary solid solution treatment, the first aging treatment and the second aging treatment, the cooling mode is selected to be air cooling.

[0021] Preferably, the second generation nickel-based single crystal superalloy is a second generation nickel-based single crystal superalloy containing Re; and in the second generation nickel-based single crystal superalloy, the content of Re is 1.5-3 wt%.

[0022] Preferably, the nickel-based single crystal superalloy to be repaired is a nickel-based single crystal superalloy having a microstructure damage under steady-state creep loading; and preferably, the creep strain of the nickel-based single crystal superalloy to be repaired is less than or equal to 5.0%.

[0023] Preferably, the nickel-based single crystal superalloy to be repaired is a nickel-based single crystal superalloy turbine blade.

[0024] In still another aspect, the present application provides a repaired second generation nickel-based single crystal superalloy, which has a gamma prime phase with an edge length of 300-400 nm, and a gamma / gamma prime phase interface existing in a coherent manner; preferably, the volume fraction of the gamma prime phase in the repaired second generation nickel-based single crystal superalloy is 65-70%; and preferably, the performance of the repaired second generation nickel-based single crystal superalloy is restored to the state before the alloy is loaded to failure; wherein the repaired second generation nickel-based single crystal superalloy is obtained by repairing a nickel-based single crystal superalloy to be repaired by using the recovery heat treatment method of the second generation nickel-based single crystal superalloy according to any one of the above.

[0025] Compared with the prior art, the recovery heat treatment method of the second generation nickel-based single crystal superalloy has at least the following beneficial effects:

[0026] The present application provides a recovery heat treatment method of the second generation nickel-based single crystal superalloy. The present application can make the strengthening phase γ' phase and TCP phase and other impurity phases caused by creep damage all solid solution to the γ matrix by performing three-step solid solution treatment on the nickel-based single crystal superalloy to be repaired under specific conditions, forming a γ phase single-phase structure; then the obtained solid solution nickel-based single crystal superalloy is subjected to aging treatment under specific conditions, so that the γ' phase with suitable morphology, size and volume fraction of 65-70% (the volume fraction of the γ' phase is determined by the solid solution treatment and the first step of aging treatment) is obtained, the γ' phase is precipitated from the γ phase in the form of interface coherent, forming a regularly arranged cubic structure, so that the alloy organization is restored to the initial morphology, and the creep performance of the alloy is basically restored, the service life of the alloy is prolonged, and the cost is saved.

[0027] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, and can be implemented according to the content of the specification, the following will be described in detail with the preferred embodiments of the present application and with the help of the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The schematic diagram of the recovery heat treatment method of the second generation nickel-based single crystal superalloy described in Example 1;

[0029] Figure 2 The microstructure morphology comparison of the second generation nickel-based single crystal superalloy of Example 1 and Comparative Example 1 after repair;

[0030] Figure 3 The surface recrystallization comparison chart of the creep damage state and the recovery heat treatment state (here, the recovery heat treatment state refers to the alloy after repair) of the second generation nickel-based single crystal superalloy described in Example 2;

[0031] Figure 4 The SEM diagram of the alloy microstructure of the creep damage sample obtained when the creep strain in Example 3 is 5.0%;

[0032] Figure 5 The element segregation coefficient distribution chart (γ / γ', wt%) of the second generation nickel-based single crystal superalloy of Example 3 and Comparative Example 1 after damage and recovery heat treatment according to the present application;

[0033] Figure 6 The high-temperature creep curve of the second generation nickel-based single crystal superalloy of Example 4 and Comparative Example 1 in the standard heat treatment state and the recovery heat treatment state after damage;

[0034] Figure 7 The creep life improvement comparison of Comparative Example 2 and Example 1 alloy after recovery heat treatment. DETAILED DESCRIPTION

[0035] To further clarify the technical means and effects taken by the present application to achieve the intended purpose, the following describes the specific embodiments, structures, features and effects according to the present application in detail with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "embodiments" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0036] The present application aims to provide a recovery heat treatment method suitable for second-generation single crystal superalloys. The method provided by the present application can repair the second-generation nickel-based single crystal superalloy, restore its microstructure to the original morphology, and basically restore the creep performance of the alloy, thereby prolonging the service life of the alloy and saving costs.

[0037] The main scheme of the present application is as follows:

[0038] The present application provides a recovery heat treatment method for a second-generation nickel-based single crystal superalloy. The second-generation nickel-based single crystal superalloy comprises the following chemical components in mass percentage: Cr: 3-9wt%, Co: 6-9wt%, Mo: 4-7wt%, W: 4-8wt%, Ta: 4-7wt%, Al: 5-7wt%, Re: 1.5-3wt%, and the balance of Ni. The method comprises the following steps under vacuum or protective atmosphere:

[0039] First-stage solid solution treatment: the nickel-based single crystal superalloy to be repaired is heated to a first temperature at a rate of 20-25℃ / min, and is kept at the first temperature for 4-6h; wherein the first temperature is 1280-1300℃.

[0040] Second-stage solid solution treatment: the temperature of the nickel-based single crystal superalloy after the first-stage solid solution treatment is increased to a second temperature at a rate of 3-5℃ / min from the first temperature, and is kept at the second temperature for 2-4h; wherein the second temperature is 1300-1320℃, and the second temperature is higher than the first temperature.

[0041] Third-stage solid solution treatment: the temperature of the nickel-based single crystal superalloy to be repaired after the second-stage solid solution treatment is increased to a third temperature at a rate of 3-5℃ / min from the second temperature, and is kept at the third temperature for 2-4h to obtain the nickel-based single crystal superalloy after the third-stage solid solution treatment after cooling; wherein the third temperature is 1320-1350℃, and the third temperature is higher than the second temperature.

[0042] First-step aging treatment: the nickel-based single crystal superalloy after the third-stage solid solution treatment is heated to 1100-1150℃ at a rate of 20-25℃ / min, and is kept at the temperature for 4-8h to perform the first-step aging treatment, and the nickel-based single crystal superalloy after the first-step aging treatment is obtained after cooling.

[0043] Second aging treatment: the nickel-based single crystal superalloy after the first aging treatment is heated to 840-880℃ at a rate of 20-25℃ / min, and is kept for 20-24h to perform the second aging treatment. After cooling, the repaired nickel-based single crystal superalloy is obtained.

[0044] The nickel-based single crystal superalloy to be repaired is a nickel-based single crystal superalloy with microstructure damage under steady-state creep loading. The creep strain of the nickel-based single crystal superalloy to be repaired is ≤5.0%. The nickel-based single crystal superalloy to be repaired is an alloy turbine blade after coating removal by corrosion treatment.

[0045] Both the solution treatment and the aging treatment are performed in a vacuum air quenching furnace. When the solution treatment and the aging treatment are performed in a protective atmosphere, the heating and keeping processes of the solution treatment and the aging treatment are performed under the condition of <1×10 5 Pa.

[0046] It should be noted that the above scheme is that: by performing the solution treatment on the nickel-based single crystal superalloy to be repaired under specific conditions, the strengthening phase γ' phase and the TCP phase caused by creep damage and other impurity phases are all solid-solved into the γ matrix to form a γ phase single-phase microstructure. Then, by performing the aging treatment on the obtained solid-solution nickel-based single crystal superalloy under specific conditions, the γ' phase with appropriate morphology, size and volume fraction is obtained, the γ' phase is precipitated from the γ phase in the form of interface coherence to form a regularly arranged cubic structure, so that the alloy microstructure is restored to the initial morphology, and the creep performance of the alloy is basically restored, thereby prolonging the service life of the alloy and saving the cost.

[0047] The application is further described below through specific examples:

[0048] Example 1

[0049] In this example, a second-generation nickel-based single crystal superalloy turbine blade for an aero-engine is taken as the repair object, and the chemical composition of the turbine blade is (wt%): Al: 7%, Ta: 5%, Mo: 6%, Co: 6%, Cr: 4%, W: 6%, Re: 3%, and the rest is Ni. The service time of the turbine blade is 400h, which has reached half of the designed service life. By observing the microstructure of the tenon and the blade body section of the turbine blade after service through SEM, it is found that the microstructure of the tenon is close to the original microstructure of the alloy, and the microstructure of the blade body section is seriously degraded. The blade is subjected to recovery heat treatment, and the specific process is as follows.

[0050] Solution treatment: the turbine blade after coating removal by corrosion is placed in a vacuum air quenching furnace, and is vacuumized to 10 -2 Pa, and then is filled with Ar to 2×10 4Pa, in high-purity Ar (≥99.99%) atmosphere: the furnace temperature was raised from room temperature to 1285℃ at a temperature raising rate of 24℃ / min, and was kept at this temperature for 5h to conduct a first-stage solid solution treatment. After the end of the keeping, the furnace temperature was raised from 1285℃ to 1310℃ at a temperature raising rate of 4℃ / min, and was kept at this temperature for 3h to conduct a second-stage solid solution treatment. After the end of the keeping, the furnace temperature was raised from 1310℃ to 1330℃ at a temperature raising rate of 3℃ / min, and was kept at this temperature for 3h to conduct a third-stage solid solution treatment; after the end of the keeping, the turbine blade was air-cooled to room temperature to obtain a turbine blade after the third-stage solid solution treatment.

[0051] aging treatment: the turbine blade after the third-stage solid solution treatment was put into a vacuum air-quenching furnace, vacuumized to 10 -2 Pa, then Ar was filled to the gas pressure of 2×10 4 Pa, in high-purity Ar (≥99.99%) atmosphere: the furnace temperature was raised from room temperature to 1285℃ at a temperature raising rate of 24℃ / min, and was kept at this temperature for 5h to conduct a first-stage solid solution treatment. After the end of the keeping, the furnace temperature was raised from 1285℃ to 1310℃ at a temperature raising rate of 4℃ / min, and was kept at this temperature for 3h to conduct a second-stage solid solution treatment. After the end of the keeping, the furnace temperature was raised from 1310℃ to 1330℃ at a temperature raising rate of 3℃ / min, and was kept at this temperature for 3h to conduct a third-stage solid solution treatment; after the end of the keeping, the turbine blade was air-cooled to room temperature to obtain a turbine blade after the third-stage solid solution treatment.

[0052] The schematic diagram of the recovery heat treatment method in the embodiment is shown in Figure 1 .

[0053] It can be known from the embodiment 1 that the vacuum air-quenching furnace facing industrial application is used, in the solid solution temperature range of the alloy, the turbine blade of the nickel-based single crystal superalloy with the coating removed is completely solid-solution treated by the heating mode of continuous temperature raising, the strengthening phase γ' phase in the alloy is completely solid-solution treated into the base alloy (the nickel-based single crystal superalloy after the third-stage solid solution treatment is γ single-phase structure; the forming elements of the γ and γ' phases in the nickel-based single crystal superalloy after the third-stage solid solution treatment are uniformly distributed, so that the composition segregation phenomenon is inhibited), and then the cooling is conducted by the air cooling mode; then the alloy after the cooling is subjected to two-step aging treatment, the strengthening phase γ' is precipitated in the coherent form, and the cooling is also conducted by the air cooling mode, so that the alloy structure can be restored to the original morphology. The microstructure morphology after the recovery heat treatment is shown in Figure 2 . It can be known from the Figure 2 that: the alloy has the γ' phase with the side length of 300-400nm and the volume fraction of 68%, and the γ / γ' phase interface exists in the coherent form.

[0054] Embodiment 2

[0055] The second generation nickel-based single crystal superalloy turbine blade for a certain type of aero-engine is repaired as the repair object in the embodiment, and the chemical composition of the turbine blade is as follows (wt%): Al: 6%, Ta: 6%, Mo: 5%, Co: 6%, Cr: 3%, W: 5%, Re: 2.5%, and the balance is Ni. The turbine blade is subjected to recovery heat treatment after being subjected to high-temperature creep loading for 350 hours, and the specific process is as follows.

[0056] solution treatment: the turbine blade after the coating is removed is placed in a vacuum air quenching furnace, vacuum is extracted to 10 - 2 Pa, and then Ar is filled to a gas pressure of 2×10 4 Pa, and in a high-purity Ar (≥99.99%) atmosphere: the furnace temperature is increased from room temperature to 1290°C at a temperature increasing rate of 22°C / min, and the temperature is kept at 1290°C for 5h to perform a first-stage solution treatment. After the keeping, the furnace temperature is increased from 1290°C to 1310°C at a temperature increasing rate of 4°C / min, and the temperature is kept at 1310°C for 4h to perform a second-stage solution treatment. After the keeping, the furnace temperature is increased from 1310°C to 1340°C at a temperature increasing rate of 5°C / min, and the temperature is kept at 1340°C for 4h to perform a third-stage solution treatment; after the keeping, the turbine blade is air-cooled to room temperature to obtain the turbine blade after the third-stage solution treatment.

[0057] aging treatment: the turbine blade after the third-stage solution treatment is placed in a vacuum air quenching furnace, vacuum is extracted to 10 -2 Pa, and then Ar is filled to a gas pressure of 2×10 4 Pa, and in a high-purity Ar (≥99.99%) atmosphere: the furnace temperature is increased from room temperature to 1150°C at a temperature increasing rate of 23°C / min, and the temperature is kept at 1150°C for 4h to perform a first-step aging treatment, and after the keeping, the furnace temperature is air-cooled to room temperature; again, the furnace temperature is increased from room temperature to 880°C at a temperature increasing rate of 25°C / min, and the temperature is kept at 880°C for 22h to perform a second-step aging treatment, and after the keeping, the furnace temperature is air-cooled to room temperature to obtain the repaired turbine blade.

[0058] As known from the embodiment 2, the turbine blade after the coating is removed is subjected to complete solution treatment by a heating mode of continuous temperature increasing, so that the strengthening phase γ' in the alloy is completely dissolved into the base alloy, and then air cooling is performed; then, two-step aging treatment is performed, so that the strengthening phase γ' is precipitated in a coherent form, and air cooling is also performed, so that the alloy structure can be restored to the original morphology.

[0059] The surface recrystallization of the creep damage state and the recovery heat treatment state of the alloy of the embodiment 2 is compared as shown in the following table. Figure 3 Figure 3 ​It can be seen that, after the alloy is treated by the recovery heat treatment process, the grain boundary and recrystallization phenomenon generated during loading are effectively eliminated, so that the alloy is restored to the single crystal state before service, and the whole alloy forms a grain.

[0060] Example 3

[0061] In this embodiment, a second-generation nickel-based single crystal high-temperature alloy turbine blade for an aero-engine is taken as a repair object, and the chemical composition of the turbine blade is as follows (wt %): Al: 6.5%, Ta: 6%, Mo: 5%, Co: 7.5%, Cr: 4%, W: 6.5%, Re: 3%, and the balance is Ni. The SEM image of the microstructure of the post-alloy after high-temperature creep loading strain 4% is shown in FIG. 1, and the microstructure of the turbine blade is shown in FIG. 2. Figure 4 It can be seen that: the blade has obvious γ' rafting phenomenon, and the blade is subjected to recovery heat treatment, and the specific process is as follows. Figure 4

[0062] Solution treatment: the turbine blade after coating removal after corrosion is placed in a vacuum air quenching furnace, vacuumized to 10 -2 Pa or below, then Ar is filled to a gas pressure of 2×10 4 Pa, in a high-purity Ar (≥99.99%) atmosphere: the furnace temperature is raised from room temperature to 1300℃ at a temperature raising rate of 25℃ / min, and is kept at this temperature for 5h to perform first-stage solution treatment; after the keeping, the furnace temperature is raised from 1300℃ to 1310℃ at a temperature raising rate of 4℃ / min, and is kept at this temperature for 3h to perform second-stage solution treatment; after the keeping, the furnace temperature is raised from 1310℃ to 1340℃ at a temperature raising rate of 4℃ / min, and is kept at this temperature for 3h to perform third-stage solution treatment; after the keeping, the turbine blade is air-cooled to room temperature, and a turbine blade after third-stage solution treatment is obtained.

[0063] Aging treatment: the turbine blade after third-stage solution treatment is placed in a vacuum air quenching furnace, vacuumized to 10 -2 Pa or below, then Ar is filled to a gas pressure of 2×10 4 Pa, in a high-purity Ar (≥99.99%) atmosphere: the furnace temperature is raised from room temperature to 1130℃ at a temperature raising rate of 22℃ / min, and is kept at this temperature for 5h to perform first-step aging treatment, and after the keeping, air-cooled to room temperature; again, the furnace temperature is raised from room temperature to 850℃ at a temperature raising rate of 24℃ / min, and is kept at this temperature for 24h to perform second-step aging treatment, and after the keeping, air-cooled to room temperature, and a repaired turbine blade is obtained.

[0064] ​From the above examples, by the heating mode of continuous heating, the nickel-based single crystal superalloy turbine blade with coating removed is fully solution treated, the strengthening phase γ' phase in the alloy is fully solution treated to the matrix alloy, and then air cooling is adopted for cooling; then two-step aging treatment is adopted, the strengthening phase γ' is precipitated in coherent form, and air cooling is also adopted for cooling, so that the alloy structure can be restored to the original morphology.

[0065] The element segregation coefficient distribution diagram of the pre-damage standard heat treatment state and the post-damage recovery heat treatment of the embodiment is shown in Figure 5 It is found that the recovery heat treatment can restore the alloy to the standard heat treatment level before damage.

[0066] Example 4

[0067] In this embodiment, a second-generation nickel-based single crystal superalloy turbine blade for an aero-engine is taken as the repair object, and the chemical composition is (wt%): Al: 5%, Ta: 5.5%, Mo: 5%, Co: 8%, Cr: 8%, W: 6%, Re: 3%, and the balance is Ni. After high-temperature creep loading strain of 5%, the alloy blade is subjected to recovery heat treatment, and the specific process is as follows.

[0068] Solution treatment: the turbine blade after corrosion and coating removal is placed in a vacuum air quenching furnace, vacuumized to 10 -2 Pa, then Ar is filled to a gas pressure of 2×10 4 Pa, in a high-purity Ar (≥99.99%) atmosphere: the furnace temperature is raised from room temperature to 1285℃ at a rate of 25℃ / min, and is kept at this temperature for 6h for primary solution treatment; after the holding period, the furnace temperature is raised from 1285℃ to 1320℃ at a rate of 5℃ / min, and is kept at this temperature for 4h for secondary solution treatment; after the holding period, the furnace temperature is raised from 1320℃ to 1345℃ at a rate of 3℃ / min, and is kept at this temperature for 4h for tertiary solution treatment; after the holding period, the turbine blade is air cooled to room temperature, and the turbine blade after tertiary solution treatment is obtained.

[0069] Aging treatment: the turbine blade after tertiary solution treatment is placed in a vacuum air quenching furnace, vacuumized to 10 -2 Pa, then Ar is filled to a gas pressure of 2×10 4 Pa, in a high-purity Ar (≥99.99%) atmosphere, the furnace temperature is raised from room temperature to 1150℃ at a rate of 25℃ / min, and is kept at this temperature for 6h for the first step of aging treatment, and after the holding period, air cooling is adopted to cool to room temperature, and then the furnace temperature is raised from room temperature to 870℃ at a rate of 22℃ / min, and is kept at this temperature for 23h for the second step of aging treatment, and after the holding period, air cooling is adopted to cool to room temperature, and the repaired turbine blade is obtained.

[0070] From the above examples, it can be seen that, by using the heating method of continuous temperature rise, the nickel-based single crystal superalloy turbine blade with the coating removed is fully solution treated, so that the strengthening phase γ' phase in the alloy is fully solution treated into the base alloy, and then air cooling is performed; then two-step aging treatment is performed, so that the strengthening phase γ' is precipitated in a coherent form, and air cooling is also performed, so that the alloy structure can be restored to the original morphology.

[0071] The high-temperature creep curve (1100℃ / 137MPa) of the standard heat treatment state and the recovery heat treatment after damage of the embodiment is shown in Figure 6 , and it can be seen from Figure 6 that: the high-temperature creep performance of the alloy after recovery heat treatment of the embodiment is similar to that before damage, and therefore, the recovery heat treatment method of the embodiment is beneficial to the recovery of the alloy performance to the standard heat treatment state.

[0072] Comparative Example 1

[0073] Comparative Example 1 takes a second-generation nickel-based single crystal superalloy turbine blade for an aircraft engine as the repair object, and the chemical composition is (wt%): Al: 5%, Ta: 5.5%, Mo: 5%, Co: 8%, Cr: 8%, W: 6%, Re: 3%, and the balance is Ni. The blade is subjected to recovery heat treatment, and the specific process is as follows.

[0074] Solution treatment: the alloy standard heat treatment solution process is used, the corroded turbine blade is placed in a vacuum air quenching furnace, vacuum is extracted to 10 -2 Pa below, then Ar is filled to a gas pressure of 2×10 4 Pa, in a high-purity Ar (≥99.99%) atmosphere, the furnace temperature is raised from room temperature to 1330℃ at a temperature rise rate of 25℃ / min, and is kept at this temperature for 6h, after the end of the heat preservation, the turbine blade is air cooled to room temperature, to obtain the turbine blade after solution treatment.

[0075] Aging treatment: the turbine blade after solution treatment is placed in a vacuum air quenching furnace, vacuum is extracted to 10 -2 Pa below, then Ar is filled to a gas pressure of 2×10 4 Pa, in a high-purity Ar (≥99.99%) atmosphere, the furnace temperature is raised from room temperature to 1150℃ at a temperature rise rate of 20℃ / min, and is kept at this temperature for 3h, after the end of the heat preservation, air cooling is performed to room temperature, and then the furnace temperature is raised from room temperature to 870℃ at a temperature rise rate of 22℃ / min, and is kept at this temperature for 24h, after the end of the heat preservation, air cooling is performed to room temperature, to obtain the repaired turbine blade.

[0076] The alloy in Comparative Example 1 has a structure after recovery heat treatment as shown in Figure 2As shown in the right side of the figure in the figure, by comparison, it is obvious that the recovery heat treatment process of the embodiment of the present application is easier to restore the damaged alloy to the heat treatment state morphology.

[0077] In the comparative example 1, the high temperature creep performance of the alloy after recovery heat treatment is as shown in the figure. Figure 6 In contrast, the performance of the comparative example 1 after recovery heat treatment is much lower than the performance of the alloy after recovery heat treatment of the embodiment of the present application and the performance of the heat treatment state alloy. It can be seen that the embodiment of the present application is more beneficial to the recovery of the alloy performance to the standard heat treatment state.

[0078] Comparative example 2

[0079] The comparative example 2 uses the scheme of the patent "CN115584455 B". The second generation nickel-based single crystal superalloy is used as the repair object. The chemical composition of the second generation nickel-based single crystal superalloy is Al 7.5wt%, Ta 3wt%, Mo 8wt%, Cr 2wt%, Re 2wt%, Y 0.05wt%, and Ni balance. The solid solution temperature range of the γ' phase of the second generation nickel-based single crystal superalloy is 1295-1320℃ (i.e. the initial solid solution temperature is 1295℃, and the complete solid solution temperature is 1320℃). The single crystal test rod of the second generation nickel-based single crystal superalloy is processed into a standard creep test sample with a gauge section length of 25mm and a diameter of Φ5. The creep interruption test is carried out under the test conditions of a temperature of 1100℃ and a pressure of 137MPa. The creep interruption is carried out when the creep strain of the sample reaches 2.5%, and the creep damaged sample is obtained. The recovery heat treatment is carried out on the sample after creep damage. The solid solution treatment: the creep damaged sample is placed in a vacuum air quenching furnace, vacuumized to 10 -2 Pa below, then Ar is filled to a gas pressure of 2×104Pa, in a high-purity Ar (≥99.99%) atmosphere, the furnace temperature is raised from 25℃ to 1300±5℃ at a temperature raising rate of 10℃ / min, and the temperature is kept for 12h at this temperature. After the keeping temperature ends, the furnace temperature is raised from 1300℃ to 1320℃ at a temperature raising rate of 5℃ / min, and the temperature is kept for 10h at this temperature. After the keeping temperature ends, Ar gas is filled into the vacuum air quenching furnace through the gas station to quench the sample at a cooling rate of 250±50℃ / min to 25℃, and the solid solution sample is obtained. The aging treatment: the solid solution sample is placed in a vacuum air quenching furnace, vacuumized to 10 -2 Pa below, then Ar is filled to a gas pressure of 2×10 4Pa, in a high-purity Ar (≥99.99%) atmosphere, the furnace temperature is raised from 25°C to 1050±5°C at a temperature raising rate of 10°C / min, and is kept at this temperature for 2h, after the end of the keeping, the vacuum furnace is filled with Ar gas through the gas station, so that the sample is cooled to 25°C at a cooling rate of 250±50°C / min, to obtain the repaired sample. The alloy structure is basically restored to the initial morphology, the γ' phase shows good cubic structure, and the TCP phase is basically eliminated. Creep test is carried out at a temperature of 1100°C and a pressure of 137MPa.

[0080] The improvement of the creep life of the alloys of Comparative Example 2 and Example 1 after the recovery heat treatment is shown as Figure 7 It can be found that the life of the alloy of Comparative Example 2 after the recovery heat treatment is improved by nearly 20 hours, while the life of the alloy of Example 1 of the present application after the recovery heat treatment is improved by nearly 50 hours, therefore, the performance of the alloy after the recovery heat treatment of the present application is more excellent, and the scheme of the present application is obviously superior to the effect of Comparative Example 2.

[0081] The above is only the preferred embodiment of the present application, and does not limit the present application in any form, any simple modification, equivalent change and modification of the above embodiment according to the technical essence of the present application still belongs to the scope of the technical scheme of the present application.

Claims

1. A method of recovery heat treatment of a second generation nickel-base single crystal superalloy, characterized in that, The second generation nickel-based single crystal superalloy is a nickel-based single crystal superalloy with microstructure damage under steady-state creep loading to be repaired; wherein the following steps are carried out under vacuum or protective atmosphere: First-stage solid solution treatment: the nickel-based single crystal superalloy to be repaired is heated to a first temperature at a first set rate, and is kept at the first temperature for 4-6h; wherein the first temperature is 1280-1300℃; the first set rate is 20-25℃ / min; Second-stage solid solution treatment: the temperature of the nickel-based single crystal superalloy after the first-stage solid solution treatment is increased to a second temperature at a second set rate from the first temperature, and is kept at the second temperature for 2-4h; wherein the second temperature is 1300-1320℃, and the second temperature is higher than the first temperature; the second set rate is 3-5℃ / min; Third-stage solid solution treatment: the temperature of the nickel-based single crystal superalloy to be repaired after the second-stage solid solution treatment is increased to a third temperature at a third set rate from the second temperature, and is kept at the third temperature for 2-4h, and after cooling, the nickel-based single crystal superalloy after the third-stage solid solution treatment is obtained; wherein the third temperature is 1320-1350℃, and the third temperature is higher than the second temperature; the third set rate is 3-5℃ / min; First-step aging treatment: the nickel-based single crystal superalloy after the third-stage solid solution treatment is heated to 1100-1150℃, and is subjected to first-step aging treatment, and after cooling, the nickel-based single crystal superalloy after the first-step aging treatment is obtained; wherein the time of the first-step aging treatment is 4-8h; wherein the heating rate of the nickel-based single crystal superalloy after the third-stage solid solution treatment to 1100-1150℃ is 20-25℃ / min; Second-step aging treatment: the nickel-based single crystal superalloy after the first-step aging treatment is heated to 840-880℃, and is subjected to second-step aging treatment, and after cooling, the repaired nickel-based single crystal superalloy is obtained; wherein the time of the second-step aging treatment is 20-24h; wherein the heating rate of the nickel-based single crystal superalloy after the first-step aging treatment to 840-880℃ is 20-25℃ / min.

2. The method of recovery heat treatment of a second generation nickel-base single crystal superalloy according to claim 1, characterized in that, The nickel-based single crystal superalloy after the third-stage solid solution treatment is a γ single-phase microstructure.

3. The method of recovery heat treatment of a second generation nickel-base single crystal superalloy according to claim 2, characterized in that, The γ and The forming elements of the phases are uniformly distributed, thereby suppressing the phenomenon of composition segregation.

4. The method of claim 1, wherein the second generation nickel-base single crystal superalloy is a PWA1480 alloy. After the first aging treatment and the second aging treatment, The phase interfaces are coherent with each other in a coherent form, forming a cubic structure with regular arrangement; and / or The first step aging treatment is used to regulate the size of the phase, controlling its edge length to be 300-400 nm; and / or The second step aging treatment is used to control The morphology of the phases, making it evolve into uniform cubic, γ The phase interface exists in a coherent state.

5. The recovery heat treatment method of the second generation nickel-based single crystal superalloy according to claim 1, characterized in that, the first-stage solid solution treatment, the second-stage solid solution treatment, the third-stage solid solution treatment, the first-step aging treatment, and the second-step aging treatment are all carried out in a vacuum muffle furnace; and / or in the third-stage solid solution treatment, the first-step aging treatment, and the second-step aging treatment, air cooling is selected as the cooling mode.

6. The recovery heat treatment method of the second generation nickel-based single crystal superalloy according to claim 1, characterized in that, the second generation nickel-based single crystal superalloy is a second generation nickel-based single crystal superalloy containing Re; wherein the content of Re in the second generation nickel-based single crystal superalloy is 1.5-3wt%.

7. The recovery heat treatment method of the second generation nickel-based single crystal superalloy according to claim 1, characterized in that, The creep strain of the nickel-based single crystal superalloy to be repaired is less than or equal to 5.0%; and / or The nickel-based single crystal superalloy to be repaired is a nickel-based single crystal superalloy turbine blade.

8. A repaired second generation nickel-base single crystal superalloy, characterized in that, The repaired second-generation nickel-based single crystal superalloy has a phase boundary of a γ' phase and a γ phase The phase boundary exists in a coherent manner. The phase boundary exists in a coherent manner. The repaired second-generation nickel-based single crystal superalloy is obtained by repairing the nickel-based single crystal superalloy to be repaired using the recovery heat treatment method of the second-generation nickel-based single crystal superalloy according to any one of claims 1-7.

9. The repaired second generation nickel-base single crystal superalloy of claim 8, wherein, The repaired second-generation nickel-based single crystal superalloy has The phase volume fraction is 65-70%.

10. The repaired second generation nickel-base single crystal superalloy of claim 8, wherein, The performance of the repaired second-generation nickel-based single crystal superalloy is restored to the state before the alloy is loaded to failure.

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