A recovery treatment process for a heat-resistant corrosion-resistant directional alloy turbine blade

Abstract

The invention discloses a restoration treatment process for a heat-resistant corrosion-resistant directional alloy turbine blade, belonging to the technical field of turbine blade repair. The process includes: (1) performing internal metallurgical microstructure damage analysis and characterization and typical mechanical property tests on the part to be modified; (2) determining the damage mechanism and distribution characteristics of the part and evaluating whether hot isostatic pressing repair is required; (3) if creep holes of critical size and content are observed, then adopting hot isostatic pressing + restoration heat treatment; otherwise, directly performing restoration heat treatment; (4) using restoration heat treatment to repair the damaged microstructure and mechanical properties of the part: including high-temperature solution treatment and aging treatment carried out in sequence. This process effectively restores the microstructure and mechanical properties of the heat-resistant corrosion-resistant directional alloy turbine blade and prolongs the service life of the blade.

Description

Technical Field

[0001] The present invention relates to the technical field of turbine blade repair, and particularly relates to a restoration treatment process for a heat-resistant corrosion-resistant directionally alloyed turbine blade. Background Art

[0002] Turbine blades are the core hot-end components of aeroengines and gas turbines. Turbine blades usually encounter two types of damage forms in harsh service environments, including apparent damage and internal metallurgical structure damage. Apparent damage includes forms such as cracks, chipping, and wear of the blade, cracking and spalling of the protective coating, as well as corrosion and oxidation of the blade. Apparent damage is usually repaired by technical means such as welding, additive manufacturing repair technology, and re-preparation of the protective coating. The internal metallurgical structure damage generated during the service of turbine blades includes coarsening or rafting of the γ' phase, degradation and decomposition of carbides, precipitation of TCP harmful phases, and degradation of the grain boundary structure, etc. The internal metallurgical structure damage is usually repaired by a reasonable restoration heat treatment process for the structure and performance. The restoration treatment technology plays a very important role in the safe service of turbine blades, extending the service life, and reducing the economic cost.

[0003] Generally, the restoration treatment process of gas turbine blades mainly includes hot isostatic pressing (HIP) and rejuvenation treatment (RHT). Usually, before the rejuvenation treatment of gas turbine blades, hot isostatic pressing treatment is usually carried out. The main function of hot isostatic pressing is to eliminate service damage defects such as creep holes and microcracks and improve the service life of the blades. And the service of the blades usually does not reach the third stage of creep. If the size of the creep holes has not reached the critical level, hot isostatic pressing treatment is not necessary in the blade repair work. In order to obtain good tissue and property restoration, whether hot isostatic pressing treatment is needed or not, scientific and reasonable rejuvenation treatment is necessary. For the rejuvenation heat treatment process method of directional turbine blades, the selection of scientific and reasonable heat treatment process will have a crucial impact on the restoration of the degenerate structure and properties of the directional alloy. If the solution temperature is too high, it will bring a series of adverse effects on the restoration of the alloy structure and properties. Especially, too high solution temperature will bring the risks of primary melting and recrystallization to the directional blades. Therefore, in order to avoid recrystallization during the rejuvenation heat treatment of directional and single crystal high temperature blades, the homogenization solution heat treatment temperature usually adopted in the restoration treatment process of directional and single crystal blades is much lower than the solution temperature of the original alloy standard heat treatment. However, if the solution temperature is too low or the solution time is too short, the element segregation in the damaged alloy cannot be effectively eliminated or reduced. Not only the rafted γ′ and irregular coarse γ′ structures in the degenerate state cannot be effectively restored, but also it will have an important impact on the microstructure stability and mechanical properties of the alloy after repair. Therefore, mastering scientific and reasonable rejuvenation heat treatment process method is crucial for the effective restoration of the microstructure and mechanical properties of the hot corrosion resistant directional alloy turbine blades, extending the blade service life, improving the operation reliability and reducing the operation cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a restoration treatment process for hot corrosion resistant directional alloy turbine blades. Aiming at the service damage characteristics of long-life directional alloy turbine blades, this process conducts research on the influence of hot isostatic pressing and rejuvenation heat treatment processes on the internal metallurgical microstructure damage and typical mechanical properties of turbine blades, and establishes a restoration treatment process for long-life directional alloy turbine blades.

[0005] To achieve the above purpose, the following solutions are adopted in the present invention:

[0006] A restoration treatment process for hot corrosion resistant directional alloy turbine blades, which includes the following steps:

[0007] (1) Conduct internal metallurgical microstructure damage analysis and characterization and typical mechanical property tests on the directional alloy parts to be repaired;

[0008] (2) Analyze the test results according to step (1), determine the damage mechanism and distribution characteristics of the directionally solidified alloy part, and evaluate whether hot isostatic pressing (HIP) repair is required;

[0009] (3) If creep cavities with critical sizes and contents are observed inside the part in step (2), first perform hot isostatic pressing treatment and then perform recovery heat treatment; if no creep cavities with critical sizes and contents are observed inside the part in step (2), directly perform recovery heat treatment;

[0010] (4) Use recovery heat treatment to repair the damaged microstructure and mechanical properties of the part: including high-temperature solution treatment and aging treatment carried out in sequence.

[0011] In the above step (1), the directionally solidified alloy part to be repaired includes directionally solidified gas turbine blades that have served in power plants for a long time and long-term aging heat-resistant corrosion directionally solidified superalloy specimens under near-service conditions.

[0012] In the above step (1), the metallurgical microstructure damage includes the degradation of γ' phase, the degradation and decomposition of carbides, and the degradation of grain boundary structure; the typical mechanical property tests include creep properties and tensile properties.

[0013] In the above step (3), according to the research on the influence of hot isostatic pressing process on the microstructure and mechanical properties of directionally solidified alloy parts, determine the hot isostatic pressing process parameter conditions of directionally solidified alloy parts.

[0014] In the above step (4), the solution treatment needs to be carried out within the heat treatment window above the γ' phase solution temperature and below the incipient melting temperature.

[0015] During the solution treatment process in the above step (4), the high-temperature solution temperature is 1185 - 1220 °C, and the solution time is 2h - 4h; heating rate: the heating rate in the early stage of solution treatment heating (room temperature to 1000 °C) is controlled at ≤10 °C / min, and the heating rate in the later stage of solution treatment heating (1000 °C - high-temperature solution temperature) is controlled at ≤2 °C / min; cooling method: the cooling from the high-temperature solution temperature to 1000 °C is carried out by rapid argon fan cooling with a cooling rate > 20 °C / min, and then the cooling to room temperature is carried out by argon fan cooling.

[0016] In the above step (4), the aging treatment includes primary aging and secondary low-temperature aging carried out in sequence. The aging treatment is a process to promote the growth of the γ' phase nuclei precipitated after solution treatment and adjust them to appropriate sizes and morphologies.

[0017] In the above step (4), in the primary aging treatment, the process parameters are as follows: the primary aging temperature is 1120°C ± 10°C, the time is 2 h to 4 h. The cooling from the primary aging temperature to 900°C is carried out by rapid cooling with an argon fan at a cooling rate > 20°C / min, and then the cooling to room temperature is carried out by rapid cooling with an argon fan. The process parameters of the secondary low-temperature aging treatment are: the secondary low-temperature aging temperature is 850°C ± 10°C, the time is 20 h to 24 h, and the cooling method is rapid cooling with an argon fan.

[0018] In the above step (4), low-temperature aging pretreatment can be carried out first, and then high-temperature solution treatment.

[0019] After the restoration treatment by the process of the present invention, the microstructure in the directionally solidified superalloy parts has been fully restored, and the tensile and creep properties of the parts have been greatly restored.

[0020] The advantages and beneficial effects of the present invention are as follows:

[0021] Aiming at the urgent need for overhaul and maintenance of key core hot-end components of advanced engines and gas turbines in China, and focusing on the key problems in the long-term service damage and repair technology of directionally solidified turbine blades, the domestic DZ411 directionally solidified superalloy, which is widely used in gas turbine blades, and imported F-class gas turbine blades from power plants are selected as the research objects. A restoration treatment process method for long-life directionally solidified superalloy turbine blades is established, aiming at being applied to the engineering repair treatment of directionally solidified superalloy turbine blades. The present invention is of great significance for establishing the repair technology of directionally solidified superalloy turbine blades, extending the service life of turbine blades, reducing the operating cost of gas turbines, and improving the long-term service reliability of blades. Description of the Drawings

[0022] Figure 1 Schematic diagram for sampling the microstructure analysis and mechanical property test of the directionally solidified turbine blade in actual service.

[0023] Figure 2 Typical internal metallurgical microstructure damage of the directionally solidified turbine blade in actual service; among them: (a) γ' structure in the dendrite trunk; (b) γ' structure between dendrites; (c) grain boundary degradation and carbide decomposition structure; (d) internal dislocation configuration.

[0024] Figure 3 Internal metallurgical microscopic pore structure of the directionally solidified blade in long-term service.

[0025] Figure 4 Surface recrystallization structure of the directionally solidified blade in long-term service before and after restoration heat treatment; among them: (a) state before restoration heat treatment; (b) state after restoration heat treatment.

[0026] Figure 5is the typical microstructure of the directionally solidified blade after the rejuvenation heat treatment; where: (a) γ' structure in the dendrite trunk; (b) γ' structure between dendrites; (c) grain boundary and carbide rejuvenation structure; (d) internal dislocation configuration.

[0027] Figure 6 is the non-standard specimen of the mechanical properties of the directionally solidified blade after long-term service.

[0028] Figure 7 is the heat treatment equipment for long-term thermal exposure under near-service conditions; where (a) and (b) are views from different angles.

[0029] Figure 8 is the microstructure of DZ411 alloy after 900 °C long-term thermal exposure; where: (a) γ' structure in the dendrite trunk; (b) γ' structure between dendrites; (c) grain boundary degradation and carbide decomposition structure; (d) internal dislocation configuration.

[0030] Figure 9 is the microstructure of the damaged DZ411 alloy after hot isostatic pressing + rejuvenation heat treatment; where: (a) γ' structure in the dendrite trunk; (b) grain boundary and carbide rejuvenation structure.

[0031] Figure 10 is the microstructure of the damaged DZ411 alloy after rejuvenation heat treatment for re-service after 900 °C / 5000 h thermal exposure; where: (a) γ' structure in the dendrite trunk; (b) γ' structure between dendrites; (c) grain boundary degradation and carbide decomposition structure; (d) internal dislocation configuration. Specific implementation mode

[0032] The present invention will be described in detail below in conjunction with the drawings and embodiments.

[0033] The present invention provides a rejuvenation treatment process for a heat-resistant corrosion-resistant directionally solidified alloy turbine blade, including the following steps:

[0034] Step 1: The research objects of the present invention are the directionally solidified combustion turbine blades after long-term service in power plants and the heat-resistant corrosion-resistant directionally solidified superalloys under long-term aging under near-service conditions.

[0035] Step 2: For the directionally solidified combustion turbine blades with different operation durations in power plants and the heat-resistant corrosion-resistant directionally solidified superalloys with equivalent damage under long-term thermal exposure at different service temperatures, carry out the analysis and characterization of the internal metallurgical microstructure damage and the typical mechanical property tests of the directionally solidified alloy blades after long-term service.

[0036] Step 3: Based on the above steps, determine the damage mechanism and distribution characteristics of the directionally solidified alloy parts after long-term service, carry out the necessity assessment of hot isostatic pressing (HIP) repair, and specifically carry out the research on the influence of the hot isostatic pressing process on the microstructure and mechanical properties of the directionally solidified turbine blades, and further determine the hot isostatic pressing process parameter conditions of the directionally solidified alloy parts.

[0037] Step 4: Based on Steps 2 and 3, conduct research on the influence of recovery heat treatment (including stress relief low-temperature aging pretreatment, high-temperature solution treatment, and aging treatment) on the recrystallization control and microstructure recovery of directionally solidified alloy turbine blades.

[0038] Step 5: Based on the above steps, conduct research on the influence of recovery heat treatment on the typical mechanical properties of directionally solidified alloy turbine blades, and evaluate the recovery treatment process for long-term service directionally solidified turbine blades, including hot isostatic pressing and optimized process parameters for recovery heat treatment.

[0039] Step 6: After determining the recovery treatment process for long-term service directionally solidified alloy turbine blades based on the above steps, further conduct assessment and verification of the recovery treatment process, including the assessment of the typical properties of the blades after recovery heat treatment, as well as the research on the tissue damage characteristics and performance degradation laws during the re-service cycle after recovery treatment.

[0040] Step 7: Based on the above steps, establish a technical method for the recovery treatment process of long-life directionally solidified alloy turbine blades.

[0041] Example 1

[0042] This example is for the repair treatment of directionally solidified superalloy turbine blades, and the specific process is as follows:

[0043] Step 1: The research object of this example is the directionally solidified superalloy turbine blades that have served in a gas turbine power plant for 15,000 hours.

[0044] Step 2: For long-term service directionally solidified gas turbine blades, using analytical and testing means such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile creep testing machine, conduct analysis and characterization of the internal metallurgical microstructure damage (including the degradation of γ' phase, the degradation and decomposition of carbides, and the degradation of grain boundary tissue in the typical parts of the directionally solidified alloy blades after long-term service (the sampling positions are shown in Figure 1 ), and typical mechanical property tests (including creep and tensile properties). The typical tissue damage is shown in Figure 2 ).

[0045] Step 3: Based on the above steps, determine that the main damage mechanism of the long-term service directionally solidified turbine blades is the coarsening and coalescence growth of γ' phase, the degradation and decomposition of carbides, and the degradation of grain boundary tissue during long-term service. No obvious creep holes are observed in the blades (see Figure 3 ). Among them, the microstructure degradation in the upper half of the blade body, especially in the tip region, is the most serious. According to the damage characteristics and distribution characteristics of the blades, the hot isostatic pressing process will not be adopted in the recovery treatment process of the present invention (considering process cost, technical risk, and necessity), but directly use the recovery heat treatment method to repair the damaged tissue and mechanical properties of the long-term service directionally solidified blades.

[0046] Step 4: Based on Steps 2 and 3, perform recovery heat treatment on the long-term service directionally solidified blades. In the recovery heat treatment process, the solution temperature and heating rate are crucial for the recovery of the microstructure and properties of the directionally solidified alloy, especially for the control of recrystallization. The solution treatment needs to be carried out within the heat treatment window above the γ'-phase solution temperature and below the incipient melting temperature. Through the study of the influence of the solution temperature on the microstructure and mechanical properties of the long-term service directionally solidified alloy gas turbine blades, considering the recrystallization, incipient melting risk, and the maximum recovery of the microstructure and mechanical properties, the optimal solution temperature is 1200 ± 5 °C, and the solution time is 2 h to 4 h. The setting of the heating rate is crucial for the release of the residual stress inside the blades. In the present invention, the heating rate in the early stage of the solution treatment heating (room temperature to 1000 °C) is controlled at ≤ 10 °C / min, and the heating rate in the later stage of the solution treatment heating (1000 °C to 1200 °C) is controlled at ≤ 2 °C / min. Cooling parameter control: The cooling from 1200 °C to 1000 °C is carried out by rapid cooling with an argon fan (> 20 °C / min), and the subsequent cooling to room temperature is also carried out by rapid cooling with an argon fan. The aging treatment is a process to promote the growth of the γ'-phase nuclei precipitated after solution treatment and adjust them to an appropriate size and morphology. In this embodiment, the primary aging process parameters are: 1120 °C ± 10 °C / 2 h, the cooling from 1120 °C to 900 °C is carried out by rapid cooling with an argon fan (> 20 °C / min), and the subsequent cooling to room temperature is carried out by rapid cooling with an argon fan. The secondary low-temperature aging process parameters are: 850 °C ± 10 °C / 20 h to 24 h, and the cooling method is rapid cooling with an argon fan. The surface recrystallized microstructure of the blades before and after the recovery heat treatment is as Figure 4 shown. The results show that: compared with the blades in the service state, the increase in the surface recrystallized thickness of the blades after the recovery heat treatment is very small (3 - 5 μm), which is within the repair range during the preparation process of the secondary coating of the blades. After the recovery heat treatment, the microstructure of the tip cross-section of the blade is shown in Figure 5 , and it can be found that after the recovery heat treatment, the microstructure inside the blade, especially the γ'-phase structure, has been fully recovered.

[0047] Step 5: Based on the above recovery heat treatment process, carry out sampling and performance testing of the mechanical properties of the blade body after the recovery heat treatment. Due to the limitation of the blade wall thickness, the mechanical property specimens of the blade body adopt sheet-shaped non-standard specimens, and the specimen drawings are shown in Figure 6 .

[0048] The comparison data of the typical mechanical properties of the long-term service blades in the degraded state and the recovery heat treatment state are shown in Table 1 below. It can be found that the tensile and creep properties of the blades after the recovery heat treatment have been greatly recovered.

[0049] Table 1. Comparison data of typical mechanical properties of long-term service blades in the degraded state and the recovery heat treatment state

[0050]

[0051] Based on the study of the influence of the recovery heat treatment on the typical mechanical properties of the directional turbine blade in the above steps, the process parameters of the recovery heat treatment for the long-term service directional gas turbine blade are established as follows:

[0052] High-temperature solution temperature: 1200 ± 5 °C; solution time: 2 h to 4 h; heating rate: the heating rate in the early stage of the solution treatment heating (room temperature to 1000 °C) is controlled at ≤ 10 °C / min, and the heating rate in the later stage of the solution treatment heating (1000 °C to 1200 °C) is controlled at ≤ 2 °C / min; cooling method: the cooling from 1200 °C to 1000 °C is carried out by rapid cooling with an argon fan (> 20 °C / min), and the subsequent cooling to room temperature is carried out by rapid cooling with an argon fan.

[0053] Primary aging temperature: 1120 °C; time: 2 h to 4 h; the cooling from 1120 °C to 900 °C is carried out by rapid cooling with an argon fan (> 20 °C / min), and the subsequent cooling to room temperature is carried out by rapid cooling with an argon fan.

[0054] Secondary aging temperature: 850 °C; time: 20 h to 24 h; cooling method: carried out by rapid cooling with an argon fan.

[0055] Example 2

[0056] Step 1: The research object of this example is the DZ411 alloy with equivalent damage of long-term static thermal exposure under near-service conditions. The anti-thermal corrosion directional DZ411 high-temperature alloy test bars (specification: φ16mm * 220mm) used in the present invention are prepared by the liquid metal cooling (LMC) directional solidification process. The DZ411 directional test bars after standard heat treatment (SHT) are placed in a long-term aging furnace at 850 °C, 900 °C and 1000 °C (see Figure 7 ), and the thermal exposure time is ≥ 5000 hours.

[0057] Step 2: For the DZ411 alloy with equivalent damage of long-term static thermal exposure under near-service conditions in Step 1, using analysis and testing means such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile creep testing machine, the microscopic tissue damage of the DZ411 damaged alloy with different degrees is carried out (including the degradation of γ' phase, the degradation and decomposition of carbides and the degradation of grain boundary tissue. Taking the DZ411 alloy with long-term thermal exposure at 900 °C as an example, the typical tissue damage is shown in Figure 8 ) analysis and characterization and typical mechanical property testing.

[0058] Step 3: Based on the above steps, determine the degradation and decomposition of γ' phase and carbides, as well as the degradation characteristics of grain boundary structures, under different service temperatures in the near-service condition. The restoration treatment process in the present invention will adopt hot isostatic pressing + restoration heat treatment process to repair the tissue damage and mechanical properties of DZ411 directionally solidified superalloy after long-term service.

[0059] Step 4: Based on Steps 2 and 3, conduct restoration treatment research on DZ411 alloy with equivalent damage under long-term static thermal exposure at different service temperatures in the near-service condition. Generally, if creep cavities with critical sizes and contents appear inside the gas turbine blade, the repair treatment process of the blade usually includes hot isostatic pressing (HIP) and restoration heat treatment. The main function of hot isostatic pressing is to eliminate service defects such as creep cavities and microcracks and improve the service life of the blade. Although hot isostatic pressing can effectively eliminate creep cavities in the blade, there are also some adverse effects on the restoration of the blade. During the hot isostatic pressing process of the blade, the γ' phase and secondary MC, M 23 C6 and other carbide precipitation phases dissolve and grow back, and continuous and coarsened grain boundary structures are formed during the slow cooling process. In addition, there may be a risk of recrystallization for the repair of directionally solidified and single-crystal blades. And the service of the blade usually does not reach the third stage of creep. If the size of the creep cavity has not reached the critical level, hot isostatic pressing is not necessary in the blade repair work. Therefore, in order to obtain good tissue and performance restoration, restoration research on the microstructure and properties by hot isostatic pressing + restoration heat treatment has been carried out for DZ411 alloy with equivalent damage under long-term static thermal exposure at different service temperatures in the near-service condition.

[0060] For DZ411 alloy with equivalent damage under long-term static thermal exposure at different service temperatures in the near-service condition, conduct hot isostatic pressing treatment. The hot isostatic pressing process parameters are shown in Table 2 below:

[0061] Table 2 Hot isostatic pressing process parameters

[0062]

[0063] After hot isostatic pressing treatment, considering the maximum restoration of the alloy's microstructure and mechanical properties, the optimal solution temperature is set at 1205 °C and the solution time is 4 h. In the present invention, the heating rate in the early stage of solution treatment (from room temperature to 1000 °C) is controlled at 10 °C / min, and the heating rate in the later stage of solution treatment (1000 °C to 1205 °C) is controlled at 2 °C / min. Cooling parameter control: The cooling from 1205 °C to 1000 °C is carried out by rapid cooling with an argon fan (>20 °C / min), and the subsequent cooling to room temperature is also carried out by rapid cooling with an argon fan. Aging treatment is a process that promotes the growth of the γ' phase nuclei precipitated after solution treatment and adjusts them to an appropriate size and morphology. In this embodiment, the process parameters of the first-stage aging treatment are: 1120 °C / 2 h, the cooling from 1120 °C to 900 °C is carried out by rapid cooling with an argon fan (>20 °C / min), and the subsequent cooling to room temperature is carried out by rapid cooling with an argon fan. The process parameters of the second-stage low-temperature aging are: 850 °C / 24 h, and the cooling method is rapid cooling with an argon fan. After hot isostatic pressing + restoration heat treatment, the microstructure of DZ411 alloy is shown in Figure 9 , and it can be found that after restoration heat treatment, the microstructure inside the alloy, especially the γ' structure, has been fully restored.

[0064] Step Five: Considering that no obvious pores appear inside the static thermally exposed alloy, in the study on evaluating the influence of restoration treatment on the restoration of the mechanical properties of DZ411 damaged alloy, only the mechanical property tests of DZ411 damaged alloy after restoration heat treatment are carried out. The tensile and creep mechanical property specimens adopt national standard specimens (GB / T228.1 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature" / GB / T228.2 "Metallic materials - Tensile testing - Part 2: Method of test at elevated temperature").

[0065] The comparative data of the typical mechanical properties of the degraded state and the restored heat treatment state of DZ411 alloy with equivalent damage under long-term static thermal exposure at different service temperatures close to the service condition are shown in Table 3 below. It can be found that the tensile and creep properties of the material have been greatly restored after restoration heat treatment.

[0066] Table 3. Comparative data of typical mechanical properties of DZ411 alloy with equivalent damage under long-term static thermal exposure at different service temperatures close to the service condition in the degraded state and the restored

[0067] Table 3 Comparative data of typical mechanical properties of heat-treated alloy

[0068]

[0069]

[0070] Based on the research on the influence of the recovery heat treatment in the above steps on the microstructure recovery and typical mechanical properties of the damaged DZ411 alloy, the recovery treatment process parameters for the directionally solidified alloy gas turbine blades in long-term service are established as follows:

[0071] Hot isostatic pressing: The process parameters are shown in Table 2 in Step 4.

[0072] High-temperature solution temperature: 1200 ± 5 °C; solution time: 2 h to 4 h; heating rate: The heating rate in the early stage of the solution treatment heating (room temperature to 1000 °C) is controlled at ≤ 10 °C / min, and the heating rate in the later stage of the solution treatment heating (1000 °C to 1200 °C) is controlled at ≤ 2 °C / min; cooling method: The cooling from 1200 °C to 1000 °C is carried out by rapid cooling with an argon fan (> 20 °C / min), and then the cooling to room temperature is carried out by rapid cooling with an argon fan.

[0073] Primary aging temperature: 1120 °C; time: 2 h to 4 h; the cooling from 1120 °C to 900 °C is carried out by rapid cooling with an argon fan (> 20 °C / min), and then the cooling to room temperature is carried out by rapid cooling with an argon fan.

[0074] Secondary aging temperature: 850 °C; time: 20 h to 24 h; cooling method: Rapid cooling is carried out with an argon fan.

[0075] Step 6: In order to evaluate the recovery treatment process of the directionally solidified alloy blades, it is necessary to further study the damage law and service reliability of the directionally solidified alloy in the next service cycle after the recovery treatment. Therefore, after the near-service condition equivalent damage DZ411 alloy in the present invention is subjected to the recovery heat treatment, an equivalent damage static thermal exposure test (850 °C to 1000 °C, ≥ 5000 hours) is carried out on the directionally solidified alloy in the recovery heat treatment state under near-service condition conditions again to simulate the blade re-service process, and the differences in the microstructure degradation and property attenuation laws of the directionally solidified alloy blades in different service cycles before and after the recovery heat treatment are compared.

[0076] Taking the DZ411 alloy with static thermal exposure at 900 °C / 5000 h as an example, after the recovery heat treatment in Step 5, the static thermal exposure is carried out at 900 °C for 5000 h again. The research on the microstructure and properties of the directionally solidified alloy after re-service after the recovery heat treatment can be seen in Figure 10 and Table 4. The research results show that the recovery treatment can effectively repair the microstructure and properties of the damaged alloy, and the properties of the alloy after re-aging after the recovery heat treatment are basically equivalent to those of the primary aging. This experimental result shows that the re-service performance of the long-term service DZ411 directionally solidified alloy after the repair treatment is safe and reliable.

[0077] Table 4. Mechanical properties of the directionally solidified alloy after re-service after the recovery heat treatment

[0078]

[0079] Step 7: Based on the above steps, establish a restoration processing technology method for long-life directional alloy turbine blades.

Claims

1. A restoration treatment process for a heat-resistant corrosion-resistant directional alloy turbine blade, characterized in that: The process includes the following steps: (1) Conduct internal metallurgical microstructure damage analysis and characterization and typical mechanical property tests on the directionally solidified superalloy parts to be repaired; (2) Based on the analysis and test results in step (1), determine the damage mechanism and distribution characteristics of the directionally solidified superalloy parts, and evaluate whether hot isostatic pressing repair is required; (3) If creep cavities with critical dimensions and contents are observed inside the parts in step (2), first perform hot isostatic pressing treatment and then perform recovery heat treatment; if no creep cavities with critical dimensions and contents are observed inside the parts in step (2), directly perform recovery heat treatment; (4) Use recovery heat treatment to repair the damaged microstructure and mechanical properties of the parts: including high-temperature solution treatment and aging treatment carried out in sequence.

2. The restoration treatment process of the heat-resistant corrosion-resistant directionally alloyed turbine blade according to claim 1, characterized in that: The directionally solidified superalloy parts to be repaired described in step (1) include directionally solidified gas turbine blades that have served in power plants for a long time and directionally solidified superalloy specimens with long-term aging resistance to hot corrosion under near-service conditions.

3. The restoration treatment process of the heat-resistant corrosion-resistant directional alloy turbine blade according to claim 1, characterized in that: In step (1), the metallurgical microstructure damage includes the degradation of γ' phase, the degradation and decomposition of carbides, and the degradation of grain boundary structure; the typical mechanical property tests include creep properties and tensile properties.

4. The restoration treatment process of the heat-resistant corrosion-resistant directional alloy turbine blade according to claim 1, characterized in that: In step (3), based on the research on the influence of hot isostatic pressing process on the microstructure and mechanical properties of directionally solidified superalloy parts, determine the hot isostatic pressing process parameter conditions of the directionally solidified superalloy parts.

5. The restoration treatment process of the heat-resistant corrosion-resistant directional alloy turbine blade according to claim 1, characterized in that: In step (4), the solution treatment needs to be carried out within the heat treatment window above the γ' phase solution temperature and below the incipient melting temperature.

6. The restoration treatment process of the heat-resistant corrosion-resistant directionally solidified alloy turbine blade according to claim 5, characterized in that: During the solution treatment process in step (4), the high-temperature solution temperature is 1185 - 1220 °C, and the solution time is 2 h - 4 h; heating rate: the heating rate in the early stage of solution treatment heating is controlled at ≤10 °C / min, and the temperature in the early stage of solution treatment heating is set at room temperature to 1000 °C; the heating rate in the later stage of solution treatment heating is controlled at ≤2 °C / min, and the temperature in the later stage of solution treatment heating is set at 1000 °C - high-temperature solution temperature; cooling method: the cooling from high-temperature solution temperature to 1000 °C adopts argon fan rapid cooling with a cooling rate > 20 °C / min, and then the cooling to room temperature adopts argon fan rapid cooling.

7. The restoration treatment process of the heat-resistant corrosion-resistant directional alloy turbine blade according to claim 1, characterized in that: In step (4), the aging treatment includes primary aging and secondary low-temperature aging carried out in sequence. The aging treatment is a process to promote the growth of the γ' phase nuclei precipitated after solution treatment and adjust them to appropriate sizes and morphologies.

8. The restoration treatment process of the heat-resistant corrosion-resistant directionally solidified alloy turbine blade according to claim 7, characterized in that: In step (4), in the primary aging treatment, the process parameters are: primary aging temperature 1120 °C ± 10 °C, time 2 h - 4 h, the cooling from primary aging temperature to 900 °C adopts argon fan rapid cooling with a cooling rate > 20 °C / min, and then the cooling to room temperature adopts argon fan rapid cooling; the process parameters of the secondary low-temperature aging treatment are: secondary low-temperature aging temperature 850 °C ± 10 °C, time 20 h - 24 h, and the cooling method adopts argon fan rapid cooling.

9. The restoration treatment process of the heat-resistant corrosion-resistant directional alloy turbine blade according to claim 1, characterized in that: In step (4), low-temperature aging pretreatment is carried out before high-temperature solution treatment.

10. The restoration treatment process of the heat-resistant corrosion-resistant directional alloy turbine blade according to any one of claims 1-9, characterized in that: After the restoration treatment by this process, the microstructure in the directionally solidified superalloy parts is fully restored, and the tensile and creep properties of the parts are greatly restored.

Images