Single-crystal high-temperature alloy recrystallization control method based on eutectic and dislocation net regulation and control

Abstract

The invention belongs to the technical field of single-crystal high-temperature alloy recrystallization control, and discloses a single-crystal high-temperature alloy recrystallization control method based on eutectic and dislocation net regulation and control. The method comprises the following steps: 1, carrying out macroscopic corrosion treatment on an as-cast or deformed single-crystal high-temperature alloy sample, and removing eutectic crystals on the surface layer of the as-cast or deformed single-crystal high-temperature alloy sample; 2, heating the single-crystal high-temperature alloy sample treated in the step 1 from room temperature to trough temperature, and carrying out high-temperature circulating heat treatment for multiple times; and 3, carrying out standard heat treatment on the single-crystal high-temperature alloy sample subjected to the last high-temperature circulating heat treatment process. According to the method, the recrystallization driving force introduced by plastic deformation can be efficiently and stably reduced, so that the formation of a recrystallization structure is effectively inhibited in the subsequent solid solution heat treatment, and the method is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of single crystal superalloys, and more particularly, relates to a single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation. BACKGROUND

[0002] Single crystal superalloys are key hot end component materials for manufacturing aero-engine turbine blades and industrial gas turbine turbine blades due to their excellent high-temperature performance. However, in the single crystal superalloy preparation process, such as the metal and mold shell, core shrinkage inconsistency, shell removal treatment, sand blasting treatment and other process links, plastic deformation is easily introduced into the single crystal superalloy. These plastic deformations are prone to induce the formation of recrystallized structures with large-angle grain boundaries in the subsequent high-temperature solid solution heat treatment process. Such transverse grain boundaries of recrystallization constitute a weak link under high-temperature service conditions, posing a serious threat to the service life and reliability of single crystal blades. At present, the scrap rate caused by recrystallization even reaches more than 40%, greatly increasing the cost.

[0003] At present, the strategy for controlling recrystallization in industry mainly focuses on two directions: one is to optimize process parameters and operation procedures as much as possible to avoid or reduce plastic deformation before solid solution heat treatment; the other is to modify the surface of the blade, such as using coating or carburizing process, to improve its recrystallization resistance. However, the former is difficult to completely eliminate deformation in the actual complex production process, and may affect production; the latter will change the surface composition or state of the material, which may bring additional process complexity or potential adverse effects.

[0004] In contrast, recovery heat treatment is a proven effective and uniquely advantageous complementary means, which is usually arranged before standard heat treatment (the standard heat treatment of the present application includes solid solution heat treatment and aging treatment), and its core advantages are: (1) does not change the chemical composition of the alloy; (2) does not damage the surface topography and dimensional accuracy of the blade; (3) although the recovery heat treatment may temporarily change the morphology of the γ' phase, the subsequent solid solution and aging heat treatment will make it dissolve and precipitate again, restoring to normal size and distribution; (4) without the need to introduce additional special equipment, it is easy to integrate into the existing production line.

[0005] Conventional recovery heat treatment promotes dislocation motion at high temperatures, causing opposite dislocations to annihilate or recombine, thereby effectively reducing the recrystallization driving force stored by deformation. The recovery process is closely related to the dissolution of the γ' phase and pinning effect. Under a suitable heating rate, the dislocations pinned by the γ' phase can be released and annihilated smoothly and controllably, thereby eliminating the recrystallization driving force while avoiding the rapid motion of dislocations due to rapid γ' dissolution, which induces new recrystallization nucleation.

[0006] Although the recovery heat treatment has advantages, there are still obvious limitations in the prior art reports due to unclear deeper scientific principles (i.e. insufficient understanding of scientific principles of traditional methods), such as long processing cycle, narrow process window, poor applicability, complex control and low efficiency and the like. Therefore, it is urgent to propose a recrystallization control method of single crystal superalloy based on eutectic and dislocation network regulation. SUMMARY

[0007] The purpose of the present application is to propose a recrystallization control method of single crystal superalloy based on eutectic and dislocation network regulation in view of the deficiencies of the prior art. The method of the present application can efficiently and stably reduce the recrystallization driving force introduced by plastic deformation, thereby effectively inhibiting the formation of recrystallization structure in subsequent solid solution heat treatment, and is suitable for industrial production.

[0008] In the present application, the inventors believe that, generally speaking, the deformation inducing recrystallization is mainly concentrated in the eutectic between the dendrites, therefore, it is necessary to regulate the eutectic morphology and avoid eutectic evolution to induce recrystallization. At the same time, combined with the morphology evolution of dislocation network, the purpose of controlling recrystallization is achieved. Therefore, the present application provides a recrystallization control method of single crystal superalloy based on eutectic and dislocation network regulation in view of the limitations of the recovery heat treatment on the basis of the role of eutectic and dislocation network in the formation of recrystallization.

[0009] In order to achieve the above-mentioned purpose, the present application provides a recrystallization control method of single crystal superalloy based on eutectic and dislocation network regulation, which comprises the following steps: Step one: performing macro-etching treatment on the as-cast single crystal superalloy or the deformed single crystal superalloy sample to remove the surface eutectic of the as-cast single crystal superalloy or the deformed single crystal superalloy sample; Step two: heating the single crystal superalloy sample treated in step one from a valley temperature (T v ) to a peak temperature (T p ), and then cooling the single crystal superalloy sample from the peak temperature to the valley temperature to define a high-temperature cycle heat treatment process; and heating the single crystal superalloy sample treated in step one from room temperature to the valley temperature and undergoing multiple high-temperature cycle heat treatment processes; Step three: performing standard heat treatment on the single crystal superalloy sample after the last high-temperature cycle heat treatment process.

[0010] According to the present application, preferably, the as-cast single crystal superalloy is a single crystal superalloy after directional solidification without heat treatment.

[0011] According to the present application, preferably, the deformed single crystal superalloy sample is prepared by compression plastic deformation treatment of the as-cast single crystal superalloy.

[0012] According to the present application, preferably, the macro-etching process uses an etching solution of hydrogen peroxide and hydrochloric acid.

[0013] According to the present application, preferably, the volume ratio of the hydrogen peroxide to the hydrochloric acid is (1-2):1, and the mass concentration of the hydrochloric acid is 30-36%.

[0014] According to the present application, preferably, the etching time of the macro-etching process is 1-10 minutes, which is enough to remove the eutectic layer and avoid over-etching.

[0015] According to the present application, preferably, the valley temperature is 900-1150℃.

[0016] According to the present application, preferably, the peak temperature is 15-60℃ lower than the highest value of the solution heat treatment temperature of the single crystal superalloy.

[0017] According to the present application, preferably, in each high-temperature cycle heat treatment process, the heating rate is 2-5℃ / min, and the cooling rate is 5-10℃ / min.

[0018] According to the present application, preferably, in the second step, the single crystal superalloy sample after the first step is heated from room temperature to the valley temperature and undergoes 2-4 high-temperature cycle heat treatment processes. Preferably, the single crystal superalloy sample after the first step is heated from room temperature to the valley temperature and undergoes 3-4 high-temperature cycle heat treatment processes.

[0019] According to the present application, preferably, the single crystal superalloy sample after the first step is not subjected to heat preservation when heated to the valley temperature, when heated to the peak temperature, and when cooled to the valley temperature.

[0020] According to the present application, preferably, the third step includes: cooling the single crystal superalloy sample after the last high-temperature cycle heat treatment process from the valley temperature to room temperature (20℃) to obtain a high-temperature cycle heat treated single crystal superalloy sample; and performing solution heat treatment and aging heat treatment on the high-temperature cycle heat treated single crystal superalloy sample.

[0021] In the present application, cooling to room temperature can be achieved by furnace cooling or air cooling.

[0022] According to the present application, preferably, the third step includes: heating the single crystal superalloy sample after the last high-temperature cycle heat treatment process from the valley temperature to the solution heat treatment temperature, and then performing solution heat treatment and aging heat treatment in sequence.

[0023] The principle of controlling recrystallization in the present application is as follows: As-cast single-crystal superalloy test bars were prepared using a directional solidification apparatus and a spiral crystal selection method. Cylindrical samples (5mm diameter × 8mm) were cut from the test bars using wire cutting. The cylindrical surfaces of the samples were then compressed using a compression testing machine to induce plastic deformation, resulting in deformed samples. Figure 1 As shown, eutectic inevitably exists on the surface of single-crystal superalloys (cast single-crystal superalloy test bars), and this eutectic may induce recrystallization in the deformed single-crystal superalloy. Therefore, this invention removes the surface eutectic through macro-etching treatment, that is, hydrogen peroxide and hydrochloric acid aqueous solution are prepared into an etching solution in a certain proportion, and macro-etching is performed on cylindrical samples and deformed samples to obtain etched samples ( Figure 2 (Microstructure of the deformed sample after macro-etching treatment); turn on the heat treatment furnace, place the macro-etched cylindrical sample and the deformed sample into the heat treatment furnace, and proceed according to... Figure 4 The set heat treatment program is as follows: 240 minutes to heat from room temperature to 1100℃, 90 minutes to heat from 1100℃ to 1285℃, and 35 minutes to heat from 1285℃ to 1100℃. This high-temperature cyclic heat treatment process is repeated four times between 1100℃ and 1285℃. Upon completion of the final high-temperature cyclic heat treatment process (i.e., the temperature reaches 1100℃ again), furnace cooling is performed. Simultaneously, at the peak and trough temperatures of each high-temperature cyclic heat treatment (i.e., T... p1 T p2 T p3 T v1 T v2 T v3 Samples were taken out at each temperature point to observe their internal microstructure. Then, the single-crystal superalloy samples that had undergone the final high-temperature cyclic heat treatment process were quenched at 1315℃ for 60 seconds. After quenching, the samples were cut open to observe their internal microstructure. Through observation and analysis of the above microstructure, the principle of controlling recrystallization was found to be as follows: Figure 5 As shown, dislocations gradually disappear with the progress of high-temperature cyclic heat treatment. With the increase of the number of high-temperature cyclic heat treatments, the dislocation network gradually evolves from an irregular shape to a regular shape. Only a small amount of eutectic dissolves, but the dislocation density decreases, and the dislocation network becomes stable. Even under high-temperature short-time treatment (quenching at 1315℃ for 60s), most of the dislocation network near the eutectic remains stable, which delays the formation of small-angle grain boundaries.

[0024] The beneficial effects of the technical solution of the present invention are as follows: The single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation of the application aims to eliminate the eutectic on the surface layer of the single crystal superalloy which may induce recrystallization through early macro-etching, and then control the dislocation network and eutectic morphology through high-temperature cyclic heat treatment, efficiently and stably reduce the recrystallization driving force introduced by plastic deformation, so as to effectively inhibit the formation of recrystallization structure in the subsequent solid solution heat treatment, and is suitable for industrial production.

[0025] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

[0027] Figure 1 A surface eutectic structure diagram (metallographic microscope) of a cast single crystal superalloy test rod prepared by the single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation provided by the embodiment 1 of the application is shown.

[0028] Figure 2 A microstructure diagram (stereomicroscope) of a deformed sample after macro-etching treatment in the single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation provided by the embodiment 1 of the application is shown.

[0029] Figure 3 A sample structure diagram (metallographic microscope) after plastic deformation + standard heat treatment of the comparative example 1 is shown.

[0030] Figure 4 A high-temperature cyclic heat treatment process schematic diagram of the single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation provided by the embodiment 1 of the application is shown.

[0031] Figure 5 A schematic diagram of eutectic and dislocation network evolution and control recrystallization in the high-temperature cyclic heat treatment process of the single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation provided by the application is shown.

[0032] Figure 6 A sample structure diagram (metallographic microscope) after plastic deformation + macro-etching + 1 high-temperature cyclic heat treatment + standard heat treatment of the embodiment 1 of the application is shown.

[0033] Figure 7 A sample structure diagram (metallographic microscope) after plastic deformation + macro-etching + 3 high-temperature cyclic heat treatment + standard heat treatment of the embodiment 2 of the application is shown. DETAILED DESCRIPTION

[0034] Preferred embodiments of the present application will be described in more detail below. Although the following describes preferred embodiments of the present application, it is to be understood that the application can be carried out in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and fully convey the scope of the application to those skilled in the art.

[0035] Example 1

[0036] The present embodiment provides a single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation, which comprises the following steps: Step one: a cast DD419 single crystal superalloy test rod is prepared by a directional solidification device using a spiral selection method. A 5mm (diameter) x 8mm cylinder is cut from the test rod using wire cutting to obtain a cylindrical sample; the cylindrical surface of the cylindrical sample is compressed using a compression testing machine to produce a plastic deformation of about 3% strain to obtain a deformed sample; the deformed sample is subjected to macro etching treatment to remove the surface eutectic of the deformed sample; The etching solution used in the macro etching treatment is a mixture of hydrogen peroxide and hydrochloric acid aqueous solution, the volume ratio of the hydrogen peroxide and the hydrochloric acid aqueous solution is 1:1, and the mass concentration of the hydrochloric acid aqueous solution is 31%.

[0037] Step two: the deformed sample after step one is heated from the trough temperature 1100℃ to the peak temperature 1285℃ (time 90min), and then cooled from 1285℃ to 1100℃ (time 35min) to define a high temperature cycle heat treatment process; the deformed sample after step one is heated from room temperature to the trough temperature 1100℃ within 240min and undergoes the high temperature cycle heat treatment process once. The deformed sample after step one is not subjected to heat preservation treatment when heated to the trough temperature, when heated to the peak temperature, and when cooled to the trough temperature.

[0038] Step three: the single crystal superalloy sample after the high temperature cycle heat treatment process is heated from the trough temperature 1100℃ to the temperature for solid solution heat treatment, and then subjected to solid solution heat treatment and aging heat treatment. The solid solution heat treatment temperature of the present embodiment is 1315℃, and the time is 4 hours, and the cooling method is air cooling. The aging heat treatment of the present embodiment is divided into two steps, the first step is at a temperature of 1150℃ for 4 hours, and the cooling method is air cooling; the second step is at a temperature of 870℃ for 16 hours, and the cooling method is air cooling.

[0039] The sample after aging heat treatment is cut open using wire cutting, and the cut sample is treated by a standard metallographic treatment procedure, and the microstructure of the cut sample is observed, such as Figure 6, it is found that the sample after plastic deformation + macro corrosion + 1 high temperature cycle heat treatment + standard heat treatment has internal partial recrystallization.

[0040] Example 2

[0041] The difference between the present example and Example 1 is only that: The present example undergoes 3 high temperature cycle heat treatment processes; In the present example, the sample after aging heat treatment is cut open by wire cutting, and the sample after cutting is treated by a standard metallographic treatment procedure, and the structure of the sample after cutting is observed, such as Figure 7 , it is found that the sample after plastic deformation + macro corrosion + 3 high temperature cycle heat treatments + standard heat treatment has no internal recrystallization, which shows that the method of the present application effectively controls recrystallization.

[0042] Example 3

[0043] The present example provides a single crystal high-temperature alloy recrystallization control method based on eutectic and dislocation network regulation, which comprises the following steps: Step one: a DD419 single crystal high-temperature alloy test rod in as-cast state is prepared by a directional solidification device using a spiral selection method. A 5 (diameter) x 8 mm cylinder is cut from the test rod by wire cutting to obtain a cylindrical sample; the cylindrical surface of the cylindrical sample is compressed by a compression testing machine to produce a plastic deformation of about 3% strain to obtain a deformed sample; the deformed sample is subjected to macro corrosion treatment to remove the surface eutectic of the deformed sample; The corrosion solution used in the macro corrosion treatment is a mixture of hydrogen peroxide and hydrochloric acid aqueous solution, the volume ratio of the hydrogen peroxide and the hydrochloric acid aqueous solution is 1.5:1, and the mass concentration of the hydrochloric acid aqueous solution is 31%.

[0044] Step two: the deformed sample after step one is heated from the trough temperature 1050℃ to the peak temperature 1280℃ (time 100min), and then cooled from 1280℃ to 1050℃ (time 45min) to define a high temperature cycle heat treatment process; the deformed sample after step one is heated to the trough temperature 1050℃ within 240min and undergoes 4 high temperature cycle heat treatment processes; The deformed sample after step one is not subjected to heat preservation treatment when heated to the trough temperature, when heated to the peak temperature, and when cooled to the trough temperature.

[0045] Step three: the single crystal high-temperature alloy sample after the high temperature cycle heat treatment process is cooled from the trough temperature 1050℃ to room temperature to obtain a high temperature cycle heat treated single crystal high-temperature alloy sample; the high temperature cycle heat treated single crystal high-temperature alloy sample is heated to the solid solution heat treatment temperature within 2 hours for solid solution heat treatment and aging heat treatment; The temperature of the solution heat treatment of this example is 1315℃, the time is 4 hours, and the sample is air-cooled. The aging heat treatment of this example is divided into two steps, the first step is at a temperature of 1150℃ for 4 hours, air-cooled, and the second step is at a temperature of 870℃ for 16 hours, air-cooled.

[0046] This example cuts the sample after aging heat treatment using wire cutting, processes the cut sample through a standard metallographic processing procedure, and observes the microstructure of the cut sample. It is found that the sample after plastic deformation + macro corrosion + 4 times of high temperature cyclic heat treatment + standard heat treatment does not produce recrystallization inside, which shows that the method of the application effectively controls recrystallization.

[0047] Comparative Example 1

[0048] This comparative example provides a recrystallization control method for single crystal high-temperature alloy, which comprises the following steps: Step one: a cast DD419 single crystal high-temperature alloy test rod is prepared by a directional solidification device using a spiral selection method. A 5mm (diameter) x 8mm cylindrical sample is cut from the test rod using wire cutting, and the cylindrical surface of the cylindrical sample is compressed using a compression testing machine to produce a plastic deformation of about 3% strain, thereby obtaining a deformed sample; Step two: the deformed sample obtained in step one is subjected to solution heat treatment and aging heat treatment; The temperature of the solution heat treatment of this example is 1315℃, the time is 4 hours, and the sample is air-cooled. The aging heat treatment of this example is divided into two steps, the first step is at a temperature of 1150℃ for 4 hours, air-cooled, and the second step is at a temperature of 870℃ for 16 hours, air-cooled.

[0049] This comparative example cuts the sample after aging heat treatment using wire cutting, processes the cut sample through a standard metallographic processing procedure, and observes the microstructure of the cut sample. It is found that the sample after plastic deformation + macro corrosion + 4 times of high temperature cyclic heat treatment + standard heat treatment does not produce recrystallization inside, which shows that the method of the application effectively controls recrystallization. Figure 3 , it is found that the sample is almost completely recrystallized.

[0050] The above has described the embodiments of the application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A recrystallization control method for single-crystal high-temperature alloy based on eutectic and dislocation network regulation, characterized by, The method comprises the following steps: Step 1: macro-etching a cast single crystal superalloy or a deformed single crystal superalloy sample to remove the eutectic layer of the cast single crystal superalloy or the deformed single crystal superalloy sample; Step 2: heating the single crystal superalloy sample treated in step 1 from a valley temperature to a peak temperature, and then cooling the single crystal superalloy sample from the peak temperature to the valley temperature to define a high-temperature cycle heat treatment process; and heating the single crystal superalloy sample treated in step 1 from room temperature to the valley temperature and subjecting the single crystal superalloy sample to multiple high-temperature cycle heat treatment processes; Step 3: standard heat treatment of the single crystal superalloy sample subjected to the last high-temperature cycle heat treatment process.

2. The single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation according to claim 1, wherein the cast single crystal superalloy is a single crystal superalloy after directional solidification and before heat treatment; and the deformed single crystal superalloy sample is obtained by compressive plastic deformation treatment of the cast single crystal superalloy.

3. The single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation according to claim 1, wherein the etching solution used in the macro-etching treatment is a mixture of hydrogen peroxide and hydrochloric acid aqueous solution; preferably, the volume ratio of the hydrogen peroxide to the hydrochloric acid aqueous solution is (1-2):1, and the mass concentration of the hydrochloric acid aqueous solution is 30-36%. The etching time of the macro-etching treatment is 1-10 min.

5. The single crystal superalloy recrystallization control method based on eutectic and dislocation network regulation according to claim 1, wherein the valley temperature is 900-1150℃; and the peak temperature is 15-60℃ lower than the highest value of the solid solution heat treatment temperature of the single crystal superalloy. In each high-temperature cycle heat treatment process, the heating rate is 2-5℃ / min, and the cooling rate is 5-10℃ / min. In step 2, the single crystal superalloy sample treated in step 1 is heated from room temperature to the valley temperature and subjected to 2-4 high-temperature cycle heat treatment processes.

4. The peritectic and dislocation network based recrystallization control method for single crystal superalloys of claim 1, wherein, The single crystal superalloy sample treated in step 1 is not subjected to heat preservation treatment when heated to the valley temperature, when heated to the peak temperature, and when cooled to the valley temperature. Step 3 comprises cooling the single crystal superalloy sample subjected to the last high-temperature cycle heat treatment process from the valley temperature to room temperature to obtain a high-temperature cycle heat treated single crystal superalloy sample; and solid solution heat treatment and aging heat treatment of the high-temperature cycle heat treated single crystal superalloy sample. Step 3 comprises heating the single crystal superalloy sample subjected to the last high-temperature cycle heat treatment process from the valley temperature to a solid solution heat treatment temperature, and then sequentially performing solid solution heat treatment and aging heat treatment. ​ 6. The peritectic and dislocation network based recrystallization control method for single crystal superalloys of claim 1, wherein, ​ 7. The peritectic and dislocation network based recrystallization control method for single crystal superalloys of claim 1, wherein, ​ 8. The peritectic and dislocation network based recrystallization control method for single crystal superalloys of claim 1, wherein, ​ 9. The peritectic and dislocation network based recrystallization control method for single crystal superalloys of claim 1, wherein, ​ 10. The peritectic and dislocation network based recrystallization control method for single crystal superalloys of claim 1, wherein, ​

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