Single alloy gradient structure grain boundary serration method and application

Abstract

The invention relates to a single alloy gradient structure grain boundary serration method which comprises the following steps: preparing a halfpace sample of a single alloy for gradient thermal deformation, performing gradient thermal deformation, and performing controlled cooling and heating treatment for obtaining a serration grain boundary of a single alloy material. The invention further provides application of the method in the dual-performance turbine disc, and the dual-performance turbine disc is obtained through gradient thermal deformation in the single-alloy gradient structure grain boundary serration method in the radial direction of the turbine disc. The gradient structure interface prepared through gradient thermal deformation is more accurate in positioning, the thickness and position of a transition area are controllable, the precision is high, operation is simpler and more convenient, and the preparation cost is lower.

Description

Technical Field

[0001] The present invention relates to the field of hot working of superalloys. Background Art

[0002] The preparation of gradient structures can be classified into single alloy gradient structure preparation and dual alloy gradient structure preparation according to composition. The method of preparing dual alloy gradient structures is to connect a persistent and creep-resistant coarse-grained alloy and a high-strength fine-grained alloy by means of welding, hot isostatic pressing composite or superplastic forging. The technical difficulty in the preparation process of dual alloy gradient structures lies in how to solve the "weak connection" problem at the bonding zone of the two alloys. Because crack sources are extremely likely to form at the "weak connection" part, this is a fatal hidden danger for the safety of the gradient structure workpiece during use.

[0003] The preparation of single alloy gradient structures can avoid potential safety hazards that may exist in the connection of dissimilar metals, and significantly improve the safety factor of the entire material. At present, the industry mostly uses the Dual Microstructure Heat Treatment (DMHT) process to prepare single alloy dual-performance gradient structures. By forming a precisely controllable temperature gradient across the entire component, different regions of the same component can form differentiated microstructures. The core of this process lies in the precise design and manufacture of the process equipment, as well as the precise regulation of process parameters; since this process requires special electrical and control systems, the process is complex, costly, and prone to local abnormal grain growth to form mixed grain structures when approaching the tissue transformation temperature; at the same time, it is difficult to precisely control the thickness and size of the transition layer using this process, which is not conducive to the precise manufacture of dual-performance turbine disks.

[0004] Meanwhile, the turbine disk of an aeroengine operates under high temperature, high pressure and high rotational speed, and there are significant differences between the center and the edge. The center is connected to the shaft, with a lower service temperature and needs to withstand higher centrifugal stress; the edge contacts high-temperature gas, with a higher service temperature and lower centrifugal stress, and requires higher creep resistance. Research shows that fine-grained microstructures perform excellently under low temperature and high stress, while coarse-grained microstructures are more advantageous under high temperature and low stress. Therefore, dual-performance turbine disks with a radially gradient microstructure (fine grains at the disk center and coarse grains at the disk edge) can fully exert the performance potential of the alloy, increase the service temperature of the disk component, and are an important development direction for advanced aeroengine manufacturing technology.

[0005] Therefore, for components such as dual-performance turbine disks that serve in a complex high-temperature and high-load coupling environment, there is an urgent need to further improve their high-temperature mechanical properties, especially the high-temperature creep resistance of the coarse-grained region at the disk edge, and also a method to further reduce the cost of single alloy gradient structure preparation. Summary of the Invention

[0006] The object of the present invention is to avoid the deficiencies of the prior art and provide a single-alloy gradient structure grain boundary serration method and application that are low-cost, easy to operate, and carry out research around the serration of the grain boundaries of the dual-performance gradient structure to achieve the coordinated control of the microstructure of the single alloy gradient structure and the morphology of the serrated grain boundaries.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: A single-alloy gradient structure grain boundary serration method includes the following steps: Step 1: Prepare a stepped specimen of a single alloy for gradient hot deformation: The obtained stepped specimen by cutting includes a first hot deformation stage and a second hot deformation stage with a rectangular or square cross-section and a thickness ratio of 10:(5 - 7). The first hot deformation stage and the second hot deformation stage are integrally connected to the upper bottom surface and the lower bottom surface of the hot deformation trapezoidal stage respectively; Step 2: Gradient hot deformation: Under the condition that the strain rate is 0.01 - 0.1 s -1 , and the deformation temperature is 1170 - 1200 °C, perform gradient hot deformation on the stepped specimen, and the gradient hot deformation is such that the deformation amount of the first hot deformation stage is 40 - 70%, which is used to make the dynamic recrystallization more sufficient to obtain high-strength fine grains; at the same time, the second hot deformation stage is also deformed correspondingly to the same thickness as the first hot deformation stage, which is used to ensure that the second hot deformation stage cannot reach the dynamic recrystallization condition and maintain the high creep resistance of the original coarse grains in the gradient hot deformation; The gradient hot deformation processes the first hot deformation stage into a large-deformation fine grain area with high stress of the stepped material, and processes the second hot deformation stage into a small-deformation coarse grain area with low stress of the stepped material; when the single alloy material undergoes hot deformation, when the strain of the internal grains reaches the critical value, dynamic recrystallization will occur to form equiaxed grains; conversely, if the strain is less than the critical strain of the single alloy, dynamic recrystallization will not occur and static recovery and grain growth will occur after hot deformation, which has a great impact on the subsequent microstructure evolution. It is expected that the strain in the fine grain area is larger and dynamic recrystallization is more likely to occur, and the grains are significantly refined; the strain in the coarse grain area is small and it is difficult to induce dynamic recrystallization, thus maintaining the coarse grain structure state.

[0008] At this time, a transition area of the large-deformation fine grain area and the small-deformation coarse grain area is formed in the hot deformation trapezoidal stage during processing, which is used to obtain the interface range between the fine grains and the coarse grains, so as to realize the determination of the material tissue transition area through the thickness structure transition area of the stepped material; After the gradient hot deformation is completed, keep warm for 3 - 5 min, and then water-cool to room temperature to obtain a single alloy material with a gradient structure; Step 3: Controlled cooling heat treatment to obtain serrated grain boundaries of the single alloy material: Select the strengthening phase in the single alloy material with gradient structure. Use a solution temperature higher than the dissolution starting temperature of the strengthening phase for solution treatment. The solution time is 40 min to 2 h to fully dissolve the strengthening phase. After completion, cool at a cooling rate less than or equal to 4 °C / min and cool the single alloy material to 900 - 1050 °C, and finally water-cool to room temperature to obtain a stepped material with gradient structure and serrated grain boundaries.

[0009] It should be noted that although the controlled cooling process can form serrated grain boundaries to improve the grain boundary strength of the alloy and improve the high-temperature plasticity of the alloy, the slow cooling rate often leads to severe coarsening of the alloy, especially in the coarse grain area, weakening the intragranular structure and reducing the material strength instead; Therefore, in the present invention, under the condition of ensuring serrated grain boundaries, the fastest critical cooling rate is obtained to obtain the optimal comprehensive high-temperature performance.

[0010] Furthermore, the stepped specimen described in step one is obtained by cutting with a wire electrical discharge machine.

[0011] Furthermore, in the gradient hot deformation, the slope of the stepped surface of the hot deformed trapezoid remains unchanged to control the same gradient change in the deformation amount of the stepped materials with different thickness ratios during the gradient hot deformation.

[0012] Furthermore, after step one, it also includes surface cleaning and grinding treatment of the stepped specimen to unify the friction coefficient on the surface of the stepped specimen and reduce the influence of friction force on the material deformation during the gradient hot deformation; The specific steps of the cleaning and grinding treatment are as follows: First, remove the oil stain with acetone or alcohol, then use 80 - 240 mesh sandpaper or grinding wheel to coarsely grind to remove the oxide layer and defects, then use 400 - 800 mesh fine sandpaper to finely grind until the surface is uniform, and rinse with deionized water to remove debris after each grinding; finally, clean and dry thoroughly with anhydrous ethanol to ensure no residue on the surface and the surface finish meets the standard.

[0013] Furthermore, the gradient hot deformation of the trapezoidal specimen in step two is carried out in a thermo-mechanical simulator. At the same time, after the gradient hot deformation is completed, the deformed stepped specimen is sliced parallel to the compression axis for subsequent characterization.

[0014] Furthermore, the material of the stepped specimen of the single alloy is specifically: superalloy or magnesium alloy or stainless steel or titanium alloy.

[0015] Further, if the stepped sample material of the single alloy is a nickel-based superalloy, then in step three, the dissolution starting temperature of the γ' phase in the nickel-based superalloy is selected as 1200°C. In order to fully dissolve the γ' phase, 1210°C is chosen as the solution temperature, the solution time is 1 h, and it is cooled to 900°C at a cooling rate of 1 - 12°C / min, and finally water-cooled to room temperature, thus obtaining a stepped nickel-based superalloy material with a gradient structure and serrated grain boundaries.

[0016] During controlled cooling heat treatment, the change in the cooling rate has a great influence on the degree of grain boundary serration. Within a certain range, as the cooling rate decreases, it is beneficial to the precipitation and growth of the γ' phase at the grain boundary, and both the amplitude and wavelength of the bent grains will increase; when the cooling rate is too fast, the γ' phase and carbides do not have time to precipitate and grow, and may be distributed in a fine and dispersed state at the grain boundary, and it is impossible to induce the formation of serrated grain boundaries.

[0017] The present invention also provides an application of the single alloy gradient structure grain boundary serration method as described above in a dual-performance turbine disk. The material of the dual-performance turbine disk is a nickel-based superalloy. The structure of the disk center, disk rim, and the transition zone between the disk center and the disk rim adopts the stepped material structure composed of the first hot deformation stage, the second hot deformation stage, and the hot deformation trapezoidal stage; in the radial direction of the turbine disk, through the gradient hot deformation in the single alloy gradient structure grain boundary serration method, a dual-performance turbine disk is obtained.

[0018] The beneficial effects of the present invention are as follows: In order to reduce the cost of preparing the single alloy gradient structure, the present invention proposes a gradient hot deformation process. By controlling the temperature and stress-strain distribution during the deformation process, a gradient structure from fine grains to coarse grains is formed in the extension direction of the material; in the area perpendicular to the deformation direction, a gradient structure from fine grains to coarse grains is formed.

[0019] In order to reduce the cost of preparing the single alloy gradient structure and accurately control the position of the transition zone, the present invention proposes a new and effective process, namely gradient hot deformation. By controlling the temperature and stress-strain distribution during the deformation process, a gradient structure from fine grains to coarse grains is formed in the radial direction of the material. This method can achieve higher-precision control of the transition zone thickness and tissue gradient through the design of the blank shape. At the same time, on the basis of precisely regulating the gradient structure, by inducing the serration of the straight grain boundary through controlled cooling heat treatment, the crack initiation and propagation during the creep failure process of the alloy can be effectively inhibited, and the creep rupture strength and creep life of the alloy are significantly improved.

[0020] Compared with the existing gradient heat treatment process, the gradient structure interface prepared by the gradient hot deformation provided by the present invention is more accurately positioned, the thickness and position of the transition zone are controllable, with high precision, the operation is more convenient, and the preparation cost is lower.

[0021] Meanwhile, on the basis of precisely controlling the gradient structure, the present invention induces serration of the straight grain boundary through controlled cooling heat treatment, effectively suppressing crack initiation and propagation during the creep failure process of nickel-based superalloys, and significantly enhancing the creep rupture strength and creep resistance of the coarse grain region of the gradient structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of a stepped specimen of gradient thermoplastic deformation in Specific Example 1 of the present invention; Figure 2 is a schematic structural diagram of a stepped specimen of gradient thermoplastic deformation in Specific Example 2 of the present invention; Figure 3 is a schematic structural diagram of a stepped specimen of gradient thermoplastic deformation in Specific Example 3 of the present invention; Figure 4 is a schematic diagram of gradient thermoplastic deformation of the stepped specimen structure of the present invention; Figure 5 is a simulation result of gradient thermoplastic deformation of the stepped specimen structure of the present invention; Figure 6 is a schematic diagram of the principle of controlled cooling heat treatment of the present invention; Figure 7 is a micrograph of the gradient structure of the stepped specimen structure of the present invention; Figure 8 is a schematic diagram of the transformation between serrated grain boundaries and straight grain boundaries of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] The principles and features of the present invention will be described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0024] To achieve the above object, the present invention provides the following specific embodiments: Example 1: As Figures 4 to 8 shown, a method for serrating grain boundaries of a single alloy gradient structure includes the following steps: Step 1: Prepare a stepped specimen of a single alloy for gradient thermoplastic deformation: The stepped specimen cut by a wire electrical discharge machine includes a first thermoplastic deformation stage 1 and a second thermoplastic deformation stage 2 with a rectangular or square cross-section and a thickness ratio of 10:5 to 7. The first thermoplastic deformation stage 1 and the second thermoplastic deformation stage 2 are respectively integrally connected to the upper bottom surface and the lower bottom surface of the thermoplastic deformation trapezoidal stage 3; Among them, the material of the stepped specimen of the single alloy is specifically: superalloy or magnesium alloy or stainless steel or titanium alloy.

[0025] Step 2: Perform surface cleaning and grinding treatment on the stepped specimen to unify the friction coefficient of the surface of the stepped specimen and reduce the influence of friction on material deformation during gradient thermoplastic deformation; The specific steps of the cleaning and grinding treatment are: First, remove the oil stain with acetone or alcohol. Subsequently, use 80-240 mesh sandpaper or grinding wheel to coarsely grind to remove the oxide layer and defects. Then, use 400-800 mesh fine sandpaper to finely grind until the surface is uniform. After each grinding, rinse with deionized water to remove debris. Finally, clean and dry thoroughly with anhydrous ethanol to ensure no residue on the surface and the surface finish meets the standard.

[0026] Step three, as Figure 4 and Figure 5 shown, gradient thermal deformation: Under the conditions of strain rate of 0.01-0.1 s -1 , and deformation temperature of 1170-1200 °C, perform gradient thermal deformation on the stepped specimen. Moreover, the gradient thermal deformation is such that the deformation amount of the first thermal deformation stage 1 is 40-70%, which is used to make dynamic recrystallization more sufficient to obtain high-strength fine grains. At the same time, the second thermal deformation stage 2 is also deformed accordingly to the same thickness as the first thermal deformation stage 1, which is used to ensure that the second thermal deformation stage 2 cannot reach the dynamic recrystallization condition and maintain the high creep resistance of the original coarse grains in the gradient thermal deformation. The gradient thermal deformation processes the first thermal deformation stage 1 into a large-deformation fine-grain area with high stress of the stepped material, and processes the second thermal deformation stage 2 into a small-deformation coarse-grain area with low stress of the stepped material. The slope of the stepped surface of the thermally deformed trapezoidal stage 3 remains unchanged, which is used to control the same gradient change in the deformation amount of the stepped materials with different thickness ratios during the gradient thermal deformation.

[0027] At this time, a transition zone between the large-deformation fine-grain area and the small-deformation coarse-grain area is formed in the thermally deformed trapezoidal stage 3 during processing, which is used to obtain the interfacial range between the fine grains and the coarse grains, so as to realize determining the transition zone of the material structure through the thickness structure transition zone of the stepped material. After the gradient thermal deformation is completed, keep it warm for 3-5 minutes, and then cool it to room temperature with water, and a single alloy material with a gradient structure is obtained. The gradient thermal deformation of the trapezoidal specimen is carried out in a thermal simulation testing machine. At the same time, after the gradient thermal deformation is completed, the deformed stepped specimen is sliced parallel to the compression axis for subsequent characterization.

[0028] Step four, as Figure 6 shown, controlled cooling heat treatment is used to obtain serrated grain boundaries of the single alloy material: Select the strengthening phase in the single alloy material with a gradient structure. With a solution time of 40 minutes to 2 hours, it is used to fully dissolve the strengthening phase. Use a temperature higher than the dissolution starting temperature of the strengthening phase as the solution temperature for solution treatment. After completion, cool at a cooling rate less than or equal to 4 °C / min, and cool the single alloy material to 900-1050 °C, and finally cool it to room temperature with water, and a stepped material with serrated grain boundaries of a gradient structure is obtained.

[0029] Example 2: It is the same as Example 1, except that the stepped specimen material of the single alloy is a nickel-based superalloy. In step 4, the dissolution starting temperature of the γ' phase in the nickel-based superalloy is selected as 1200 °C. In order to fully dissolve the γ' phase, 1210 °C is selected as the solution temperature, the solution time is 1 h, and it is cooled to 900 °C at a cooling rate of 1-12 °C / min, and finally water-cooled to room temperature, thus obtaining a stepped nickel-based superalloy material with a gradient structure and serrated grain boundaries.

[0030] Example 3: The present invention also provides an application of the above-mentioned method for serrating grain boundaries of a single alloy gradient structure in a dual-performance turbine disk. The material of the dual-performance turbine disk is a nickel-based superalloy. The structure of the disk center, disk rim, and the transition zone between the disk center and the disk rim adopts the stepped material structure composed of the first hot deformation stage 1, the second hot deformation stage 2, and the hot deformation trapezoidal stage 3. In the radial direction of the turbine disk, through the gradient hot deformation in the method for serrating grain boundaries of a single alloy gradient structure, a dual-performance turbine disk is obtained.

[0031] As Figures 1 - 8 shown, in order to further illustrate the technical solution and technical effect of the present invention, the following specific examples are provided: Specific Example 1: A method for serrating grain boundaries of a superalloy gradient structure (Type T01) Step 1: Preparation of gradient hot deformation specimens Use a wire electrical discharge machine to cut out a stepped specimen as Figure 1 shown. The higher region on the left side of the specimen is the large deformation region, which is in direct contact with the mold and has a larger deformation during hot deformation. The lower region on the right side of the specimen is the small deformation region, which has a smaller deformation during hot deformation. The middle of the specimen is the transition region, connecting the large deformation region and the small deformation region, and the deformation amount decreases gradually in a gradient.

[0032] Step 2: Surface cleaning and polishing Perform surface cleaning and polishing on the stepped specimen to unify the friction coefficient of the sample surface and reduce the interference of friction force on the deformation data during the gradient hot deformation process.

[0033] Step 3: Gradient hot deformation As Figure 4 shown, use a thermal simulation testing machine to conduct a gradient hot deformation experiment, and the specific parameters are shown in Table 1. After the deformation is completed, it is immediately water-cooled to room temperature to retain the high-temperature structure. After the gradient hot deformation is completed, the deformed specimen is sliced parallel to the compression axis for subsequent characterization.

[0034] Step 4: Controlled cooling heat treatment Since the re-precipitation of phases is involved in the grain boundary serration process, the second phase inside the material needs to be solution-treated. Considering that the dissolution starting temperature of the γ' phase in the superalloy selected in this example is 1200 °C, in order to fully dissolve the γ' phase, 1210 °C is selected as the solution temperature and the solution time is set to 1 h. In the study of the controlled cooling heat treatment process, in order to study the influence of different cooling rates on the microstructure of the superalloy, as Figure 6 shown, after solution-treating the material at 1210 °C for 1 h, it is cooled to 900 °C at different cooling rates respectively, and then quenched in time to study its microstructural evolution. The specific process parameters of the controlled cooling heat treatment are shown in Table 2.

[0035] Specific Example 2: A method for serrating the grain boundaries of a superalloy with a gradient structure (Type T02) Step 1: Preparation of gradient thermally deformed specimens Use a wire electrical discharge machining (EDM) cutter to cut out a stepped specimen as Figure 2 shown, increasing the thickness of the small deformation zone and the amount of deformation in the small deformation zone on the basis of T01.

[0036] Step 2: Surface cleaning and polishing Perform surface cleaning and polishing on the stepped specimen to unify the friction coefficient of the sample surface and reduce the interference of friction force on the deformation data during the gradient thermal deformation process.

[0037] Step 3: Gradient thermal deformation As Figure 4 shown, use a thermal simulation testing machine to conduct gradient thermal deformation experiments. The specific parameters are shown in Table 1; after deformation, cool it to room temperature in time with water cooling to retain the high-temperature microstructure. After completing the gradient thermal deformation, cut the deformed specimen parallel to the compression axis for subsequent characterization.

[0038] Step 4: Controlled cooling heat treatment Since the re-precipitation of phases is involved in the grain boundary serration process, the second phase inside the material needs to be solution-treated. Considering that the dissolution starting temperature of the γ' phase in the superalloy selected in this example is 1200 °C, in order to fully dissolve the γ' phase, 1210 °C is selected as the solution temperature and the solution time is set to 1 h. In the study of the controlled cooling heat treatment process, in order to study the influence of different cooling rates on the microstructure of the superalloy, as Figure 6 shown, after solution-treating the material at 1210 °C for 1 h, it is cooled to 900 °C at different cooling rates respectively, and then quenched in time to study its microstructural evolution. The specific process parameters of the controlled cooling heat treatment are shown in Table 2.

[0039] Specific Example 3: A method for serrating the grain boundaries of a superalloy with a gradient structure (Type T03) Step 1: Preparation of gradient thermally deformed specimens Cut out a stepped specimen as shown in Figure 3 using a wire electrical discharge machining machine. The thickness of the small deformation zone is increased on the basis of T02, and the deformation amount of the small deformation zone is increased.

[0040] Step 2: Surface cleaning and polishing: Clean and polish the surface of the stepped specimen to unify the friction coefficient of the sample surface and reduce the interference of friction force on the deformation data during the gradient thermal deformation process.

[0041] Step 3: Gradient thermal deformation As shown in Figure 4 perform a gradient thermal deformation experiment using a thermal simulation testing machine. The specific parameters are shown in Table 1; after the deformation is completed, quickly cool it to room temperature in water to retain the high-temperature microstructure. After completing the gradient thermal deformation, slice the deformed specimen parallel to the compression axis for subsequent characterization.

[0042] Step 4: Controlled cooling heat treatment Since the precipitation of phases is involved in the grain boundary serration process, the second phase inside the material needs to be solution-treated. Considering that the dissolution starting temperature of the γ′ phase of the superalloy selected in this example is 1200 °C, in order to fully dissolve the γ′ phase, 1210 °C is selected as the solution temperature, and the solution time is set to 1 h. In the study of the controlled cooling heat treatment process, in order to study the influence of different cooling rates on the microstructure of the superalloy, as shown in Figure 6 after the material is solution-treated at 1210 °C for 1 h, cool it to 900 °C at different cooling rates respectively, and then quickly quench it to study its microstructural evolution. The specific process parameters of the controlled cooling heat treatment are shown in Table 2.

[0043] Table 1

[0044] Table 2

[0045] Research findings: (1) Use DEFORM simulation software to perform finite element analysis on the gradient thermal deformation of the superalloy in this example. The results are shown in Figure 5 . The left end of the specimen is the high-strain zone, indicating that this area has experienced large plastic deformation and is the place where the material is most stressed; the strain in the middle area shows a decreasing trend, indicating that the deformation of the material is progressive when subjected to external force; the right end of the specimen is the low-strain zone, indicating that the deformation here is small.

[0046] (2) As shown in Figure 7 , after the gradient thermal deformation, a gradient structure from fine grains to coarse grains is successfully formed in the area perpendicular to the deformation direction of the specimen, and the interface of the gradient structure is clearly distinguishable.

[0047] (3) When the cooling rate of controlled cooling heat treatment is greater than 4 °C / min, the cooling time is short at this time, and the γ' phase has no time to grow, resulting in a small protrusion amplitude. Moreover, the migration of grain boundaries is not obvious and the undulation is small. The superalloy only shows slight serration at some grain boundaries. When the cooling rate is less than or equal to 4 °C / min, a series of protrusions, that is, serrated grain boundaries, begin to appear on more and more grain boundaries. At this time, the γ' phase at the grain boundaries has enough time to grow and coarsen, and the grain boundary migration effect is also obvious, as Figure 8 shown. Therefore, 4 °C / min is the critical value of this example.

[0048] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for serrating grain boundaries of a single alloy gradient structure, characterized in that, It includes the following steps: Step 1: Prepare a stepped specimen of a single alloy for gradient hot deformation: The obtained stepped specimen by cutting includes a first hot deformation stage (1) and a second hot deformation stage (2) with a rectangular or square cross-section and a thickness ratio of 10: (5 - 7). The first hot deformation stage (1) and the second hot deformation stage (2) are integrally connected to the upper and lower bottom surfaces of the hot deformation trapezoidal stage (3) respectively; Step 2: Gradient hot deformation: At a strain rate of 0.01~0.1 s -1 , under the condition that the deformation temperature is 1170~1200 °C, gradient hot deformation is carried out on the stepped specimen, And the gradient hot deformation is such that the deformation amount of the first hot deformation stage (1) is 40 - 70%, which is used to make the dynamic recrystallization more sufficient to obtain high-strength fine grains. At the same time, the second hot deformation stage (2) is also deformed accordingly to be the same thickness as the first hot deformation stage (1), which is used to ensure that the second hot deformation stage (2) cannot reach the dynamic recrystallization condition and maintain the high creep resistance of the original coarse grains in the gradient hot deformation; The gradient hot deformation processes the first hot deformation stage (1) into a large-deformation fine grain area with high stress of the stepped material, and processes the second hot deformation stage (2) into a small-deformation coarse grain area with low stress of the stepped material; At this time, a transition area between the large-deformation fine grain area and the small-deformation coarse grain area is formed in the hot deformation trapezoidal stage (3) during processing, which is used to obtain the interface range between the fine grains and the coarse grains, so as to realize determining the transition area of the material structure through the thickness structure transition area of the stepped material; After the gradient hot deformation is completed, after heat preservation for 3 - 5 min, then water-cooled to room temperature, a single alloy material with a gradient structure is obtained; Step 3: Controlled cooling heat treatment to obtain serrated grain boundaries of the single alloy material: Select the strengthening phase in the single alloy material with a gradient structure, use a temperature higher than the dissolution starting temperature of the strengthening phase as the solution temperature, carry out solution treatment, and the solution time is 40 min - 2 h, which is used to make the strengthening phase dissolve sufficiently. After completion, cool at a cooling rate less than or equal to 4 °C / min, and cool the single alloy material to 900 - 1050 °C, and finally water-cool to room temperature, and a stepped material with serrated grain boundaries of a gradient structure is obtained.

2. The method for serrating grain boundaries of a single alloy gradient structure according to claim 1, characterized in that The stepped specimen described in Step 1 is obtained by cutting with a wire electrical discharge machine.

3. The method for serrating grain boundaries of a single alloy gradient structure according to claim 1, characterized in that In the gradient hot deformation, the slope of the stepped surface of the hot deformation trapezoidal stage (3) remains unchanged, which is used to control the same gradient change of the deformation amount of the stepped materials with different thickness ratios during the gradient hot deformation.

4. The method for serrating grain boundaries of a single alloy gradient structure according to claim 1, wherein, After Step 1, it also includes surface cleaning and grinding treatment of the stepped specimen, which is used to unify the friction coefficient of the surface of the stepped specimen and reduce the influence of friction force on the material deformation during the gradient hot deformation; The specific steps of the cleaning and grinding treatment are: First, remove the oil stain with acetone or alcohol, and then use 80 - 240 mesh sandpaper or grinding wheel to coarsely grind to remove the oxide layer and defects; then, use 400 - 800 mesh fine sandpaper to finely grind until the surface is uniform, and rinse with deionized water to remove debris after each grinding; finally, clean and dry thoroughly with anhydrous ethanol to ensure that there is no residue on the surface and the surface finish meets the standard.

5. The method for serrating grain boundaries of a single alloy gradient structure according to claim 1, characterized in that, The gradient hot deformation of the trapezoidal specimen in Step 2 is carried out in a hot simulation testing machine. At the same time, after the gradient hot deformation is completed, the deformed stepped specimen is sliced parallel to the compression axis for subsequent characterization.

6. The method for serrating grain boundaries of a single alloy gradient structure according to any one of claims 1-5, characterized in that, The material of the stepped specimen of the single alloy is a superalloy, a magnesium alloy, a stainless steel, or a titanium alloy.

7. The method for serrating grain boundaries of a single alloy gradient structure according to any one of claims 1-5, characterized in that, If the material of the stepped specimen of the single alloy is a nickel-based superalloy, then in Step 3, the starting temperature of dissolution of the γ' phase in the nickel-based superalloy is selected to be 1200°C. In order to fully dissolve the γ' phase, 1210°C is chosen as the solution temperature, the solution time is 1 h, and it is cooled to 900°C at a cooling rate of 1 - 12°C / min, and finally water-cooled to room temperature, thus obtaining a stepped nickel-based superalloy material with a gradient structure and serrated grain boundaries.

8. Application of the single-alloy gradient structure grain boundary serration method according to claims 1-7 in a dual-performance turbine disk, characterized in that The material of the dual-property turbine disk is a nickel-based superalloy. The structure of the disk center, disk rim, and the transition zone between the disk center and the disk rim of the turbine disk adopts the stepped material structure composed of the first hot deformation stage (1), the second hot deformation stage (2), and the hot deformation trapezoidal stage (3); in the radial direction of the turbine disk, through the gradient hot deformation in the single alloy gradient structure grain boundary serration method, a dual-property turbine disk is obtained.

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