Heat treatment method and system for reinforcing and toughening additive forming heterogeneous nickel-based alloy

Abstract

The invention belongs to but is not limited to the technical field of nickel-based alloy additive manufacturing, and discloses a heat treatment method and system for reinforcing and toughening an additive-formed heterogeneous nickel-based alloy, and the chemical components of the additive-manufactured nickel-based alloy are qualitatively and quantitatively analyzed by utilizing EPMA; carrying out homogenization heat treatment design by utilizing Thermo-Calc software; based on the obtained heat treatment temperature and dendritic crystal spacing, a linear curve of distribution of elements along with time diffusion is obtained, and the optimal temperature and time of homogenization heat treatment of the nickel-based alloy are obtained; and respectively calculating TTT phase diagrams corresponding to dendritic crystal nuclei and interdendritic crystal regions by utilizing a TTT phase diagram module in JMatPro software, and obtaining the optimal temperature and time of the stress relief heat treatment of the nickel-based alloy based on the characteristics of the precipitated phase of the nickel-based alloy. According to the method, a uniform grain structure is obtained after the material is rapidly cooled, the residual stress level in a component is reduced, and the strength and toughness of the material are improved.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the field of nickel-based alloy additive manufacturing technology, and in particular relates to a heat treatment method and system for enhancing and toughening an additively formed heterogeneous nickel-based alloy. Background Art

[0002] Nickel-based alloy is an alloy with excellent mechanical properties and corrosion resistance under high temperature conditions. It is mainly based on nickel, with alloying elements such as chromium, molybdenum, tungsten, cobalt, aluminum, titanium, boron, and zirconium added. By controlling the types and contents of these elements, nickel-based alloys with different properties can be obtained. Nickel-based alloys usually have the characteristics of high strength, good toughness, excellent high-temperature oxidation resistance and corrosion resistance. Due to the excellent performance of nickel-based alloys, they are widely used as basic materials for key components such as aerospace engine components, offshore platform components, oil and gas transportation facilities, chemical reaction vessels, nuclear reactor components, and solar high-temperature molten salt pipeline pumps and valves. Traditional forged nickel-based alloys and nickel-based alloy welds have caused phase composition changes of different degrees and types during the heat treatment process. This is because the organizational structures formed by the two manufacturing methods are very different, and the heat treatment processes and results are naturally different. Although welding and additive manufacturing are both local non-equilibrium solidification forming processes, their microstructures are essentially very different because the temperature gradient and cooling rate of the two can differ by up to 3 orders of magnitude.

[0003] Laser additive manufacturing technology is widely used in high-quality forming of nickel-based alloys due to its advantages such as high energy density, small heat-affected zone, high forming quality, high level of automation, fast cooling rate, and grain refinement. However, the extreme deposition conditions in the additive manufacturing process, such as local rapid melting and solidification, and cyclic heating and cooling of the deposited layer by the subsequent deposited layer, often lead to special microstructures and chemical composition distributions in the formed parts. In addition, the large thermal expansion coefficient and local rapid melting and solidification of the material will also cause the nickel-based alloy manufactured by laser additive manufacturing to be at a high residual stress level. If not handled, it is likely to cause plastic deformation of the component and even the initiation of microcracks, which will eventually lead to fracture failure of the material at a stress level far below the expected allowable stress.

[0004] In summary, the problems existing in the prior art are:

[0005] (1) The large thermal expansion coefficient and the local rapid melting and solidification of the material will also cause the nickel-based alloy manufactured by laser additive manufacturing to be in a high level of residual stress. If it is not treated, it is likely to cause plastic deformation of the component and even the initiation of microcracks.

[0006] (2) The inhomogeneity of composition may lead to the formation of large-volume hard and brittle phases such as Laves phase and carbide in the enriched areas of elements such as Nb, Mo, C, and Si, which significantly reduces the mechanical properties and corrosion resistance of the material. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a heat treatment method and system for strengthening and toughening a heterogeneous nickel-based alloy formed by additive manufacturing.

[0008] The present invention is achieved by providing a heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy, comprising the following steps:

[0009] Step 1: Use electron probe microscopy (EPMA) to qualitatively and quantitatively analyze the chemical composition of the additively manufactured nickel-based alloy.

[0010] Step 2, designing homogenization heat treatment according to the element content of the nickel-based alloy using the diffusion module (DICTRA) of Thermo-Calc software;

[0011] Step 3, using the diffusion module (DICTRA) of Thermo-Calc software, based on the obtained heat treatment temperature and dendrite spacing, a linear curve of the distribution of element diffusion over time is obtained; the time when all elements truly achieve uniform diffusion is determined, and the optimal temperature and time for homogenization heat treatment of the nickel-based alloy are obtained;

[0012] Step 4, according to the EPMA quantitative analysis results of the composition of the dendrite core and the interdendritic region of the nickel-based alloy, the TTT phase diagram module in the JMatPro software is used to calculate the TTT phase diagrams corresponding to the dendrite core and the interdendritic region respectively;

[0013] Step 5: According to the TTT phase diagram corresponding to the dendrite core and the interdendritic region, based on the characteristics of the nickel-based alloy precipitation phase, the optimal temperature and time for stress relief heat treatment of the nickel-based alloy are obtained.

[0014] Furthermore, in step 1, the nickel-based alloy is qualitatively analyzed to determine that it has segregation characteristics, and its element content is measured in the dendrite core and inter-dendritic region.

[0015] Further, the step 2 specifically includes:

[0016] (1) EPMA was used to sample the dendrite core and interdendritic region at fixed points to obtain the quantitative analysis results of the composition differences between the two regions. Six sets of data were collected from each region and the average value was taken.

[0017] (2) In Thermo-Calc (DICTRA), the proportion of each element in the dendrite core and interdendritic region is used as the initial composition condition, and the composition distribution between the two regions is approximately simplified to a linear distribution. Then, the dendrite spacing is observed on the microstructure diagram of the formed nickel-based alloy and set according to the observed dendrite spacing;

[0018] (3) Select the appropriate heat treatment temperature according to the characteristics of different nickel-based alloys, and then calculate the composition distribution of each component after diffusing in the matrix phase for a certain period of time at the target temperature to determine the homogenization process.

[0019] Furthermore, in step three, an optical microscope is used to observe the microstructure, and the dendrite spacing is determined from the obtained microstructure image, and a suitable heat treatment temperature is selected according to the characteristics of the nickel-based alloy itself.

[0020] Furthermore, in step three, according to the obtained diffusion curve distribution and based on the principle of "ensuring complete diffusion and avoiding grain growth", the heat treatment time is determined, and the optimal temperature and time for homogenization heat treatment is 1150° C. for 1 hour.

[0021] Furthermore, in step five, based on the obtained TTT phase diagram, the stress relief effect, time control window and time cost are comprehensively considered to determine the temperature and time of stress relief heat treatment suitable for nickel-based alloys, and the optimal temperature and time of stress relief heat treatment are obtained as follows: keeping at 750°C for 2 hours and then slowly cooling with the furnace.

[0022] Another object of the present invention is to provide a heat treatment method for additively forming a heterogeneous nickel-based alloy to strengthen and toughen the heat treatment system for additively forming a heterogeneous nickel-based alloy to strengthen and toughen the heat treatment method, comprising:

[0023] Qualitative and quantitative analysis module, which uses electron probe microscopy (EPMA) to perform qualitative and quantitative analysis of the chemical composition of additively manufactured nickel-based alloys;

[0024] Homogenization heat treatment module, which uses the diffusion module (DICTRA) of Thermo-Calc software to design homogenization heat treatment according to the element content of nickel-based alloy;

[0025] The homogenization heat treatment parameter determination module uses the diffusion module (DICTRA) of Thermo-Calc software to obtain a linear curve of the distribution of elements diffused over time based on the heat treatment temperature and dendrite spacing; determines the time when all elements truly achieve uniform diffusion, obtains the optimal heat treatment temperature and time, and obtains the optimal solution for homogenization heat treatment of nickel-based alloys;

[0026] TTT phase diagram calculation module, based on the EPMA quantitative analysis results of the composition of the dendrite core and interdendritic region of the nickel-based alloy, uses the TTT phase diagram module in the JMatPro software to calculate the TTT phase diagrams corresponding to the dendrite core and interdendritic region respectively;

[0027] The stress relief heat treatment parameter determination module selects appropriate heat treatment temperature and time according to the TTT phase diagrams corresponding to the dendrite core and the interdendritic region, based on the characteristics of the precipitation phase of the nickel-based alloy, to obtain the stress relief heat treatment plan for the nickel-based alloy.

[0028] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the heat treatment method for enhancing and toughening the additively formed heterogeneous nickel-based alloy.

[0029] Another object of the present invention is to provide a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of the heat treatment method for enhancing and toughening the additively formed heterogeneous nickel-based alloy.

[0030] Another object of the present invention is to provide an information data processing terminal, which includes the heat treatment system for enhancing and toughening the additively formed heterogeneous nickel-based alloy.

[0031] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0032] First, the heat treatment method for strengthening and toughening the additively formed heterogeneous nickel-based alloy proposed in the present invention can not only enable the chemical components inside the material to fully diffuse and the harmful phases to completely dissolve, thereby obtaining a uniform grain structure after rapid cooling, but also reduce the residual stress level inside the component, thereby achieving performance improvements in material strength and toughness.

[0033] The present invention quantitatively analyzes nickel-based alloys and obtains the distribution curve of nickel-based alloy elements over time through thermodynamic simulation, providing a scientific basis for establishing a heat treatment system to achieve uniform composition of nickel-based alloys. This method is universal and provides a new idea for strengthening and toughening nickel-based alloys and even other metal material additive parts.

[0034] The present invention is based on the quantitative analysis results of the composition of the dendrite core and interdendritic region of the nickel-based alloy. Through the TTT phase diagram module in the JMatPro software, the TTT phase diagrams corresponding to the dendrite core and interdendritic region are calculated respectively. Based on the obtained TTT phase diagram, a scientific basis is provided for establishing stress relief heat treatment of the shaped nickel-based alloy with significant segregation. This method is universal and provides a reference and reference for the enhancement and toughening of nickel-based alloys and even other metal material additive parts.

[0035] Second, the expected benefits and commercial value of the technical solution of the present invention after transformation are as follows: The present invention provides a heat treatment method for strengthening and toughening a heterogeneous nickel-based alloy by additive forming, which reduces the time and energy consumption in the production process and can more accurately control the organizational structure of the material, thereby improving the strength and toughness of the product. This can not only improve the service life and reliability of the product, but also reduce the return and repair costs caused by quality problems.

[0036] The technical solution of the present invention solves the technical problem that people have been eager to solve but have never succeeded in solving: the technical solution solves the residual stress generated by the local rapid melting and solidification of the heterogeneous nickel-based alloy in additive forming, reduces the possibility of crack initiation, and solves the problem of mechanical property degradation caused by element segregation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a flow chart of a heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy provided by an embodiment of the present invention;

[0038] Figure 2 It is a structural diagram of a heat treatment system for strengthening and toughening an additively formed heterogeneous nickel-based alloy provided by an embodiment of the present invention;

[0039] Figure 3 This is a microstructure diagram of a deposited nickel-based alloy provided in Example 1 of the present invention; (a) axial direction; (b) axial enlargement; (c) radial direction; (d) radial enlargement;

[0040] Figure 4 The subgrain segregation results of the main chemical components of the deposited nickel-based alloy provided in Example 1 of the present invention are as follows: (a) Ni element; (b) Cr element; (c) Mo element; (d) Fe element; (e) Nb element; (f) Ti element;

[0041] Figure 5 It is the predicted result of the distribution of the main solute elements in the dendrite core and the interdendritic region in the nickel-based alloy provided in Example 1 of the present invention; (a) Mo element; (b) Nb element; (c) Ti element; (d) Cr element;

[0042] Figure 6is a microstructure diagram of the nickel-based alloy provided in Example 1 of the present invention after homogenization annealing;

[0043] Figure 7 The TTT phase diagrams of the dendrite core and inter-dendritic region of the formed nickel-based alloy provided in Example 1 of the present invention are respectively corresponding; (a) TTT phase diagram of the dendrite core region; (b) TTT phase diagram of the inter-dendritic region;

[0044] Figure 8 The microstructure of the nickel-based alloy provided in Example 1 of the present invention after stress relief annealing; (a) 2h microstructure; (b) partial enlarged view; (c) γ”;

[0045] Fig. 9 is the room temperature engineering stress-strain curve of the nickel-based alloy after the morphology and different heat treatments provided in Example 1 of the present invention;

[0046] Fig.10 These are the room temperature Charpy impact toughness measurement results of the nickel-based alloys after the as-formed and different heat treatments provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] like Figure 1 As shown, an embodiment of the present invention provides a heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy, comprising the following steps:

[0049] Step 1: Qualitative and quantitative analysis of additively manufactured nickel-based alloys;

[0050] Step 2: Based on the element content of the nickel-based alloy, the homogenization heat treatment design was carried out with the help of the diffusion module (DICTRA) of Thermo-Calc software;

[0051] Step 3: Obtain the homogenization heat treatment scheme of the nickel-based alloy according to the curve obtained in the diffusion module (DICTRA) of Thermo-Calc software;

[0052] Step 4: Based on the quantitative analysis results of nickel-based alloys, the TTT phase diagrams corresponding to the dendrite core and interdendritic region were calculated respectively with the help of the TTT phase diagram module in the JMatPro software;

[0053] Step 5: According to the TTT phase diagram corresponding to the dendrite core and the interdendritic region, the stress relief heat treatment scheme of the nickel-based alloy is obtained.

[0054] The following is a detailed and meticulous description of the above-mentioned heat treatment method for strengthening and toughening the heterogeneous nickel-based alloy for additive forming:

[0055] In step 1, electron probe microprobe technology (EPMA) is preferably used to perform qualitative and quantitative analysis of the chemical composition of the additively manufactured nickel-based alloy. The present invention determines that the nickel-based alloy has segregation characteristics through qualitative analysis, so there are significant differences in element distribution in different regions, so the element content is measured in the dendrite core and interdendritic region.

[0056] In step 2, the homogenization heat treatment design was carried out with the help of the diffusion module (DICTRA) of Thermo-Calc software. First, the dendrite core and interdendritic regions were sampled at fixed points by EPMA to obtain the quantitative analysis results of the composition difference between the two regions. Six sets of data were collected in each region and the average value was taken. Subsequently, the proportion of each element in the dendrite core and interdendritic regions was used as the initial composition condition in Thermo-Calc (DICTRA), and the composition distribution between the two regions was approximately simplified to a linear distribution. Then, the dendrite spacing was observed on the microstructure diagram of the morphological nickel-based alloy, and the setting was made according to the observed dendrite spacing. According to the characteristics of different nickel-based alloys, the appropriate heat treatment temperature is selected, and then the composition distribution of each component after diffusion in the matrix phase for a certain period of time at the target temperature is calculated to determine the homogenization process.

[0057] In step 3, according to the obtained diffusion curve distribution, based on the principle of "ensuring complete diffusion and avoiding grain growth", the heat treatment time is determined, and finally the homogenization heat treatment temperature and time are determined.

[0058] In one implementation scheme, an optical microscope is used to observe the microstructure, and the dendrite spacing is determined from the obtained microstructure image, and a suitable heat treatment temperature is selected according to the characteristics of the nickel-based alloy itself. Studies have found that if the heat treatment time is too short, the columnar crystals cannot be completely transformed into equiaxed crystals, and the selected heat treatment time will widen the annealing twins. In order to achieve complete recrystallization, grain coarsening is avoided as much as possible. Using the diffusion module (DICTRA) of the Thermo-Calc software, based on the heat treatment temperature and dendrite spacing, according to the simulation software, a linear curve of the distribution of elements diffused over time is obtained, and finally the time for all elements to truly achieve uniform diffusion is determined. The optimal heat treatment temperature and time are obtained, and the optimal heat treatment solution is determined.

[0059] In step 4, the chemical composition of the additively manufactured nickel-based alloy is qualitatively and quantitatively analyzed according to the preferred electron probe microanalysis (EPMA). The present invention determines that the nickel-based alloy has segregation characteristics through qualitative analysis, so there are significant differences in the element distribution in different regions, so the element content is measured in the dendrite core and interdendritic region. According to the EPMA quantitative analysis results of the composition of the dendrite core and interdendritic region of the nickel-based alloy, the TTT phase diagram corresponding to the dendrite core and interdendritic region is calculated respectively with the help of the TTT phase diagram module in the JMatPro software.

[0060] In step 5, according to the obtained TTT phase diagram, based on the characteristics of the precipitated phase of the nickel-based alloy, select the appropriate heat treatment temperature and time. The main factor affecting the quality of stress relief annealing is the heating temperature. If a relatively high temperature is selected, on the one hand, according to the characteristics of the nickel-based alloy, it may accelerate the precipitation of some phases that reduce the material properties, and the effective time window for stress removal will also be narrowed accordingly. On the other hand, if the selected temperature is too high, the strength and hardness of the workpiece will be greatly reduced, affecting the product quality, so the temperature should not continue to rise. If the heating temperature is selected too low, it will take a long heating time to fully eliminate the internal stress, affecting production efficiency. Therefore, based on the comprehensive consideration of stress relief effect, time control window and time cost, the temperature and time suitable for the stress relief heat treatment of this nickel-based alloy are selected to obtain the best stress relief heat treatment scheme.

[0061] like Figure 2 As shown, an embodiment of the present invention provides a heat treatment method for additively forming a heterogeneous nickel-based alloy to strengthen and toughen the heat treatment system for additively forming a heterogeneous nickel-based alloy to strengthen and toughen the heat treatment method, comprising:

[0062] Qualitative and quantitative analysis module, which uses electron probe microscopy (EPMA) to perform qualitative and quantitative analysis of the chemical composition of additively manufactured nickel-based alloys;

[0063] Homogenization heat treatment module, which uses the diffusion module (DICTRA) of Thermo-Calc software to design homogenization heat treatment according to the element content of nickel-based alloy;

[0064] The homogenization heat treatment parameter determination module uses the diffusion module (DICTRA) of Thermo-Calc software to obtain a linear curve of the distribution of elements diffused over time based on the heat treatment temperature and dendrite spacing; determines the time when all elements truly achieve uniform diffusion, obtains the optimal heat treatment temperature and time, and obtains the optimal solution for homogenization heat treatment of nickel-based alloys;

[0065] TTT phase diagram calculation module, based on the EPMA quantitative analysis results of the composition of the dendrite core and interdendritic region of the nickel-based alloy, uses the TTT phase diagram module in the JMatPro software to calculate the TTT phase diagrams corresponding to the dendrite core and interdendritic region respectively;

[0066] The stress relief heat treatment parameter determination module selects appropriate heat treatment temperature and time according to the TTT phase diagrams corresponding to the dendrite core and the interdendritic region, based on the characteristics of the precipitation phase of the nickel-based alloy, to obtain the stress relief heat treatment plan for the nickel-based alloy.

[0067] In the embodiment of the present invention, tensile tests and impact tests are performed on the deposited nickel-based alloy to determine the strength and toughness of the material. The tensile performance test of the deposited nickel-based alloy is performed according to the ASTM E8 metal material tensile test standard. The impact performance test of the deposited nickel-based alloy is performed according to the ASTM E23 metal material impact test standard.

[0068] After the nickel-based alloy is heat treated in the embodiment of the present invention, the tensile test and impact test are respectively performed on the samples after the homogenization heat treatment and the stress relief heat treatment to determine the strength and toughness of the material. According to the ASTM E8 metal material tensile test standard, the tensile performance test is performed on the nickel-based alloy after the homogenization heat treatment and the stress relief heat treatment. According to the ASTME23 metal material impact test standard, the impact performance test is performed on the nickel-based alloy after the homogenization heat treatment and the stress relief heat treatment.

[0069] Example 1

[0070] For high-speed laser fuse forming Inconel 625 alloy, wire cutting was used to cut the samples into 20×8×2mm.

[0071] (1) The microstructure of the formed Inconel 625 alloy was observed using an optical microscope (OM). The samples used for OM observation need to be polished with sandpaper first, then mechanically polished to a mirror surface on a polishing machine with diamond polishing spray, then etched in aqua regia, and finally ultrasonically cleaned in alcohol and blown dry. Electron probe microscopy (EPMA) was then used to qualitatively and quantitatively analyze the chemical composition of the Inconel 625 alloy formed parts before and after heat treatment, providing a basis for the element segregation phenomenon that occurs during the HE-WLAM process and the formulation of subsequent customized heat treatment processes. After being polished to a mirror surface, the samples used for EPMA observation should be corroded as lightly as possible. Under the premise that the target area can be determined by electron microscopy, excessive corrosion should be avoided to affect the distribution of chemical composition on the sample surface.

[0072] Figure 3 This is the microstructure diagram of deposited Inconel 625 alloy. Figure 4It is the subgrain segregation result of the main chemical components of deposited Inconel 625 alloy:

[0073] (2) Based on the actual characteristics of Inconel 625 alloy prepared by high-speed laser fuse, the homogenization heat treatment design was carried out with the help of the diffusion module (DICTRA) of Thermo-Calc software. First, the dendrite core and interdendritic region were sampled at fixed points by EPMA to obtain the quantitative analysis results of the composition difference between the two regions. Six sets of data were collected in each region and the average value was taken. The results are shown in Table 1. Subsequently, in Thermo-Calc (DICTRA), the proportion of each element in the dendrite core and interdendritic region was used as the initial composition condition, and the composition distribution between the two regions was approximately simplified to a linear distribution. The dendrite spacing was set to 8μm, and the composition distribution of each component after diffusion in the matrix phase for a certain period of time at the target temperature was calculated to determine the homogenization process. Considering time and cost, the optimal homogenization heat treatment temperature of Inconel 625 formed parts was selected as 1150℃. After diffusion at 1150℃ for 300s, 900s, 1800s, 3600s and 7200s, the distribution of the main solute elements in the alloy in the dendrite core and interdendritic region is as follows: Figure 5 As shown, the abscissa distance of 0 μm represents the center of the dendrite core region, and the distance of 8 μm represents the center of the inter-dendritic region.

[0074] Table 1 EPMA quantitative analysis results of the composition of dendrite core and interdendritic region

[0075]

[0076] (3) According to the distribution curve, it can be seen that

[0077] After 1800s, most elements are close to uniform distribution, and the composition difference between dendrite core and dendrite is no longer obvious; but after 3600s, all elements are truly evenly diffused, and the chemical composition between dendrite core and dendrite is basically the same; there is no obvious change in the chemical composition distribution after 3600s and 7200s. Therefore, based on the principle of "ensuring complete diffusion and avoiding grain growth", the best homogenization heat treatment scheme predicted by this study for Inconel 625 alloy prepared by high-speed laser fuse is to keep it at 1150℃ for 1 hour. Figure 6 Shown is the microstructure after homogenization annealing.

[0078] (4) Based on the EPMA quantitative analysis results of the composition of the dendrite core and interdendritic region of the deposited Inconel 625 alloy in Table 1, the present invention calculates the TTT phase diagrams corresponding to the dendrite core and interdendritic region respectively with the help of the TTT phase diagram module in the JMatPro software. The results are as follows: Figure 7 shown.

[0079] (5) According to the obtained TTT phase diagram, it can be seen that the composition segregation leads to obvious differences in the TTT phase diagrams of the two regions. For Inconel 625 alloy, the γ" phase is a metastable precipitation phase with a body-centered tetragonal D022 crystal structure. The phase composition is also Ni3 (Nb, Mo). It is generally considered to be a strengthening phase that can improve the mechanical properties of the material through dispersion strengthening. However, as the heat treatment time increases, the metastable γ" phase will eventually transform into a stable δ phase. Therefore, it is necessary to pay attention to the evolution of the γ" phase and the δ phase during the stress relief heat treatment process. Therefore, based on the comprehensive consideration of stress relief effect, time control window and time cost, the present invention selects 750°C as the stress relief heat treatment temperature. From Figure 7 It can be seen from the figure that at 750 degrees Celsius, the dendrite core region is expected to have δ phase precipitation after 66 hours, while the interdendritic region begins to generate beneficial γ" phase at 7-8 minutes, and the harmful δ phase begins to precipitate at about 2 hours and 23 minutes. In this way, the two hours before the precipitation of δ phase is enough to eliminate most of the residual stress, and a sufficiently wide time control window can be left, and the cost will not be wasted due to too long insulation time. Therefore, the optimal stress relief heat treatment process finally proposed by the present invention is to keep the temperature at 750℃ for 2 hours, and then slowly cool it with the furnace to avoid new residual stress caused by thermal expansion and contraction of the material due to rapid cooling at high temperature. Figure 8 Shown is the microstructure of Inconel 625 after stress relief annealing.

[0080] (6) Fig. 9 The room temperature tensile test results of the formed Inconel 625 alloy after the above-mentioned stress relief heat treatment and homogenization heat treatment process are shown, and compared with the formed Inconel 625 alloy. In order to avoid the influence of organizational anisotropy, the sampling positions of all specimens are kept consistent, and the tensile direction is perpendicular to the axial plane. The corresponding tensile performance parameters are shown in Table 2. It can be seen that the tensile strength, yield strength, elastic modulus and elongation of the formed Inconel 625 alloy reached 807.43MPa, 536.95MPa, 173.03GPa and 37.15%, respectively. After stress relief heat treatment, the tensile strength, yield strength, elastic modulus and elongation of the alloy increased by 15.42%, 15.18%, 5.64% and 3.88%, respectively. After uniform annealing, the yield strength decreased by 35.87%, but the elongation increased by 89.13%, and the tensile strength and elastic modulus were not much different.

[0081] Table 2 Tensile performance parameters

[0082]

[0083] (8) To evaluate the absorbed energy, the three groups of specimens were subjected to Charpy V-notch impact toughness tests. Fig.10 In all cases, the impact toughness of the homogenized heat treated specimens is much higher than that of the stress relief heat treated specimens. The impact toughness of the homogenized heat treated specimens is almost 1.6 times that of the stress relief heat treated specimens, while the impact toughness of the as-deposited specimens is not much different from that of the stress relief heat treated specimens.

[0084] The present invention is widely used to improve the mechanical properties of basic materials of key components such as marine platform components, oil and gas transportation facilities, chemical reaction vessels, nuclear reactor parts and solar high-temperature molten salt pipeline pumps and valves.

[0085] The heat treatment method for strengthening and toughening the additively formed heterogeneous nickel-based alloy provided by the present invention mainly realizes the composition homogenization and stress relief treatment of the nickel-based alloy and improves the mechanical properties of the material through precise chemical composition analysis, diffusion calculation and phase diagram selection. The method is divided into multiple steps to ensure the microstructural uniformity and enhanced toughness of the nickel-based alloy after processing.

[0086] First, the chemical composition of the additively manufactured nickel-based alloy is qualitatively and quantitatively analyzed by electron probe microanalysis (EPMA) technology to detect the difference in element content between the dendrite core and the interdendritic region and identify the component segregation phenomenon in the alloy. This step is crucial and can help accurately determine the element content in different regions and provide accurate initial composition data for subsequent homogenization heat treatment design.

[0087] Next, based on the quantitative analysis data, the composition information of the nickel-based alloy is input into the diffusion module of the Thermo-Calc software to design the homogenization heat treatment process. By setting a reasonable heat treatment temperature and dendrite spacing, the software calculates the diffusion of different components in the matrix phase and generates a linear curve of time versus diffusion process. Based on this curve, the uniform diffusion time of different components is determined, and finally the optimal homogenization heat treatment temperature and time are obtained to ensure the uniformity of component distribution while avoiding excessive grain growth.

[0088] On this basis, by further analyzing the composition of the dendrite core and interdendritic region, the TTT (time-temperature-transformation) phase diagrams of different regions were generated using the TTT phase diagram module of the JMatPro software. Due to the differences in the characteristics of the precipitated phases in different regions of the nickel-based alloy, the TTT phase diagram can help design heat treatment conditions suitable for the two regions to ensure the stability and consistency of material properties during the stress relief process.

[0089] Finally, based on the TTT phase diagram, the stress relief heat treatment parameters of the nickel-based alloy were determined to ensure that the material maintained uniformity of the structure while reducing residual stress. Taking into account the stress relief effect, time control and cost factors, the stress relief heat treatment scheme of 750℃ insulation for 2 hours and slow cooling with the furnace was finally determined, so as to obtain better crack resistance and toughness enhancement effects in the additive forming of heterogeneous nickel-based alloys.

[0090] Example 1: Heat treatment of heterogeneous nickel-based alloy blades for aircraft engines

[0091] 1. Material preparation and preliminary analysis

[0092] The nickel-based alloy blades manufactured by additive manufacturing technology have composition segregation in the dendrite core and interdendritic region. First, the electron probe microanalysis (EPMA) technology was used to quantitatively analyze the additively manufactured blades to measure the content of the main elements in the dendrite core and interdendritic region. The analysis showed that the dendrite core was enriched with molybdenum and chromium elements, while there was a certain amount of aluminum and titanium segregation in the interdendritic region, indicating that the blades had obvious compositional inhomogeneity.

[0093] 2. Homogenization heat treatment

[0094] The analysis data was input into the diffusion module of Thermo-Calc software, and the homogenization heat treatment scheme was designed using the software. Based on the dendrite spacing of the blade, the heat treatment temperature of 1150°C was selected, and the required uniform diffusion time was calculated. It was finally determined that keeping at 1150°C for 1 hour could achieve composition homogenization, while avoiding grain growth and ensuring the uniformity of the overall structure of the blade.

[0095] 3. Stress relief heat treatment

[0096] Based on the composition data of the dendrite core and interdendritic region, the TTT phase diagram of different regions was calculated using JMatPro software. Based on the TTT phase diagram and combined with the working requirements of the aero-engine blades, the optimal temperature and time for stress relief heat treatment were determined to be 750℃ for 2 hours followed by slow cooling in the furnace to reduce residual stress and improve the toughness and fatigue performance of the blades.

[0097] 4. Verification of heat treatment effect

[0098] The heat-treated blades were examined using an optical microscope and a scanning electron microscope (SEM), which showed that the composition of the dendrite core and interdendritic regions became more uniform, and the material's toughness and fatigue properties were significantly improved, meeting the performance requirements of aircraft engine blades.

[0099] Example 2: Heat treatment of nickel-based alloy turbine disks for heavy-duty gas turbines

[0100] 1. Material preparation and preliminary analysis

[0101] The nickel-based alloy turbine disk made by additive manufacturing technology produces a dendrite structure during the additive process, and forms a clear component segregation in the dendrite core and interdendritic region. First, the element content of the dendrite core and interdendritic region was measured by electron probe analysis (EPMA), and it was found that the dendrite core was enriched with chromium and molybdenum, while the interdendritic region contained a higher content of titanium and aluminum.

[0102] 2. Homogenization heat treatment

[0103] According to the EPMA analysis data, the composition information was input into the diffusion module of the Thermo-Calc software, and the appropriate heat treatment temperature and dendrite spacing were selected. Through simulation calculation, the optimal conditions for homogenization heat treatment were determined to be 1150℃ for 1 hour, which homogenized the composition of the dendrite core and interdendritic region, avoided local grain growth, and improved the structural consistency of the turbine disk.

[0104] 3. Stress relief heat treatment

[0105] According to the TTT phase diagram of the dendrite core and interdendritic region, a stress relief heat treatment scheme of keeping at 750℃ for 2 hours followed by slow cooling in the furnace was selected to eliminate the residual stress in the turbine disk and enhance the toughness and thermal fatigue resistance of the material, thereby meeting the requirements of the high temperature and high pressure working environment of the gas turbine.

[0106] 4. Verification of heat treatment effect

[0107] After heat treatment, the microstructure and mechanical properties of the turbine disc were tested, and the results showed that the composition was uniform, and the toughness and fatigue life were significantly improved. The test results show that the heat treatment process meets the long-term working requirements of the gas turbine turbine disc under extreme conditions. The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited to this. Any technician familiar with the technical field within the technical scope disclosed by the present invention, any modification, equivalent substitution and improvement made within the spirit and principle of the present invention, etc., should be covered within the protection scope of the present invention.

Claims

1. A heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy, characterized in that: The following steps are involved: Step 1: Use electron probe technology to conduct qualitative and quantitative analysis of the chemical composition of the additively manufactured nickel-based alloy; Step 2: Design homogenization heat treatment using the diffusion module of Thermo-Calc software according to the element content of the nickel-based alloy; Step 3, using the diffusion module of Thermo-Calc software, based on the obtained heat treatment temperature and dendrite spacing, obtain a linear curve of the distribution of element diffusion over time; determine the time when all elements truly achieve uniform diffusion, and obtain the optimal temperature and time for homogenization heat treatment of the nickel-based alloy; Step 4, according to the EPMA quantitative analysis results of the composition of the dendrite core and the interdendritic region of the nickel-based alloy, the TTT phase diagram module in the JMatPro software is used to calculate the TTT phase diagrams corresponding to the dendrite core and the interdendritic region respectively; Step 5: According to the TTT phase diagram corresponding to the dendrite core and the interdendritic region, based on the characteristics of the nickel-based alloy precipitation phase, the optimal temperature and time for stress relief heat treatment of the nickel-based alloy are obtained.

2. The heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy according to claim 1, characterized in that: The step 1 determines that the nickel-based alloy has segregation characteristics by qualitatively analyzing the nickel-based alloy, and measures the element content in the dendrite core and inter-dendrite region.

3. The heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy according to claim 1, characterized in that: The step 2 specifically includes: (1) EPMA was used to sample the dendrite core and interdendritic region at fixed points to obtain the quantitative analysis results of the composition differences between the two regions. Six sets of data were collected from each region and the average value was taken. (2) In Thermo-Calc, the proportion of each element in the dendrite core and interdendritic region is used as the initial composition condition, and the composition distribution between the two regions is approximately simplified to a linear distribution. Then, the dendrite spacing is observed on the microstructure diagram of the formed nickel-based alloy, and the setting is made according to the observed dendrite spacing; (3) Select the appropriate heat treatment temperature according to the characteristics of different nickel-based alloys, and then calculate the composition distribution of each component after diffusing in the matrix phase for a certain period of time at the target temperature to determine the homogenization process.

4. The heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy according to claim 1, characterized in that: In the step three, an optical microscope is used to observe the microstructure, and the dendrite spacing is determined from the obtained microstructure image, and a suitable heat treatment temperature is selected according to the characteristics of the nickel-based alloy itself.

5. The heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy according to claim 1, characterized in that: In step 3, according to the obtained diffusion curve distribution and based on the principle of "ensuring complete diffusion and avoiding grain growth", the heat treatment time is determined, and the homogenization heat treatment temperature and time are finally determined to be 1150° C. and kept warm for 1 hour.

6. The heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy according to claim 1, characterized in that: In step 5, based on the obtained TTT phase diagram, the stress relief effect, time control window and time cost are comprehensively considered to determine that the optimal temperature and time for the stress relief heat treatment of the nickel-based alloy are to keep the temperature at 750° C. for 2 hours and then slowly cool it in the furnace.

7. A heat treatment system for additively forming a heterogeneous nickel-based alloy reinforcement and toughening according to any one of claims 1 to 6, characterized in that: include: Qualitative and quantitative analysis module, which uses electron probe technology to conduct qualitative and quantitative analysis of the chemical composition of additively manufactured nickel-based alloys; Homogenization heat treatment module, which uses the diffusion module of Thermo-Calc software to design homogenization heat treatment according to the element content of nickel-based alloy; The homogenization heat treatment parameter determination module uses the diffusion module of Thermo-Calc software to obtain a linear curve of the element diffusion distribution over time based on the heat treatment temperature and dendrite spacing; determines the time when all elements truly achieve uniform diffusion, obtains the optimal heat treatment temperature and time, and obtains the optimal solution for homogenization heat treatment of nickel-based alloys; TTT phase diagram calculation module, based on the EPMA quantitative analysis results of the composition of the dendrite core and interdendritic region of the nickel-based alloy, uses the TTT phase diagram module in the JMatPro software to calculate the TTT phase diagrams corresponding to the dendrite core and interdendritic region respectively; The stress relief heat treatment parameter determination module selects appropriate heat treatment temperature and time according to the TTT phase diagrams corresponding to the dendrite core and the interdendritic region, based on the characteristics of the precipitation phase of the nickel-based alloy, to obtain the stress relief heat treatment plan for the nickel-based alloy.

8. A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to perform the steps of the heat treatment method for strengthening and toughening an additively formed heterogeneous nickel-based alloy as described in any one of claims 1 to 6.

10. An information data processing terminal, comprising the heat treatment system for strengthening and toughening an additively formed heterogeneous nickel-based alloy according to claim 7.

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