Heat treatment method for additive repair of single-crystal high-temperature alloy and single-crystal high-temperature alloy part

Abstract

The invention provides a heat treatment method of an additive repair single-crystal high-temperature alloy and a single-crystal high-temperature alloy part, and relates to the technical field of heat treatment processing of metal alloy materials, and the heat treatment method comprises the following steps: carrying out annealing treatment on the additive repair single-crystal high-temperature alloy to release residual stress in the additive repair single-crystal high-temperature alloy, and the annealed additive repair single-crystal high-temperature alloy is obtained. And aging treatment is conducted on the additive repair single-crystal high-temperature alloy part obtained after annealing treatment, and the additive repair single-crystal high-temperature alloy part obtained after heat treatment is obtained. According to the method, residual stress is removed through annealing treatment, and solid cracks and recrystallization occurring in the subsequent aging treatment process are avoided; and then through aging treatment, the structures of an alloy repair area, a matrix area and a heat affected area are improved at the same time, and the purpose of optimizing the alloy performance is achieved.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment processing technology for metal alloy materials, specifically relating to a heat treatment method for additive repair of single-crystal high-temperature alloys and additive repair of single-crystal high-temperature alloy parts. Background Technology

[0002] Nickel-based superalloys possess excellent creep resistance, fatigue corrosion resistance, and good corrosion resistance, making them a primary material for manufacturing turbine blades in gas turbines and aero-engines. To further optimize their mechanical properties at high temperatures, these materials are typically cast into single-crystal structures. However, after prolonged service under harsh conditions, single-crystal turbine blades are prone to surface defects such as tip wear and crack initiation. Due to the high cost of replacement, employing appropriate repair techniques to quickly and efficiently repair damaged blades, rather than replacing them, is of significant economic and engineering importance.

[0003] The advent of laser-directed energy deposition (LDED) technology has provided a feasible approach for the repair of single-crystal turbine blades. This technology injects metal powder into a molten pool formed by a moving laser beam. During the LDED repair process, heat input can be strictly controlled, resulting in a small heat-affected zone. The repaired area forms a dense metallurgical bond with the as-cast single-crystal matrix, making it difficult to peel off. When specific solidification conditions are met, dendrites grow epitaxially along the orientation of the matrix without forming stray grains, thus providing a viable method for the repair of single-crystal blades.

[0004] Researchers have successfully repaired crack-free single-crystal superalloy components using laser-directed energy deposition (EDD). To achieve excellent mechanical properties, the repaired single-crystal alloy must undergo heat treatment before reuse. However, the repaired alloy consists of a cast matrix region and a repair region, and contains fusion lines. Heat treatment of the repaired alloy requires consideration of the effects of the heat treatment regime on the matrix, the repair region, and the heat-affected zone (HAZ). Previous studies have largely focused on the effects of heat treatment on the microstructure evolution and mechanical properties of the repair region, with little consideration given to the effects of heat treatment on the matrix, especially the HAZ.

[0005] Current research on laser additive manufacturing for repairing single-crystal superalloys generally focuses on optimizing the forming process, with less attention paid to subsequent heat treatment. Researchers typically continue to use standard heat treatment protocols from superalloy handbooks for repaired single-crystal nickel-based superalloys. However, these standard protocols are designed for as-cast superalloys and have significant limitations for additively repaired single-crystal nickel-based superalloys. Using standard heat treatment protocols for as-cast alloys involves a high-temperature solution treatment step that utilizes the high level of deformation energy stored in the repair zone during additive manufacturing as a driving force to induce recrystallization, disrupting the single-crystal structure of the repair zone. Simultaneously, this high-temperature treatment causes the already optimized matrix to dissolve again, dissolving the original γ′ phase. Furthermore, recrystallization leads to grain boundaries in the repair zone that become weak points at high temperatures, severely deteriorating the alloy's high-temperature performance. The dissolution and re-precipitation of the γ′ phase in the matrix results in a significant decrease in squareness compared to before heat treatment and the emergence of obvious rafting characteristics, which also contributes to a decline in high-temperature performance. The combination of these two factors leads to the deterioration of the microstructure of the repaired alloy (formation of grain boundaries and changes in the γ′ phase state), ultimately resulting in its key high-temperature mechanical properties (especially creep and fatigue properties) being far below the expected values. Summary of the Invention

[0006] Therefore, the present invention provides a heat treatment method for additive repair of single-crystal superalloys and additive repair of single-crystal superalloy parts, to solve the problems in the prior art where the single-crystal structure of the repair zone is destroyed after heat treatment, and the poor squareness of the γ' phase in the matrix zone ultimately leads to poor high-temperature mechanical properties of the alloy.

[0007] To achieve the above objectives, the technical solution of the present invention will now be described in detail.

[0008] This invention provides a heat treatment method for additive repair of single-crystal superalloys, comprising the following steps:

[0009] Step 1): Anneal the additive repair single crystal superalloy to release the residual stress in the additive repair single crystal superalloy and obtain the annealed additive repair single crystal superalloy.

[0010] Step 2): The annealed additive repair monocrystalline high-temperature alloy part is subjected to aging treatment to obtain the heat-treated additive repair monocrystalline high-temperature alloy part.

[0011] Furthermore, in step 1), the annealing process includes a first annealing process and a second annealing process performed sequentially.

[0012] Preferably, the first annealing process includes: heating the additively repaired single-crystal high-temperature alloy part to 500-700°C, holding it at that temperature for 8-10 hours, and then cooling it to room temperature;

[0013] Preferably, the second annealing process includes: heating the single-crystal high-temperature alloy part after the first annealing process to 700-900°C, holding it at that temperature for 8-10 hours, and then cooling it to room temperature to obtain the annealed additive repair single-crystal high-temperature alloy.

[0014] Furthermore, in step 2), the timeliness processing includes a first timeliness processing and a second timeliness processing performed sequentially.

[0015] Preferably, the first aging treatment step includes: heating the annealed single crystal high-temperature alloy to 1000-1200°C, holding it at that temperature for 3-5 hours, and then cooling it to room temperature;

[0016] The second aging treatment includes: heating the single-crystal high-temperature alloy part after the first aging treatment to 800-900°C, holding it at that temperature for 20-30 hours, and then cooling it to room temperature.

[0017] Furthermore, in step 1), the chemical composition of the additive repair single-crystal superalloy, by mass percentage, is: C 0.12–0.18 wt.%, Cr 4.3–5.6 wt.%, Co 8–10 wt.%, W 7.7–9.5 wt.%, Mo 0.8–1.4 wt.%, Al 5.6–6.3 wt.%, Nb 1.4–1.8 wt.%, Ta 3.5–4.5 wt.%, Re 3.5–4.5 wt.%, with the balance being Ni.

[0018] Furthermore, prior to step 1), the process includes: remelting the top layer of the additive repair single-crystal superalloy to remove impurities from the top layer of the additive repair single-crystal superalloy.

[0019] Furthermore, after step 2) and before step 3), the following steps are also included:

[0020] Step S1): The annealed additive repair single crystal high-temperature alloy is sliced ​​and sampled for microstructure characterization and crystal orientation analysis, and the crystal orientation analysis results are observed.

[0021] Furthermore, if there are no cracks or large-area recrystallization on the sample, then proceed to step 3); otherwise, repeat the second annealing process in step 2) until there are no cracks or large-area recrystallization on the sample.

[0022] Furthermore, the heat treatment method further includes:

[0023] Step 4): The heat-treated single-crystal high-temperature alloy part is sliced ​​and sampled for microstructure characterization and crystal orientation analysis, and the crystal orientation analysis results are observed.

[0024] Furthermore, if the observation results of the sample preparation show that the expected effect has been achieved, the heat treatment method ends; otherwise, the second aging treatment step in step 3) is repeated until the observation results of the sample preparation show that the expected effect has been achieved.

[0025] Preferably, the expected effect refers to the morphology of the γ′ precipitate in the repair area being nearly cubic, with a volume fraction of 65-70% and an average size of 200-400 nm, and the repair area being free of recrystallization and cracks.

[0026] On the other hand, the present invention provides a single-crystal high-temperature alloy part, wherein the single-crystal high-temperature alloy part is a heat-treated additive repair single-crystal high-temperature alloy part, which is obtained by any of the heat treatment methods described above; in the heat-treated additive repair single-crystal high-temperature alloy part, there is no recrystallization or cracks in the repair area; the morphology of the precipitated phase γ′ in the repair area is a near-cubic shape, with a volume fraction of 65-70% and an average size of 200-400 nm; the additive repair single-crystal high-temperature alloy part has a high-temperature creep life of more than 18 hours at 1000℃ / 280MPa.

[0027] The heat treatment method for additive repair of single-crystal superalloys and the single-crystal superalloy parts provided by this invention have the following beneficial effects:

[0028] 1. On one hand, the present invention provides a heat treatment method for additive repair of single-crystal superalloys, comprising the following steps: annealing the additive repair single-crystal superalloy to release residual stress in the additive repair single-crystal superalloy, and obtaining an annealed additive repair single-crystal superalloy; aging the annealed additive repair single-crystal superalloy part to obtain a heat-treated additive repair single-crystal superalloy part. It should be noted that the present invention removes residual stress through annealing, avoiding solid-state cracks and recrystallization during subsequent aging; then, the aging treatment simultaneously improves the microstructure of the alloy repair zone, the matrix zone, and the heat-affected zone, thereby optimizing the alloy properties.

[0029] 2. Furthermore, to avoid recrystallization or solid-state cracking during subsequent aging treatment, gradient annealing is employed to release residual stress in the repair zone. The first annealing releases some of the deformation energy stored in the repair zone, ensuring that recrystallization does not occur during the second annealing. The second annealing further releases residual stress in the repair zone, preventing potential solid-state cracking and recrystallization during subsequent aging treatment. The purpose of the two annealing treatments is to release residual stress in the repair zone to the maximum extent possible without recrystallization. During the annealing process, due to the relatively low holding temperature and time, a solid-state phase transformation cannot be induced; only the γ′ phase undergoes slight coarsening, without other structural changes. Furthermore, the microstructure of both the alloy repair zone and the matrix zone is improved simultaneously through two aging treatments. The first aging treatment regulates the size and morphology of carbides in the repair zone, causing short rod-shaped and bone-like carbides to melt during the first aging process and precipitate again as granular carbides. Granular carbides can effectively pin dislocations, hindering dislocation slip and grain boundary migration at high temperatures, thereby improving the high-temperature mechanical properties of the alloy. The second aging treatment improves the size, volume fraction, and morphology of the γ′ phase in the alloy repair zone, obtaining a γ′ phase with uniform size distribution and regular shape, thus improving the alloy microstructure and optimizing alloy performance. At the same time, the two aging treatments also coarsen the γ′ phase in the matrix zone and avoid the formation of secondary γ′ phase precipitation in the heat-affected zone caused by high-temperature solution treatment, thereby optimizing the performance of the matrix zone.

[0030] 3. On the other hand, the present invention provides an additive repair single-crystal superalloy part, which is a heat-treated additive repair single-crystal superalloy part obtained by any of the above heat treatment methods; in the heat-treated additive repair single-crystal superalloy part, there is no recrystallization or cracks in the repair area; the morphology of the precipitated phase γ′ in the repair area is a near-cubic shape, with a volume fraction of 65-70% and an average size of 200-400 nm.

[0031] 4. On the other hand, since the matrix undergoes solution treatment before repair to achieve homogenization and eliminate eutectic, if the standard heat treatment of solution treatment + aging is applied to the additive repair of single-crystal superalloy, the heat-affected zone will undergo solution treatment again. Repeated solution treatment cycles will lead to irreversible damage to the high-temperature mechanical properties of the heat-affected zone. Therefore, this invention abandons the solution treatment, which has a significant impact on the heat-affected zone, and instead uses annealing and aging treatments, which have a smaller impact on the heat-affected zone, to strengthen the repaired area. Attached Figure Description

[0032] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0033] Figure 1 This is a flowchart of the heat treatment method of the present invention.

[0034] Figure 2 middle: Figure 2 (a) is a micrograph of the repaired area of ​​the additive repaired single-crystal superalloy that was not processed using the method of the present invention. Figure 2 (b) shows the carbide morphology of the additive repaired single-crystal superalloy repair area that was not treated using the method of this invention. Figure 2 (c) is the IPF-X image of the additive repaired single-crystal superalloy repair area that was not treated using the method of this invention. Figure 2 (d) is a photograph of the γ′ phase in the additive repaired single-crystal superalloy repair area that was not treated using the method of this invention. Figure 2 (e) shows the morphology of the heat-affected zone of the additively repaired single-crystal superalloy that was not treated using the method of the present invention. Figure 2 (f) shows the morphology of the additive repair single-crystal superalloy matrix region that was not treated using the method of the present invention.

[0035] Figure 3 middle: Figure 3 (a) is a micrograph of the repaired area of ​​the additive repaired single-crystal superalloy processed using the method of the present invention. Figure 3 (b) shows the carbide morphology of the additive repaired single-crystal superalloy repair area processed using the method of the present invention. Figure 3 (c) is the IPF-X image of the repaired area of ​​the additive repaired single-crystal superalloy processed using the method of the present invention. Figure 3 (d) is a photograph of the γ′ phase in the repaired region of the additive-repaired single-crystal superalloy processed using the method of the present invention. Figure 3 (e) shows the morphology of the heat-affected zone of the additively repaired single-crystal superalloy processed using the method of the present invention. Figure 3 (f) shows the morphology of the additive repair single-crystal superalloy matrix region processed using the method of the present invention.

[0036] Figure 4 middle: Figure 4 (a) is a micrograph of the repaired area of ​​the additive repair of single-crystal superalloy processed using a comparative method. Figure 4 (b) shows the morphology of the repaired region γ′ of the additive repaired single-crystal superalloy, processed using a comparative method. Figure 4 (c) is the IPF-X image of the repaired area of ​​the additive-repaired single-crystal superalloy processed using a comparative method. Figure 4 (d) shows the low-magnification morphology of the heat-affected zone of a single-crystal superalloy repaired using the comparative method. Figure 4 (e) shows the high-magnification morphology of the heat-affected zone of a single-crystal superalloy repaired using a comparative method. Figure 4 (f) shows the morphology of the single-crystal superalloy matrix region repaired by additive manufacturing using a comparative method. Detailed Implementation

[0037] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0038] This invention provides a heat treatment method for additive repair of single-crystal superalloys, comprising the following steps:

[0039] Step 1): Perform top-layer remelting on the additive repair single-crystal superalloy to remove the top impurities of the additive repair single-crystal superalloy and obtain the additive repair single-crystal superalloy part after top-layer remelting.

[0040] Among them, the single-crystal superalloy is the single-crystal superalloy repaired by additive manufacturing; the chemical composition of the single-crystal superalloy by mass percentage is: C 0.12~0.18wt.%, Cr 4.3~5.6wt.%, Co 8~10wt.%, W 7.7~9.5wt.%, Mo 0.8~1.4wt.%, Al 5.6~6.3wt.%, Nb 1.4~1.8wt.%, Ta 3.5~4.5wt.%, Re 3.5~4.5wt.%, with the balance being Ni.

[0041] Step 2): The single crystal high-temperature alloy parts after top layer remelting are subjected to first annealing and second annealing in sequence to remove the residual stress of the single crystal high-temperature alloy parts after top layer remelting and to obtain the annealed single crystal high-temperature alloy parts.

[0042] The first annealing process specifically includes: heating the single-crystal high-temperature alloy part after top layer remelting to 500-700℃, holding it at that temperature for 8-10 hours, and then cooling it to room temperature to obtain the single-crystal high-temperature alloy part after the first annealing process; the second annealing process specifically includes: heating the single-crystal high-temperature alloy part after the first annealing process to 700-900℃, holding it at that temperature for 8-10 hours, and then cooling it to room temperature to obtain the single-crystal high-temperature alloy part after the annealing process.

[0043] Step 3): The annealed single-crystal superalloy parts are subjected to a first aging treatment and a second aging treatment in sequence to obtain the heat-treated single-crystal superalloy parts.

[0044] The first aging treatment specifically includes: heating the annealed single-crystal high-temperature alloy part to 1000-1200℃, holding it at that temperature for 3-5 hours, and then cooling it to room temperature; the second aging treatment specifically includes: heating the single-crystal high-temperature alloy part after the first aging treatment to 800-900℃, holding it at that temperature for 20-30 hours, and then cooling it to room temperature.

[0045] Based on the above method, remelting is used to remove top impurities in the additive-repaired single-crystal superalloy, preventing the presence of grain boundaries from deteriorating the alloy's high-temperature performance. Annealing is then used to remove residual stress, preventing solid-state cracks and recrystallization during subsequent aging treatments. Two aging treatments simultaneously improve the microstructure of the repair zone, matrix zone, and heat-affected zone, thereby optimizing the alloy's performance. Specifically, the first aging treatment regulates the size and morphology of carbides in the repair zone, causing short rod-shaped and bone-like carbides to melt and precipitate again as granular carbides. These granular carbides effectively pin dislocations, hindering dislocation slip and grain boundary migration at high temperatures, thus improving the alloy's high-temperature mechanical properties. The second aging treatment improves the size, volume fraction, and morphology of the γ′ phase in the repair zone, obtaining a uniformly distributed and regularly shaped γ′ phase, thereby improving the alloy's microstructure and optimizing its performance. Meanwhile, the two aging treatments also coarsen the γ′ phase in the matrix region and prevent the formation of secondary γ′ phase precipitation in the heat-affected zone caused by high-temperature solution treatment, thus achieving the goal of optimizing the performance of the matrix region.

[0046] To prevent recrystallization or solid-state cracking during subsequent aging treatment, gradient annealing is used to release residual stress in the repair zone. The first annealing releases some of the deformation energy stored in the repair zone, ensuring that recrystallization will not occur during the second annealing. The second annealing further releases residual stress in the repair zone, preventing potential solid-state cracking and recrystallization during subsequent aging. The purpose of the two annealing treatments is to release residual stress in the repair zone to the maximum extent possible without recrystallization. Furthermore, due to the relatively low holding temperature and time during annealing, solid-state phase transformation cannot be induced; only the γ′ phase undergoes slight coarsening, without other structural changes.

[0047] In some implementations, after steps 2) and 3), the method further includes:

[0048] The annealed single-crystal superalloy parts are sliced ​​for microstructure characterization and crystal orientation analysis, and the results of the crystal orientation analysis are observed. If there are no cracks or large-area recrystallization on the sample, proceed to step 3); otherwise, repeat the second annealing process in step 2) until there are no cracks or large-area recrystallization on the sample.

[0049] In some embodiments, the heat treatment method further includes: Step 4): Slicing the heat-treated additively repaired single-crystal superalloy part for microstructure characterization and crystal orientation analysis, and observing the results of the crystal orientation analysis. If the observation results of the sample preparation show that the expected effect is achieved, the heat treatment method ends; otherwise, the second aging treatment step in step 3) is repeated until the observation results of the sample preparation show that the expected effect is achieved; wherein, the expected effect means that the morphology of the precipitated phase γ′ in the repair area is nearly cubic, the volume fraction is 65-70%, the average size is 200-400 nm, and there is no recrystallization or cracks in the repair area.

[0050] On the other hand, the present invention provides an additive repair single-crystal superalloy part, which is a heat-treated additive repair single-crystal superalloy part; in the heat-treated additive repair single-crystal superalloy part, there is no recrystallization or cracks in the repair area; the morphology of the precipitated phase γ′ in the repair area is a near-cubic shape, with a volume fraction of 65-70% and an average size of 200-400 nm; preferably, the heat-treated additive repair single-crystal superalloy part is obtained by any of the above heat treatment methods.

[0051] The invention will be further described below with reference to specific embodiments and comparative examples.

[0052] The single-crystal superalloys in the examples and comparative examples are additively repaired single-crystal superalloys, and their chemical composition by mass percentage is as follows: C 0.18wt.%, Cr 5.6wt.%, Co 8wt.%, W 9.5wt.%, Mo 1.4wt.%, Al 5.6wt.%, Nb 1.8wt.%, Ta 4.5wt.%, Re 3.5wt.%, with the balance being Ni.

[0053] Example 1

[0054] This embodiment provides a heat treatment method for additive repair of single-crystal superalloys, including the following steps:

[0055] Step 1): Perform top-layer remelting on the additive repair single-crystal superalloy to remove the top impurities of the repaired single-crystal superalloy and obtain the remelted additive repair single-crystal superalloy part.

[0056] Step 2): The additive repair single-crystal superalloy part after top-layer remelting is heated to 600℃, held for 8 hours, and then cooled to room temperature to obtain the additive repair single-crystal superalloy part after the first annealing treatment; then the additive repair single-crystal superalloy part after the first annealing treatment is heated to 1000℃, held for 8 hours, and then cooled to room temperature to obtain the annealed additive repair single-crystal superalloy part; the annealed additive repair single-crystal superalloy part is sliced ​​and sampled, and then sent to a scanning electron microscope to observe the crystal orientation of the repair area. The microstructure reaches the expected effect, and the annealing treatment is completed.

[0057] Step 3): The annealed additive repair single-crystal superalloy part is heated to 1100℃, held for 4 hours, and then cooled to room temperature; then the first aging treatment additive repair single-crystal superalloy part is heated to 870℃, held for 25 hours, and then cooled to room temperature to obtain the heat-treated additive repair single-crystal superalloy part; the heat-treated additive repair single-crystal nickel-based superalloy is sliced ​​and sampled, and sent to a scanning electron microscope to observe the crystal orientation and γ′ phase morphology of the repair area. The microstructure achieves the expected effect, and the heat treatment is completed.

[0058] Example 2

[0059] This embodiment provides a heat treatment method for additive repair of single-crystal superalloys, including the following steps:

[0060] Step 1): Perform top-layer remelting on the additive repair single-crystal superalloy to remove the top impurities of the repaired single-crystal superalloy and obtain the remelted additive repair single-crystal superalloy part.

[0061] Step 2): The additive repair single-crystal superalloy part after top-layer remelting is heated to 500℃, held for 8 hours, and then cooled to room temperature to obtain the additive repair single-crystal superalloy part after the first annealing treatment; then the additive repair single-crystal superalloy part after the first annealing treatment is heated to 900℃, held for 8 hours, and then cooled to room temperature to obtain the annealed additive repair single-crystal superalloy part; the annealed additive repair single-crystal superalloy part is sliced ​​and sampled, and sent to a scanning electron microscope to observe the crystal orientation of the repair area. The microstructure reaches the expected effect, and the annealing treatment is completed.

[0062] Step 3): The annealed additive repair single-crystal superalloy part is heated to 1150℃, held for 4 hours, and then cooled to room temperature; then the first aging treatment additive repair single-crystal superalloy part is heated to 875℃, held for 25 hours, and then cooled to room temperature to obtain the heat-treated additive repair single-crystal superalloy part; the heat-treated additive repair single-crystal nickel-based superalloy is sliced ​​and sampled, and sent to a scanning electron microscope to observe the crystal orientation and γ′ phase morphology of the repair area. The microstructure achieves the expected effect, and the heat treatment is completed.

[0063] Comparative Example 1

[0064] Step 1): The single-crystal superalloy is heated to 1280℃ and held for 4 hours to perform the first solution treatment, and then cooled to room temperature to obtain the single-crystal superalloy part after the first solution treatment; then the single-crystal superalloy part after the first solution treatment is heated to 1290℃ and held for 4 hours to perform the second solution treatment, and then cooled to room temperature to obtain the single-crystal superalloy part after the solution treatment.

[0065] Step 2): The solution-treated single-crystal superalloy part is heated to 1150℃, held for 4 hours, and then cooled to room temperature; then the single-crystal superalloy part after the first aging treatment is heated to 870℃, held for 24 hours, and then cooled to room temperature to obtain the heat-treated single-crystal superalloy part; the heat-treated additive repair single-crystal nickel-based superalloy is sliced ​​and sampled, and sent to a scanning electron microscope to observe the crystal orientation and γ′ phase morphology of the repair area. The presence of recrystallization in the sample indicates that the heat treatment has failed.

[0066] Comparative Example 2

[0067] Step 1): Heat the additive repair single crystal high temperature alloy to 800℃ and hold for 8 hours for annealing. Then cool it to room temperature to obtain the annealed single crystal high temperature alloy part.

[0068] Step 2): The additive repair single-crystal superalloy part, which has only undergone one annealing treatment, is heated to 1150℃ and held for 4 hours for the first aging treatment. Then it is cooled to room temperature to obtain the single-crystal superalloy part after the first aging treatment. The single-crystal superalloy part after the first aging treatment is then heated to 870℃ and held for 24 hours before being cooled to room temperature to obtain the additive repair single-crystal superalloy part after heat treatment. The additive repair single-crystal nickel-based superalloy after heat treatment is sliced ​​and sent to a scanning electron microscope to observe the crystal orientation and γ′ phase morphology of the repair area. The presence of recrystallization in the sample indicates that the heat treatment has failed.

[0069] Figure 1 This is a schematic diagram of the heat treatment process of the present invention. Before heat treatment, the metallographic structure of the repair area of ​​the additive repair single-crystal superalloy is as follows: Figure 2 As shown in (a), there are fine columnar crystals epitaxially grown along the

[001] direction. Figure 2 (b) Before heat treatment, the carbides in the repair area are distributed in short rod-shaped shapes in the interdendritic region. Figure 2 (c) is the IPF-X map of the repair area. Figure 2 (d) shows the γ′ phase in the repaired area before heat treatment, with a size of approximately 50 nm. Figure 2 (e) shows the γ′ phase near the heat-affected zone before heat treatment, with obvious remelting and precipitation of secondary γ′ phase. Figure 2 (f) is the γ′ phase of the matrix before heat treatment, with a size of approximately 200 nm.

[0070] The metallographic structure of the single-crystal superalloy repaired areas in Examples 1 and 2 after treatment by the method of this invention is as follows: Figure 3 As shown in (a). Figure 3 (b) are the carbides in the repair areas of Examples 1 and 2, which are distributed in granular form in the interdendritic region. Figure 3 The EBSD plot in (c) proves that the repaired region is a single-crystal structure. Figure 3 (d) is the expected γ′ phase structure of the repaired area after treatment by the method of the present invention. The γ′ phase is nearly cubic in shape, arranged relatively regularly, with an average size of 250 nm and a volume fraction of 66%. Figure 3 (e) shows the γ′ phase near the heat-affected zone after treatment by this method. The phases are arranged relatively regularly, and no secondary γ′ phase precipitation was observed. Figure 3 (f) shows the γ′ phase of the matrix after treatment by this method, with a size of approximately 350 nm.

[0071] The microstructure of the repaired area of ​​the additively repaired single-crystal superalloy, after treatment with standard heat treatment methods, is shown in the example. Figure 4 As shown in (a), obvious recrystallized grains can be observed in the structure, which leads to the presence of grain boundaries in the repair area, thereby severely deteriorating the high-temperature performance of additive repair single-crystal superalloys. Figure 4 (b) is the γ′ phase in the repaired area after the comparative method. The squareness of the γ′ phase is poor, and a lot of secondary γ′ phase appears in the γ channel, which will significantly reduce the high-temperature performance of the alloy. Figure 4 (c) The EBSD plot demonstrates the formation of recrystallization in the repair zone. Figure 4 (d) and (e) show the microstructure of the heat-affected zone after treatment by the comparative method. γ′ showed obvious rafting, and secondary γ′ phase precipitation appeared in the γ phase channel, which is considered detrimental to the mechanical properties of the alloy. Figure 4 (f) shows the γ′ phase of the matrix after treatment by the comparative method, with a size of approximately 400 nm.

[0072] High-temperature creep rupture tests at 1000℃ / 280MPa were conducted on Examples 1 and 2 and Comparative Examples 1 and 2. The results are shown in Table 1. The high-temperature creep rupture lifetimes of Examples 1 and 2 at 1000℃ / 280MPa were 18.42h and 19.76h, respectively, which were significantly higher than the 5.17h of Comparative Example 1. This is because the high temperature of the solution treatment caused recrystallization of grains in the repair zone of Comparative Example 1, resulting in grain boundaries in the repair zone, which severely deteriorates the mechanical properties of the single-crystal alloy. Furthermore, the squareness of the γ′ phase in the heat-affected zone of the comparative examples was poor, and a large number of secondary γ′ phases appeared in the γ channels, which significantly reduced the high-temperature performance of the alloy. Meanwhile, Examples 1 and 2 maintained the single-crystal orientation of the repair zone and the matrix zone, and the size and morphology of the γ′ phase in the repair zone were controlled by aging treatment. Moreover, the solution treatment, which would have a significant impact on the matrix and the heat-affected zone, was avoided, resulting in a much higher high-temperature creep rupture lifetime for Examples 1 and 2 than for the comparative examples. Since recrystallization also occurred in the repair area of ​​Comparative Example 2, the high-temperature performance of Comparative Example 2 decreased, ultimately resulting in a high-temperature creep life of only 2.28h at 1000℃ / 280MPa.

[0073] Table 1. High-Temperature Duration (1000℃ / 280MPa) Performance Test Results

[0074]

[0075] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method of heat treatment of an additively repaired single crystal superalloy, characterized in that, The method comprises the following steps: Step 1): annealing the additively repaired single crystal superalloy to release residual stress in the additively repaired single crystal superalloy, and obtaining the annealed additively repaired single crystal superalloy; Step 2): aging the annealed additively repaired single crystal superalloy to obtain the heat-treated additively repaired single crystal superalloy.

2. The heat treatment method of additively repaired single crystal superalloy of claim 1, wherein, In the step 1), the annealing comprises first annealing and second annealing performed in sequence; Preferably, the first annealing comprises the following steps: heating the additively repaired single crystal superalloy to 500-700 DEG C, holding for 8-10 hours, and then cooling to room temperature; Preferably, the second annealing comprises the following steps: heating the single crystal superalloy after the first annealing to 700-900 DEG C, holding for 8-10 hours, and then cooling to room temperature, to obtain the annealed additively repaired single crystal superalloy.

3. The heat treatment method of additively repaired single crystal superalloy of claim 1, wherein, In the step 2), the aging comprises first aging and second aging performed in sequence; Preferably, the first aging comprises the following steps: heating the annealed single crystal superalloy to 1000-1200 DEG C, holding for 3-5 hours, and then cooling to room temperature; The second aging comprises the following steps: heating the single crystal superalloy after the first aging to 800-900 DEG C, holding for 20-30 hours, and then cooling to room temperature.

4. The heat treatment method of additively repaired single crystal superalloy of claim 1, wherein, In the step 1), the chemical composition of the additively repaired single crystal superalloy, in mass percentage, is as follows: C 0.12-0.18 wt.%, Cr 4.3-5.6 wt.%, Co 8-10 wt.%, W 7.7-9.5 wt.%, Mo 0.8-1.4 wt.%, Al 5.6-6.3 wt.%, Nb 1.4-1.8 wt.%, Ta 3.5-4.5 wt.%, Re 3.5-4.5 wt.%, and the balance of Ni.

5. The heat treatment method for additively repaired single crystal superalloys of claim 1, wherein, Before the step 1), the method further comprises: remelting the top layer of the additively repaired single crystal superalloy to remove the heterogeneous crystals in the top layer of the additively repaired single crystal superalloy.

6. The heat treatment method of additively repaired single crystal superalloy of claim 3, wherein, After the step 2) and before the step 3), the method further comprises: Step S1): slicing and sampling the annealed additively repaired single crystal superalloy, performing microstructure characterization and crystal orientation analysis, and observing the results of the crystal orientation analysis.

7. The heat treatment method of the additively repaired single crystal superalloy according to claim 6, characterized in that if there is no crack or large-area recrystallization in the sample, the step 3) is performed; otherwise, the second annealing step in the step 2) is repeatedly performed until there is no crack or large-area recrystallization in the sample.

8. The heat treatment method of additively repaired single crystal superalloy of claim 3, wherein, The heat treatment method further comprises: Step 4): slicing and sampling the heat-treated single crystal superalloy, performing microstructure characterization and crystal orientation analysis, and observing the results of the crystal orientation analysis.

9. The heat treatment method of additively repaired single crystal superalloy of claim 8, wherein, If the observation of the sample shows that the expected effect is achieved, the heat treatment method ends; otherwise, the second aging treatment step in the step 3) is repeatedly performed until the observation of the sample shows that the expected effect is achieved. Preferably, the expected effect refers to that the morphology of the γ' precipitated phase in the repair region is in a near-cubic shape, the volume fraction is 65-70%, and the average size is 200-400 nm, and the repair region is free of recrystallization and cracks.

10. A single crystal superalloy article, characterized by, The single crystal superalloy part is an additive repair single crystal superalloy part after heat treatment; in the additive repair single crystal superalloy part after heat treatment, the repair region is free of recrystallization and cracks; the morphology of the precipitated γ' phase in the repair region is in a near-cubic shape, the volume fraction is 65-70%, and the average size is 200-400 nm; the high-temperature stress-rupture life of the additive repair single crystal superalloy part at 1000°C / 280MPa is 18h or more; Preferably, the single crystal superalloy part after heat treatment is obtained by the heat treatment method of any one of claims 1-9.

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