A single crystal repair method based on laser gradient deposition and remelting of molten pool shape regulation

Abstract

A single crystal repair method based on laser gradient deposition and remelting of molten pool shape regulation belongs to the technical field of laser melting deposition. The present application solves the problem that the existing single crystal high-temperature alloy laser repair method cannot eliminate different growth direction dendrite turning intersection impurities, deposition layer side wall impurities and deposition layer top impurities at the same time. Method: one, pretreatment; two, fixation; three, gradient deposition and layer-by-layer remelting of transition layer; four, deposition and layer-by-layer remelting of formal layer. The present application is used for single crystal repair based on laser gradient deposition and remelting of molten pool shape regulation.

Description

Technical Field

[0001] This invention belongs to the field of laser melting deposition technology. Background Technology

[0002] Single-crystal nickel-based superalloys are the preferred material for high-pressure turbine blades in modern aero-engines, as their excellent creep and thermal fatigue properties significantly improve the efficiency of aero-engines. However, the manufacturing process of single-crystal high-pressure turbine blades is complex, time-consuming, and extremely costly. Furthermore, blades undergo fatigue cracking, wear, hot corrosion, and creep failures during long-term service. Simply scrapping and replacing them with new blades would result in significant waste of materials and energy. Therefore, developing an effective method for repairing single-crystal blades is of significant economic importance.

[0003] Laser melting deposition is currently the mainstream technology for repairing single-crystal blades, offering advantages such as high energy density, large temperature gradient, and high dimensional accuracy. However, despite these advantages, impurities and hot cracks are still prone to appear in the laser-repaired layers of single-crystal superalloys. The presence of impurities disrupts the continuity of single-crystal growth, and the large-angle grain boundaries introduced by these impurities further increase the hot cracking susceptibility of the deposited layer. Therefore, suppressing the formation of impurities in the laser-repaired layers of single-crystal superalloys is crucial for improving repair quality. Impurities in the deposition layer mainly appear at the intersection of dendrites with different growth directions, the sidewalls of the deposition layer, and the top of the deposition layer: Impurities at the intersection of dendrites with different growth directions originate from the intersection of dendrites with different growth directions in the initial deposition layer of single crystal repair, such as the intersection line of the

[001] dendrite region and the

[010] dendrite region. Avoiding the formation of the

[010] dendrite region is the key to suppressing impurities. The traditional method is to reduce the laser energy input and increase the defocusing amount, so that the angle α between the fusion line and the horizontal line is less than 45°. On the one hand, this requires the laser melting deposition equipment to have a large defocusing amount control range. On the other hand, even if the equipment meets the requirements, this will significantly reduce the process window for single crystal repair. Impurities on the sidewalls and top of the deposition layer are mostly due to the transformation of columnar crystals to equiaxed crystals caused by the feeding of powder or changes in the solidification conditions of the molten pool. In order to ensure the continuity of the single crystal structure, it is necessary to obtain a complete single crystal structure on the basis of completely remelting the previous deposition layer.

[0004] Impurities on the top of the deposited layer can be eliminated as much as possible through remelting during the deposition of the next layer or through additional remelting processes. For example, patent CN104947175 A discloses a method for preparing a single-crystal nickel-based superalloy bulk based on 3D printing technology, which eliminates impurities by remelting the previous layer during the deposition of the next layer. However, this method cannot eliminate impurities on the top of the last layer, requiring additional machining processes, and the remelting effect of layer-by-layer deposition is not good, making it difficult to ensure the complete elimination of top impurities. Patent CN202010649845.9 discloses a synchronous melting deposition-remelting method for eliminating impurity defects in single-crystal superalloys based on dual-beam lasers, which uses the remelting effect of an independent post-laser to eliminate impurities on the top of the deposited layer. However, the setting of the post-laser power in this method relies too much on theoretical calculations, resulting in insufficient remelting power of the post-laser. In addition, the above methods also have the following problems: 1. They cannot eliminate impurities on the sidewalls of the deposited layer; 2. They cannot eliminate impurities at the junctions of turning dendrites. Therefore, how to eliminate the above-mentioned impurities during the deposition process is the key to obtaining a fully single-crystal structure in the repair layer. Summary of the Invention

[0005] This invention aims to address the problem that existing laser repair methods for single-crystal high-temperature alloys cannot simultaneously eliminate impurities at the intersection of dendrites with different growth directions, impurities on the sidewalls of the deposited layer, and impurities on the top of the deposited layer. Instead, it provides a single-crystal repair method based on laser gradient deposition and remelting with controlled molten pool shape.

[0006] A single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control is performed according to the following steps:

[0007] I. Preprocessing:

[0008] The surface of the single-crystal high-temperature alloy to be repaired is processed to be parallel to the (001) crystal plane, and then polished, cleaned and dried to obtain the pretreated single-crystal specimen.

[0009] II. Fixed:

[0010] The pretreated single crystal specimen was fixed on the fixture and placed in an argon atmosphere;

[0011] III. Gradient deposition and layer-by-layer remelting of the transition layer:

[0012] ① Under the conditions of laser power of 200W~800W, laser scanning speed of 5mm / s~20mm / s, defocusing amount of -8mm~+8mm, powder feeding amount of 5g / m~20g / m and single-layer lifting amount of 0.1mm~0.2mm, a transition deposition layer is obtained by depositing on the surface of the pretreated single crystal specimen to be repaired.

[0013] ② Under the conditions of laser power of 300W~1000W, laser scanning speed of 10mm / s~25mm / s and defocusing amount of -8mm~+8mm, the transition deposition layer is remelted to obtain a specimen that has completed one transition layer deposition.

[0014] ③ Repeat steps 1 to 3 times for the specimen after one transition layer deposition, and increase the laser power of step 1 layer by layer as deposition progresses, to obtain the specimen after the transition layer deposition is completed;

[0015] IV. Deposition and Layer-by-Layer Remelting of the Formal Layer:

[0016] ① Under the conditions of laser power of 300W~1000W, laser scanning speed of 5mm / s~20mm / s, defocusing amount of -8mm~+8mm, powder feeding amount of 5g / m~20g / m and single-layer lifting amount of 0.2mm~0.4mm, the surface to be repaired of the specimen after the completion of the transition layer deposition is deposited to obtain the formal deposition layer;

[0017] ② Under the conditions of laser power of 500W~1200W, laser scanning speed of 10mm / s~25mm / s and defocusing amount of -8mm~+8mm, the formal deposition layer is remelted to obtain a specimen that has completed one deposition of the formal layer;

[0018] ③ Repeat steps 4.1 and 2 for the specimen after completing one formal layer deposition until the required height or number of layers is reached, thus completing the single crystal repair method based on laser gradient deposition and remelting with molten pool shape control.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention addresses the problem of directional dendrites and impurities easily appearing in the initial layer during laser repair of single-crystal high-temperature alloys. By using laser gradient deposition of a transition layer, the directional dendrites and impurities in the previous layer are eliminated layer by layer based on the shape of the molten pool, while reducing the angle between the fusion line and the horizontal line at the weld toe. Ultimately, a transition layer without directional dendrites and impurities is deposited, providing a foundation for subsequent deposition.

[0021] 2. The gradient deposition method in this invention, which gradually transitions from low power to high power, ensures a relatively low energy input for the first layer of gradient deposition. The resulting lower stress and strain and Marangoni convection intensity in the molten pool can reduce the formation of poorly oriented dendrites at the fusion line, thereby obtaining good single crystal repair quality.

[0022] 3. By introducing a gradient deposition transition layer, this invention not only enables process parameters that were originally impossible to deposit due to the generation of impurities to be used for laser melting deposition repair of single crystals, thus significantly expanding the process window for laser repair of single crystal high-temperature alloys, but also makes the operation simple and easy, reducing the requirements for laser cladding equipment for single crystal repair.

[0023] 4. In view of the impurities that appear on the sidewalls and top of the deposited layer during the single-crystal laser repair of multilayer deposition, the present invention proposes a process of layer-by-layer deposition + high-speed and high-power remelting. On the basis of achieving full coverage remelting of the previous deposited layer, the characteristic size ratio L / W of the molten pool is controlled to be greater than or equal to 2, thereby eliminating the impurities in the deposited layer after remelting and promoting the growth of full

[001] dendrites.

[0024] This invention relates to a single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the characteristic dimensions of the molten pool during the eight-stage melting process in a specific implementation method.

[0026] Figure 2 This is a schematic diagram illustrating the principles of conventional continuous depositional remediation and gradient deposition in the transition layer. (a) Continuous deposition, (b) Gradient deposition in the transition layer.

[0027] Figure 3 To compare the metallographic structure of the cross-section of a single-crystal superalloy after conventional continuous deposition repair;

[0028] Figure 4 Example 1 shows the cross-sectional metallographic structure of a single-crystal superalloy after laser gradient deposition and remelting repair based on molten pool shape control. Detailed Implementation

[0029] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0030] Specific Implementation Method 1: This implementation method is a single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control. It is carried out according to the following steps:

[0031] I. Preprocessing:

[0032] The surface of the single-crystal high-temperature alloy to be repaired is processed to be parallel to the (001) crystal plane, and then polished, cleaned and dried to obtain the pretreated single-crystal specimen.

[0033] II. Fixed:

[0034] The pretreated single crystal specimen was fixed on the fixture and placed in an argon atmosphere;

[0035] III. Gradient deposition and layer-by-layer remelting of the transition layer:

[0036] ① Under the conditions of laser power of 200W~800W, laser scanning speed of 5mm / s~20mm / s, defocusing amount of -8mm~+8mm, powder feeding amount of 5g / m~20g / m and single-layer lifting amount of 0.1mm~0.2mm, a transition deposition layer is obtained by depositing on the surface of the pretreated single crystal specimen to be repaired.

[0037] ② Under the conditions of laser power of 300W~1000W, laser scanning speed of 10mm / s~25mm / s and defocusing amount of -8mm~+8mm, the transition deposition layer is remelted to obtain a specimen that has completed one transition layer deposition.

[0038] ③ Repeat steps 1 to 3 times for the specimen after one transition layer deposition, and increase the laser power of step 1 layer by layer as deposition progresses, to obtain the specimen after the transition layer deposition is completed;

[0039] IV. Deposition and Layer-by-Layer Remelting of the Formal Layer:

[0040] ① Under the conditions of laser power of 300W~1000W, laser scanning speed of 5mm / s~20mm / s, defocusing amount of -8mm~+8mm, powder feeding amount of 5g / m~20g / m and single-layer lifting amount of 0.2mm~0.4mm, the surface to be repaired of the specimen after the completion of the transition layer deposition is deposited to obtain the formal deposition layer;

[0041] ② Under the conditions of laser power of 500W~1200W, laser scanning speed of 10mm / s~25mm / s and defocusing amount of -8mm~+8mm, the formal deposition layer is remelted to obtain a specimen that has completed one deposition of the formal layer;

[0042] ③ Repeat steps 4.1 and 2 for the specimen after completing one formal layer deposition until the required height or number of layers is reached, thus completing the single crystal repair method based on laser gradient deposition and remelting with molten pool shape control.

[0043] Figure 2 This diagram illustrates the principles of conventional continuous depositional remediation and gradient deposition in transition layers. (a) Conventional continuous depositional remediation; (b) Gradient deposition in transition layers. Figure 2As shown in (a), during the deposition of the first layer, the angle α between the fusion line and the horizontal line exceeds 45°, leading to the formation of transversely growing dendritic regions on both sides of the deposition area. At the intersection of these dendritic regions and the vertically growing

[001] dendritic regions, the local solidification conditions tend to cause a columnar-equiaxed crystal transformation, easily forming impurities. In subsequent depositions, the same energy input is insufficient to completely remelt the oriented dendrites and corresponding impurities, causing the impurities to grow continuously, ultimately leading to repair failure. When using gradient deposition, the first layer of the transition layer will also form oriented dendrites and impurities, such as... Figure 2 As shown in (b), a laser power slightly greater than that of the first layer is used during the deposition of the second transition layer, along with a small lift, to reduce the α angle based on the complete remelting of the previous layer's directional dendrites and impurities. Through three layers of gradient deposition, the directional dendrites and impurities can be eliminated layer by layer, resulting in an α angle of less than 45°. At this point, there are no more directional dendrites and corresponding impurities, laying the foundation for subsequent formal layer deposition. It is worth noting that the layer-by-layer remelting applied during gradient deposition cannot achieve the effect of gradient deposition in eliminating directional dendrites and impurities at the intersection of directional dendrites. Its purpose is to eliminate as much as possible the impurities introduced by powder feeding and the impurities in the

[001] dendrite region, and to promote the growth of

[001] dendrites.

[0044] The beneficial effects of this embodiment are:

[0045] 1. This embodiment addresses the problem of directional dendrites and impurities easily appearing in the initial layer during the laser repair process of single-crystal high-temperature alloys. By using laser gradient deposition of a transition layer, the directional dendrites and impurities of the previous layer are eliminated layer by layer based on the shape of the molten pool, while reducing the angle between the fusion line and the horizontal line at the weld toe. Ultimately, a transition layer without directional dendrites and impurities is deposited, providing a foundation for subsequent deposition.

[0046] 2. In this embodiment, the gradient deposition method, which gradually transitions from low power to high power, ensures a relatively low energy input for the first layer of gradient deposition. The resulting lower stress and strain and Marangoni convection intensity in the molten pool can reduce the formation of poorly oriented dendrites at the fusion line, thereby obtaining good single crystal repair quality.

[0047] 3. By introducing a gradient deposition transition layer, this embodiment not only enables the process parameters that were originally impossible to deposit due to the generation of impurities to be used for laser melting deposition repair of single crystals, thus significantly expanding the process window for laser repair of single crystal high-temperature alloys, but also makes the operation simple and easy, reducing the requirements for laser cladding equipment for single crystal repair.

[0048] 4. In this embodiment, for the repair of impurities on the sidewalls and top of the deposited layer during the single-crystal laser repair of multilayer deposition, a process of layer-by-layer deposition + high-speed and high-power remelting is proposed. On the basis of achieving full coverage remelting of the previous deposited layer, the characteristic size ratio L / W of the molten pool is controlled to be greater than or equal to 2, so as to eliminate impurities in the deposited layer after remelting and promote the growth of full

[001] dendrites.

[0049] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the single-crystal high-temperature alloy mentioned in step one is PWA1480, DD407, DD6, CMSX-4, DD9, or CMSX-10. Everything else is the same as in Specific Implementation Method One.

[0050] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, wire cutting is used to process the surface of the single-crystal high-temperature alloy to be repaired to be parallel to the (001) crystal plane. Then, sandpaper is used to polish the surface to be repaired to remove wire cutting marks. Finally, acetone is used to clean the surface to be repaired and then it is dried. The rest is the same as Specific Implementation Method One or Two.

[0051] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the oxygen content in the argon environment described in step two is less than 100 ppm. Everything else is the same as in Specific Implementation Methods One to Three.

[0052] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One through Four in that: the laser power for the nth deposition is set to W. n The laser power for the (n+1)th deposition is W. n+1 W n+1 -W n =5W~100W, where n=1~3. Other aspects are the same as in specific implementation methods one through four.

[0053] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One through Five in that: W n+1 -W n =25W~50W, or W n+1 -W n =50W~100W. Other aspects are the same as in specific implementation methods one to five.

[0054] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the fusion area of ​​the remelting in steps Three ② and Four ② covers the previous deposition layer. Everything else is the same as in Specific Implementation Methods One to Six.

[0055] Specific implementation method eight, combined with Figure 1Specific explanation: This embodiment differs from one of the specific embodiments one to seven in that the characteristic dimension ratio L / W of the molten pool is maintained at greater than or equal to 2 during the remelting process, where W is half of the maximum width of the molten pool and L is the tail length of the molten pool. Everything else is the same as in specific embodiments one to seven.

[0056] In a specific implementation, the molten pool tail length is the distance from the intersection of the maximum width and the maximum length of the molten pool to the tail of the molten pool.

[0057] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: Step Three ①, under the conditions of laser power of 200W to 400W, laser scanning speed of 10mm / s to 15mm / s, defocusing amount of -5mm to +5mm, powder feeding amount of 5g / m to 8g / m, and single-layer lifting amount of 0.1mm, a transition deposition layer is deposited on the surface to be repaired of the pretreated single-crystal specimen to obtain a transition deposition layer; Step Three ②, under the conditions of laser power of 300W to 600W, laser scanning speed of 15mm / s to 25mm / s, and defocusing amount of -5mm to +5mm, the transition deposition layer is remelted to obtain a specimen that has completed one transition layer deposition; Step 3.③ Repeat steps 3.① and 2 twice for the specimen with the completed transition layer deposition. Step 4.① Deposit on the surface to be repaired of the specimen with the completed transition layer deposition under the conditions of laser power of 300W-600W, laser scanning speed of 10mm / s-15mm / s, defocusing amount of -5mm-+5mm, powder feed of 5g / m-8g / m, and single-layer lift of 0.2mm-0.3mm to obtain the formal deposition layer. Step 4.② Remelt the formal deposition layer under the conditions of laser power of 500W-800W, laser scanning speed of 15mm / s-25mm / s, and defocusing amount of -5mm-+5mm to obtain the specimen with the completed formal layer deposition. Other aspects are the same as in specific implementation methods one to eight.

[0058] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: Step Three ①, under conditions of laser power of 400W to 600W, laser scanning speed of 10mm / s to 15mm / s, defocusing amount of -5mm to +5mm, powder feeding amount of 8g / m to 15g / m, and single-layer lifting amount of 0.1mm to 0.2mm, deposits are performed on the surface to be repaired of the pretreated single-crystal specimen to obtain a transition deposition layer; Step Three ②, under conditions of laser power of 500W to 1000W, laser scanning speed of 15mm / s to 25mm / s, and defocusing amount of -5mm to +5mm, the transition deposition layer is remelted to obtain a specimen with one transition layer deposition completed; Step 3 ③: Repeat steps 3 ① and ② 2 to 3 times on the specimen after completing one transition layer deposition. Step 4 ①: Deposit on the surface to be repaired of the specimen after completing the transition layer deposition under the conditions of laser power of 500W to 1000W, laser scanning speed of 10mm / s to 15mm / s, defocusing amount of -5mm to +5mm, powder feed of 8g / m to 15g / m, and single-layer lift of 0.3mm to 0.4mm to obtain the formal deposition layer. Step 4 ②: Remelt the formal deposition layer under the conditions of laser power of 600W to 1200W, laser scanning speed of 15mm / s to 25mm / s, and defocusing amount of -5mm to +5mm to obtain the specimen after completing one formal layer deposition. Other aspects are the same as in specific implementation methods one to nine.

[0059] The beneficial effects of the present invention are verified using the following embodiments:

[0060] Example 1:

[0061] A single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control is performed according to the following steps:

[0062] I. Preprocessing:

[0063] The surface of the single crystal high-temperature alloy to be repaired was machined by wire cutting to be parallel to the (001) crystal plane. Then, the surface to be repaired was polished with sandpaper to remove the wire cutting marks. Finally, the surface to be repaired was cleaned with acetone and dried.

[0064] II. Fixed:

[0065] The pretreated single crystal specimen was fixed on the fixture and placed in an argon atmosphere;

[0066] III. Gradient deposition and layer-by-layer remelting of the transition layer:

[0067] ① Under the conditions of laser power of 400W, laser scanning speed of 12.5mm / s, defocusing amount of -3.8mm, powder feeding amount of 8g / m and single-layer lifting amount of 0.1mm, a transition deposition layer was deposited on the surface of the pretreated single crystal specimen to be repaired.

[0068] ② Under the conditions of laser power of 500W, laser scanning speed of 17.5mm / s and defocusing amount of -3.8mm, the transition deposition layer was remelted to obtain a specimen that completed one transition layer deposition.

[0069] ③ Under the conditions of laser power of 450W, laser scanning speed of 12.5mm / s, defocusing amount of -3.8mm, powder feeding amount of 8g / m and single-layer lifting amount of 0.1mm, the surface to be repaired of the specimen after the first transition layer deposition is deposited. Then, under the conditions of laser power of 550W, laser scanning speed of 17.5mm / s and defocusing amount of -3.8mm, the transition deposition layer is remelted to obtain the specimen after the second transition layer deposition.

[0070] ④ Under the conditions of laser power of 500W, laser scanning speed of 12.5mm / s, defocusing amount of -3.8mm, powder feed of 8g / m and single-layer lifting amount of 0.1mm, the surface to be repaired of the specimen after the secondary transition layer deposition is deposited. Then, under the conditions of laser power of 600W, laser scanning speed of 17.5mm / s and defocusing amount of -3.8mm, the transition deposition layer is remelted to obtain the specimen after the transition layer deposition is completed.

[0071] IV. Deposition and Layer-by-Layer Remelting of the Formal Layer:

[0072] ① Under the conditions of laser power of 500W, laser scanning speed of 12.5mm / s, defocusing amount of -3.8mm, powder feeding amount of 8g / m and single-layer lifting amount of 0.2mm, the surface of the specimen to be repaired after the transition layer deposition is completed is deposited to obtain the formal deposition layer.

[0073] ② Under the conditions of laser power of 600W, laser scanning speed of 17.5mm / s and defocusing amount of -3.8mm, the formal deposition layer was remelted to obtain a specimen that completed one deposition of the formal layer;

[0074] ③ Repeat steps 4.1 and 2 six times on the specimen after completing one formal layer deposition to obtain a single crystal high-temperature alloy after laser gradient deposition and remelting repair based on molten pool shape control.

[0075] The single-crystal high-temperature alloy mentioned in step one is DD6.

[0076] The oxygen content in the argon atmosphere described in step two is less than 100 ppm.

[0077] In steps 3② and 4②, the fusion area of ​​the remelted material covers the previous deposition layer.

[0078] During the remelting process, the characteristic size ratio of the molten pool, L / W, is kept greater than or equal to 2, where W is half of the maximum width of the molten pool and L is the length of the molten pool tail.

[0079] Comparative Experiment: This comparative experiment differs from Example 1 in that steps three and four are omitted. Under conditions of 500W laser power, 12.5mm / s laser scanning speed, -3.8mm defocusing, 8g / m powder feed, and 0.2mm single-layer lift, deposition was performed on the surface of the pretreated single-crystal specimen to be repaired. Five layers were deposited, resulting in a single-crystal high-temperature alloy after conventional continuous deposition repair. All other aspects are the same as in Example 1.

[0080] Figure 3 To compare the metallographic structure of the cross-section of a single-crystal superalloy after conventional continuous deposition repair; Figure 4 Example 1: Metallographic profile of a single-crystal superalloy cross section after repair by laser gradient deposition and remelting based on molten pool shape control; Figure 3 As can be seen, during the deposition of the first layer, the angle between the fusion line at the weld toe and the horizontal line exceeded 45°, causing a directional-disorientation transformation on both sides of the molten pool, resulting in the formation of oriented dendrites. At the intersection of the

[001] dendrite region and the

[010] dendrite region on the left, the temperature gradient component in the dendrite growth direction was the smallest, while the dendrite growth rate was the largest, leading to a columnar-equiaxed crystal transformation and the formation of impurities. Because the comparative experiment used conventional continuous deposition, the oriented dendrites and impurities of the first layer were not completely remelted during the subsequent deposition of the second layer, causing the impurities of the first layer to grow continuously in the subsequent deposition layers, forming a large area of ​​impurities on the sidewalls. At the same time, because a high-speed, high-power remelting process was not used, the impurities on the sidewalls and top layer in the comparative experiment were obvious, and even impurities appeared in the

[001] dendrite growth region. In comparison, the gradient deposition process used in Example 1 effectively eliminated the impurities at the turning dendrites. At the same time, a smaller angle α between the fusion line and the horizontal line was obtained when entering the formal layer deposition. The high-speed, high-power remelting layer by layer ensured the complete remelting of impurities in the sidewalls, top, and

[001] dendrite region of the deposited layer and promoted the growth of

[001] dendrites, thereby achieving high-quality single-crystal laser melting deposition repair.

Claims

1. A single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control, characterized in that... It is done in the following steps: I. Preprocessing: The surface of the single-crystal high-temperature alloy to be repaired is processed to be parallel to the (001) crystal plane, and then polished, cleaned and dried to obtain the pretreated single-crystal specimen. II. Fixed: The pretreated single crystal specimen was fixed on the fixture and placed in an argon atmosphere; III. Gradient deposition and layer-by-layer remelting of the transition layer: ① Under the conditions of laser power of 200W~800W, laser scanning speed of 5mm / s~20mm / s, defocusing amount of -8mm~+8mm, powder feeding amount of 5g / m~20g / m and single-layer lifting amount of 0.1mm~0.2mm, a transition deposition layer is obtained by depositing on the surface of the pretreated single crystal specimen to be repaired. ② Under the conditions of laser power of 300W~1000W, laser scanning speed of 10mm / s~25mm / s and defocusing amount of -8mm~+8mm, the transition deposition layer is remelted to obtain a specimen that has completed one transition layer deposition. ③ Repeat steps 1 to 3 times for the specimen after one transition layer deposition, and increase the laser power of step 1 layer by layer as deposition progresses, to obtain the specimen after the transition layer deposition is completed; IV. Deposition and Layer-by-Layer Remelting of the Formal Layer: ① Under the conditions of laser power of 300W~1000W, laser scanning speed of 5mm / s~20mm / s, defocusing amount of -8mm~+8mm, powder feeding amount of 5g / m~20g / m and single layer lifting amount of 0.2mm~0.4mm, the surface to be repaired of the specimen after the completion of the transition layer deposition is deposited to obtain the formal deposition layer; ② Under the conditions of laser power of 500W~1200W, laser scanning speed of 10mm / s~25mm / s and defocusing amount of -8mm~+8mm, the formal deposition layer is remelted to obtain a specimen that has completed one deposition of the formal layer; ③ Repeat steps 4.1 and 2 for the specimen after completing one formal layer deposition until the required height or number of layers is reached, thus completing the single crystal repair method based on laser gradient deposition and remelting with molten pool shape control.

2. The single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 1, characterized in that... The single-crystal high-temperature alloy mentioned in step one is PWA1480, DD407, DD6, CMSX-4, DD9 or CMSX-10.

3. The single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 1, characterized in that... In step one, wire cutting is used to process the surface of the single crystal high-temperature alloy to be repaired to be parallel to the (001) crystal plane. Then, sandpaper is used to polish the surface to be repaired to remove the wire cutting marks. Finally, acetone is used to clean the surface to be repaired and then it is dried.

4. The single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 1, characterized in that... The oxygen content in the argon atmosphere described in step two is less than 100 ppm.

5. The single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 1, characterized in that... Let the laser power of the nth deposition be W. n The laser power for the (n+1)th deposition is W. n+1 W n+1 -W n =5W~100W, where n=1~3.

6. The single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 5, characterized in that... W n+1 -W n = 25 W to 50 W, or W n+1 -W n = 50 W to 100 W.

7. The single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 1, characterized in that... In steps 3② and 4②, the fusion area of ​​the remelted material covers the previous deposition layer.

8. A single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 7, characterized in that... During the remelting process, the characteristic size ratio of the molten pool, L / W, is kept greater than or equal to 2, where W is half of the maximum width of the molten pool and L is the tail length of the molten pool.

9. A single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 1, characterized in that... Step 3 ① Under conditions of laser power of 200W~400W, laser scanning speed of 10mm / s~15mm / s, defocusing amount of -5mm~+5mm, powder feed of 5g / m~8g / m, and single-layer lift of 0.1mm, a transition deposition layer is deposited on the surface to be repaired of the pretreated single crystal specimen to obtain a transition deposition layer; Step 3 ② Under conditions of laser power of 300W~600W, laser scanning speed of 15mm / s~25mm / s, and defocusing amount of -5mm~+5mm, the transition deposition layer is remelted to obtain a specimen with one transition layer deposition completed; Step 3 ③ The specimen with one transition layer deposition completed is arranged according to... Step 3 ① and ② are repeated twice; Step 4 ① is performed on the surface of the specimen to be repaired after the transition layer deposition is completed, under the conditions of laser power of 300W~600W, laser scanning speed of 10mm / s~15mm / s, defocusing amount of -5mm~+5mm, powder feed of 5g / m~8g / m and single-layer lift of 0.2mm~0.3mm, to obtain the formal deposition layer; Step 4 ② is performed on the formal deposition layer under the conditions of laser power of 500W~800W, laser scanning speed of 15mm / s~25mm / s and defocusing amount of -5mm~+5mm, to obtain the specimen after one formal layer deposition.

10. A single-crystal repair method based on laser gradient deposition and remelting with molten pool shape control according to claim 1, characterized in that... Step 3 ① Under conditions of laser power of 400W~600W, laser scanning speed of 10mm / s~15mm / s, defocusing amount of -5mm~+5mm, powder feed of 8g / m~15g / m, and single-layer lift of 0.1mm~0.2mm, a transition deposition layer is deposited on the surface to be repaired of the pretreated single-crystal specimen to obtain a transition deposition layer; Step 3 ② Under conditions of laser power of 500W~1000W, laser scanning speed of 15mm / s~25mm / s, and defocusing amount of -5mm~+5mm, the transition deposition layer is remelted to obtain a specimen with one transition layer deposition completed; Step 3 ③ The specimen with one transition layer deposition completed is... Repeat steps 3.1 and 2.2 to 3 times. In step 4.1, under the conditions of laser power of 500W to 1000W, laser scanning speed of 10mm / s to 15mm / s, defocusing amount of -5mm to +5mm, powder feed of 8g / m to 15g / m, and single-layer lift of 0.3mm to 0.4mm, deposit a formal deposition layer on the surface of the specimen to be repaired after the transition layer deposition is completed, to obtain the formal deposition layer. In step 4.2, under the conditions of laser power of 600W to 1200W, laser scanning speed of 15mm / s to 25mm / s, and defocusing amount of -5mm to +5mm, remelt the formal deposition layer to obtain the specimen after one formal layer deposition.

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