In-situ repair method for local damage of aircraft titanium alloy skin

Abstract

The invention discloses an in-situ repairing method for local damage of an aircraft titanium alloy skin, and belongs to the field of repairing methods. The repairing method comprises the steps that pure Ni powder with the purity larger than 99%, the particle size ranging from 0 micrometer to 30 micrometers and D50 smaller than 15 micrometers, pure Al powder with the purity larger than 99%, the particle size ranging from 0 micrometer to 20 micrometers and the D50 about 10 micrometers and spherical 316L stainless steel powder with the purity larger than 99% and the particle size ranging from 50 micrometers to 150 micrometers are selected as raw materials to be fully mixed; the local damaged area of the titanium alloy skin is pretreated; a low-pressure cold spraying process is adopted, the mixed powder is sprayed to the local damage area, and the Ni10Al coating is obtained; and a visual inspection method is adopted to inspect the surface of the low-pressure cold spraying Ni10Al coating in the local damage area. According to the method, the damaged titanium alloy skin does not need to be disassembled, and in-situ repair can be directly carried out on the damaged area on the machine in situ; and the prepared coating is large in thickness, capable of repairing millimeter-level damage, large in repair tolerance and suitable for repairing various damage depths.

Description

Technical Field

[0001] This application relates to the field of skin local damage repair methods, and specifically to an in-situ repair method for local damage of aircraft titanium alloy skin. Background Art

[0002] The aircraft skin has functions such as forming the aircraft aerodynamic shape and bearing aerodynamic loads, and the flatness of its outer surface will also affect the flatness of the aircraft surface paint layer. Since the engine generates extremely high temperatures during operation, the fuselage skin near the aircraft engine is generally made of titanium alloy materials.

[0003] During the aircraft manufacturing process, before the skin is installed, for defects such as depressions and shrinkage grooves on the outer surface of the titanium alloy skin, the method of plasma spraying Ni10Al coating can be used for repair. However, during aircraft service, due to the variable and harsh service environment, local damages such as wear and corrosion will inevitably occur on the skin surface, resulting in depressions on its surface, thereby reducing the flatness of the aircraft titanium alloy skin surface and causing a step difference on its surface. The appearance of the skin step difference will, on the one hand, affect the aircraft aerodynamic shape and increase the flight drag; on the other hand, it will reduce the flatness of the aircraft surface paint layer and affect the performance of the aircraft paint layer and other problems.

[0004] Since the aircraft titanium alloy skin is fixed into a preset curved shape during manufacturing and installed on the aircraft surface, if it is disassembled for plasma spraying repair, it is extremely easy for the shape of the disassembled titanium alloy skin to change due to reasons such as material residual stress, and thus it cannot be reinstalled. Therefore, an in-situ repair method must be used to repair the step difference of the titanium alloy skin. However, due to problems such as light, sound, and electromagnetic pollution generated during the operation of the plasma spraying process, it must be used in a spraying room, so it is impossible to perform in-situ repair on the non-detachable titanium alloy skin of the aircraft. Summary of the Invention

[0005] The purpose of this application is to provide an in-situ repair method for local damage of aircraft titanium alloy skin, so as to solve the problems that existing plasma spraying of Ni10Al coating will generate problems such as light, sound, and electromagnetic pollution, and must be used in a spraying room, and cannot meet the performance requirements for in-situ repair of local damage of aircraft titanium alloy skin.

[0006] To achieve the above purpose, this application provides the following technical solutions:

[0007] An in-situ repair method for local damage of aircraft titanium alloy skin, comprising the following steps:

[0008] Step 1: Select pure Ni powder with a purity greater than 99%, a particle size of (0-30) μm, and a D50 less than 15 μm, pure Al powder with a purity greater than 99%, a particle size of (0-20) μm, and a D50 of about 10 μm, and spherical 316L stainless steel powder with a purity greater than 99% and a particle size of (50-150) μm as raw materials, and fully mix the three powders according to the ratio of (63±1) wt.% of Ni powder, (7±1) wt.% of Al powder, and the remainder of 316L stainless steel powder to obtain a mixed powder for standby use;

[0009] Step 2: pre-treating the local damaged area of the titanium alloy skin so that the surface roughness of the local damaged area reaches Ra3.5 to Ra7.0; the pre-treatment includes at least one of grinding, sandblasting and purging;

[0010] Step 3: Use a low-pressure cold spraying process to spray the mixed powder on the local damaged area to obtain a Ni10Al coating; wherein the process parameters of the low-pressure cold spraying process include: (1) process gas: nitrogen with a purity of not less than 99.9%; (2) spraying pressure: 1.3MPa~2.1MPa; (3) gas heating temperature: 400℃~550℃; (4) powder feeding rate 40g / min~90g / min; (5) spraying distance: 10mm~30mm; (6) spraying angle: 90°±20°; (7) spray gun moving speed: 10mm / s~300mm / s; Step 4: Use a visual inspection method to inspect the surface of the low-pressure cold sprayed Ni10Al coating in the local damaged area to rule out cracks, warping, peeling or shedding of the coating.

[0011] Optionally, in the step three, during the process of low-pressure cold spraying, an infrared thermometer is used to monitor the surface temperature of the titanium alloy skin in real time so that the surface temperature is not higher than 120°C, and the Ni10Al coating obtained in the step three is 0.1 mm higher than the undamaged titanium alloy skin surface.

[0012] Optionally, in step 2, the specific process of pre-treating the local damaged area of the titanium alloy skin is:

[0013] Use fine sandpaper to smoothen the local damaged area and edge of the titanium alloy skin;

[0014] Cleaning the local damaged area with acetone;

[0015] Using a sandblasting machine and 36-60 mesh white corundum sand, the local damaged area is sandblasted so that the surface roughness of the local damaged area reaches Ra3.5-Ra7.0;

[0016] After sandblasting, compressed air is used to purge the local damage area.

[0017] Optionally, in step three, within 4 hours after the powder mixing in step one and within 2 hours after the sandblasting in step two, a low-pressure cold spraying process is carried out for spraying.

[0018] Optionally, before step one, the method further includes:

[0019] According to the contour of the damaged area of the titanium alloy skin, a spraying protection tooling is prepared, and the spraying protection tooling is fixed on the surface of the titanium alloy skin with high-temperature resistant tape, which is used for spraying protection of the undamaged area when repairing the damaged area of the titanium alloy skin; wherein, the spraying protection tooling is a metal thin plate with holes in the middle, and the area of the holes is 0.5-1 mm larger than the contour edge of the damaged area of the titanium alloy skin.

[0020] Optionally, after obtaining the Ni10Al coating in step five, the method further includes:

[0021] The surface of the obtained coating is polished with fine sandpaper so that the surface roughness of the obtained coating is not higher than Ra1.6 μm, and the edge of the coating is smoothly transitioned.

[0022] Optionally, the method further includes: after polishing the surface of the obtained coating with fine sandpaper, the method further includes: removing the spraying protection tooling and the high-temperature resistant tape, purging the surface with compressed air to remove floating powder, and then cleaning the protected area with acetone to remove residual glue.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] Adopting the low-pressure cold spraying technology, selecting Ni and Al powders suitable for the low-pressure cold spraying process, and assisting with large-size 316L stainless steel powder to improve the fluidity of the spraying powder, developing a low-pressure cold spraying Ni10Al coating process suitable for in-situ repair: (1) It is not necessary to disassemble the damaged titanium alloy skin, and the damaged area can be directly repaired in-situ on the aircraft; (2) The prepared coating has a large thickness, can repair millimeter-level damage, has a large repair tolerance, and is suitable for repairing various damage depths; (3) The repair protection difficulty is low, only the surrounding position of the repair area needs to be shielded, and it is suitable for repairing the damage of any large-size and complex-shaped titanium alloy skin. It solves the problems that after the aircraft is in service, when the titanium alloy skin cannot be disassembled, due to the skin step difference, (1) it affects the aerodynamic shape of the aircraft and increases the flight wind resistance; (2) it reduces the flatness of the aircraft surface paint layer and affects the performance of the aircraft paint layer. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of coating polishing after the titanium alloy skin of the present application is repaired.

[0026] Figure 2 Schematic diagram of bonding of the bonding strength specimen for this application;

[0027] Figure 3 Metallographic structure of the coating of Comparative Group 1 for this application;

[0028] Figure 4 Metallographic structure of the coating of Comparative Group 2 for this application;

[0029] Figure 5 Metallographic structure of the coating of Comparative Group 4 for this application;

[0030] Figure 6 Metallographic structure of the low-pressure cold-sprayed Ni10Al coating for this application. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of this application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of this application.

[0032] As mentioned in the background art of this application, since the titanium alloy skin of the aircraft is fixed into a preset curved shape during manufacturing and installed on the aircraft surface, if it is disassembled for plasma spraying repair, it is extremely easy for the shape of the disassembled titanium alloy skin to change due to reasons such as material residual stress, etc., so that it cannot be reinstalled. Moreover, when the existing plasma spraying Ni10Al coating is carried out, problems such as light, sound, and electromagnetic pollution will occur, and it must be used in a spraying room, which cannot meet the performance requirements for in-situ repair of local damage to the titanium alloy skin of the aircraft.

[0033] To solve the above defects, this application discloses an in-situ repair method for local damage to the titanium alloy skin of the aircraft, and develops a low-pressure cold-spraying Ni10Al coating process suitable for in-situ repair to meet the performance requirements for local damage repair of the titanium alloy skin of the aircraft.

[0034] It should be noted that according to the performance requirements for plasma spraying Ni10Al coating repair of local damage to the titanium alloy skin of the aircraft, the coating porosity and oxide should not be greater than 5%, the interface inclusion should not be greater than 20%, the microhardness should not be less than 150 HV, the bonding strength should be greater than 35 MPa, and there should be no coating spalling or coating separation from the substrate on the surface of the bending specimen. Cracks are allowed in the coating. An in-situ repair method for local damage to the titanium alloy skin of the aircraft in this application will be compared and described in conjunction with the performance requirements for plasma spraying Ni10Al coating repair.

[0035] The following will describe in detail how the solution of the present application solves the above technical problems in conjunction with the accompanying drawings.

[0036] See also Figure 1-6 In the embodiment of the present application, an in-situ repair method for local damage of aircraft titanium alloy skin comprises the following steps:

[0037] Step 1: Select pure Ni powder with a purity greater than 99%, a particle size of (0-30) μm, and a D50 less than 15 μm, pure Al powder with a purity greater than 99%, a particle size of (0-20) μm, and a D50 of about 10 μm, and spherical 316L stainless steel powder with a purity greater than 99% and a particle size of (50-150) μm as raw materials, and fully mix the three powders according to the ratio of (63±1) wt.% of Ni powder, (7±1) wt.% of Al powder, and the remainder of 316L stainless steel powder to obtain a mixed powder for standby use;

[0038] Exemplarily, in order to fully mix the powders, a powder mixer may be used to mix the powders at a rotation speed of 5 rpm to 15 rpm for not less than 60 minutes, thereby obtaining mixed spray powders.

[0039] Step 2: pre-treating the local damaged area of the titanium alloy skin so that the surface roughness of the local damaged area reaches Ra3.5 to Ra7.0; the pre-treatment includes at least one of grinding, sandblasting and purging;

[0040] Step 3: Use a low-pressure cold spraying process to spray the mixed powder on the local damaged area to obtain a Ni10Al coating; wherein the process parameters of the low-pressure cold spraying process include: (1) process gas: nitrogen with a purity of not less than 99.9%; (2) spraying pressure: 1.3MPa~2.1MPa; (3) gas heating temperature: 400℃~550℃; (4) powder feeding rate 40g / min~90g / min; (5) spraying distance: 10mm~30mm; (6) spraying angle: 90°±20°; (7) spray gun moving speed: 10mm / s~300mm / s; Step 4: Use a visual inspection method to inspect the surface of the low-pressure cold sprayed Ni10Al coating in the local damaged area to rule out cracks, warping, peeling or shedding of the coating.

[0041] In this application, low-pressure cold spraying technology is adopted, Ni and Al powders suitable for low-pressure cold spraying process are selected, and large-size 316L stainless steel powder is used to improve the fluidity of spraying powder, and a low-pressure cold spray Ni10Al coating process suitable for in-situ repair is developed to meet the performance requirements of local damage repair of aircraft titanium alloy skin.

[0042] To prove the beneficial effects of the low-pressure cold-sprayed Ni10Al coating and the powder ratio of this application, a plasma-sprayed Ni10Al coating and three other low-pressure cold-sprayed Ni10Al coatings with different raw material powder ratios were set as control groups, as follows:

[0043] Control Group 1: Plasma-sprayed Ni10Al coating

[0044] During the aircraft manufacturing stage, for local damage to the titanium alloy skin, a method of off-machine repair using a plasma-sprayed Ni10Al coating was adopted. The prepared coating had a porosity of approximately 3.1%, oxides of approximately 4.7%, and interfacial inclusions of approximately 15% (see Figure 3 ), a microhardness of approximately 151 HV, a bonding strength of approximately 38 MPa, and qualified bending properties.

[0045] Control Group 2: Low-pressure cold-sprayed Ni10Al coating

[0046] The same pure Al powder and spherical 316L stainless steel powder as in this application were selected as raw materials. The Ni powder was prepared by electrolysis with the same particle size. The powders were mixed in the same proportion as in this application. A coating was prepared using the same low-pressure cold-spraying process as in this application. Compared with the plasma-spraying process, due to the low temperature of the cold-spraying process, there were no oxides in the coating. And because the spherical 316 stainless steel powder had a larger size, it would not deposit in the coating. The prepared coating did not contain 316L stainless steel particles, and the coating composition was Ni10Al. The coating porosity was approximately 0.7%, and the interfacial inclusions were approximately 10% (see Figure 4 ), a microhardness of approximately 168 HV, a bonding strength of approximately 37 MPa, and qualified bending properties.

[0047] Control Group 3: Low-pressure cold-sprayed Ni10Al coating

[0048] The same pure Ni powder and pure Al powder as in this application were selected as raw materials, and 316L stainless steel powder was not added. The powders were mixed in a ratio of (90 ± 1.5) wt.% Ni powder and the balance Al powder. Spraying was carried out using the same low-pressure cold-spraying process as in this application. During the spraying process, since the particle sizes of both the Ni powder and Al were small, the fluidity of the spraying powder was extremely poor, and it was impossible to send the powder from the powder feeder to the spray gun, so it was impossible to prepare the coating.

[0049] Control Group 4: Low-pressure cold-sprayed Ni10Al coating

[0050] The same pure Ni powder, pure Al powder and spherical 316L stainless steel powder as those in this application are selected as raw materials. Among them, the proportion of spherical 316L stainless steel powder is 5% - 20%, the Ni:Al ratio is 9:1, and then mechanical mixing is carried out. The coating is prepared by using the same low-pressure cold spraying process as this application. After adding a small amount of spherical 316L stainless steel powder, the fluidity of the spraying powder mixed by Ni, Al and 316L powders is improved. Compared with the plasma spraying process, due to the low temperature of the cold spraying process, there are no oxides in the coating. And because the size of the spherical 316 stainless steel powder is large, it will not deposit in the coating, and the prepared coating does not contain 316L stainless steel particles. The coating composition is Ni10Al, the coating porosity is about 0.3%, and the interface inclusion is about 10% (see Figure 5 ). The microhardness is about 160HV, the bonding strength is about 78MPa, and the bending performance is qualified. However, during the spraying process, due to the relatively large proportion of the spherical 316L stainless steel powder mixed in, the improvement of the powder fluidity is limited, and the problem of barrel blockage still occurs during spraying.

[0051] Performance test results of the low-pressure cold-sprayed Ni10Al coating of this application: Compared with the plasma spraying process, due to the low temperature of the cold spraying process, there are no oxides in the coating. And because the size of the spherical 316 stainless steel powder is large, it will not deposit in the coating, and the prepared coating does not contain 316L stainless steel particles. The coating composition is Ni10Al, the coating porosity is only 0.2%, and the interface inclusion is about 5% (see Figure 6 ). The microhardness is about 166HV, the bonding strength is greater than 100MPa, and the bending performance is qualified.

[0052] The advantages of this application are as follows:

[0053] (1) Compared with Comparative Group 1, there are no oxides in the coating, and the coating components are the same as the powder components, both being Ni10Al; the coating porosity decreases, and the density is significantly improved; the bonding performance between the coating and the titanium alloy substrate is greatly improved, making the use reliability of the cold-sprayed Ni10Al coating significantly better than that of the plasma-sprayed Ni10Al coating; compared with the plasma spraying process, the cold spraying process used in this application can realize the in-situ repair of the damage of the aircraft titanium alloy skin.

[0054] (2) Compared with Comparative Group 2 using electrolytic Ni powder as the raw material, the coating porosity prepared in this application decreases slightly, and the density is improved; the bonding performance between the coating and the titanium alloy substrate is greatly improved, and the use reliability of the cold-sprayed Ni10Al coating is greatly improved.

[0055] (3) Compared with Comparative Group 3, this application mixes spherical 316L stainless steel powder into the spraying powder, and without changing the coating composition, the fluidity of the spraying powder is greatly improved, and the preparation of the cold-sprayed Ni10Al coating is realized.

[0056] (4) Compared with Comparative Group 4, by regulating the mixing ratio of spherical 316L stainless steel powder, the present application solves the problem of unstable powder flow during the in-situ repair of aircraft titanium alloy skins by cold spraying, further improves the coating bonding strength, and improves the service reliability of the cold-sprayed Ni10Al coating.

[0057] The present application mixes Ni-Al-316L powder in a certain proportion. By regulating the powder preparation process, particle size, proportion of Ni-Al-316L in the powder raw materials, and the supporting low-pressure cold spraying process parameters, a Ni10Al coating is successfully prepared, realizing the low-pressure cold spraying in-situ repair of local damage to aircraft titanium alloy skins, and is applicable to the repair of titanium alloy skin damage of any part, shape and size on the aircraft.

[0058] The repair method (1) of the present application can directly perform in-situ repair on the damaged area in-situ on the aircraft without disassembling the damaged titanium alloy skin; (2) The prepared coating has a large thickness, can repair millimeter-level damage, has a large repair tolerance, and is applicable to the repair of various damage depths; (3) The repair and protection difficulty is low, and only the surrounding position of the repair area needs to be shielded, which is applicable to the repair of damage to titanium alloy skins of any large size and complex shape. It solves the problems caused by the skin step difference after the aircraft is in service when the titanium alloy skin cannot be disassembled, including (1) affecting the aerodynamic shape of the aircraft and increasing the flight wind resistance; (2) reducing the flatness of the aircraft surface paint layer and affecting the performance of the aircraft paint layer.

[0059] In another embodiment of the present application, in Step 3, during the process of using the low-pressure cold spraying process, an infrared thermometer is used to monitor the surface temperature of the titanium alloy skin in real time so that the surface temperature does not exceed 120°C, and the Ni10Al coating obtained in Step 3 is 0.1 mm higher than the surface of the undamaged titanium alloy skin.

[0060] In another embodiment of the present application, in Step 2, the specific process of pre-treating the local damage area of the titanium alloy skin is as follows:

[0061] Use fine sandpaper to polish the local damage area of the titanium alloy skin and its edge to be flat;

[0062] Clean the local damage area with acetone;

[0063] Use a sandblaster and white corundum sand with a mesh size of 36 - 60 to perform sandblasting on the local damage area so that the surface roughness of the local damage area reaches Ra3.5 - Ra7.0;

[0064] After sandblasting, use compressed air to blow the local damage area to prevent the attachment of sand particles and floating dust.

[0065] It is understandable that grinding the locally damaged area of the titanium alloy skin can avoid factors such as sharp burrs that affect coating deposition.

[0066] In another embodiment of the present application, in step three, within 4 hours after the powder mixing in step one and within 2 hours after sandblasting in step two, a low-pressure cold spraying process is carried out for spraying.

[0067] In another embodiment of the present application, before step one, the method further includes:

[0068] According to the contour of the damaged area of the titanium alloy skin, a spraying protection tooling is prepared and the spraying protection tooling is fixed on the surface of the titanium alloy skin with high-temperature resistant tape for spraying protection of the undamaged area when repairing the damaged area of the titanium alloy skin; wherein, the spraying protection tooling is a metal thin plate with holes in the middle, and the area of the holes is 0.5 - 1 mm larger than the contour edge of the damaged area of the titanium alloy skin.

[0069] In another embodiment of the present application, after obtaining the Ni10Al coating in step five, the method further includes:

[0070] Use fine sandpaper to polish the surface of the obtained coating so that the surface roughness of the obtained coating is not higher than Ra1.6 μm and the coating edge has a smooth transition. The schematic diagram is shown in Figure 1 .

[0071] In another embodiment of the present application, the method further includes: after using fine sandpaper to polish the surface of the obtained coating, the method further includes: removing the spraying protection tooling and high-temperature resistant tape, using compressed air to blow the surface to remove floating powder, and then using acetone to clean the protected area to remove residual glue.

[0072] It is understandable that since the cold spraying process is a special process and the coating performance cannot be characterized by non-destructive testing methods after the coating is formed, in the embodiments of the present application, furnace specimens can be prepared for destructive testing to characterize the coating performance. Exemplarily, using the same titanium alloy matrix material and the same batch of raw material powders, and using the same sandblasting and cold spraying processes, furnace specimens for metallography and microhardness (coating thickness not less than 200 μm), bonding strength (coating thickness not less than 300 μm), and bending performance (coating thickness (25 - 75) μm) are prepared.

[0073] The detection of the coating performance of the furnace specimens can include the following process:

[0074] (1) For the surface coating of the metallographic and microhardness specimens, cut the specimens along the cross-section, and successively polish them with sandpapers of 600 mesh, 800 mesh, 1000 mesh, and 2000 mesh, and then polish the coating with 3μm diamond polishing fluid and 0.02μm silica polishing fluid. Observe the microstructure of the low-pressure cold-sprayed Ni10Al coating using a metallographic microscope, and analyze the properties such as porosity and interfacial inclusions of the coating with reference to the standard of HB 20195-2014 "Metallographic Inspection of Thermal Spray Coatings".

[0075] (2) Measure the microhardness of the low-pressure cold-sprayed Ni10Al coating using an automatic micro Vickers hardness tester.

[0076] (3) By means of machining, polish the surface of the coating of the bond strength specimen to a roughness of about Ra1.6μm, and then perform sandblasting on the surface coating of the bond strength specimen and the bonding surface of the counterpiece. As shown in Figure 2 , the components in the figure are: 1. Bond strength specimen (with coating), 2. Coating, 3. FM1000 film, 4. Counterpiece (without coating). Stack the counterpiece 4 - FM1000 film 3 - bond strength specimen 1 in sequence, and apply a pressure of 5 kg to 6 kg at both ends. Under the condition of maintaining the pressure, put it into an oven, heat the whole to 180°C to 190°C, keep warm for 2 h to 2.5 h, and finally cool it in the furnace. Evaluate the bond strength of the low-pressure cold-sprayed Ni10Al coating with reference to the standard of GB / T 8642-2002 "Determination of Tensile Bond Strength of Thermal Sprays".

[0077] (4) Bend the bending specimen by 90° around a round bar with a diameter of 12.7 mm and keep it, and visually observe the coating state at the bending part.

[0078] This application realizes the in-situ repair of local damage of aircraft titanium alloy skins by low-pressure cold spraying, and is applicable to the repair of damage of titanium alloy skins at any part, shape, and size on the aircraft. It has a wide application prospect in the field of in-situ repair of local damage of aircraft titanium alloy skins.

[0079] Obviously, those skilled in the art can make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalent technologies, this application is also intended to include these changes and modifications.

[0080] The above-mentioned are only the preferred specific embodiments of this application, but the protection scope of this application is not limited thereto. Any person skilled in the art within the technical scope disclosed by this application, according to the technical solution and inventive concept of this application, makes equivalent substitutions or changes, and all should be covered within the protection scope of this application.

Claims

1. An in-situ repair method for local damage of aircraft titanium alloy skin, characterized in that, The following steps are involved: Step 1: Select pure Ni powder with a purity greater than 99%, a particle size of (0-30) μm, and a D50 less than 15 μm, pure Al powder with a purity greater than 99%, a particle size of (0-20) μm, and a D50 of about 10 μm, and spherical 316L stainless steel powder with a purity greater than 99% and a particle size of (50-150) μm as raw materials, and fully mix the three powders according to the ratio of (63±1) wt.% of Ni powder, (7±1) wt.% of Al powder, and the remainder of 316L stainless steel powder to obtain a mixed powder for standby use; Step 2: pre-treating the local damaged area of the titanium alloy skin so that the surface roughness of the local damaged area reaches Ra4.0 to Ra6.0; the pre-treatment includes at least one of grinding, sandblasting and purging; Step 3: adopt a low-pressure cold spraying process to spray the mixed powder on the local damaged area to obtain a Ni10Al coating; wherein the process parameters of the low-pressure cold spraying process include: (1) process gas: nitrogen with a purity of not less than 99.9%; (2) spraying pressure: 1.3MPa~2.1MPa; (3) gas heating temperature: 400℃~550℃; (4) powder feeding rate 40g / min~90g / min; (5) spraying distance: 10mm~30mm; (6) spraying angle: 90°±20°; (7) spray gun moving speed: 10mm / s~300mm / s; Step 4: Use a visual inspection method to inspect the surface of the low-pressure cold sprayed Ni10Al coating in the local damaged area to ensure that the coating has no cracks, warping, peeling or shedding.

2. The in-situ repair method for local damage of aircraft titanium alloy skin according to claim 1, characterized in that In the step three, during the process of low-pressure cold spraying, an infrared thermometer is used to monitor the surface temperature of the titanium alloy skin in real time so that the surface temperature is not higher than 120°C. The Ni10Al coating obtained in the step three is 0.1 mm higher than the undamaged titanium alloy skin surface.

3. The in-situ repair method for local damage of an aircraft titanium alloy skin according to claim 2, characterized in that, In the step 2, the specific process of pre-treating the local damaged area of the titanium alloy skin includes: Use fine sandpaper to smoothen the local damaged area and edge of the titanium alloy skin; Cleaning the local damaged area with acetone; Using a sandblasting machine and 36-60 mesh white corundum sand, the local damaged area is sandblasted so that the surface roughness of the local damaged area reaches Ra3.5-Ra7.0; After sandblasting, the local damaged area is purged with compressed air.

4. The in-situ repair method for local damage of aircraft titanium alloy skin according to claim 3, characterized in that In the step three, a low-pressure cold spraying process is performed within 4 hours after the powder mixing in the step one and within 2 hours after the sandblasting in the step two.

5. A method for in-situ repair of local damage of an aircraft titanium alloy skin according to any one of claims 1-4, characterized in that, Before step 1, the method further includes: Prepare a spraying protection tooling according to the contour of the damaged area of the titanium alloy skin, and fix the spraying protection tooling on the surface of the titanium alloy skin with high-temperature resistant tape, which is used for spraying protection of the undamaged area when repairing the damaged area of the titanium alloy skin; wherein, the spraying protection tooling is a metal thin plate with holes in the middle, and the area of the holes is 0.5-1 mm larger than the contour edge of the damaged area of the titanium alloy skin.

6. A method for in-situ repair of local damage to the titanium alloy skin of an aircraft according to claims 1-4, characterized in that, After obtaining the Ni10Al coating in the said step five, the method further includes: Use fine sandpaper to polish the surface of the obtained coating so that the surface roughness of the obtained coating is not higher than Ra1.6 μm, and the edge of the coating has a smooth transition.

7. The in-situ repair method for local damage of aircraft titanium alloy skin according to claim 6, characterized in that, The method further includes: after using fine sandpaper to polish the surface of the obtained coating, the method further includes: removing the spraying protection tooling and the high-temperature resistant tape, using compressed air to blow the surface to remove floating powder, and then using acetone to clean the protected area to remove residual glue.

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