Supersonic flame spraying method for irregular arc surface of titanium alloy

Abstract

The invention discloses a high velocity oxy-fuel spraying method for a titanium alloy irregular arc surface. The high velocity oxy-fuel spraying method comprises the following steps that S1, the titanium alloy with the irregular arc surface is pretreated; s2, shielding the non-spraying surface of the irregular arc surface titanium alloy pretreated in the S1; s3, carrying out sand blasting treatment on the to-be-sprayed surface of the irregular arc surface titanium alloy subjected to shielding treatment in S2; and S4, the spraying face of the irregular arc face titanium alloy subjected to sand blasting treatment in the S3 is preheated through supersonic flame, spraying is conducted on the spraying face, when the variable cross section of the irregular arc face titanium alloy is met, the distance between a spraying gun and the spraying face is adjusted to be 5-20 mm, meanwhile, the angle of the spraying gun is adjusted to be 70-90 degrees, overall spraying is conducted for 15-20 times, and the final thickness of a coating is 40-80 microns. By means of the method, the uniformity and compactness of the flame spraying coating of the irregular arc surface of the titanium alloy can be guaranteed, and the coating with the wear resistance superior to the function of a chromium plating layer can be obtained.

Description

Technical Field

[0001] This invention relates to a supersonic flame spraying method for irregular arc surfaces of titanium alloys, belonging to the field of supersonic flame spraying technology. Background Technology

[0002] The landing gear locking arm is a critical safety component operating in extreme environments characterized by high loads, strong vibrations, severe corrosion, and wide temperature variations. During takeoff, landing, turning, and retraction, the landing gear's shock absorber system absorbs the majority of kinetic energy as the primary load-bearing system. However, the locking arm components connecting the shock absorber system to the retraction system need to maintain high strength while also possessing high wear resistance. One domestically produced civil aircraft landing gear locking arm adopts a "gate"-shaped structure, such as... Figure 1 As shown, the area to be sprayed by supersonic flame spraying is the outermost arc surface of the gas contour and the plane connecting to the arc surface, with the flame spraying surface angle changing by more than 165°. The part is made of Ti-5Al-5Mo-5V-1Cr-1Fe (TC18) titanium alloy. Traditional flame spraying processes are only suitable for spraying the cylindrical surfaces of relatively regular rotating parts, and cannot effectively spray the outer surfaces of irregular arc surfaces, let alone guarantee the uniformity of the coating. Furthermore, due to the poor thermal conductivity and low heat dissipation coefficient of titanium alloy parts, the temperature during the spraying process must be strictly controlled and cannot exceed 177°C. Chinese patent application CN109182948A discloses a flame spraying method, which is of some reference value, but the key information such as pretreatment and spraying equipment is unclear, and it cannot provide more guidance for flame spraying of non-rotating complex structural parts.

[0003] Chinese Patent CN107142443B discloses a method for applying a coating using supersonic flame spraying to the bottom surface of a shielded grooved part. Addressing the difficulty of continuous spraying on the bottom surface of shielded grooved parts, the method employs a two-segment supersonic flame spraying approach. By precisely controlling the step distance and spraying angle, a coating with good thickness uniformity is formed on the bottom surface of the shielded grooved part. Furthermore, by finely controlling the interval between the two spraying segments, the coatings overlap well, achieving the preparation of a uniform and continuous coating on the bottom surface of the shielded grooved part. Specifically, the steps include: 1) Effectively shielding and protecting the non-spraying areas of the shielded grooved part; 2) Installing a laser positioning device on the spray gun of the supersonic flame spraying equipment, and setting a left-side spraying trajectory I on the supersonic flame spraying robot for the bottom width direction of the shielded grooved part. Spraying trajectory I is a planar serpentine trajectory with a spraying step distance σ of 2mm to 4mm and a spraying angle θ between the spray gun flame direction and the surface to be sprayed of 56° to 63°; 3) Setting a right-side spraying trajectory II on the bottom width direction of the shielded grooved part, using the spraying method, step distance σ, and spraying angle θ, and the interval between spraying trajectory I and spraying trajectory II; 4) After the spraying trajectory is set, keeping the part fixed, applying the coating using the supersonic flame spraying process, determining the number of spraying passes according to the coating thickness, and obtaining the required coating on the bottom surface of the shielded grooved part. This solution is simple to implement and effectively solves the problem of difficult spraying on the bottom surface of shielded grooved parts. The prepared coating has excellent thickness uniformity and surface continuity, effectively meeting the usage characteristics and requirements of the spraying area of ​​shielded grooved parts. However, it cannot provide more guidance for flame spraying of non-rotating complex structural parts. Summary of the Invention

[0004] In order to overcome the lack of disclosed flame spraying methods applicable to complex non-rotating structural parts in the prior art, this invention provides a supersonic flame spraying method for irregular arc surfaces of titanium alloys, the specific technical solution of which is as follows.

[0005] A method for supersonic flame spraying of irregular arc surfaces of titanium alloys, comprising the following steps:

[0006] S1. Pre-treatment is performed on the irregular arc surface titanium alloy to obtain the pre-treated irregular arc surface titanium alloy.

[0007] S2. Mask the uncoated surface of the irregular arc-shaped titanium alloy after pretreatment in S1 to obtain the masked irregular arc-shaped titanium alloy.

[0008] S3. The irregular arc-shaped titanium alloy surface to be sprayed after the masking treatment in S2 is subjected to sandblasting treatment to obtain the irregular arc-shaped titanium alloy surface after sandblasting treatment.

[0009] S4. Use a supersonic flame to preheat the irregular arc-shaped titanium alloy surface after sandblasting in S3, and then spray the surface. When encountering the variable cross-section of the irregular arc-shaped titanium alloy, the distance between the spray gun and the spray surface changes by 5-20mm to ensure that the vertical distance between the spray gun nozzle and the part remains consistent during the spraying process. At the same time, adjust the spray gun angle to 70°-90°. Spray the entire surface 15-20 times. The coating thickness obtained is ≥100um. Finally, machine grinding is used to ensure that the final coating thickness is between 40um and 80um.

[0010] The sandblasting process in S3 increases the roughness of the substrate, improves the adhesion of the flame-sprayed coating, and enhances the bonding strength between the coating and the substrate. In S4, the flame is used without spraying powder, only for preheating. When encountering irregularly shaped, curved titanium alloy surfaces in S4, the distance between the spray gun and the spraying surface varies by 5–20 mm. Simultaneously, the spray gun angle is adjusted to 70°–90° to maintain the uniformity of coating deposition rate and thickness throughout the spraying area.

[0011] The components made of titanium alloy have an irregularly shaped arc-like curved surface on their outer surface, and the cross-sectional shape or size varies at different locations along the extension direction of the component (such as length or height). The variable cross-section of the irregular arc-shaped titanium alloy refers to the regular arc-shaped sprayed surface 2, which has a different cross-sectional shape or size from the previously sprayed regular arc-shaped sprayed surface 1.

[0012] "Spray gun angle" refers to the angle formed between the axis of the spray gun nozzle and the surface being sprayed during spraying operations. After adjusting the distance and angle of the spray gun, it is necessary to ensure the perpendicular distance from the spray gun nozzle to the part and the spraying angle. The spraying operation will proceed normally when the spray gun angle is adjusted.

[0013] The pretreatment in S1 includes one or both of degreasing and rust removal.

[0014] In one preferred embodiment, when encountering an irregular arc-shaped titanium alloy with a variable cross-section in S4, the distance between the spray gun and the spraying surface is increased by 10-20 mm, and the spray gun angle is adjusted to 75°-85°. Preferably, when encountering an irregular arc-shaped titanium alloy with a variable cross-section in S4, the distance between the spray gun and the spraying surface is increased by 10-15 mm.

[0015] In one preferred embodiment, the irregular arc-shaped titanium alloy includes at least a regular arc-shaped sprayed surface 1 and a regular arc-shaped sprayed surface 2, wherein the cross-sectional shapes or dimensions of the regular arc-shaped surface region 1 and the regular arc-shaped surface region 2 are different.

[0016] In one preferred embodiment, in step S4, the regular arc surface area I is first sprayed 15 to 20 times, starting from the masked area, with each spray width being 9 to 11 mm, then shifted 8 to 10 mm, and then sprayed in a zigzag pattern.

[0017] The width of each spray and the distance of translation can maintain the uniformity of coating deposition rate and coating thickness throughout the spraying area.

[0018] In one preferred embodiment, the part temperature does not exceed 177°C during the spraying process, and the preheating temperature in S4 is 50°C to 70°C.

[0019] In one preferred embodiment, the sandblasting medium in S3 is white corundum, 50-70 mesh, the sandblasting pressure is controlled at 0.4-0.6 MPa, the distance between the sandblasting gun and the part is 100-200 mm, and the gun moving speed is 200-350 mm / s.

[0020] Sandblasting increases the roughness of the part substrate, which is beneficial for the adhesion of flame-sprayed coatings and improves the bonding strength between the coating and the substrate.

[0021] In one preferred embodiment, the spraying powder selected in S4 is: domestically produced WC-10Co4Cr, with a particle size of 15-45 μm, a particle size of less than 45 μm accounting for 93%, a flow density of <35 s / 50 g, and a bulk density of <3.5 g / cm³. 3 The mass percentages of the chemical components are shown below:

[0022]

[0023] In one preferred embodiment, the spraying equipment selected in S4 is a UniCoatPro+WokaStar601-SZ HVOF Spray Gun. Based on previous spraying experience, the oxygen flow rate and kerosene ratio directly affect the microhardness of the coating. The amount of powder fed is the main factor affecting the coating deposition rate. The main factors affecting the bonding strength are the spraying distance and the ratio of oxygen flow rate to kerosene. After extensive verification and testing, the spraying parameters were finally set as follows: oxygen flow rate 600-700 L / min, kerosene flow rate 15-19 L / h, powder feeding percentage of the powder feeding tray 13-16%, powder feeding agitator speed 60 r / min, powder feeding amount 63-67 g / min, spraying distance 310-340 mm, number of round trips per spray gun cycle 15-20, and spray gun moving speed 550-650 mm / s.

[0024] In one preferred embodiment, S3 and S4 further include masking the non-coated surface of the part with high-temperature tape. The high-temperature tape serves to supplement and improve the tooling masking, because the tooling design itself is not problematic, but the fit between the tooling and the part is not ideal during manufacturing. The main function of the high-temperature tape is to mask areas where the dedicated tooling is not properly shielded or where there is a possibility of missed coating.

[0025] In one preferred embodiment, after S4, S5 is further included: after cooling to room temperature, grinding, non-destructive testing and coordinate measuring machine are used to ensure that the coating thickness, quality and the dimensions of the part after spraying meet the design requirements.

[0026] Before S1, the process parameters for part coating were determined. One microhardness test specimen, one metallographic specimen, one bending specimen, three bond strength specimens, and one Almen N-type residual stress specimen were prepared using the same process parameters as the part coating. These specimens underwent physicochemical property testing, and the test results met the relevant design and specification requirements. Finally, non-destructive testing was used to confirm that the part coating was free of cracks, burns, and other quality defects, ensuring that the coating quality met the technical specifications, and that the thickness and post-coating dimensions met the design requirements.

[0027] In S1, one or more of 3M polishing cotton, alcohol, and acetone are used to remove oil and rust from irregularly curved titanium alloy surfaces.

[0028] In S2, tooling and protective tape are used to mask the non-painted surfaces.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] This invention improves upon existing WC flame spraying processes. Through extensive process verification, it rationally determines supersonic flame spraying parameters and innovatively completes a flame spraying process for irregular arc surfaces of non-rotating titanium alloy parts. This method ensures the uniformity and density of the flame-sprayed coating on irregular arc surfaces of titanium alloys, resulting in a coating with wear resistance superior to chromium plating, while also being a green and environmentally friendly process that reduces pollution. Attached Figure Description

[0031] Figure 1 This is a simplified schematic diagram of an irregularly shaped arc-shaped titanium alloy. The marked area in the diagram is the surface to be coated.

[0032] Figure 2 This is a top view of an irregularly shaped, curved titanium alloy surface after it has been masked.

[0033] Figure 3 yes Figure 2 Front view.

[0034] Figure 4 This is a schematic diagram of the spraying angle.

[0035] Figure 5 This is a schematic diagram of the spraying path.

[0036] Figure 6 These are images showing the bending, hardness, metallographic structure, and bonding strength of the resulting coating. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings.

[0038] Example 1

[0039] The specific method of this invention is as follows:

[0040] 1. Determination of process parameters before part spraying. One microhardness test specimen, one metallographic specimen, one bending test specimen, three bond strength test specimens, and one Almen N-type residual stress test specimen were prepared using the same process parameters as the part spraying. The physical and chemical properties were tested, and the test results met the relevant design and specification requirements.

[0041] 2. Use 3M polishing sponge on the parts to be painted (e.g. Figure 1 Grind and remove rust (if necessary, depending on the surface condition of the parts), use organic solvents such as alcohol and acetone to degrease the surface to be sprayed, and wipe it clean with a clean white non-woven cloth.

[0042] 3. Use tooling (the tooling should be heat-resistant and fit as closely as possible to the masked surface of the part) and protective tape to mask the non-sprayed surfaces, and then perform sandblasting on the surfaces to be sprayed. The sandblasting medium is white corundum, 60 mesh, and the sandblasting pressure is controlled at 0.4-0.6MPa. The distance between the sandblasting gun and the part is 100-200mm, and the gun moving speed is 200-350mm / s. Increasing the roughness of the part substrate is beneficial to the adhesion of the flame-sprayed coating and improves the bonding strength between the coating and the substrate.

[0043] 4. Use tooling and high-temperature tape to mask the non-painted surfaces of the parts; see parts protection and placement instructions. Figures 2-3 .

[0044] 5. The coating is applied using a supersonic flame spraying device, resulting in a final coating thickness of 40-80 μm.

[0045] 1) The selected spraying powder is domestic WC-10Co4Cr powder, with chemical composition shown in Table 1. The powder particle size is 15-60 μm, flow density is <35 s / 50 g, and loose packing density is less than 3.5 g / cm³. 3 .

[0046] Table 1 Chemical composition of the sprayed powder (wt%)

[0047]

[0048] 2) The spraying equipment is a UniCoatPro+WokaStar 601SZ HVOF Spray Gun. Spraying parameters are set as follows: oxygen flow rate 600-700 L / min, kerosene flow rate 15-19 L / h, powder feeding percentage on the powder feeding tray 13-16%, powder mixing wheel speed 60 r / min, powder feeding amount 63-67 g / min, spraying distance 310-340 mm, 15-20 round trips per spray gun cycle, and spray gun moving speed 550-650 mm / s. See the single spraying path below. Figures 4-5 When encountering parts with varying cross-sections, increase the distance between the spray gun and the part by 10mm, and simultaneously adjust the spray gun angle to 80°±5°. For example, first... Figure 1 Spray the coating on surface 1. When spraying surface 2, increase the distance between the spray gun and the part by 10mm, and adjust the spray gun angle to 80°±5°. Maintain the uniformity of coating deposition rate and coating thickness throughout the spraying area, and ensure that the part temperature does not exceed 177°C during the spraying process.

[0049] 6. After the spraying is completed and the parts have cooled down, remove the protective tape and tooling, perform coating grinding and coordinate measuring machine measurement on the parts after grinding, determine the coating thickness and the final size of the parts by measuring the dimensional difference before and after spraying, and finally determine the coating thickness and the final size of the parts by non-destructive testing to ensure that the coating of the parts is free from quality defects such as cracks and burns, and ensure that the coating quality meets the technical specifications and the size of the parts meets the design requirements.

[0050] 7. For example Figure 6 As shown in a-6d, the prepared samples underwent coating bending tests according to AMS2447 specifications. After bending the samples to 180°, the coating showed no peeling or through cracks. Hardness was tested according to AMS 7887 requirements, with a required HV value. 300 The ≥950 test result requires all 12 points to be greater than HV. 300 The coating strength is ≥950 MPa, the metallographic test shows that the porosity is ≤1%, and the interface contamination is ≤10%, all of which meet the above standard requirements.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that when encountering irregular arc-shaped titanium alloy with variable cross-section, the coating thickness on the part surface is 54-226um when the number of spraying times is 14, and the coating thickness after grinding is 46.4-174um, which does not meet the final thickness size requirements, and the uniformity of the coating layer in different spraying areas is poor.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 1 is that when encountering irregular arc-shaped titanium alloys with varying cross-sections, the coating thickness is between 90-320 μm when the number of spraying cycles is 21. The overall thickness is relatively thick, and the subsequent grinding workload is huge, resulting in a long grinding cycle and poor economic efficiency.

[0055] Example 2

[0056] In this embodiment, when encountering irregularly shaped, curved titanium alloy surfaces with varying cross-sections, the distance between the spray gun and the surface to be coated is adjusted by 5-20 mm when the number of spraying passes is 18, ensuring that the perpendicular distance between the spray gun and the part surface remains constant. Simultaneously, the spray gun angle is adjusted to 80±5°. The coating thickness on the part surface is 80-262 μm, and after grinding, the coating thickness is between 52.4-78.9 μm, indicating a relatively uniform coating thickness that meets the technical requirements.

[0057] The embodiments of the present invention have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention is not limited to the specific embodiments described above; these embodiments are merely illustrative and not limiting. Those skilled in the art, under the guidance of the present invention, can make many modifications without departing from the spirit and scope of the claims, and all such modifications fall within the scope of protection of the present invention.

Claims

1. A method for supersonic flame spraying of irregular arc surfaces of titanium alloys, characterized in that, It includes the following steps: S1. Pre-treatment is performed on the irregular arc surface titanium alloy to obtain the pre-treated irregular arc surface titanium alloy. S2. Mask the uncoated surface of the irregular arc-shaped titanium alloy after pretreatment in S1 to obtain the masked irregular arc-shaped titanium alloy. S3. The irregular arc-shaped titanium alloy surface to be sprayed after the masking treatment in S2 is subjected to sandblasting treatment to obtain the irregular arc-shaped titanium alloy surface after sandblasting treatment. S4. Use a supersonic flame to preheat the irregular arc-shaped titanium alloy surface after sandblasting in S3, and then spray the surface. When encountering the variable cross-section of the irregular arc-shaped titanium alloy, the distance between the spray gun and the spray surface changes by 5-20mm to ensure that the vertical distance between the spray gun nozzle and the part remains consistent during the spraying process. At the same time, adjust the spray gun angle to 70°-90°. Spray the entire surface 15-20 times. The coating thickness obtained is ≥100um. Finally, machine grinding is used to ensure that the final coating thickness is between 40um and 80um.

2. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to claim 1, characterized in that, When encountering an irregularly shaped arc-shaped titanium alloy with a variable cross-section in S4, the distance between the spray gun and the spraying surface is increased by 10-20 mm, and the spray gun angle is adjusted to 75°-85°. Preferably, when encountering an irregularly shaped arc-shaped titanium alloy with a variable cross-section in S4, the distance between the spray gun and the spraying surface is increased by 10-15 mm.

3. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to claim 1, characterized in that, The irregular arc surface titanium alloy includes at least a regular arc sprayed surface 1 and a regular arc sprayed surface 2, wherein the cross-sectional shape or size of the regular arc sprayed surface 1 and the regular arc sprayed surface 2 are different.

4. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to claim 3, characterized in that, In S4, the regular arc surface area I is first sprayed 15 to 20 times, starting from the masked area. The width of each spray is 9 to 11 mm, then shifted 8 to 10 mm, and then sprayed in a zigzag pattern.

5. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to any one of claims 1-4, characterized in that, During the spraying process, the part temperature should not exceed 177℃, and the preheating temperature in S4 is 50℃-70℃.

6. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to any one of claims 1-4, characterized in that, In S3, the sandblasting medium is white corundum, 50-70 mesh, the sandblasting pressure is controlled at 0.4-0.6MPa, the distance between the sandblasting gun and the part is 100-200mm, and the gun moving speed is 200-350mm / s.

7. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to any one of claims 1-4, characterized in that, The powder used in S4 is domestically produced WC-10Co4Cr, with a particle size of 15-45µm, 93% of which are below 45µm, a flow density of <35s / 50g, and a bulk density of <3.5g / cm³. 3 The mass percentages of the chemical components are shown below:

8. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to any one of claims 1-4, characterized in that, The spraying equipment selected in S4 is a UniCoatPro+WokaStar 601-SZ HVOF Spray Gun. The spraying parameters are set as follows: oxygen flow rate 600-700L / min, kerosene flow rate 15-19L / h, powder feeding percentage of the powder feeding tray 13-16%, powder feeding agitator speed 60r / min, powder feeding amount 63-67g / min, spraying distance 310-340mm, number of round trips per spray gun program 15-20, and spray gun moving speed 550-650mm / s.

9. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to any one of claims 1-4, characterized in that, Between S3 and S4, high-temperature tape is also used to mask the non-painted surfaces of the parts.

10. The supersonic flame spraying method for irregular arc surfaces of titanium alloys according to any one of claims 1-4, characterized in that, S4 is followed by S5. After cooling to room temperature, grinding, non-destructive testing, and coordinate measuring machine are used to ensure that the coating thickness, quality, and dimensions of the parts after spraying meet the design requirements.

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