Composite Coating for Laser Shock Peening, Preparation Method and Usage Method

Abstract

The present invention provides a composite coating for laser shock peening, its preparation method and usage method, belonging to the field of laser shock peening. The composite coating consists of an absorption layer coating and a constraint layer coating. The constraint layer coating includes: 15% - 25% sodium carboxymethylcellulose, 10% - 15% gelatin, 5% - 7% glycerol, 4% - 8% propylene glycol, 2% - 5% polyethylene glycol, 0.1% - 0.5% calcium citrate and the balance of water. The absorption layer coating includes: 45% - 55% waterborne acrylic resin, 5% - 10% absolute ethanol, 2% - 3% polyvinylpyrrolidone, 15% - 20% nano carbon black and 25% - 30% nano coating powder. Through the composite coating provided by the present invention, the coating and shock strengthening of the shaped workpiece material can be synchronously achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of laser shock peening, and specifically, to a composite coating for laser shock peening, a preparation method of the composite coating for laser shock peening, and a use method of the composite coating for laser shock peening. Background Art

[0002] Laser shock peening technology significantly improves the fatigue life, wear resistance, and corrosion resistance of materials by generating a controllable residual compressive stress layer, and is widely used in fields such as aerospace, energy equipment, and automotive manufacturing.

[0003] Laser shock peening technology is a new type of surface strengthening technology and also an efficient surface modification technology. This technology uses the extreme instantaneous energy of high-power short-pulse lasers (nanosecond level, power density about 109W / cm 2 2) to induce rapid melting and vaporization of the surface layer material. During the laser shock peening process, on the one hand, by pre-depositing an absorption layer such as black paint or aluminum foil on the metal surface, the laser energy absorption rate is significantly enhanced, the expansion of the heat-affected area is suppressed, and material damage caused by the thermal effect is reduced; on the other hand, by covering a transparent medium such as flowing water or K9 optical glass as a constraint layer, the expansion of the high-temperature and high-pressure plasma formed by the ionization of the vaporized metal is constrained, generating a reverse high-pressure shock wave (up to GPa) acting on the material surface to achieve shock strengthening. The shock wave causes plastic deformation of the surface layer material, and the depth of the residual compressive stress layer formed is usually 0.1mm - 2mm.

[0004] However, common laser shock peening constraint layers in the prior art, such as flowing water and K9 optical glass, are difficult to achieve uniform constraint on shaped workpieces. Uneven thickness of the constraint layer may form a local laser focusing effect, affecting the uniformity of strengthening, and it is difficult to fully utilize the high controllability and complex shape adaptability characteristics of the laser. More critically, the existing laser shock peening process mainly suppresses the thermal influence of pulsed lasers through rapid cooling and low-thermal-conductivity absorption materials, resulting in 60% - 70% of the laser energy being wasted, and the potential of laser thermal-mechanical synergistic strengthening has not been fully exploited.

[0005] Therefore, there is an urgent need to develop a new composite coating system to achieve uniform constraint on shaped workpieces while exerting the thermal-mechanical synergistic effect of high-energy pulsed lasers. Summary of the Invention

[0006] Aiming at the technical problem that common laser shock peening constraint layers in the prior art, such as flowing water and K9 optical glass, are difficult to achieve uniform constraint on shaped workpieces, the present invention provides a composite coating for laser shock peening, its preparation method, and its use method. Using this composite coating can achieve uniform constraint on shaped workpieces, fully exert the thermal-mechanical synergistic effect of pulsed lasers, and synchronously achieve coating and shock strengthening of materials.

[0007] To achieve the above object, a first aspect of the present invention provides a composite coating for laser shock peening, including an absorption layer coating and a constraint layer coating. The absorption layer coating is a black coating material, and the constraint layer coating includes: 15% - 25% sodium carboxymethylcellulose, 10% - 15% gelatin, 5% - 7% glycerol, 4% - 8% propylene glycol, 2% - 5% polyethylene glycol, 0.1% - 0.5% calcium citrate, and the balance of water.

[0008] In an exemplary embodiment of the present invention, the degree of substitution of the sodium carboxymethylcellulose is preferably 0.7 - 1.2.

[0009] In an exemplary embodiment of the present invention, the absorption layer coating may include: 45% - 55% waterborne acrylic resin, 5% - 10% absolute ethanol, 2% - 3% polyvinylpyrrolidone, 15% - 20% nano carbon black, and 25% - 30% nano coating powder.

[0010] In an exemplary embodiment of the present invention, the nano coating powder may be at least one of tungsten disulfide nano powder, ceramic nano powder, silicon dioxide nano powder, and zirconium dioxide nano powder.

[0011] In an exemplary embodiment of the present invention, the particle size of the nano coating powder may be less than 50 nm.

[0012] A second aspect of the present invention provides a preparation method of a composite coating for laser shock peening. The preparation method of the composite coating for laser shock peening includes: preparing an absorption layer coating and preparing a constraint layer coating; wherein, the preparation of the constraint layer coating includes the following steps: adding 15% - 25% sodium carboxymethylcellulose into deionized water, stirring and standing to obtain a CMC homogeneous colloid; adding 10% - 15% gelatin, 5% - 7% glycerol, 4% - 8% propylene glycol, and 2% - 5% polyethylene glycol into the CMC homogeneous colloid in a water bath environment in sequence, and obtaining an intermediate product after ultrasonic oscillation; adding 0.1% - 0.5% calcium citrate into the intermediate product, and forming a constraint layer coating after ionic crosslinking.

[0013] In another exemplary embodiment of the present invention, when the degree of substitution of the sodium carboxymethylcellulose is 0.7 - 1.2, the hydration temperature of the sodium carboxymethylcellulose can be set at 45°C - 60°C.

[0014] In another exemplary embodiment of the present invention, the water bath temperature can be set at 45°C - 50°C.

[0015] In another exemplary embodiment of the present invention, the preparation of the absorbent layer coating may include the following steps: premixing 15% - 20% carbon black nanoparticles, 25% - 30% nano-coating powder, 5% - 10% absolute ethanol, and 2% - 3% polyvinylpyrrolidone, and obtaining a black slurry after ball milling; adding 45% - 55% waterborne acrylic resin to the black slurry and stirring to obtain the absorbent layer coating.

[0016] In another exemplary embodiment of the present invention, the nano-coating powder may be at least one of tungsten disulfide nano-powder, ceramic nano-powder, silica nano-powder, and zirconia nano-powder.

[0017] The third aspect of the present invention provides a method for using the composite coating for laser shock peening. The method for using the composite coating for laser shock peening includes the following steps: coating the composite coating on the surface of a metal component to form the surface of the metal component to be laser shock peened; performing laser shock peening on the surface of the metal component to be laser shock peened; using hot water at 60°C - 80°C to wash the surface of the metal component after laser shock peening to remove the residual composite coating.

[0018] In another exemplary embodiment of the present invention, the coating of the composite coating on the surface of the metal component to form the surface of the metal component to be laser shock peened may include: spraying the absorbent layer coating on the surface of the metal component, and after drying and curing, forming an absorbent layer film on the surface of the metal component; scraping the constraint layer coating on the surface of the absorbent layer film, and after drying and curing, forming the surface of the metal component to be laser shock peened.

[0019] In another exemplary embodiment of the present invention, the coating of the composite coating on the surface of the metal component to form the surface of the metal component to be laser shock peened may also include: spraying the absorbent layer coating on the surface of the metal component, and after drying and curing, forming an absorbent layer film on the surface of the metal component; using the casting film-forming method to scrape the constraint layer coating into a mold, and after drying and curing, forming a constraint layer gel film; adhering the constraint layer gel film to the surface of the absorbent layer film to form the surface of the metal component to be laser shock peened.

[0020] Through the technical solution provided by the present invention, the present invention has at least the following technical effects:

[0021] (1) To overcome the defect that the unevenness of the common constraint layer results in poor laser shock peening effect, the present invention provides a novel high-transparency gel as a constraint layer coating. This gel has characteristics such as high light transmittance, high elasticity, heat resistance, and rapid film formation, and can effectively constrain the heat and shock wave pressure generated by mJ-level laser energy. Applying the composite coating system for laser shock peening formed by this high-transparency gel and a conventional absorption layer coating (such as black paint) can achieve uniform constraint on shaped workpieces, thus fully exerting the characteristics of high controllability and complex shape adaptability of the laser;

[0022] (2) Aiming at the usage requirements of different material surfaces, the present invention forms a nano hybrid paint by doping different types of nano-coating powders in the absorption layer coating. Applying the composite coating system for laser shock peening formed by this nano hybrid paint and the high-transparency gel provided by the present invention can not only improve the laser shock peening effect, but also realize the preparation of different types of nano films on the material surface through the synergistic thermal-mechanical effect of pulsed laser;

[0023] (3) The composite coating provided by the present invention can be quickly removed by hot water at 60°C - 80°C, which is convenient for carrying out repeated spraying and coating processing;

[0024] (4) The preparation method of the composite coating provided by the present invention is simple and can be prepared and used immediately.

[0025] Other features and advantages of the present invention will be described in detail in the following specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the specification. Together with the following specific implementation manners, they are used to explain the embodiments of the present invention, but do not constitute a limitation to the embodiments of the present invention. In the drawings:

[0027] Figure 1 is a schematic diagram of the application of the composite coating provided by the embodiment of the present invention;

[0028] Figure 2A is a surface morphology diagram of the material of the unprocessed TC4 alloy sheet sample provided by the embodiment of the present invention;

[0029] Figure 2B is a surface morphology diagram of the material of the TC4 alloy sheet sample processed without using the composite coating provided by the embodiment of the present invention;

[0030] Figure 2C is a surface morphology diagram of the material of the TC4 alloy sheet sample processed using the composite coating provided by the embodiment of the present invention;

[0031] Figure 3 is a comparison diagram of the phase change of the material surface before and after processing with the composite coating provided by the embodiment of the present invention.

[0032] Description of Reference Numerals

[0033] 1 - Green light pulse laser, 2 - Frequency doubling crystal, 3 - Focusing lens, 4 - Laser beam, 5 - Nano hybrid paint, 6 - High - transparency gel, 7 - Metal material, 8 - Processing and clamping device. Specific Embodiment

[0034] The following will describe in detail the specific embodiments of the embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention.

[0035] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0036] In the present invention, unless otherwise stated, the orientation terms such as "upper, lower, top, bottom" are usually relative to the direction shown in the accompanying drawings or relative to the vertical, perpendicular or gravitational direction for the description of the mutual positional relationship of each component. "First", "second", etc. are only for convenience of description and easy distinction, and cannot be understood as indicating or implying relative importance.

[0037] In the description of the present invention, it should also be noted that K9 in "K9 optical glass" refers to the grade of optical glass, "PVP" represents "polyvinylpyrrolidone", "CMC" represents "sodium carboxymethyl cellulose", "DS" represents "degree of substitution", "PEG - 400" represents "polyethylene glycol", "PTFE" represents "tetrafluoroethylene", and "TC4" represents "titanium alloy". For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0038] The following will describe the present invention in detail with reference to the accompanying drawings and in combination with embodiments.

[0039] The principle of laser shock peening technology is as follows: When a nanosecond pulsed laser bombards the surface of a metal material, the absorption layer absorbs the laser energy and is vaporized and ionized into a plasma state in a very short time (ns order of magnitude). The plasma will continue to absorb energy and expand rapidly. Since there is also a constraint layer on the surface of the absorption layer, the shock wave formed after the plasma expands can only continue to propagate in the direction of the material. The pressure generated by the plasma shock wave is much greater than the yield strength of the metal material. Under the pressure of the shock wave, a series of changes will occur, including the formation of a residual stress field inside, improving the microstructure near the surface of the material and forming residual stress on the surface of the material, thereby significantly improving the fatigue life, corrosion resistance and wear resistance of the metal material.

[0040] Currently, common laser shock peening constraint layers such as flowing water and K9 optical glass are difficult to achieve uniform constraint on shaped workpieces. Specifically, flowing water forms a laser shock constraint layer by sputtering on the surface of the specimen in a liquid state. Its thickness is difficult to control, and bubbles are likely to occur. K9 optical glass, on the other hand, is a solid material that is only suitable for simple planes and is difficult to match the surface of shaped workpieces. The uneven thickness of the constraint layer may form a local laser focusing effect, affecting the uniformity of strengthening and making it difficult to fully utilize the high controllability and complex shape adaptability of the laser. In addition, the uneven thickness of the constraint layer will also result in 60% - 70% of the laser energy being wasted, failing to fully exploit the potential of laser thermo-mechanical synergistic strengthening.

[0041] To solve the technical problem that common laser shock peening constraint layers such as flowing water and K9 optical glass in the prior art are difficult to achieve uniform constraint on shaped workpieces, an embodiment of the present invention provides a composite coating for laser shock peening. This composite coating consists of an absorption layer coating and a constraint layer coating. After the absorption layer coating is sprayed and dried, the constraint layer coating is applied, and uniform constraint on shaped workpieces (such as complex three-dimensional surfaces) can be achieved.

[0042] Specifically, the absorption layer coating is a black coating material, which is used to absorb the laser energy on the surface of the metal material and efficiently convert the laser energy into shock waves, thereby strengthening the surface of the substrate. For example, the absorption layer coating can be a black paint coating with bonding function.

[0043] Preferably, the absorption layer coating can also be set as a nano hybrid paint, and its component ratio can be: 45% - 55% waterborne acrylic resin, 5% - 10% absolute ethanol, 2% - 3% polyvinylpyrrolidone (PVP), 15% - 20% nano carbon black, and 25% - 30% nano coating powder. The nano coating powder can be set as at least one of tungsten disulfide (WS2) nano powder, ceramic nano powder, silicon dioxide (SiO2) nano powder, and zirconium dioxide (ZrO2) nano powder. In addition, the particle size of the nano coating powder ≤ 50nm. For example, it can be set as 20nm, 25nm, 30nm, 40nm, etc.

[0044] The constraint layer coating is a new type of high-transparency gel, which is used to constrain the shock waves generated by plasma expansion and react the shock waves on the material. The component ratio of this constraint layer coating is: 15% - 25% sodium carboxymethyl cellulose (CMC), 10% - 15% gelatin, 5% - 7% glycerol, 4% - 8% propylene glycol, 2% - 5% polyethylene glycol (PEG - 400), 0.1% - 0.5% calcium citrate, and the balance of water.

[0045] It should be noted that the inventor has found through research that the high elasticity of medical hydrocolloid can effectively constrain the heat and shock wave pressure generated by mJ-level laser energy, but it generally has problems such as poor light transmittance, lack of directivity in design, and high usage costs. In order to configure a highly transparent gel specifically applicable to laser shock peening, the present invention selects CMC, PEG-400, gelatin, glycerol, calcium citrate, and propylene glycol as raw materials, and finally obtains a new type of highly transparent gel material through targeted design and adjustment of the ratios of each component. This gel material has characteristics such as high light transmittance, high elasticity, heat resistance, and rapid film formation.

[0046] Among them, the role of CMC is to serve as the base material of the gel skeleton. CMC with a low degree of substitution (DS = 0.7 - 1.2) is preferred, which can effectively reduce light scattering. If the content of CMC is reduced, such as when the content of CMC is less than 15%, it will lead to poor gel continuity.

[0047] The role of gelatin is to enhance the mechanical strength of the gel and assist in gel formation. If the content of gelatin is too small, it will result in poor mechanical strength of the gel.

[0048] The role of glycerol is to increase the toughness and ductility of the gel and reduce brittleness. If the content of glycerol is reduced, such as when the content of oil is less than 5%, it will lead to poor water retention.

[0049] The role of PEG-400 is to reduce the turbidity caused by local aggregation of the gel and further improve the light transmittance of the gel. In addition, since high-purity low-degree-of-substitution CMC will increase costs, the addition of this component can improve the transparency of the gel at a low cost.

[0050] Calcium citrate acts as an ionic cross-linking agent. By slightly cross-linking calcium ions with the carboxyl groups of CMC, it enhances the strength of the gel network and controls the swelling rate. When the content of calcium citrate is less than 0.3%, the cross-linking is milder, but when the content of calcium citrate exceeds 0.5%, it will cause the gel to become turbid and brittle.

[0051] Propylene glycol acts as a plasticizer to adjust the viscosity. Deionized water acts as a solvent, which can fully hydrate CMC and gelatin to form a homogeneous system and maintain the fluidity of the gel.

[0052] In addition, it should be noted that in order to simultaneously achieve surface strengthening and coating of metal materials, the present invention improves the composition ratio of the absorbent layer coating. An aqueous acrylic resin is used as a binder, nano carbon black is used as the main light absorber, absolute ethanol is used as a solvent, PVP is used as a dispersant, and nano coating powder is doped, finally forming a nano hybrid paint. The role of the aqueous acrylic resin is to assist in film formation. If the content of the aqueous acrylic resin is too low, for example, when the content of the aqueous acrylic resin is less than 45%, the film-forming performance of the paint spraying will deteriorate, and cracking and peeling are likely to occur. The role of nano carbon black is to absorb light. If the content of nano carbon black is too low, for example, when the content of nano carbon black is less than 15%, the obtained nano hybrid paint will be overall grayish-white, which will significantly reduce the absorption rate of laser energy. The nano coating powder is the coating powder selected for coating the metal material, and the nano size is for better activation by small energy. If the content of the nano coating powder is too low, the coating efficiency and uniformity will be reduced. The role of absolute ethanol is to act as a solvent to adjust the viscosity. The role of PVP is to act as a dispersant to prevent powder agglomeration.

[0053] During the laser shock peening process, other components except the nano coating powder will vaporize to form a plasma under the action of a high-power density laser, generating a shock wave, while the nano coating powder is deposited on the metal surface and finally forms a film through the thermo-mechanical effect of the cooperative pulsed laser. For different surface usage requirements of materials, different nano coating powders can be doped in the nano hybrid paint.

[0054] If the high-transparency gel material provided by the present invention is used alone to coat the metal surface, laser shock peening can also be achieved, but the strengthening effect will be weakened. This is because most metal surfaces are not black and have a poor absorption effect on lasers, so it is necessary to coat an absorbent layer material to enhance the laser absorption effect. If this high-transparency gel material and a conventional absorbent layer coating (such as black paint) are used to form a composite coating system for laser shock peening, uniform constraint of the shaped workpiece can be achieved, thereby fully exerting the characteristics of high controllability and complex shape adaptability of the laser.

[0055] If the nano hybrid paint provided by the present invention is used alone to coat the metal surface, since the laser will only directly remove the sprayed nano hybrid paint layer on the surface, the nano coating particles are not constrained and volatilize into the air, and laser shock peening cannot be achieved. If this nano hybrid paint and the above-mentioned high-transparency gel material are used to form a composite coating system for laser shock peening, not only can uniform constraint of the shaped workpiece be achieved, but also the thermo-mechanical synergistic effect of the pulsed laser can be fully exerted to simultaneously achieve coating and shock strengthening of the metal material.

[0056] In summary, the composite coating provided by the present invention can be directly coated on the surface of the shaped workpiece, and compared with liquid water, the thickness of the composite coating that is solidified from liquid in the early stage is more controllable, and self-adaptive spraying and curing can be achieved.

[0057] Correspondingly, an embodiment of the present invention further provides a method for preparing a composite coating for laser shock peening, including the following steps:

[0058] Step S101, preparing an absorption layer coating;

[0059] Step S102, preparing a constraint layer coating.

[0060] Wherein, when the absorption layer coating selects the nano hybrid paint provided by the present invention, in step S101, the process of preparing the absorption layer coating may include but is not limited to the following sub-steps:

[0061] Sub-step S1011, premixing 15% - 20% nano carbon black, 25% - 30% nano coating powder, 5% - 10% absolute ethanol and 2% - 3% polyvinylpyrrolidone, and obtaining a black slurry after ball milling for 1h - 2h (rotation speed 300rpm);

[0062] Sub-step S1012, adding 45% - 55% waterborne acrylic resin to the black slurry, and obtaining the absorption layer coating after stirring.

[0063] In step S102, the process of preparing the constraint layer coating may include but is not limited to the following sub-steps:

[0064] Sub-step S1021, adding 15% - 25% CMC into deionized water, magnetically stirring until the CMC is completely dissolved, and standing for 1h to fully hydrate it to form a CMC homogeneous colloid;

[0065] Sub-step S1022, sequentially adding 10% - 15% gelatin, 5% - 7% glycerol, 4% - 8% propylene glycol and 2% - 5% polyethylene glycol to the CMC homogeneous colloid under a water bath environment, and obtaining an intermediate product after removing bubbles by ultrasonic oscillation;

[0066] Sub-step S1023, adding 0.1% - 0.5% calcium citrate to the intermediate product, and forming the constraint layer coating after ionic crosslinking.

[0067] Here, it should be noted that the hydration temperature should be determined according to the degree of substitution of the selected CMC. The lower the degree of substitution, the higher the energy required to break the crystalline region of CMC. For example, when the degree of substitution of sodium carboxymethyl cellulose is 0.7 - 1.2, the hydration temperature of sodium carboxymethyl cellulose can be set to 45°C - 60°C. In other words, in sub-step S1021, 15% - 25% CMC should be added to deionized water at 45°C - 60°C for stirring.

[0068] Since the gel point of the Mingjiao is typically 30°C to 35°C, the fusion temperature is slightly above this range to prevent localized gelation. Therefore, the water bath temperature in sub-step S1022 needs to be set to 45°C to 50°C to prevent the water bath temperature from being too low, which would lead to uneven dispersion of the additive. Furthermore, in sub-step S1023, the intermediate product needs to be cooled to 30°C to 40°C before adding calcium citrate for ionic crosslinking.

[0069] An embodiment of the present invention further provides a method for using the composite coating for laser shock peening, the method comprising the following steps:

[0070] Step S201, coating the composite coating on the surface of a metal component to form a surface of the metal component to be laser shock peened;

[0071] Step S202, performing laser shock peening on the surface of the metal component to be laser shock peened;

[0072] Step S203 , using hot water at 60° C. to 80° C. to wash the surface of the metal component after laser shock peening to remove residual composite coating.

[0073] Furthermore, in a possible embodiment, the surface of the metal component to be laser shock peened can be formed by first spraying the absorbing layer coating and then directly coating the constraining layer material.

[0074] Specifically, in step S201, the process of coating the composite coating on the surface of the metal component to form the surface of the metal component to be laser shock peened may include but is not limited to the following sub-steps S2011 and S2012:

[0075] Sub-step S2011, spraying the absorption layer coating on the surface of the metal component, and forming an absorption layer film on the surface of the metal component after drying and curing;

[0076] Sub-step S2012: scraping the constraining layer coating onto the surface of the absorbing layer film, and after drying and curing, forming the surface of the metal component to be laser shock peened.

[0077] Furthermore, in another possible embodiment, in order to make the thickness of the high-transmittance gel film more uniform and more efficient to use, the surface of the metal part to be laser shock strengthened can be formed by first spraying the absorption layer coating and then using the cast film method to coat the constraint layer material.

[0078] Specifically, in step S201, the process of coating the composite coating on the surface of the metal component to form the surface of the metal component to be laser shock peened may also include but is not limited to the following sub-steps S2011' to S2013':

[0079] Sub-step S2011': Spray the absorbent layer coating on the surface of the metal component. After drying and curing, an absorbent layer film is formed on the surface of the metal component.

[0080] Sub-step S2012': Use the casting film-forming method to scrape the constraint layer coating into a mold. After drying and curing, a constraint layer gel film is formed.

[0081] Sub-step S2013': Adhere the constraint layer gel film to the surface of the absorbent layer film to form the surface of the metal component to be laser shock strengthened.

[0082] To better understand the above exemplary embodiments of the present invention, the following further describes them with specific examples and drawings.

[0083] Example 1

[0084] In this embodiment, the specific steps of a preparation method of a composite coating for laser shock strengthening are as follows.

[0085] Step 1: Prepare a nano hybrid paint.

[0086] First, premix 8 g of anhydrous ethanol, 2 g of PVP, 15 g of carbon black (100 nm), and 25 g of WS2 powder (50 nm), and ball mill for 1 h to 2 h (rotation speed 300 rpm) to obtain a black slurry; then add 50 g of waterborne acrylic resin to the black slurry and obtain a nano hybrid paint by magnetic stirring.

[0087] Step 2: Prepare a high-transparency gel.

[0088] First, add 20 g of CMC (DS = 0.9) to 60 g of deionized water at 50 °C, use magnetic stirring until the CMC is completely dissolved, and let it stand for 1 h to fully hydrate to form a CMC homogeneous colloid; sequentially add 10 g of gelatin, 5 g of glycerol, 3 g of PEG-400, and 4 g of propylene glycol in a 60 °C water bath environment, stir well and then use ultrasonic oscillation to remove bubbles to obtain an intermediate product; finally, cool the intermediate product to 30 °C, add 0.3 g of calcium citrate, and stir to form a high-transparency gel.

[0089] Through the above preparation method, the nano hybrid paint and the high-transparency gel can be respectively prepared, and then combined to form a composite coating for laser shock strengthening. The specific steps of using this composite coating for laser shock strengthening are as follows.

[0090] Step 1: Use a spray gun with a 0.3 mm nozzle to evenly spray the nano hybrid paint on the surface of the metal material at a pressure of 0.5 Mpa, and dry it at room temperature. The thickness is about 20 μm.

[0091] Step 2: Scrape and coat the high-transparency gel onto the surface of the nano hybrid paint after drying, and dry it at room temperature for 3 hours to form a high-transparency gel film with a thickness of about 100 μm.

[0092] Step 3: Use a 532-nm green light pulsed laser to perform laser shock peening on the surface of TC4 coated with the composite coating. Among them, the laser energy is set to 60 mJ, the spot diameter is set to 0.4 mm, and the laser overlap rate is set to 50%.

[0093] Step 4: Use hot water at 60 °C to 80 °C to wash the surface of the metal material to remove the residual composite coating on the material surface.

[0094] Figure 1 The application schematic diagram of the composite coating provided by this embodiment is as Figure 1 shown. During the laser shock peening process, after fixing the metal material 7 using the processing clamping device 8, the nano hybrid paint 5 and the high-transparency gel 6 are coated on the surface of the metal material 7, and the high-transparency gel 6 is located above the nano hybrid paint 5. When the laser beam 4 formed by the laser generated by the green light pulsed laser 1 passing through the frequency doubling crystal 2 and the focusing lens 3 acts on the surface of the metal material, the nano hybrid paint 5 will absorb the laser energy and convert it into a shock wave. The high-transparency gel 6, as a constraint layer for the shock wave energy, makes the shock wave act on the material in two ways. One is to introduce residual compressive stress to strengthen the surface of the metal material, and the other is to assist the nano coating powder to deposit on the surface of the metal material.

[0095] Figure 2A shows the surface morphology of the material of the unprocessed TC4 alloy sheet specimen, Figure 2B shows the surface morphology of the material of the TC4 alloy sheet specimen processed without using the composite coating, Figure 2C shows the surface morphology of the material of the TC4 alloy sheet specimen processed using the composite coating provided by this embodiment. Figure 3 shows the phase change of the material surface before and after processing with the composite coating. It can be seen that, Figure 3 using an X-ray diffractometer to detect the phase composition of the material surface, on the Figure 2C material surface, the phase of the WS2 coating powder is detected, and there is a pit texture unique to laser shock peening on the material surface, which proves that the composite coating of this embodiment can be used to simultaneously achieve laser coating and shock strengthening.

[0096] Example 2

[0097] In this embodiment, the preparation method of Example 1 is continued to prepare the composite coating for laser shock peening. The specific steps for performing laser shock peening using this composite coating are as follows.

[0098] Step 1: Use a spray gun with a 0.3-mm nozzle to evenly spray the nano hybrid paint on the surface of the metal material at a pressure of 0.5 Mpa, and dry it at room temperature with a thickness of about 20 μm.

[0099] Step 2: Prepare a highly transparent gel by the casting film method. Coat it with a thickness of 100 μm into a polytetrafluoroethylene (PTFE) mold. Set the humidity of the drying oven to 40%, and conduct preliminary drying for 30 min in an environment at a temperature of 30 °C, and then conduct final drying for 1 h in an environment at a temperature of 45 °C to form a dry, cured and uniform-thickness finished highly transparent gel film.

[0100] Step 3: The finished highly transparent gel film can be directly peeled off and adhered to the dried surface of the nano hybrid paint.

[0101] Step 4: Use a green light pulse laser with a wavelength of 532 nm to perform laser shock peening on the surface of TC4 coated with the composite coating. Among them, the laser energy is set to 60 mJ, the spot diameter is set to 0.4 mm, and the laser overlap rate is set to 50%.

[0102] Step 5: Flush the surface with hot water at 60 °C - 80 °C to remove the residual composite coating on the material surface. Wipe the surface of the specimen with anhydrous ethanol and dry it with hot air.

[0103] Step 6: Steps 1, 3, and 5 can be cyclically repeated to achieve laser coating and shock peening with multiple cycle numbers.

[0104] Example 3

[0105] In this example, the specific steps of a preparation method of a composite coating for laser shock peening are as follows.

[0106] Step 1: Prepare a nano hybrid paint.

[0107] First, premix 10 g of anhydrous ethanol, 2 g of PVP, 18 g of carbon black (100 nm), and 25 g of ceramic powder (50 nm), and ball mill for 1 h - 2 h (rotation speed 300 rpm) to obtain a black slurry; then add 45 g of waterborne acrylic resin to the black slurry and obtain a nano hybrid paint through magnetic stirring.

[0108] Step 2: Prepare a highly transparent gel.

[0109] First, add 15 g of CMC (DS = 0.7) to 55 g of deionized water at 50 °C, and use magnetic stirring until the CMC is completely dissolved, and let it stand for 1 h to fully hydrate to form a CMC homogeneous colloid; in a water bath environment at 60 °C, add 15 g of gelatin, 5 g of glycerol, 5 g of PEG - 400, and 4 g of propylene glycol in sequence, and after sufficient stirring, use ultrasonic oscillation to remove bubbles to obtain an intermediate product; finally, cool the intermediate product to 30 °C, add 0.5 g of calcium citrate, and stir to form a highly transparent gel.

[0110] The above preparation method can be used to prepare nano-hybrid paint and high-transmittance gel respectively, and then combine them to form a composite coating for laser shock peening. The specific steps of using the composite coating for laser shock peening are as follows.

[0111] Step 1: Use a spray gun with a 0.3mm nozzle to evenly spray the nano-mixed paint on the surface of the metal material at an air pressure of 0.5 MPa, and dry it at room temperature to a thickness of about 20 μm.

[0112] In step 2, the high-transmittance gel is scraped onto a tetrafluoroethylene (PTFE) mold using a cast film method. After drying, a cured finished high-transmittance gel film with a thickness of approximately 100 μm is formed. The finished high-transmittance gel film is then adhered to the dried surface of the nano-hybrid paint.

[0113] Step three: Use a 532nm green pulse laser to perform laser shock peening on the TC4 surface coated with the composite coating, wherein the laser energy is set to 60mJ, the spot diameter is set to 0.4mm, and the laser overlap rate is set to 50%.

[0114] Step 4: Use 60℃~80℃ hot water to rinse the surface of the metal material to remove the residual composite coating on the surface of the material.

[0115] Example 4

[0116] In this embodiment, the specific steps of a method for preparing a composite coating for laser shock peening are as follows.

[0117] Step 1: prepare nano-hybrid paint.

[0118] First, 8g of anhydrous ethanol, 2g of PVP, 20g of carbon black (100nm), and 25g of SiO2 powder (20nm) were pre-mixed and ball-milled for 1h~2h (speed 300rpm) to obtain a black slurry; then, 45g of water-based acrylic resin was added to the black slurry, and nano-hybrid paint was obtained by magnetic stirring.

[0119] Step 2: Prepare high-permeability gel.

[0120] First, add 25g CMC (DS=1.0) to 50g deionized water at 50℃, use magnetic stirring to completely dissolve CMC, and let it stand for 1h to fully hydrate to form a CMC homogeneous colloid; then add 12g gelatin, 7g glycerol, 4g PEG-400, and 4g propylene glycol in a 60℃ water bath environment, stir thoroughly, and use ultrasonic vibration to remove bubbles to obtain an intermediate product; finally, cool the intermediate product to 30℃, add 0.4g calcium citrate, and stir to form a highly permeable gel.

[0121] Through the above preparation methods, nano hybrid paint and high-transparency gel can be prepared respectively, and then combined to form a composite coating for laser shock peening. The specific steps of applying this composite coating for laser shock peening are as follows.

[0122] Step 1: Use a spray gun with a 0.3 mm nozzle to evenly spray the nano hybrid paint on the surface of the metal material at a pressure of 0.5 Mpa, and dry it at room temperature. The thickness is about 20 μm.

[0123] Step 2: Use the casting film-forming method to scrape the high-transparency gel into a polytetrafluoroethylene (PTFE) mold. After drying, a cured high-transparency gel film with a thickness of about 100 μm is formed. Then, adhere the finished high-transparency gel film to the surface of the nano hybrid paint after drying.

[0124] Step 3: Use a green light pulse laser with a wavelength of 532 nm to perform laser shock peening on the surface of TC4 coated with the composite coating. Among them, the laser energy is set to 60 mJ, the spot diameter is set to 0.4 mm, and the laser overlap rate is set to 50%.

[0125] Step 4: Use hot water at 60 °C to 80 °C to wash the surface of the metal material to remove the residual composite coating on the surface of the material.

[0126] Example 5

[0127] In this example, the specific steps of a preparation method of a composite coating for laser shock peening are as follows.

[0128] Step 1: Prepare nano hybrid paint.

[0129] First, premix 5 g of absolute ethanol, 2 g of PVP, 18 g of carbon black (100 nm), and 25 g of ZrO2 powder (20 nm), and ball mill for 1 h to 2 h (rotation speed 300 rpm) to obtain a black slurry; then add 50 g of waterborne acrylic resin to the black slurry and obtain nano hybrid paint through magnetic stirring.

[0130] Step 2: Prepare high-transparency gel.

[0131] First, add 20 g of CMC (DS = 1.2) to 60 g of deionized water at 50 °C, use magnetic stirring until CMC is completely dissolved, and let it stand for 1 h to fully hydrate to form a CMC homogeneous colloid; in a 60 °C water bath environment, add 10 g of gelatin, 5 g of glycerol, 4 g of PEG-400, and 4 g of propylene glycol in sequence, fully stir and then use ultrasonic oscillation to remove bubbles to obtain an intermediate product; finally, cool the intermediate product to 30 °C, add 0.1 g of calcium citrate, and stir to form high-transparency gel.

[0132] Through the above preparation methods, nano hybrid paint and high-transparency gel can be prepared respectively, and then combined to form a composite coating for laser shock peening. The specific steps of applying this composite coating for laser shock peening are as follows.

[0133] Step 1: Use a spray gun with a 0.3 mm nozzle to evenly spray the nano hybrid paint on the surface of the metal material at a pressure of 0.5 Mpa, and dry it at room temperature. The thickness is about 20 μm.

[0134] Step 2: Use the casting film-forming method to scrape the high-transparency gel into a polytetrafluoroethylene (PTFE) mold. After drying, a cured high-transparency gel film with a thickness of about 100 μm is formed. Then, adhere the finished high-transparency gel film to the surface of the nano hybrid paint after drying.

[0135] Step 3: Use a green light pulse laser with a wavelength of 532 nm to perform laser shock peening on the surface of TC4 coated with the composite coating. Among them, the laser energy is set to 60 mJ, the spot diameter is set to 0.4 mm, and the laser overlap rate is set to 50%.

[0136] Step 4: Use hot water at 60°C to 80°C to wash the surface of the metal material to remove the residual composite coating on the surface of the material.

[0137] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0138] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0139] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A composite coating for laser shock peening, comprising an absorbing layer coating and a constraining layer coating, characterized in that: The absorption layer coating is a black coating material, and the constraint layer coating includes: 15% to 25% sodium carboxymethyl cellulose, 10% to 15% gelatin, 5% to 7% glycerol, 4% to 8% propylene glycol, 2% to 5% polyethylene glycol, 0.1% to 0.5% calcium citrate and the balance water.

2. The composite coating for laser shock peening according to claim 1, characterized in that: The degree of substitution of the sodium carboxymethyl cellulose is 0.7-1.

2.

3. The composite coating for laser shock peening according to claim 1, characterized in that: The absorption layer coating comprises: 45% to 55% water-based acrylic resin, 5% to 10% anhydrous ethanol, 2% to 3% polyvinyl pyrrolidone, 15% to 20% nano carbon black and 25% to 30% nano coating powder.

4. The composite coating for laser shock peening according to claim 3, characterized in that: The nano coating powder is at least one of tungsten disulfide nano powder, ceramic nano powder, silicon dioxide nano powder and zirconium dioxide nano powder.

5. The composite coating for laser shock peening according to claim 3, characterized in that: The particle size of the nano coating powder is less than 50 nm.

6. A method for preparing a composite coating for laser shock peening, characterized in that: The method for preparing the composite coating for laser shock peening comprises: preparing an absorption layer coating and preparing a constraint layer coating; Wherein, the preparation of the constrained layer coating comprises the following steps: Add 15% to 25% sodium carboxymethyl cellulose into deionized water, stir and let stand to obtain CMC homogeneous colloid; 10%-15% gelatin, 5%-7% glycerol, 4%-8% propylene glycol, and 2%-5% polyethylene glycol were sequentially added to the CMC homogeneous colloid in a water bath, and ultrasonically vibrated to obtain an intermediate product; 0.1%~0.5% calcium citrate is added to the intermediate product to form a constrained layer coating after ion cross-linking.

7. The method for preparing the composite coating for laser shock peening according to claim 6, characterized in that: When the degree of substitution of sodium carboxymethyl cellulose is 0.7-1.2, the hydration temperature of sodium carboxymethyl cellulose is set to 45°C-60°C.

8. The method for preparing the composite coating for laser shock peening according to claim 6, characterized in that: The water bath temperature was set to 45°C~50°C.

9. The method for preparing the composite coating for laser shock peening according to claim 6, characterized in that: The preparation of the absorbing layer coating comprises the following steps: 15% to 20% nano carbon black, 25% to 30% nano coating powder, 5% to 10% anhydrous ethanol and 2% to 3% polyvinyl pyrrolidone were pre-mixed and ball-milled to obtain a black slurry; Add 45% to 55% water-based acrylic resin to the black slurry and stir to obtain the absorption layer coating.

10. The method for preparing the composite coating for laser shock peening according to claim 9, characterized in that: The nano coating powder is at least one of tungsten disulfide nano powder, ceramic nano powder, silicon dioxide nano powder and zirconium dioxide nano powder.

11. A method for using the composite coating for laser shock peening according to any one of claims 1 to 5, characterized in that: The method for using the composite coating for laser shock peening comprises the following steps: Coating the composite coating on the surface of a metal component to form a surface of the metal component to be laser shock strengthened; Perform laser shock strengthening on the surface of metal parts to be laser shocked; Use 60℃~80℃ hot water to wash the surface of the metal parts after laser shock strengthening to remove the residual composite coating.

12. The method for using the composite coating for laser shock peening according to claim 11, characterized in that: The method of coating the composite coating on the surface of the metal component to form the surface of the metal component to be laser shock peened comprises: Spraying the absorption layer coating on the surface of the metal part, and forming an absorption layer film on the surface of the metal part after drying and curing; The constraining layer coating is scraped onto the surface of the absorbing layer film, and after drying and curing, the surface of the metal part to be laser shock strengthened is formed.

13. The method for using the composite coating for laser shock peening according to claim 11, characterized in that: The method of coating the composite coating on the surface of the metal component to form the surface of the metal component to be laser shock peened comprises: Spraying the absorption layer coating on the surface of the metal part, and forming an absorption layer film on the surface of the metal part after drying and curing; The constrained layer coating is applied to the mold by a tape casting method, and after drying and curing, a constrained layer gel film is formed; The constraining layer gel film is adhered to the surface of the absorbing layer film to form the surface of the metal component to be laser shock strengthened.

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