Nanosecond laser-sand blasting composite pretreatment method for repairing thermal spraying local coating

Abstract

The invention discloses a nanosecond laser-sand blasting composite pretreatment method for repairing a thermal spraying local coating, and belongs to the technical field of surface engineering and remanufacturing. According to the method, high-precision selective removal of a local damaged coating is realized by introducing nanosecond pulse laser, and a geometric transition boundary morphology beneficial to gentle release of stress is constructed; and then impurity removal and roughening treatment are carried out on the surface subjected to the laser action with the assistance of a sand blasting process, so that the repaired matrix obtains ideal macroscopic structure transition, a microscopic rough structure and high surface cleanliness. According to the method, a laser morphology precise regulation and control technology is combined with a sand blasting surface strengthening mechanism, so that the size precision and the position controllability in the coating removing process are greatly improved, the industrial problem that'coating edge connection 'and'interface combination' are difficult to consider by a single process is effectively solved from the two dimensions of structure and interface physical characteristics, and the method is suitable for industrial production. And finally, a firm and stable mechanical embedding interface can be formed in the local repairing area in the subsequent thermal spraying process.

Description

Technical Field

[0001] This invention belongs to the field of surface engineering and remanufacturing technology, and relates to a nanosecond laser-sandblasting composite pretreatment method for localized repair of thermal spray coatings. Background Technology

[0002] Metal-ceramic composite coatings combine the excellent toughness of a metallic substrate with the high hardness, wear resistance, and high-temperature resistance of a ceramic phase, making them a crucial functional coating system in the field of surface engineering for modern high-end equipment. These coatings typically consist of a metallic binder phase and a ceramic reinforcing phase, deposited on the substrate surface using surface strengthening technologies such as thermal spraying. They are used to improve the wear resistance, corrosion resistance, high-temperature oxidation resistance, and erosion resistance of components. With the rapid development of industries such as aerospace, power energy, and transportation, the service conditions of critical components are becoming increasingly demanding. Metal-ceramic composite coatings play an irreplaceable role in ensuring the safe operation of components under complex conditions. Among numerous coating systems, nickel-based metal-ceramic composite coatings have gained widespread application on the surfaces of critical components such as gas turbine blades, compressor impellers, combustion chamber components, and high-temperature friction pairs due to their excellent high-temperature oxidation resistance, good wettability, and thermal expansion matching with nickel-based superalloys and alloy steel substrates. The nickel-based binder phase provides toughness, while the ceramic phase (such as WC and Cr3C2) provides hardness, together significantly improving the service life of the components. However, such coatings are prone to localized peeling, cracking, and pitting during long-term service. Due to cost control needs, localized coating repair of failed high-value components has become a consensus in the remanufacturing field. In existing technologies, localized repair of cermet coatings often employs re-thermal spraying. However, before thermal spraying, the damaged area and its surrounding coating must be pre-treated to remove the failed coating and obtain a surface conducive to the mechanical bonding of the old and new coatings.

[0003] In recent years, laser removal technology, due to its controllable high-energy beam, has been explored for the fine removal of metal-ceramic coatings. However, in practical engineering applications, the "edge effect" caused by a single laser removal process has become a technical bottleneck restricting the lifespan of the repair coating. Existing laser removal often creates steep edges perpendicular to the substrate. This abrupt change in geometry has serious negative effects on subsequent thermal spraying: on the one hand, the sprayed particle stream experiences kinetic shielding or rebound when passing through the steep edge, resulting in significant micropores and unmelted particle aggregation at the interface between the old and new coatings; on the other hand, the huge abrupt change in geometric stiffness at the edge triggers severe thermal stress concentration, making the repair coating highly susceptible to microcracks initiating at the interface and propagating to both sides during cooling or service thermal cycling, ultimately causing the entire repaired block to peel off. Therefore, how to construct a "sloping edge" morphology with transitional characteristics through precise pretreatment processes to optimize stress release and interface physical bonding is a key scientific problem that urgently needs to be solved in the remanufacturing field.

[0004] Furthermore, while laser ablation can achieve highly precise selective stripping of coatings, its energy mechanism often results in the formation of a remelted layer and ablation oxidation products several to tens of micrometers thick on the exposed substrate surface. After undergoing intense thermal cycling, these remelted layers typically exhibit grain coarsening, increased brittleness, and reduced chemical activity. Simultaneously, the surface texture formed by laser ablation is relatively regular and flat, lacking sufficient mechanical interlocking structures. If thermal spraying is directly applied to this surface, the bonding between the new coating and the substrate often relies only on limited physical adsorption or local interlocking, making it difficult to maintain long-term stability under complex service conditions. Although traditional high-intensity sandblasting can remove surface contaminants and create a rough structure, for precise local repairs, excessive sandblasting impact can easily disrupt the boundary geometry formed by laser ablation, rendering the original edge structure meaningless. Therefore, there is an urgent need to develop a composite pretreatment method that can achieve surface cleaning and micro-roughening control while maintaining the edge geometric transition structure. By rationally matching the action modes of laser processing and sandblasting, the remelted layer and oxidation products formed by laser are removed while maintaining the macroscopic edge slope structure, and a uniform rough structure is formed on the substrate surface. This creates a deposition interface that simultaneously possesses reasonable geometric transition and stable mechanical interlocking conditions, which is of great engineering significance for improving the interface reliability of the local repair area of ​​metal-ceramic composite coatings.

[0005] Existing patent literature has discussed laser removal technology, but its application scenarios and technical objectives differ fundamentally from those of this invention. For example, Chinese patent CN111203414A discloses a laser cleaning method suitable for oxide layers, mainly targeting thin oxide layers generated during the production or use of metal parts. This technology focuses on the physical removal of foreign matter layers, has a low energy threshold, and its technical logic is limited to "surface cleaning," without considering the impact of the substrate morphology after removal on subsequent coating remanufacturing, especially droplet spreading and interface bonding during thermal spraying.

[0006] Furthermore, Chinese patent CN119406852A discloses a wet high-power combined laser cleaning method suitable for heavily corroded steel structures. This method mainly targets loose rust products on the surface of building or bridge steel structures, and its core lies in improving removal efficiency through the synergistic effect of a water film. However, for metal-ceramic composite coatings with high melting points, high hardness, and strong interfacial adhesion, this cleaning method targeting loose products is difficult to achieve precise peeling of the coating, and it cannot solve the crucial problem of boundary stress gradient control in local repair. Summary of the Invention

[0007] Based on the aforementioned technical pain points, this invention aims to improve and perfect the existing technologies for pretreatment of localized repairs of metal-ceramic composite coatings. This invention provides a nanosecond laser-sandblasting composite pretreatment method for localized repair of thermally sprayed coatings. Addressing the failure phenomena such as peeling, cracking, pitting, and thinning that occur in localized areas of metal-ceramic composite coatings (preferably nickel-based metal-ceramic composite coatings) after long-term service, this method combines nanosecond laser fine removal with synergistic surface strengthening through sandblasting to achieve highly efficient selective removal of locally damaged coatings and deep optimization of surface physical states. The core value of this invention lies in enabling the treated substrate surface and residual coating edges to directly enter the thermal spraying process without additional mechanical finishing, secondary roughening, or complex chemical activation steps, significantly improving the response speed and repair quality of remanufacturing.

[0008] The present invention solves the above-mentioned technical problems through the following technical solution:

[0009] A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings includes the following steps:

[0010] 1. Damage Area Assessment and Target Area Delineation: Observe the locally damaged areas of the metal-ceramic composite coating on the surface of the service component, delineate the areas where the coating needs to be removed, and physically mark them; these are the target areas. During the observation process, it is necessary to determine the extent of the locally damaged coating area, the depth of coating peeling, and the morphology of the damage.

[0011] 2. Nanosecond laser removal of coating in target area: Using a nanosecond pulsed laser, the coating in the target area is removed by setting the laser power, laser pulse frequency, scanning speed and scanning trajectory.

[0012] 3. Target area edge coating morphology control processing: A nanosecond pulsed laser is used to process the coating at the edge of the target area by adjusting the angle between the laser beam and the coating at the edge of the target area, so as to obtain a slope transition edge of the coating with a certain slope angle.

[0013] 4. Substrate surface cleaning and roughening: Sandblasting is performed on the target area and the transition edge of the coating slope. The air pressure, sandblasting angle and sandblasting distance of the sandblasting machine are set to remove the adhering particles and oxides generated by the laser action, and to form a rough surface in the target area and the transition surface of the coating slope.

[0014] In step 1, the metal-ceramic composite coating is made of metal-based (preferably nickel-based, iron-based, or aluminum-based) doped ceramic particles (preferably alumina ceramic), and the bonding strength of the metal-ceramic composite coating is >20 MPa. The thickness of the metal-ceramic composite coating is 300 μm to 600 μm.

[0015] In step 2, the process parameters of the nanosecond pulsed laser are set as follows: laser power 30W~50W, laser pulse width 10ns, laser wavelength 1064nm, laser pulse frequency 2000kHz, and laser scanning speed 10mm / s.

[0016] In step 2, the laser scanning spacing of the nanosecond laser is smaller than the effective diameter of the laser spot, which is 70μm~80μm. The laser scanning path adopts a line-by-line scanning method, and the line spacing is precisely controlled to 0.01mm.

[0017] In step 2, when the nanosecond laser removes the coating in the target area, the laser beam axis is perpendicular to the coating surface of the target area.

[0018] In step 3, when the nanosecond laser processes the coating at the edge of the target area, a specific process angle is formed between the laser beam and the normal of the coating surface, with the angle being 45°-60°.

[0019] In step 4, the air pressure of the sandblasting machine is 0.5MPa-0.6MPa, the sandblasting angle is 60°-80°, and the sandblasting distance is 70mm-90mm.

[0020] This invention proposes a nanosecond laser-blasting composite pretreatment method for repairing locally damaged coatings in thermal spraying. This method first utilizes the high peak power, short pulse width, and controllable micro-area energy characteristics of nanosecond pulsed lasers to achieve precise and selective peeling of locally damaged coatings, with both boundary and contour morphology adjustable as needed.

[0021] One of the core highlights of this invention lies in the "geometric reshaping" of the coating at the edge of the damaged area. After the core process of laser removal of the damaged coating is completed, a secondary laser processing step is added to the coating at the edge of the damaged area to form a gentle slope transition. By processing the coating edge with a laser beam, a smooth, sloping transition surface is constructed at the interface between the old and new coatings. This structure changes the stress concentration state caused by the "steep steps" of the coating at the edge of the damaged area in traditional repairs, effectively eliminating the shielding effect of the molten particle flow during thermal spraying, so that the edge of the damaged area is no longer a weak point of stress concentration. At the same time, the sloping structure significantly improves the spreading characteristics of thermally sprayed particles at the interface and the degree of lateral integration with the old coating, greatly enhancing the overall stability of the remanufacturing system.

[0022] Another key highlight of this invention lies in the construction of a "synergistic strengthening mechanism" between laser processing and sandblasting. Following the laser treatment process, sandblasting is introduced as a second crucial strengthening method. Its function not only includes removing surface residues but also completely eliminating resolidified particles, remelted layers, and surface oxidation products generated by laser thermal action. If this remelted layer is not removed, it will severely reduce surface wettability. This invention, by precisely controlling the sandblasting kinetic energy, further constructs microscopic roughness features without damaging the inclined surface geometry established by the previous laser step.

[0023] It is worth emphasizing that the synergistic effect of this composite process—nanosecond laser precision removal, edge bevel construction, and sandblasting roughening—allows the damaged area to directly enter the thermal spraying stage after pretreatment, without any subsequent processing. This integrated "coating removal-bevel construction-cleaning roughening" technology significantly shortens the process flow, reduces repetitive positioning and processing time in traditional coating repair processes, improves repair efficiency, and fundamentally reduces the risk of secondary damage to the substrate caused by excessive grinding. Simultaneously, this process ensures that the damaged area fully meets the stringent deposition requirements of thermal spraying in terms of interface morphology, micro-roughness, and surface cleanliness.

[0024] Therefore, the composite pretreatment process proposed in this invention can not only achieve high-precision selective removal of local metal-ceramic composite coatings, but also actively construct a slope transition structure conducive to the fusion of thermal spraying interfaces, completely solving long-standing technical problems such as difficulty in fusion and easy crack initiation at the junction of new and old coatings. Through the synchronous control of laser and sandblasting at the macro and micro scales, the interfacial bonding stability, density, and cycle life of thermal spraying repair coatings in complex service environments are significantly improved, demonstrating strong engineering application relevance and technological innovation.

[0025] This invention proposes a nanosecond laser-sandblasting composite pretreatment method for localized thermal spraying coating repair. By introducing the high energy density and non-contact characteristics of nanosecond pulsed lasers, it achieves high-precision selective removal of locally damaged coatings and creatively constructs a geometric transition boundary morphology conducive to the gradual release of stress. Subsequently, sandblasting is used to remove impurities and roughen the surface after laser treatment, resulting in an ideal macroscopic structural transition, microscopic rough structure, and high surface cleanliness for the repaired substrate. By combining precise laser morphology control technology with sandblasting surface strengthening mechanisms, this invention not only significantly improves the dimensional accuracy and positional controllability of the coating removal process but also effectively solves the industry challenge of simultaneously addressing "coating edge connection" and "interface bonding" in a single process from both structural and interface physical properties perspectives. Ultimately, this allows the locally repaired area to form a strong and stable mechanically bonded interface during subsequent thermal spraying. Attached Figure Description

[0026] Figure 1 This is the macroscopic morphology of the sample after laser treatment of the edge coating of the target area in Embodiment 1 of the present invention;

[0027] Figure 2 The macroscopic morphology of the sample after laser treatment and sandblasting treatment of the edge coating of the target area in Embodiment 1 of the present invention;

[0028] Figure 3 The image shows the SEM microstructure of the edge coating and sandblasting treatment of the target area after laser processing in Embodiment 1 of the present invention.

[0029] Figure 4 The image shows the SEM microstructure of the edge coating of the target area after remanufacturing in Embodiment 1 of the present invention.

[0030] Figure 5 The results show the bond strength performance of the original coating and the remanufactured coating in Example 1 of this invention.

[0031] Figure 6 The image shows the SEM microstructure of the edge coating of the target area after laser processing and sandblasting in Embodiment 2 of the present invention.

[0032] Figure 7 The image shows the SEM microstructure of the target area edge coating after remanufacturing in Embodiment 2 of the present invention.

[0033] Figure 8 This is the SEM microstructure of the edge coating of the target area after laser processing in Comparative Example 1 of the present invention.

[0034] Figure 9 This is the SEM microstructure of the edge coating of the target area after remanufacturing in Comparative Example 1 of the present invention.

[0035] Figure 10The image shows the SEM microstructure of the edge coating of the target area after remanufacturing in Comparative Example 2 of this invention. Detailed Implementation

[0036] This invention provides a nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings, comprising the following steps:

[0037] 1. Damage area assessment and target area delineation: Observe the local damaged areas of the metal-ceramic composite coating on the surface of the service component, determine the extent of the local damaged area, the depth of coating peeling and the morphology of the damage, delineate the area where the coating needs to be removed and mark it physically, which is the target area;

[0038] 2. Nanosecond laser removal of coating in target area: Set the nanosecond pulsed laser power to 30W~50W, laser pulse width to 10ns, laser wavelength to 1064nm, laser pulse frequency to 2000kHz, laser scanning speed to 10mm / s, and effective laser spot diameter to 70μm~80μm. Control the laser beam axis to be perpendicular to the coating surface of the target area. Use a line-by-line scanning method with high overlap rate and control the line spacing to 0.01mm to remove the coating in the target area.

[0039] 3. Target area edge coating morphology control processing: A nanosecond pulsed laser is used to adjust the angle between the laser beam and the coating at the edge of the target area, so that the laser beam and the normal of the coating surface at the edge of the target area form an angle of 45°-60°. The coating at the edge of the target area is then finely processed to obtain a sloped transition edge with a certain slope angle.

[0040] 4. Substrate surface cleaning and roughening: Sandblasting is performed on the target area and the surrounding coating slope transition edge. The sandblasting machine air pressure is set to 0.5MPa-0.6MPa, the sandblasting angle is 60°-80°, and the sandblasting distance is 70mm-90mm. This removes the adhering particles and oxides generated by the laser action and forms a rough surface on the target area and the edge coating slope transition surface, which is conducive to the mechanical interlocking of the subsequent thermal spray coating.

[0041] In the solution provided by this invention, the metal-ceramic composite coating is made of metal-based (preferably nickel-based, iron-based, or aluminum-based) doped ceramic particles (preferably alumina ceramic), and the bonding strength of the metal-ceramic composite coating is >20 MPa. The thickness of the metal-ceramic composite coating is 300 μm to 600 μm.

[0042] In this embodiment of the invention, Q235 steel is used as the service component. A plasma-enhanced high-speed arc spraying process is employed to deposit a metal-ceramic composite coating on the surface of the Q235 steel. After air cooling, the average thickness of the metal-ceramic composite coating is 300 μm, and the bonding strength of the metal-ceramic composite coating is 34 MPa-36 MPa. The surface of the metal-ceramic composite coating is cleaned of dust and oil, and then set aside for later use.

[0043] The present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0044] Example 1:

[0045] This embodiment provides a nanosecond laser-sandblasting composite pretreatment method for localized repair of thermal spray coatings, including the following steps:

[0046] 1. Damage area assessment and target area delineation: Observe the local damaged areas of the metal-ceramic composite coating on the surface of the service component, determine the extent of the local damaged area, the depth of coating peeling and the morphology of the damage, delineate the area where the coating needs to be removed and mark it physically, which is the target area;

[0047] 2. Nanosecond Laser Removal of Coating in Target Area: Place the sample to be treated stably directly below the nanosecond laser stage, ensuring the surface of the composite coating is parallel to the laser platform. Activate the autofocus system to precisely focus the laser onto the coating surface. Configure the nanosecond laser process parameters according to the shape and size of the target area: laser power 30W, laser pulse width 10ns, laser wavelength 1064nm, laser pulse frequency 2000kHz, and laser scanning speed 10mm / s. Perform a zigzag scan perpendicular to the coating surface, setting the effective laser spot diameter to 70μm~80μm, spot overlap rate to 65%-75%, and line spacing to 0.01mm. Remove the coating from the target area through scanning until the underlying steel substrate is exposed.

[0048] 3. Target Area Edge Coating Morphology Control: After laser removal of the damaged coating, surface debris is cleaned. The position of the laser beam relative to the target area edge coating is adjusted so that a 45° processing angle is formed between the laser beam and the normal to the coating surface at the target area edge. With the laser parameters remaining constant, secondary processing is performed only on the target area edge coating. The processed coating edge transforms from an initial steep vertical state to a gentle slope structure, which provides favorable conditions for the smooth spread of subsequent sprayed particles.

[0049] 4. Surface Cleaning and Roughening of the Substrate: After laser treatment, the sample is allowed to cool naturally to room temperature in air. A soft brush is then used to remove any loose residue from the surface. At this point, it can be observed that although the laser-scanned area exposes the substrate, the surface is covered with a thin layer of black material, such as... Figure 1As shown. The sample was then placed in a sandblasting machine for sandblasting treatment of the target area and edge slope structure. The sandblasting air pressure was set to 0.6 MPa, the sandblasting angle to 70°, and the sandblasting distance to 80 mm.

[0050] Sandblasting effectively removes the microscopic remelted layer on the substrate surface after laser coating removal, exposing a steel substrate surface with uniform roughness distribution, such as... Figure 2 As shown; simultaneously, the macroscopic morphology of the slope-like coating at the edge of the damaged area constructed by laser is completely preserved, and the slope surface is also sandblasted, resulting in a clean and uniformly rough surface morphology, achieving a synergistic effect of maintaining macroscopic geometry and forming microscopic coarsening structures, such as... Figure 3 As shown.

[0051] Coatings are prepared using the samples that have undergone the above composite pretreatment, such as Figure 4 As shown. Experimental results show that:

[0052] High interface integration: Observation of the metallographic cross-section of the coating in the repaired damaged area revealed that the old and new coatings were tightly connected at the slope boundary, with no obvious pore aggregation or delamination.

[0053] The bonding strength remains at a high level: Tensile testing showed that the bonding strength of the original coating was 34MPa-36MPa, while the bonding strength of the coating repaired by the pretreatment process of this invention in the damaged area reached 31MPa-33MPa (e.g., ...). Figure 5 (As shown).

[0054] Data shows that the bonding strength of the repair coating in the damaged area is basically the same as that of the original coating, with the error within the measurement accuracy range. This near-equal strength repair effect fully demonstrates that the "sloping surface construction-sandblasting cleaning" pretreatment process described in this invention greatly optimizes the physical state of the remanufacturing interface, enabling the surface properties of damaged components to be restored, and has extremely high engineering application value.

[0055] Example 2:

[0056] This embodiment provides a nanosecond laser-sandblasting composite pretreatment method for localized repair of thermal spray coatings, including the following steps:

[0057] 1. Damage area assessment and target area delineation: Observe the local damaged areas of the metal-ceramic composite coating on the surface of the service component, determine the extent of the local damaged area, the depth of coating peeling and the morphology of the damage, delineate the area where the coating needs to be removed and mark it physically, which is the target area;

[0058] 2. Nanosecond Laser Removal of Coating in Target Area: Place the sample to be treated stably directly below the nanosecond laser stage, ensuring the surface of the composite coating is parallel to the laser platform. Activate the autofocus system to precisely focus the laser onto the coating surface. Configure the nanosecond laser process parameters according to the shape and size of the target area: laser power 40W, laser pulse width 10ns, laser wavelength 1064nm, laser pulse frequency 2000kHz, and laser scanning speed 10mm / s. Perform a zigzag scan perpendicular to the coating surface, setting the effective laser spot diameter to 70μm~80μm, spot overlap rate to 65%-75%, and line spacing to 0.01mm. Remove the coating from the target area through scanning until the underlying steel substrate is exposed.

[0059] 3. Target Area Edge Coating Morphology Control: After laser removal of the damaged coating, surface debris is cleaned. The position of the laser beam relative to the target area edge coating is adjusted so that a 60° processing angle is formed between the laser beam and the normal to the coating surface at the target area edge. While keeping the laser parameters constant, secondary processing is performed only on the target area edge coating. The processed coating edge transforms from an initial steep vertical state to a gentle slope structure, which provides favorable conditions for the smooth spread of subsequent sprayed particles.

[0060] 4. Surface Cleaning and Roughening of the Substrate: After laser treatment, the sample was allowed to cool naturally to room temperature in air. A soft brush was then used to remove loose residue from the surface. At this point, it was observed that although the laser-scanned area exposed the substrate, a thin layer of black substance covered the surface. The sample was then placed in a sandblasting machine for sandblasting treatment of the target area and the edge slope structure. The sandblasting pressure was set to 0.6 MPa, the sandblasting angle to 80°, and the sandblasting distance to 80 mm.

[0061] After sandblasting, the microscopic remelted layer on the substrate surface after laser coating removal was effectively removed, exposing a steel substrate surface with uniform roughness distribution. Simultaneously, the slope-like macroscopic morphology of the coating edge in the laser-constructed damaged area was completely preserved, and the slope surface, also treated with sandblasting, possesses a clean and uniformly rough surface morphology, achieving a synergistic effect of maintaining macroscopic geometry and forming microscopic coarsening structures. Figure 6 As shown.

[0062] Coatings are prepared using the samples that have undergone the above composite pretreatment, such as Figure 7 As shown. Experimental results show that:

[0063] High interface integration: Observation of the metallographic cross-section of the coating in the repaired damaged area revealed that the old and new coatings were well connected at the slope boundary.

[0064] Comparative Example 1:

[0065] This comparative example provides a nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings, including the following steps:

[0066] 1. Damage area assessment and target area delineation: Observe the local damaged areas of the metal-ceramic composite coating on the surface of the service component, determine the extent of the local damaged area, the depth of coating peeling and the morphology of the damage, delineate the area where the coating needs to be removed and mark it physically, which is the target area;

[0067] 2. Nanosecond Laser Removal of Coating in Target Area: Place the sample to be treated stably directly below the nanosecond laser stage, ensuring the surface of the composite coating is parallel to the laser platform. Activate the autofocus system to precisely focus the laser onto the coating surface. Configure the nanosecond laser process parameters according to the shape and size of the target area: laser power 50W, laser pulse width 10ns, laser wavelength 1064nm, laser pulse frequency 2000kHz, and laser scanning speed 10mm / s. Perform a zigzag scan perpendicular to the coating surface, setting the effective laser spot diameter to 70μm~80μm, spot overlap rate to 65%-75%, and line spacing to 0.01mm. Remove the coating from the target area through scanning until the underlying steel substrate is exposed.

[0068] 3. Edge Coating Morphology Control in the Target Area: After laser removal of the damaged coating, surface debris is cleaned. However, since the laser beam axis is at a 90° angle to the coating surface during step 2, the edge coating after laser removal of the target area is equivalent to being processed by a laser beam at a 90° angle. Therefore, no further processing is required. Figure 8 As shown.

[0069] 4. Surface Cleaning and Roughening of the Substrate: After laser treatment, the sample was allowed to cool naturally to room temperature in air. A soft brush was then used to remove loose residue from the surface. At this point, it was observed that although the laser-scanned area exposed the substrate, a thin layer of black substance covered the surface. The sample was then placed in a sandblasting machine, and the target area and its edges were sandblasted. The sandblasting pressure was set to 0.6 MPa, the sandblasting angle to 80°, and the sandblasting distance to 90 mm.

[0070] After sandblasting, the micro-remelted layer on the substrate surface after laser removal of the coating is effectively removed, exposing the steel substrate surface with uniform roughness distribution; at the same time, the macro-morphology of the edge coating of the damaged area constructed by laser is completely preserved.

[0071] Coatings are prepared using the samples that have undergone the above composite pretreatment, such as Figure 9 As shown. Experimental results show that:

[0072] Interface cracking: The coating edges exhibit a steep edge structure, creating a shielding effect that prevents sprayed particles from effectively filling the vertical edge roots, resulting in interface discontinuity. Scanning electron microscopy clearly shows microcracks originating from the interface and extending into the new coating. After thermal spraying repair, significant cracking between the old and new coatings was clearly observed at the edge structure.

[0073] Comparative Example 1 illustrates that the edge structure of the damaged area lacking slope control leads to severe interface failure, failing to meet the requirements of remanufacturing, thus demonstrating the inventiveness of the slope transition process of this invention.

[0074] Comparative Example 2:

[0075] This comparative example provides a nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings, including the following steps:

[0076] 1. Damage area assessment and target area delineation: Observe the local damaged areas of the metal-ceramic composite coating on the surface of the service component, determine the extent of the local damaged area, the depth of coating peeling and the morphology of the damage, delineate the area where the coating needs to be removed and mark it physically, which is the target area;

[0077] 2. Nanosecond Laser Removal of Coating in Target Area: Place the sample to be treated stably directly below the nanosecond laser stage, ensuring the surface of the composite coating is parallel to the laser platform. Activate the autofocus system to precisely focus the laser onto the coating surface. Configure the nanosecond laser process parameters according to the shape and size of the target area: laser power 40W, laser pulse width 10ns, laser wavelength 1064nm, laser pulse frequency 2000kHz, and laser scanning speed 10mm / s. Perform a zigzag scan perpendicular to the coating surface, setting the effective laser spot diameter to 70μm~80μm, spot overlap rate to 65%-75%, and line spacing to 0.01mm. Remove the coating from the target area through scanning until the underlying steel substrate is exposed.

[0078] 3. Target Area Edge Coating Morphology Control: After laser removal of the damaged coating, surface debris is cleaned. The position of the laser beam relative to the target area edge coating is adjusted so that a 60° processing angle is formed between the laser beam and the normal to the coating surface at the target area edge. While keeping the laser parameters constant, secondary processing is performed only on the target area edge coating. The processed coating edge transforms from an initial steep vertical state to a gentle slope structure, which provides favorable conditions for the smooth spread of subsequent sprayed particles.

[0079] 4. Cooling: Allow the laser-treated sample to cool naturally to room temperature in the air. Use a soft brush to remove loose residues from the surface. No further sandblasting is required.

[0080] Coatings are prepared using the samples that have undergone the above composite pretreatment, such as Figure 10 As shown. Experimental results show that:

[0081] Interface cracking: Although the coating at the edge of the damaged area has a sloping structure, there are a large number of oxidation products from laser-removed coatings at this location. The repair coating failed to achieve effective physical interlocking with the substrate, exhibiting a clear tendency for delamination. Due to the lack of sandblasting treatment, the substrate and sloping surfaces are covered with oxidation products, and the substrate surface is smooth with microscopic thermal cracks, preventing the thermally sprayed particles from forming a mechanical interlock when spreading on its surface.

[0082] Comparative Example 2 illustrates that even with an optimized slope morphology, the repair coating will still crack and fail due to a lack of interfacial bonding if the oxidation products generated by the laser are not removed and the surface is not roughened through sandblasting. This demonstrates the irreplaceable synergistic effect of the "slope construction-sandblasting cleaning" composite process.

Claims

1. A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings, characterized in that, Includes the following steps: S1. Damage Area Assessment and Delineation: Observe the locally damaged areas of the metal-ceramic composite coating on the surface of the service component, delineate the areas where the coating needs to be removed and mark them, which are the target areas; S2. Nanosecond laser removal of coating in target area: Using a nanosecond pulsed laser, the coating in the target area is removed by setting the laser power, laser pulse frequency, scanning speed and scanning trajectory; S3. Target area edge coating morphology control processing: Adjust the angle between the nanosecond laser beam and the target area edge coating to refine the original coating at the target area edge and obtain a coating slope transition edge with a certain slope angle; S4. Surface cleaning and roughening of the substrate: Set the air pressure, blasting angle and blasting distance of the sandblasting machine to sandblast the target area and the transition edge of the coating slope to form a rough surface and remove the adhering particles and oxides generated by the laser action.

2. The nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 1, characterized in that, In S3, the laser beam forms an angle between itself and the normal of the edge coating surface of the target area, with the angle being 45°-60°.

3. A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 1 or 2, characterized in that, In S4, the air pressure of the sandblasting machine is set to 0.5MPa-0.6MPa, the sandblasting angle is 60°-80°, and the sandblasting distance is 70mm-90mm.

4. A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 1 or 2, characterized in that, In S1, the observation process needs to determine the extent of the locally damaged area of ​​the coating, the depth of coating peeling, and the morphology of the damage.

5. A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 1 or 2, characterized in that, In S1, the material of the metal-ceramic composite coating is metal-based doped ceramic particles; The bonding strength of the metal-ceramic composite coating is >20MPa; The thickness of the metal-ceramic composite coating is 300μm~600μm.

6. The nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 5, characterized in that, The metal base is one of nickel-based, iron-based, and aluminum-based; The ceramic particles are alumina ceramic particles.

7. A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 1 or 2, characterized in that, In S2, the process parameters of the nanosecond pulsed laser are set as follows: laser power 30W~50W, laser pulse width 10ns, laser wavelength 1064nm, laser pulse frequency 2000kHz, and laser scanning speed 10mm / s.

8. A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 1 or 2, characterized in that, In S2, the laser scanning spacing of the nanosecond laser is smaller than the effective diameter of the laser spot, and the laser spot diameter is 70μm~80μm. The laser scanning path uses a line-by-line scanning method with a line spacing of 0.01mm.

9. A nanosecond laser-blasting composite pretreatment method for localized repair of thermal spray coatings according to claim 1 or 2, characterized in that, In S2, when the nanosecond laser removes the damaged coating, the laser beam axis is perpendicular to the coating surface of the target area.

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