Preparation method for metal coating layering defect

Abstract

The invention relates to a preparation method of a metal coating with a layering defect, belongs to the technical field of nondestructive testing, and solves the problems that the defect position is limited, a thin coating is easy to damage and the parameter control precision is poor in the existing insertion piece pulling method. Comprising the following steps: determining target geometric parameters of a preset defect; pulse laser is adopted to etch a blind hole type groove matched with the metal matrix in the designated position of the metal matrix, and the depth precision is controlled; preparing a solid filling material sheet matched with the groove and placing the solid filling material sheet; the surface is subjected to flattening treatment, so that the filling piece and the surface of the base body are coplanar, and a to-be-sprayed composite surface is formed; depositing a metal coating on the surface by adopting a thermal spraying process; and finally, curing treatment is conducted, and the metal coating part with the preset layering defect is obtained. Wherein the selected filling material sheet can form a weak bonding interface or a non-bonding interface with the metal coating and the substrate under the thermal spraying condition. The controllable layering defect suitable for the thin coating is prepared at any position (including the center) of the base body in a high-precision mode.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology, and in particular to a method for preparing a delamination defect in a metal coating. Background Technology

[0002] Metal coatings are widely used in aerospace, energy, and chemical industries due to their excellent corrosion resistance, high temperature resistance, and wear resistance. However, due to the difference in thermal expansion coefficients and elastic moduli between the coating and the metal substrate, delamination defects are prone to occur under service conditions such as thermal loads, which seriously affect the safety and lifespan of components. The morphology (shape, size, location, and depth) of these defects in real components is random, posing a significant challenge to the failure analysis, life prediction, and evaluation of non-destructive testing methods for coated structural components.

[0003] To study the impact of delamination defects on coating performance and to calibrate and evaluate the detection capabilities and accuracy of nondestructive testing techniques (such as ultrasound and infrared thermography), it is necessary to prepare standard samples containing delamination defects with known characteristics (i.e., controllable shape, size, location, and depth). Currently, the commonly used method is the "insertion-pulling method," which involves placing a thin film such as polytetrafluoroethylene (PTFE) on the substrate, spraying a coating, and then pulling it out to create a void as a defect. However, this method has significant limitations: 1) It can usually only prepare defects at the edge of the sample, making it difficult to set them at arbitrary locations inside; 2) It is only suitable for thicker coatings. For thin coatings of tens to hundreds of micrometers commonly found in practice, it is very easy for the filler to fail to be pulled out or for the entire coating to peel off; 3) The geometric parameters of the defects (especially depth and interface morphology) have poor control precision and low repeatability, making it impossible to accurately simulate the real interface delamination state.

[0004] Therefore, existing technologies lack a method for preparing layered defects with real interface morphology and controllable parameters at any location inside a metal coating, especially for thin coatings. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a method for preparing delamination defects in metal coatings, in order to solve at least one of the following problems in the existing methods for preparing delamination defects in metal coatings: 1. The location of delamination defects is limited and can only be located at the edge of the sample; 2. It is not suitable for thin coatings and the preparation process is prone to coating damage; 3. The control accuracy and repeatability of the geometric parameters (shape, size, depth) of delamination defects are poor.

[0006] The objective of this invention is mainly achieved through the following technical solutions: This invention provides a method for preparing a metal coating delamination defect, comprising the following steps: S1: Select a metal substrate of a preset size as the metal sample; S2: Based on the actual delamination defects that may occur during the actual preparation or use of the metal coating, determine the target geometric parameters of at least one delamination defect to be pre-placed between the metal substrate and the subsequent coating; S3: Based on the target geometric parameters, pulsed laser is used to etch at a specified position on the surface of the metal substrate to be coated. The laser etches blind hole grooves that match the shape and size of the target defect, and controls the depth processing accuracy of the grooves. S4: Prepare a solid filler material sheet that matches the shape, size and depth of the groove, and place the filler material sheet into the corresponding groove; S5: After the filler material sheet is inserted, the surface of the metal substrate to be sprayed is flattened so that the upper surface of the filler material sheet is coplanar with the surrounding surface of the metal substrate to form a composite surface to be sprayed. S6: A metal coating is deposited on the composite surface to be sprayed using a thermal spraying process; S7: The coated sample is cured to complete the preparation of delamination defects and obtain a metal coated part containing pre-set delamination defects; The filler material sheet forms a weakly bonded interface or a non-bonded interface with the metal coating and the metal substrate under the thermal spraying process conditions.

[0007] Furthermore, in step S2, the target geometric parameters include the planar shape and size, location, and depth of the pre-defined layered defect; The planar shape and size of the pre-defined delamination defect refer to the outline shape and size of the defect in a plane parallel to the surface of the metal substrate to be coated; The pre-set delamination defect location refers to the planar coordinate position of the defect on the surface of the metal substrate to be coated; The pre-set layered defect depth refers to the gap thickness of the defect in the direction perpendicular to the surface of the metal substrate to be coated.

[0008] Furthermore, in step S3, the process parameters for laser etching include: laser power of 0.5W-50W, scanning speed of 100mm / s-1000mm / s, and scanning spacing of 60-80% of the spot diameter.

[0009] Furthermore, in step S4, the filler material sheet is one or more of the following: polymer film material, special material with adhesive or isolation function, metal foil, metal sheet, and composite material.

[0010] Furthermore, in step S5, the absolute value of the height difference between the upper surface of the filling material sheet and the surrounding metal substrate surface is less than 2 μm.

[0011] Further, in step S6, the thermal spraying process is a plasma spraying process, and the plasma spraying process parameters are: arc current 400-600 A, working voltage 40-60V, main gas Ar flow rate 30-50 SLPM, auxiliary gas H2 flow rate 5-15 SLPM, powder feed rate 20-40 g / min, spraying distance 80-120 mm, and spray gun moving speed 300-700 mm / s.

[0012] Furthermore, in step S7, the curing temperature of the curing treatment is 100℃-300℃, and the curing holding time is 0.5-4h.

[0013] Furthermore, before depositing the metal coating using the plasma spraying process, the preparation method further includes cleaning and roughening the composite surface to be sprayed.

[0014] Furthermore, the roughening treatment is a sandblasting treatment, with a blasting pressure of 0.3 MPa-0.7 MPa and a blasting angle of 60°-80°.

[0015] The present invention also provides a metal-coated part containing a pre-existing delamination defect, wherein the pre-existing delamination defect is prepared by the above-described preparation method, and the metal coating comprises: Metal matrix; A metal coating covering the metal substrate; and At least one pre-defined delamination defect region located between the interface between the metal coating and the metal substrate; The pre-set delamination defect area is located inside the area covered by the metal coating.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. Traditional "insertion plate extraction method" requires pulling out the filler plate from the edge, so the defect can only be pre-positioned at the edge of the sample, and the extraction process is prone to tearing or peeling of the thin coating. This invention uses a method of first laser etching blind hole grooves inside the substrate and inserting filler material, and then performing surface planarization and coating deposition, so that the defect can be pre-positioned at any specified coordinate position on the substrate surface; since the defect is formed in situ by relying on the weak bonding between the filler material and the coating, the physical extraction step is avoided, so it is particularly suitable for preparing defects in thin coatings with a thickness of 50-500μm, and will not cause mechanical damage to the coating; it realizes high-precision pre-positioning of layered defects at any position inside the metal coating, overcoming the position limitations and coating damage problems of traditional methods.

[0017] 2. Traditional "insertion and extraction method" cannot precisely control key parameters such as defect depth and interface flatness, resulting in large differences between samples. The laser precision processing parameter combination of this invention achieves precise control of groove depth better than ±0.02 mm. At the same time, through surface flattening treatment, the coplanarity of the filling material and the substrate surface is ensured. The final prepared defect has good consistency in depth and size, and the defect interface is flat and clear, so that the prepared sample can be used as a high-precision standard test block with traceable quantifiable values ​​for the determination of sensitivity threshold, quantitative evaluation and instrument calibration of non-destructive testing methods.

[0018] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0019] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 This is a physical image of the standard specimen of the TA2 titanium alloy-based NiCrAlY coating prepared in Example 1; Figure 2 C-scan image of the standard specimen of TA2 titanium alloy-based NiCrAlY coating prepared in Example 1; Figure 3 C-scan image of the TA2 titanium alloy-based NiCrAlY coating specimen prepared in Comparative Example 2; Figure 4 C-scan image of the TA2 titanium alloy-based NiCrAlY coated specimen prepared in Comparative Example 3. Detailed Implementation

[0020] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0021] This invention provides a method for preparing a metal coating delamination defect, comprising the following steps: S1: Select a metal substrate of a preset size as the metal sample; S2: Based on the actual delamination defects that may occur during the actual preparation or use of the metal coating, determine the target geometric parameters of at least one delamination defect to be pre-placed between the metal substrate and the subsequent coating; Specifically, the target geometric parameters of the delamination defect include: the planar shape and size, position, and depth of the delamination defect; the planar shape and size of the delamination defect refer to the outline shape and size of the defect in a plane parallel to the surface of the metal substrate to be coated; the position of the delamination defect refers to the planar coordinate position of the defect on the surface of the metal substrate to be coated; and the depth of the delamination defect refers to the gap thickness of the defect in a direction perpendicular to the surface of the metal substrate to be coated.

[0022] S3: According to the target geometric parameters, a pulsed laser is used to etch at a designated position on the surface of the metal substrate to be coated. The laser etches a blind hole-type groove that matches the shape and size of the target defect, and controls the depth processing accuracy of the groove. Specifically, the pulsed laser is an ultrafast laser with a pulse width of less than 100 picoseconds. The core advantage of using an ultrafast laser lies in its "cold processing" characteristic, which can instantly vaporize the material with extremely low heat input, thereby minimizing the thermal impact on the sidewalls and bottom of the groove and avoiding the formation of slag, microcracks, or material phase transformations. This ensures that the processed groove has clear geometric boundaries, precise dimensions, and steep sidewalls. The laser etching process parameters include: laser power of 0.5 W-50 W, scanning speed of 100 mm / s-1000 mm / s, and scanning spacing of 60-80% of the spot diameter. Too low a power will lead to unstable processing or ineffective material removal; too high a power will exacerbate the thermal effect and may damage the substrate. The scanning speed and power work together to determine the removal depth and heat accumulation of a single scan. By optimizing the parameter combination within this range and precisely controlling the number of scans, a depth processing accuracy of ≤±0.02 mm can be achieved, ensuring high repeatability of the pre-set layered defect thickness.

[0023] It should be noted that the groove depth is precisely controlled by controlling the number of laser scans. Specifically, firstly, calibration data for the single-scan removal depth (Δd) for the metal substrate material and laser parameter combination is established through process experiments. Then, based on the ratio of the target groove depth (D) to the single-scan removal depth (Δd), the required number of scans (N, N = D / Δd, rounded down) is determined. Since ultrafast laser processing has minimal thermal impact, the material removal process is stable and highly predictable; therefore, a depth control accuracy of ≤±0.02 mm can be achieved using the above control method. Preferably, online monitoring or offline measurement after a certain number of processing cycles for closed-loop correction can be further supplemented to improve consistency in mass production.

[0024] S4: Prepare a solid filling material sheet that matches the shape, size and depth of the groove, and place the filling material sheet into the corresponding groove; Specifically, the filler material sheet is a material with weak adhesion to the metal coating and the metal substrate. It can be one or more of the following: polymer film materials (such as polytetrafluoroethylene, polyimide, or polyetheretherketone films), special materials with adhesive or isolating functions (such as peelable adhesive layers, release films, or graphite release sheets), metal foils (such as aluminum foil or copper foil), metal sheets (such as molybdenum sheets or stainless steel sheets), and composite materials (such as metal-polymer laminate sheets, ceramic matrix composite sheets, or fiber-reinforced resin matrix sheets). These materials have low surface energy, non-wetting properties, or high melting points compared to typical metal coating materials (such as Ni-based or Co-based alloys). Under the high-temperature particle impact of thermal spraying, these materials do not undergo violent reactions or melting, and can effectively prevent molten metal droplets from forming effective metallurgical or mechanical bonds on their surface. This ensures that a clear and stable weak bonding interface, i.e., the target delamination defect, is "self-formed" after spraying.

[0025] The planar dimensions of the filler material sheet are 10 μm-100 μm smaller than the corresponding dimensions of the groove. If the dimensions are too large (interference fit), the filler sheet will arch, disrupting surface coplanarity. If the dimensions are too small (excessive gap), displacement is likely to occur during placement and subsequent processing, and additional, undesigned air gaps may be introduced, interfering with the realistic simulation of defects. This micro-gap range ensures that the filler sheet can be stably placed and tightly fitted to the groove, while allowing for possible thermal expansion of the material.

[0026] S5: After the filler material sheet is inserted, the surface of the metal substrate to be sprayed is flattened so that the upper surface of the filler material sheet is coplanar with the surrounding surface of the metal substrate to form a composite surface to be sprayed. Specifically, the treatment of the surface of the metal substrate to be coated after the filler material sheet is inserted includes physical polishing, chemical treatment, or a combination thereof. The absolute value of the height difference Δh between the upper surface of the filler material sheet and the surrounding metal substrate surface after treatment is less than 2 μm, preferably less than 1 μm, achieving submicron-level coplanarity. For example, the physical polishing includes, but is not limited to, one or more methods selected from 80-800 grit sandpaper polishing, mechanical grinding, or polishing. The chemical treatment includes, but is not limited to, applying, soaking, or wiping the surface with a treatment solution and allowing it to air dry for 0.5 h to 48 h. The treatment solution is one or a combination of several selected from acetone, ethanol, isopropanol, deionized water, or a specific surfactant solution. Surface treatment improves the interfacial strength between the metal coating and the metal substrate.

[0027] If the height difference is too large, the particle flow and heat flow of the spray gun will be disturbed at the "step" caused by the height difference during subsequent thermal spraying. This will cause abnormalities in the coating thickness, porosity, and even residual stress in this area, thus causing the coating performance in the non-defect area around the defect to deviate from the true state and affecting the accuracy of the standard test block. Strict coplanarity ensures the uniformity of the spraying process and the consistency of coating performance.

[0028] S6: A metal coating is deposited on the composite surface to be sprayed using a thermal spraying process; Specifically, the thermal spraying process is preferably plasma spraying. Plasma spraying can be performed in an atmospheric or inert gas environment, facilitating operation and controlling coating oxidation. The plasma spraying flame is controllable, achieving uniform coverage of complex surfaces with microgrooves (i.e., substrates after filling and leveling), with no obvious spraying dead corners, ensuring the integrity of the coating around defect areas. It can be applied on-site or used for batch preparation of standard test blocks in laboratories or workshops. The coating thickness can be precisely controlled by the number of sprays and parameters, adapting to different research needs ranging from tens to hundreds of micrometers. The concentrated plasma flame results in extremely short particle residence time on the substrate surface, effectively controlling the substrate temperature below 300℃, preferably below 200℃. This minimizes the risk of deformation, phase transformation, or mechanical property degradation of the metal substrate due to overheating, while also preventing the filler material from decomposing, failing, or excessively deforming due to excessive temperature, thus ensuring the stability of the morphology and interface state of the pre-set defects. In this invention, the spraying material is metal or alloy powder. The plasma spraying process parameters are: arc current 400-600 A, working voltage 40-60 V, main gas (Ar) flow rate 30-50 SLPM (standard liters per minute), auxiliary gas (H2) flow rate 5-15 SLPM, powder feed rate 20-40 g / min, spraying distance 80-120 mm, and spray gun moving speed 300-700 mm / s. By controlling the number of scans or the spraying time, the coating thickness is controlled within the target range. The coating thickness is 20 μm-1000 μm, preferably 50 μm-500 μm. This method is particularly suitable for preparing thin to medium thickness coatings of 50-500 μm to address delamination defects, solving the problem that traditional extraction methods can only prepare defects at the edge of the sample.

[0029] It should be noted that by controlling the number of scans by the spray gun, the coating thickness can be controlled within the target range. Specifically, a fixed scanning path (such as unidirectional or reciprocating linear scanning) and a fixed moving speed are set for the spray gun relative to the substrate. The coating thickness formed on the substrate surface by a single scan is constant (called "single-pass thickness," typically in the range of a few micrometers to tens of micrometers). Through pre-conducted process experiments, the "single-pass thickness" value under specific plasma spraying process parameters (arc current, operating voltage, main gas flow rate, auxiliary gas flow rate, powder feed rate, spraying distance, and spray gun moving speed) can be calibrated. When the target total thickness (H_target) needs to be obtained, the required number of scans (N) can be calculated using the formula: N = H_target / single-pass thickness, and the result can be rounded or fine-tuned. By precisely controlling the spray gun to perform N scans through a program, the coating thickness can be precisely controlled near H_target.

[0030] By controlling the spraying time, the coating thickness can be controlled within the target range. Specifically, for a specific area, the spray gun is kept fixed or oscillated within a certain range, and the thickness is controlled by directly controlling the cumulative spraying time (t) of the spray gun on that area. Similarly, the average deposition rate (V_d, unit: μm / s) under these parameters needs to be determined through preliminary experiments. The target spraying time can be calculated using the formula: t = H_target / V_d. Thickness control can be achieved by precisely controlling the spraying time with a timer. This method is suitable for manual spraying or fixed-point spraying.

[0031] It should be noted that the filler material sheet does not bond with the metal coating or only weakly bonds with it during the plasma spraying process, thereby forming a pre-set delamination defect with the same target geometric parameters in the region corresponding to the groove between the metal coating and the metal substrate.

[0032] Preferably, before plasma spraying, the composite surface to be sprayed can be cleaned and roughened to improve the bonding strength of the coating in non-defect areas. For example, roughening is performed by sandblasting, using abrasives including brown fused alumina, white fused alumina, or silicon carbide, with a particle size range of 16-60 mesh, a spraying pressure of 0.3 MPa-0.7 MPa, and a spraying angle of 60°-80°. After the roughening treatment, the roughness Ra of the metal substrate surface to be sprayed reaches 3μm-10μm, preferably 5μm-8μm. This roughness range can form a uniform and moderate anchoring morphology on the substrate surface, providing a good mechanical interlocking foundation for the molten coating particles, thereby ensuring that the coating obtains sufficient bonding strength (typically above 50 MPa) in normal areas other than the pre-designed defect areas, while avoiding stress concentration points due to excessive roughness or bonding failure due to incomplete cleaning.

[0033] S7: The coated sample is cured to complete the preparation of delamination defects and obtain a metal coated part containing pre-set delamination defects.

[0034] Specifically, the curing process aims to eliminate internal stress in the coating, promote coating densification, and stabilize its microstructure, while ensuring that the interfacial state of the pre-existing defects is not damaged. The curing process is typically carried out in an oven or heat treatment furnace, with process parameters including: a curing temperature of 100℃-300℃, preferably 120℃-180℃; this temperature range ensures stress relaxation and micro-diffusion within the coating, while its upper limit is strictly controlled below the thermal decomposition temperature or significant softening point of the filler material (such as polytetrafluoroethylene PTFE) (for example, the upper limit of the long-term service temperature of PTFE is approximately 260℃, but its dimensional stability may decrease above 180℃), preventing coating decomposition, excessive shrinkage, or deformation, thereby compromising the geometric accuracy and interfacial characteristics of the pre-existing defects. The holding time is 0.5h-4h, preferably 1h-2h; too short a time results in insufficient stress relief; too long a time may lead to unnecessary excessive diffusion between the substrate and the coating or increased energy consumption. The process is usually carried out in an air atmosphere. For easily oxidized coatings or substrates, it can also be carried out under the protection of an inert gas (such as argon). The heating and cooling rates are usually controlled at 1-5℃ / min to avoid cracking of the coating or separation from the substrate due to thermal shock.

[0035] The present invention also provides a metal coating sample containing pre-defined delamination defects prepared by the above method. The sample includes a metal substrate, a metal coating covering the substrate, and a delamination defect region present at a specific location between the coating and the substrate interface; the horizontal projection shape, size, position in the plane, and depth of the defect gap of the delamination defect region are all pre-designed and precisely controlled; and the defect is located inside the coating coverage area, rather than being limited to the edge.

[0036] Example 1 This embodiment describes the fabrication of three different geometrical parameters of delamination defects on a titanium alloy substrate, including the following steps: S1: Select a TA2 titanium alloy plate substrate with a preset size of 100 mm × 100 mm × 3 mm as the metal sample; S2: Based on the actual delamination defects that may occur during the actual preparation or use of the metal coating, determine the target geometric parameters of three delamination defects to be pre-placed between the metal substrate and the subsequent coating, as shown in Table 1; Table 1 Target geometric parameters of pre-defined layered defects in Example 1

[0037] S3: According to the target geometric parameters, a pulsed laser is used to etch at a designated position on the surface of the metal substrate to be coated. The laser etches a blind hole-type groove that matches the shape and size of the target defect, and controls the depth processing accuracy of the groove. Specifically, using an IPG Photonics picosecond laser (pulse width 10 ps, ​​wavelength 1064 nm), with laser power set to 20 W, scanning speed to 800 mm / s, and scanning spacing (70% of the spot diameter), a single scan was performed on waste material of the same type. The depth of the shallow groove formed was measured using a white light interferometer, and the average removal depth per scan was found to be Δd = 0.025 mm. Calculation: The target depth D of the equilateral triangular defect is 0.50 mm. Therefore, the theoretical number of scans N = D / Δd = 20. Twenty scans are performed at the target location. After processing, the depth of multiple points within the groove is randomly measured using the same white light interferometer. The measurement results are (0.498 mm, 0.502 mm, 0.501 mm), with an average depth of 0.500 mm, a range of 0.004 mm, and a depth control accuracy of < ±0.02 mm. Similarly, the average depth of the circular defect is 1.001 mm, and the average depth of the square defect is 1.501 mm.

[0038] S4: Based on the three target defect shapes, sizes, and thicknesses determined in step S2, prepare the corresponding filler material sheets: For defect #1 (triangle): cut an equilateral triangular polytetrafluoroethylene (PTFE) film sheet with a side length of 9.98 mm and a thickness of 0.50 mm; For defect #2 (circular): cut a circular PTFE film sheet with a diameter of 14.98 mm and a thickness of 1.00 mm; For defect #3 (square): cut a square PTFE film sheet with a side length of 19.98 mm and a thickness of 1.50 mm; Place the cut PTFE film sheets into their respective grooves. During placement, a small amount of anhydrous ethanol can be dropped into the groove to utilize capillary action, helping the film sheets to smoothly embed into the bottom of the groove and ensuring a tight fit. Then, allow the mixture to stand at room temperature until the ethanol has completely evaporated.

[0039] S5: After the filler material sheet is inserted, the surface of the metal substrate to be sprayed is flattened so that the upper surface of the filler material sheet is coplanar with the surrounding surface of the metal substrate, forming a flat composite surface to be sprayed. Specifically, firstly, the surface is finely sanded using 200-grit silicon carbide sandpaper to remove any PTFE material that may protrude above the substrate surface until the surface feels smooth. After sanding, the surface is thoroughly cleaned with compressed air and anhydrous ethanol. Then, a suitable amount of acetone is applied evenly to the entire surface to be coated using a lint-free cloth, and the sample is then placed in a clean environment to air dry for 2 hours. After this treatment, the surface of the PTFE filler sheet and the surrounding titanium alloy substrate surface are highly coplanar. Using a white light interferometer for sampling measurement, the absolute value of the height difference Δh is less than 1 μm.

[0040] S6: On the smooth composite surface to be coated, a metal coating is deposited using a plasma spraying process. Pre-coating treatment: The entire surface is roughened by sandblasting with 24-mesh brown corundum abrasive, with a particle size range of 30 mesh, a spraying pressure of 0.5 MPa, and a spraying angle of 75°, so that the surface roughness Ra reaches 5-8 μm to enhance the adhesion of the coating. Atmospheric plasma spraying equipment was used, and the spraying material was NiCrAlY alloy powder. The process parameters were as follows: arc current of 550 A, working voltage of 45V, main gas (Ar) flow rate of 40 SLPM, auxiliary gas (H2) flow rate of 10 SLPM, powder feed rate of 30g / min, spraying distance of 100 mm, and spray gun moving speed of 500 mm / s. By controlling the number of reciprocating scans of the spray gun under the aforementioned parameters, the average coating thickness was controlled to approximately 300 μm. Throughout the spraying process, the temperature of the substrate back side was monitored by thermocouples and never exceeded 180°C. Argon gas is ionized by a high-frequency electric arc to form a high-temperature plasma jet. The powder is sent into the plasma jet and melted instantly. The molten powder impacts the surface of the titanium alloy plate at high speed, cools and solidifies rapidly, and stacks layer by layer to form a dense coating.

[0041] S7: After spraying, place the sample in an oven at 150℃ for 1 hour to release the internal stress of the coating and complete the curing.

[0042] In this embodiment, a standard test block with a TA2 titanium alloy-based NiCrAlY coating (such as...) was prepared. Figure 1 As shown in the figure, it has three pre-set layered defects with precise control over their shape, size, position and depth, and the coating surface is complete and uniform, without any visible damage or peeling.

[0043] To verify the accuracy and usability of the pre-set defects, the sample prepared in Example 1 was subjected to ultrasonic testing (using a 15 MHz focusing probe). C-scan image ( Figure 2The results clearly show three independent, sharply defined defect signals. Their shape, relative position, and size closely match the design parameters (Table 1), and the signal intensity is uniform, indicating a consistent defect interface state. This directly proves that the method of this invention can prepare high-quality standard test blocks that can be used for the calibration and evaluation of quantitative nondestructive testing methods.

[0044] Example 2 This embodiment describes the fabrication of a delamination defect with specific geometric parameters on a 304 stainless steel substrate, comprising the following steps: S1: Select a 304 stainless steel plate with dimensions of 50 mm × 50 mm × 2 mm as the metal sample; S2: Design target defect: A circular delamination defect with a diameter of 5.0 mm and a depth of 0.20 mm is pre-placed at the center of the substrate; S3: According to the target geometric parameters, a pulsed laser is used to etch at a designated position on the surface of the metal substrate to be coated. The laser etches a blind hole-type groove that matches the shape and size of the target defect, and controls the depth processing accuracy of the groove. Specifically, an IPG Photonics picosecond laser (pulse width 10 ps, ​​wavelength 1064 nm) was used. The laser etching process parameters were: laser power 15 W, scanning speed 1200 mm / s. The single removal depth Δd = 0.008 mm was measured through calibration. Therefore, the number of scans N = 0.20 / 0.008 = 25 times was set. The actual measured groove depth after processing was 0.201 mm, and the accuracy met the requirement of ≤±0.02 mm.

[0045] S4: Prepare a circular polyimide film with a diameter of 4.98 mm and a thickness of 0.20 mm as a filler material sheet and place it into the groove; S5: After the filler material sheet is inserted, the surface of the metal substrate to be sprayed is flattened so that the upper surface of the filler material sheet is coplanar with the surrounding surface of the metal substrate, forming a flat composite surface to be sprayed. Specifically, firstly, the surface is finely sanded using 800-grit silicon carbide sandpaper to remove any PTFE material that may protrude above the substrate surface until the surface feels smooth. After sanding, the surface is thoroughly cleaned with compressed air and anhydrous ethanol. Then, a suitable amount of acetone is applied evenly to the entire surface to be coated using a lint-free cloth. The sample is then placed in a clean environment and left to air dry for 2 hours. After this treatment, the surface of the PTFE filler sheet and the surrounding titanium alloy substrate surface are highly coplanar. Using a white light interferometer for sampling measurement, the absolute value of the height difference Δh is less than 1 μm.

[0046] S6: On the smooth composite surface to be coated, a metal coating is deposited using a plasma spraying process. Pre-coating treatment: The entire surface is roughened by sandblasting with 24-mesh brown corundum abrasive, with a particle size range of 50 mesh, a spraying pressure of 0.7 MPa, and a spraying angle of 80°, so that the surface roughness Ra reaches 5-8 μm to enhance the adhesion of the coating. Atmospheric plasma spraying equipment was used, and the spraying material was 316L stainless steel powder. The process parameters were as follows: arc current of 500A, working voltage of 40V, main gas (Ar) flow rate of 35SLPM, auxiliary gas (N2) flow rate of 8SLPM, powder feed rate of 25g / min, spraying distance of 90 mm, and spray gun moving speed of 400 mm / s. By controlling the number of reciprocating scans of the spray gun under the aforementioned parameters, the average coating thickness was controlled to approximately 150 μm. Throughout the spraying process, the temperature of the substrate back side was monitored by thermocouples and never exceeded 250°C. S7: After spraying, place the sample in an oven at 180℃ for 1 hour to release the internal stress of the coating and complete the curing.

[0047] In this embodiment, a standard test block with a 304 stainless steel base and a 316L stainless steel coating was prepared. The block contained a pre-set circular delamination defect with precise control over its size, position, and depth. The coating surface was intact and uniform, with no visible damage or peeling.

[0048] Comparative Example 1 This comparative example uses the traditional insert-and-pull method to prepare the same circular delamination defect as in Example 1. The steps include: S1: Select a TA2 titanium alloy plate (100 mm × 100 mm × 3 mm) with the same specifications as in Example 1, and design a circular delamination defect with a diameter of 15 mm and a target depth of 1.0 mm to be pre-placed at the center of the substrate (the same position as in Example 1). S2: Cut a circular PTFE film with a diameter of 15 mm and a thickness of 1.0 mm. Without performing any laser etching, directly lay this PTFE film flat on the surface to be coated in the center of the titanium alloy plate; S3: Perform the same sandblasting roughening and plasma spraying process (with the same parameters) on the substrate with PTFE film as in Example 1 to prepare a NiCrAlY coating with an average thickness of about 300 μm. S4: After the coating has cured, try to use precision tweezers to find and clamp the edge of the PTFE film from the edge of the sample, apply uniform tension to try to pull it out, so as to form an artificial delamination defect between the coating and the substrate.

[0049] During the extraction process, the PTFE film could not be completely extracted because it was completely encapsulated by a dense and thin coating (300 μm). When tension was applied, the PTFE film fractured, with some remaining inside the coating. The extraction action caused significant warping, cracking, and even localized peeling of the coating from the substrate in an area of ​​approximately Φ30 mm around the extraction point. The final sample exhibited severe macroscopic mechanical damage around the target defect area, and the coating was discontinuous, rendering it unusable as a valid, intact "standard test block" for nondestructive testing calibration or quantitative performance studies.

[0050] Comparative Example 2 In this comparative example, three delamination defects with different geometric parameters, identical to those in Example 1, were prepared on a titanium alloy substrate. The preparation method was similar to that in Example 1, except that: In step S4, instead of cutting the filler sheet as required by the present invention, an equilateral triangle with a side length of 10.2 mm (thickness still 0.5 mm), a circle with a diameter of 15.2 mm (thickness still 1.0 mm), and a square with a side length of 20.2 mm (thickness still 1.5 mm) are cut, that is, a PTFE film that is 0.1 mm larger than one side of the groove.

[0051] An attempt was made to press the PTFE sheet of the interference size into the groove, but it was found that it could not be inserted flat, the middle was obviously arched, and the periphery was still warped after being pressed forcibly.

[0052] Although step S5 attempted to polish the surface, it could not eliminate the arching, resulting in a severely uneven surface.

[0053] The other steps are the same as in Example 1.

[0054] After spraying, obvious protrusions and unevenness can be seen on the coating surface in the area corresponding to the triangular defect.

[0055] Metallographic sectioning analysis: After cutting the sample, it was found that the coating on the PTFE sheet was abnormally thickened in some areas due to the PTFE sheet arching. There were also irregular gaps between the coating and the PTFE sheet, as well as between the PTFE sheet and the bottom of the groove, which failed to form the designed parallel layers with consistent thickness.

[0056] Non-destructive testing: Ultrasonic C-scan images ( Figure 3 The results show that the "defect" signal is distorted in shape, has a diffused boundary, and is accompanied by noise, making it unsuitable as a standard defect with well-defined characteristics.

[0057] Comparative Example 3 In this comparative example, three delamination defects with the same geometric parameters as in Example 1 were prepared on a titanium alloy substrate. The preparation method was similar to that in Example 1, except that: In step S6, the arc current is 700 A (higher than the upper limit of 650 A in this invention). Main gas (Ar) flow rate: 25 SLPM (below the lower limit of 30 SLPM of this invention, aimed at increasing the jet enthalpy). Auxiliary gas (H2) flow rate: 15 SLPM (Use the upper limit to further increase temperature) Powder feed rate: 15 g / min (significantly lower than the lower limit of 20 g / min in this invention, resulting in powder over-melting and relatively higher heat input) Spraying distance: 70 mm (lower than the lower limit of 80 mm in this invention, to improve particle impact kinetic energy and heat conduction) Spray gun moving speed: 200 mm / s (lower than the lower limit of 300 mm / s of this invention, to prolong the local heating time).

[0058] During the spraying process, an infrared thermal imager was used to monitor the temperature of the back side of the substrate. Records show that the substrate temperature rose rapidly after the start of spraying and remained above 350°C, reaching a maximum of approximately 420°C.

[0059] The other steps are the same as in Example 1.

[0060] The coating surface in this comparative example exhibits an over-melted state, a dark color, and numerous oxide spots. Metallographic observation of the cut sample revealed that the pre-placed PTFE filler material had undergone severe thermal decomposition. The original filler sheet was no longer a complete film, but rather contained a small amount of black carbides and numerous voids, making its original shape and thickness unrecognizable.

[0061] Due to the decomposition and ablation of PTFE, the intended weak bonding interface of "metal coating-PTFE-metal substrate" is completely destroyed, and what is actually formed is an irregular, porous and contaminant-filled melting-type void, whose geometry and interface state are completely out of control; this area can no longer simulate the delamination defects generated in actual service.

[0062] Non-destructive testing: Ultrasonic C-scan inspection was performed on the area, and the ultrasonic C-scan image ( Figure 4 The displayed signal is extremely chaotic, manifesting as a high-noise area with blurred boundaries and cluttered internal reflections, unable to provide any calibrable, clear defect signal.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a metal coating delamination defect, characterized in that, Includes the following steps: S1: Select a metal substrate of a preset size as the metal sample; S2: Based on the actual delamination defects that may occur during the actual preparation or use of the metal coating, determine the target geometric parameters of at least one delamination defect to be pre-placed between the metal substrate and the subsequent coating; S3: Based on the target geometric parameters, pulsed laser is used to etch at a specified position on the surface of the metal substrate to be coated. The laser etches blind hole grooves that match the shape and size of the target defect, and controls the depth processing accuracy of the grooves. S4: Prepare a solid filler material sheet that matches the shape, size and depth of the groove, and place the filler material sheet into the corresponding groove; S5: After the filler material sheet is inserted, the surface of the metal substrate to be sprayed is flattened so that the upper surface of the filler material sheet is coplanar with the surrounding surface of the metal substrate to form a composite surface to be sprayed. S6: A metal coating is deposited on the composite surface to be sprayed using a thermal spraying process; S7: The coated sample is cured to complete the preparation of delamination defects and obtain a metal coated part containing pre-set delamination defects; The filler material sheet forms a weakly bonded interface or a non-bonded interface with the metal coating and the metal substrate under the thermal spraying process conditions.

2. The preparation method according to claim 1, characterized in that, In step S2, the target geometric parameters include the planar shape and size, location, and depth of the pre-defined layered defect; The planar shape and size of the pre-defined delamination defect refer to the outline shape and size of the defect in a plane parallel to the surface of the metal substrate to be coated; The pre-set delamination defect location refers to the planar coordinate position of the defect on the surface of the metal substrate to be coated; The pre-set layered defect depth refers to the gap thickness of the defect in the direction perpendicular to the surface of the metal substrate to be coated.

3. The preparation method according to claim 1, characterized in that, In step S3, the laser etching process parameters include: laser power of 0.5W-50W, scanning speed of 100mm / s-1000mm / s, and scanning spacing of 60-80% of the spot diameter.

4. The preparation method according to claim 1, characterized in that, In step S4, the filler material sheet is one or more of the following: polymer film material, special material with adhesive or isolation function, metal foil, metal sheet, and composite material.

5. The preparation method according to claim 1, characterized in that, In step S5, the absolute value of the height difference between the upper surface of the filling material sheet and the surrounding metal substrate surface is less than 2 μm.

6. The preparation method according to claim 1, characterized in that, In step S6, the thermal spraying process is a plasma spraying process. The plasma spraying process parameters are: arc current 400-600 A, working voltage 40-60V, main gas Ar flow rate 30-50 SLPM, auxiliary gas H2 flow rate 5-15 SLPM, powder feed rate 20-40 g / min, spraying distance 80-120 mm, and spray gun moving speed 300-700 mm / s.

7. The preparation method according to claim 1, characterized in that, In step S7, the curing temperature of the curing treatment is 100℃-300℃, and the curing holding time is 0.5-4h.

8. The preparation method according to claim 1, characterized in that, Before depositing the metal coating using the plasma spraying process, the preparation method further includes cleaning and roughening the composite surface to be sprayed.

9. The preparation method according to claim 8, characterized in that, The roughening treatment is sandblasting, with a blasting pressure of 0.3 MPa-0.7 MPa and a blasting angle of 60°-80°.

10. A metal coated part containing a pre-defined delamination defect, characterized in that, The pre-formed delamination defect is prepared by the preparation method according to any one of claims 1-9, and the metal coating comprises: Metal matrix; A metal coating covering the metal substrate; and At least one pre-defined delamination defect region located between the interface between the metal coating and the metal substrate; The pre-set delamination defect area is located inside the area covered by the metal coating.

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