Graphite components, preparation methods, applications and evaluation methods

Abstract

This invention discloses a graphite part, its preparation method, its application, and its evaluation method. The graphite part includes a graphite substrate and an amorphous carbon coating disposed on the surface of the graphite substrate. The graphite part satisfies Q=Y×Δρ×(Ra^0.5) / d≥4.0: By coupling the coating's energy dissipation capacity (Y), the substrate's gradient densification degree (Δρ), the substrate's surface morphology characteristics (Ra^0.5), and the coating's geometric constraints (d) to a single parameter Q, quantitative characterization and engineering controllability of the crack resistance performance of the amorphous carbon coating during high-temperature carbonization are achieved. In the graphite part prepared when Q≥4.0, the amorphous carbon coating does not crack or shed powder, which is beneficial for its application in ion implanters.

Description

Technical Field

[0001] This invention relates to the field of graphite materials technology, and more specifically, to graphite components, preparation methods, applications, and evaluation methods. Background Technology

[0002] Ion implantation, a key technology in semiconductor doping, involves high-energy ion beams (such as boron, phosphorus, and arsenic) within the process chamber that can cause significant physical sputtering damage and thermal stress to graphite components. Although high-purity, high-density, and high-strength (referred to as "three-high") graphite materials possess excellent high-temperature resistance and electrical conductivity, their relatively porous structure (volume density typically ranging from 1.70 to 1.85 g / cm³) makes them prone to surface delamination under continuous ion bombardment, becoming a significant source of particulate contaminants in semiconductor manufacturing.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide graphite parts, preparation methods, applications and evaluation methods. The graphite parts of this application are not prone to surface peeling under continuous ion bombardment.

[0005] This invention is implemented as follows: In a first aspect, the present invention provides a graphite component, comprising a graphite substrate and an amorphous carbon coating disposed on the surface of the graphite substrate, wherein the graphite component satisfies formula I: Q=Y×Δρ×(Ra^0.5) / d≥4.0 Formula I Where: Y is the energy dissipation factor of the amorphous carbon coating, Y=H / μ; H is the Vickers hardness value of the amorphous carbon coating, and the unit of Vickers hardness is HV; μ is the coefficient of friction of the amorphous carbon coating; Δρ is the gradient densification factor of the substrate, Δρ=ρ1-ρ0, ρ0 is the volume density of the graphite substrate, ρ1 is the volume density of the graphite part, and the unit of the volume density is g / cm³. Ra is the numerical value of the surface roughness of the substrate, and the unit of surface roughness is μm; d represents the thickness of the amorphous carbon coating, with the unit of thickness being μm.

[0006] In an optional implementation, the value of Y ranges from 125 to 200.

[0007] In an optional implementation, the value of Δρ ranges from 0.03 to 0.08.

[0008] In an optional implementation, the value of μ ranges from 0.15 to 0.20.

[0009] In an optional implementation, the value of H ranges from 25 to 30.

[0010] In an optional implementation, when Δρ = 0.05 and Y = 154.28: In the graphite component, 0.4≤Ra≤1.6, d≤1.0+0.833×(Ra-0.4)=0.6668+0.833Ra; And / or, in the graphite part, 1.6≤Ra≤3.2, d≤2.0+(1.0 / 1.6)×(Ra-1.6)=2.0+0.625×(Ra-1.6)=1+0.625Ra; And / or, in the graphite component, Ra < 0.4, d ≤ (Ra / 0.4)^0.5; And / or, in the graphite component, Ra>3.2, d≤3.0×(Ra / 3.2)^0.5; In a second aspect, the present invention provides a method for preparing the graphite part described in the foregoing embodiments, comprising: sequentially impregnating the graphite substrate with resin and then curing it in one stage to obtain an intermediate graphite part; A resin layer is formed on the surface of the intermediate graphite part, followed by two-stage curing to obtain a cured graphite part; The cured graphite part is carbonized to obtain the graphite part.

[0011] In an optional embodiment, the resin is selected from at least one of phenolic resin and furan resin; And / or, the curing process includes: increasing the temperature to 85-95℃ at a rate of 0.4-0.6℃ / min, holding for 1.5-2.5 hours, and then increasing the temperature to 145-455℃ at a rate of 0.4-0.6℃ / min and holding for 4.5-5.5 hours for curing; And / or, the two-stage curing includes: increasing the temperature to 85-95℃ at a rate of 0.4-0.6℃ / min, holding for 1.5-2.5 hours, and then increasing the temperature to 145-455℃ at a rate of 0.4-0.6℃ / min and holding for 4.5-5.5 hours for curing; And / or, the carbonization temperature is 900-1200℃, the time is 4-10 min, and the atmosphere is an inert atmosphere.

[0012] Thirdly, the present invention provides an application of the graphite component described in the foregoing embodiments in an ion implanter.

[0013] Fourthly, the present invention provides a method for predicting the cracking performance of graphite parts, wherein the graphite parts are prepared by the method described in the foregoing embodiments. When the graphite parts satisfy Formula I, the graphite parts are free from cracks and powder shedding after carbonization; when the amorphous carbon coating does not satisfy Formula I, the graphite parts will produce cracks or powder shedding after carbonization. Q=Y×Δρ×(Ra^0.5) / d≥4.0 Formula I Where: Y is the energy dissipation factor of the coating, Y=H / μ; H is the Vickers hardness of the coating, and the unit of Vickers hardness is HV; μ is the coefficient of friction of the coating; Δρ is the gradient densification factor of the substrate, Δρ=ρ1-ρ0, ρ0 is the volume density of the graphite substrate before impregnation, ρ1 is the volume density of the graphite substrate after impregnation, and the unit of volume density is g / cm³. Ra is the numerical value of the surface roughness of the substrate, and the unit of surface roughness is μm; d represents the thickness of the coating, with the unit of thickness being μm.

[0014] The present invention has the following beneficial effects: By coupling the coating's energy dissipation capacity (Y), the substrate's gradient densification degree (Δρ), the substrate's surface morphology characteristics (Ra^0.5), and the coating's geometric constraints (d) to the parameter Q, the quantitative characterization and engineering control of the crack resistance of amorphous carbon coatings during high-temperature carbonization were achieved. In graphite parts prepared with Q≥4.0, the amorphous carbon coating did not crack or shed powder, which is beneficial for its application in ion implanters. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 The results are the friction coefficient test results of the graphite component in Example 1; Figure 2 The Vickers hardness test results are for the graphite parts in Example 1; Figure 3 Here is a SEM image of the graphite component in Example 1; Figure 4 This is a SEM image of the graphite component in Example 3. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] The applicant's research found that to suppress surface delamination of graphite parts under continuous ion bombardment, an amorphous carbon coating with a dense structure, high hardness, and chemical inertness can be applied to the surface of the graphite parts. However, two key technical bottlenecks remain in the high-temperature carbonization process of amorphous carbon coatings: first, the balance between stress control and crack resistance within the coating; and second, insufficient interfacial compatibility between the coating and the substrate material. These factors have prevented an effective solution to the cracking problem of the coating during high-temperature preparation.

[0019] Therefore, embodiments of the present invention provide a graphite component, comprising a graphite substrate and an amorphous carbon coating disposed on the surface of the graphite substrate, wherein the graphite component satisfies formula I: Q=Y×Δρ×(Ra^0.5) / d≥4.0 Formula I Where: Y is the energy dissipation factor of the amorphous carbon coating, Y=H / μ; H is the Vickers hardness value of the amorphous carbon coating, and the unit of Vickers hardness is HV; μ is the coefficient of friction of the amorphous carbon coating; Δρ is the gradient densification factor of the substrate, Δρ=ρ1-ρ0, ρ0 is the volume density of the graphite substrate, ρ1 is the volume density of the graphite part, and the unit of the volume density is g / cm³. Ra is the numerical value of the surface roughness of the substrate, and the unit of surface roughness is μm; d represents the thickness of the amorphous carbon coating, with the unit of thickness being μm.

[0020] By coupling the coating's energy dissipation capacity (Y), the substrate's gradient densification degree (Δρ), the substrate's surface morphology characteristics (Ra^0.5), and the coating's geometric constraints (d) to the parameter Q, the quantitative characterization and engineering control of the crack resistance of amorphous carbon coatings during high-temperature carbonization were achieved. In graphite parts prepared with Q≥4.0, the amorphous carbon coating did not crack or shed powder, which is beneficial for its application in ion implanters.

[0021] In an optional implementation, the value of Y ranges from 125 to 200. In Y=H / μ, the Vickers hardness H reflects the coating's ability to suppress local yielding and microcrack nucleation, while the friction coefficient μ characterizes the controllable microslip resistance of the coating / graphite matrix interface under thermal stress. The two are coupled to form the energy dissipation factor Y of the amorphous carbon coating. The higher the value of Y, the greater the coating's resistance to deformation that can be supported by the unit interfacial shear resistance, thus making it less prone to powder shedding or cracking when applied to an ion implanter. However, if the value of Y is too high, it will reduce the toughness of the amorphous carbon coating. Therefore, the value of Y ranges from 125 to 200.

[0022] In an optional implementation, the value of Δρ is in the range of 0.03-0.08, which solves the problem that the prior art ignores the influence of substrate densification on the crack resistance of the coating. The value of Δρ in the range of 0.03-0.08 is conducive to ensuring a significant improvement in the interfacial support strength, while preventing excessive densification from causing thermal expansion mismatch and inducing interfacial peeling.

[0023] In an optional implementation, the value of μ ranges from 0.15 to 0.20. Changes in the coefficient of friction often indicate changes in the stress distribution within the coating. A coefficient of friction ranging from 25 to 30 is often accompanied by lower internal stress and a certain degree of plastic deformation capacity, which helps to alleviate stress accumulation and delay crack initiation. If the coefficient of friction μ is too low, it will weaken the interfacial bonding. Conversely, a high coefficient of friction makes it easier for shear stress to concentrate at the surface and interface, which can easily accelerate the nucleation and propagation of microcracks under cyclic friction.

[0024] In an optional implementation, the value of H is in the range of 25-30 to prevent excessive hardness from increasing brittleness or excessive hardness from causing interlayer instability due to plastic rheology. Increasing the Vickers hardness H in Y=H / μ is beneficial for imparting excellent resistance to plastic deformation to the coating and avoiding excessive brittleness, which can delay crack initiation; however, excessively high Vickers hardness H is often accompanied by increased internal stress and decreased fracture toughness in the coating, making the coating more prone to brittle cracking under the disturbance of interface defects in the thermal expansion of the matrix. Therefore, the value of H is 25-30.

[0025] In an optional implementation, when Δρ = 0.05 and Y = 154.28: In the graphite component, 0.4≤Ra≤1.6, d≤1.0+0.833×(Ra-0.4)=0.6668+0.833Ra; And / or, in the graphite part, 1.6≤Ra≤3.2, d≤2.0+(1.0 / 1.6)×(Ra-1.6)=2.0+0.625×(Ra-1.6)=1+0.625Ra; And / or, in the graphite component, Ra < 0.4, d ≤ (Ra / 0.4)^0.5; And / or, in the graphite component, Ra>3.2, d≤3.0×(Ra / 3.2)^0.5; By establishing a nonlinear mapping relationship between Ra and d, the coating thickness is dynamically adapted to the substrate roughness. This prevents stress concentration cracking caused by excessive thickness of the amorphous carbon coating when Ra is too low, and avoids incomplete coverage or amplified interface disturbances caused by excessive thinness of the amorphous carbon coating when Ra is too high, thus achieving morphology-thickness synergistic crack control.

[0026] This invention also provides a method for preparing the graphite part described in the foregoing embodiments, comprising: The graphite substrate is sequentially impregnated with resin and then cured in one stage to obtain an intermediate graphite part; A resin layer is formed on the surface of the intermediate graphite part, followed by two-stage curing to obtain a cured graphite part; The cured graphite part is carbonized to obtain the graphite part.

[0027] It should be noted that ρ0 is the bulk density of the graphite substrate material before impregnation.

[0028] In an optional embodiment, the resin is selected from at least one of phenolic resin and furan resin; phenolic resin has a high carbon yield and a dense residual carbon structure, which is beneficial to increasing Δρ and supporting the interfacial bonding of the subsequent amorphous carbon coating; furan resin contains furan rings, releases more small molecule gases during pyrolysis, easily forms micropores, can improve interfacial stress relaxation, and indirectly increase γ. The combination of the two is beneficial to the balance between densification and toughness.

[0029] In an optional embodiment, the first-stage curing includes: increasing the temperature at 0.4-0.6℃ / min to 85-95℃, holding for 1.5-2.5 hours, and then increasing the temperature at 0.4-0.6℃ / min to 145-455℃ and holding for 4.5-5.5 hours for curing. This first-stage curing determines the degree of cross-linking of the impregnating resin within the graphite pores. If the temperature is too low or the time is insufficient, the resin will not be fully cured, resulting in significant loss during carbonization and a lower Δρ value. If the temperature is too high or the time is too long, the resin will prematurely polycondense excessively, increasing brittleness and raising the risk of microcracks in the matrix after carbonization, which in turn leads to a decrease in the measured Δρ value. Precise control of this stage is a key prerequisite for ensuring Δρ is 0.03-0.08, directly affecting the Q value of the graphite part.

[0030] In an optional embodiment, the two-stage curing includes: increasing the temperature at 0.4-0.6℃ / min to 85-95℃, holding for 1.5-2.5 hours, and then increasing the temperature at 0.4-0.6℃ / min to 145-455℃ and holding for 4.5-5.5 hours for curing. The two-stage curing is specifically for shaping the surface resin layer, and its temperature / time directly controls the crosslinking density and thickness uniformity of the surface resin. Insufficient curing will result in a soft surface layer, flow / collapse during carbonization, and a measured d value lower than the design value. Over-curing will cause premature coking and cracking of the surface resin, forming initial defects after carbonization, resulting in a falsely high Y value but a decrease in actual crack resistance, leading to cracking and powder shedding of the graphite parts even though Q≥4.0.

[0031] In an optional embodiment, the carbonization temperature is 900-1200℃, the time is 4-10 min, and the atmosphere is an inert atmosphere. The carbonization temperature determines the sp² / sp³ ratio and residual stress of the amorphous carbon coating: if the temperature is too low or the carbonization time is too short, the graphitization of the coating will be insufficient, and Y will decrease; if the temperature is too high, the thermal expansion mismatch will be aggravated, which will easily induce microcracks in the coating, reduce the measured effective load-bearing thickness d, and cause Q to be artificially high. Long carbonization time is prone to interfacial debonding and will also lead to errors in the prediction of whether the graphite part will crack based on the Q value.

[0032] The present invention also provides an application of the graphite component described in the foregoing embodiments in an ion implanter.

[0033] The present invention also provides a method for predicting the cracking performance of graphite parts, wherein the graphite parts are prepared by the method described in the foregoing embodiments. When the graphite parts satisfy Formula I, the graphite parts are free of cracks and powder after carbonization; when the amorphous carbon coating does not satisfy Formula I, the graphite parts will produce cracks or powder after carbonization.

[0034] Q=Y×Δρ×(Ra^0.5) / d≥4.0 Formula I Where: Y is the energy dissipation factor of the coating, Y=H / μ; H is the Vickers hardness of the coating, and the unit of Vickers hardness is HV; μ is the coefficient of friction of the coating; Δρ is the gradient densification factor of the substrate, Δρ=ρ1-ρ0, ρ0 is the volume density of the graphite substrate before impregnation, ρ1 is the volume density of the graphite substrate after impregnation, and the unit of volume density is g / cm³. Ra is the numerical value of the surface roughness of the substrate, and the unit of surface roughness is μm; d represents the thickness of the coating, with the unit of thickness being μm.

[0035] This evaluation method can predict the cracking situation during the carbonization process of graphite parts before they are prepared, thus guiding the production of graphite parts.

[0036] It should be noted that, since the amorphous carbon coating in the graphite part of this application accounts for a relatively small proportion of the graphite substrate thickness, the changes in the thickness of the amorphous carbon coating and the changes in the surface roughness of the graphite substrate have a negligible impact on Y and Δρ within the scope of this application. Therefore, when determining the d value based on Ra, other samples with different Ra and d values ​​can be measured as a basis for predicting the graphite part to be evaluated.

[0037] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0038] Example 1 This embodiment provides a graphite component for an ion implanter, comprising a graphite substrate and an amorphous carbon coating disposed on the surface of the graphite substrate. The expected surface roughness of the graphite substrate is 0.4 μm, the initial bulk density of the graphite substrate is 1.85 g / cm³, the bulk density of the graphite component is 1.90 g / cm³, and the calculated gradient density enhancement factor Δρ = 0.05. The hardness of the amorphous carbon coating is 27.77 HV, the coefficient of friction is 0.18, and the calculated energy dissipation factor Y = 27.77 / 0.18 = 154.28. Based on the expected parameters, when Ra = 0.4 μm, d ≤ 1.0 μm; therefore, the preset thickness of the amorphous carbon coating is d = 0.9 μm, leaving a certain safety margin.

[0039] The graphite component was prepared according to the following method: Ultrasonic-cleaned and dried graphite was impregnated with 2130 phenolic resin at an impregnation pressure of 0.5 MPa. The resin on the graphite surface was then wiped off. The temperature was increased to 90°C at a rate of 0.5°C / min and held for 2 hours, followed by a rate of 0.5°C / min to 150°C and held for 5 hours for curing. Resin was then brushed onto the surface of the cured graphite component. The component was then fixed in place using a fixture (without damaging the surface resin layer). The temperature was increased to 90°C at a rate of 0.5°C / min and held for 2 hours, followed by a rate of 0.5°C / min to 150°C and held for 5 hours for curing. The component was then placed in a carbonization furnace or tube furnace for carbonization under an inert gas atmosphere at a temperature of 1100°C for 8 minutes.

[0040] Actual measured value of graphite component: The surface roughness of the substrate measured by a roughness meter is 0.42μm.

[0041] Crack factor verification: Ra^0.5=0.648, Q=(154.28×0.05×0.648) / 0.9=5.00 / 0.9=5.56≥4.0, which meets the requirements.

[0042] The cracking and powder shedding of the graphite parts prepared in the above embodiments were observed, and the results are shown in Table 1.

[0043] Example 2-23 Based on Example 1, the surface roughness of the graphite substrate and the thickness of the amorphous carbon coating were adjusted. Specifically, the surface roughness of the graphite substrate was changed by sanding with sandpaper of different grits, and the coating thickness could be adjusted by the number of brushings. Graphite parts numbered 1-22 were prepared, and the cracking and powder shedding conditions are shown in Table 1.

[0044] Table 1

[0045] In Table 1, whether the graphite parts are cracked is determined by observing whether there are cracks in the SEM images.

[0046] The graphite parts prepared in Example 1 and Comparative Example 1 were subjected to a powder shedding test. The specific steps included: sticking transparent tape to the surface of the graphite block, then peeling off the transparent tape, and testing the light transmittance before and after the transparent tape was stuck to the graphite block. If the light transmittance changed greatly, it indicated that a lot of powder was shed.

[0047] The light transmittance of the transparent tape used in the test before sticking to the graphite was 97.2%. The light transmittance of the transparent tape after being torn off in Example 1 was 93.5%, and the light transmittance of the transparent tape after being torn off in Comparative Example 1 was 65.4%. This shows that there was almost no powder shedding in Example 1 (the decrease in light transmittance was caused by the reduction in light transmittance after the tape was torn off), while there was more powder shedding in Comparative Example 1.

[0048] The friction coefficient and Vickers hardness test results of the amorphous carbon coating on the graphite part prepared in Example 1 are as follows: Figure 1 and Figure 2 As shown, the SEM images after the high-temperature carbonization test in Examples 1 and 3 are as follows. Figure 3 and Figure 4 As shown in the figure, the results show that the coating of the graphite part is intact after high-temperature carbonization, with no visible cracks and no powder shedding.

[0049] As can be seen from the above embodiments, when Y and Δρ are fixed, the greater the surface roughness of the substrate, the greater the allowable coating thickness will be.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A graphite component, characterized in that, The graphite component comprises a graphite substrate and an amorphous carbon coating disposed on the surface of the graphite substrate, wherein the graphite component satisfies formula I: Q=Y×Δρ×(Ra^0.5) / d≥4.0 Formula I Where: Y is the energy dissipation factor of the amorphous carbon coating, Y=H / μ; H is the Vickers hardness value of the amorphous carbon coating, and the unit of Vickers hardness is HV; μ is the coefficient of friction of the amorphous carbon coating; Δρ is the gradient densification factor of the substrate, Δρ=ρ1-ρ0, ρ0 is the volume density of the graphite substrate, ρ1 is the volume density of the graphite part, and the unit of the volume density is g / cm³. Ra is the numerical value of the surface roughness of the substrate, and the unit of surface roughness is μm; d represents the thickness of the amorphous carbon coating, with the unit of thickness being μm.

2. The graphite component according to claim 1, characterized in that, The value of Y ranges from 125 to 200.

3. The graphite component according to claim 1, characterized in that, The value of Δρ ranges from 0.03 to 0.

08.

4. The graphite component according to claim 1, characterized in that, The value of μ ranges from 0.15 to 0.

20.

5. The graphite component according to claim 1, characterized in that, The value of H ranges from 25 to 30.

6. The graphite component according to claim 1, characterized in that, When Δρ=0.05 and Y=154.28: In the graphite component, 0.4≤Ra≤1.6, d≤0.6668+0.833Ra; And / or, in the graphite element, 1.6≤Ra≤3.2, d≤1+0.625Ra; And / or, in the graphite component, Ra < 0.4, d ≤ (Ra / 0.4)^0.5; And / or, in the graphite component, Ra>3.2, d≤3.0×(Ra / 3.2)^0.

5.

7. A method for preparing a graphite part according to claim 1, characterized in that, include: The graphite substrate is sequentially impregnated with resin and then cured in one stage to obtain an intermediate graphite part; A resin layer is formed on the surface of the intermediate graphite part, followed by two-stage curing to obtain a cured graphite part; The cured graphite part is carbonized to obtain the graphite part.

8. The method for preparing a graphite part according to claim 7, characterized in that, The resin is selected from at least one of phenolic resin and furan resin; And / or, the curing process includes: increasing the temperature to 85-95℃ at a rate of 0.4-0.6℃ / min, holding for 1.5-2.5 hours, and then increasing the temperature to 145-455℃ at a rate of 0.4-0.6℃ / min and holding for 4.5-5.5 hours for curing; And / or, the two-stage curing includes: increasing the temperature to 85-95℃ at a rate of 0.4-0.6℃ / min, holding for 1.5-2.5 hours, and then increasing the temperature to 145-455℃ at a rate of 0.4-0.6℃ / min and holding for 4.5-5.5 hours for curing; And / or, the carbonization temperature is 900-1200℃, the time is 4-10 min, and the atmosphere is an inert atmosphere.

9. The application of a graphite component according to any one of claims 1-6 in an ion implanter.

10. A method for predicting the cracking performance of graphite parts, characterized in that, The graphite part is prepared by the method described in claim 7 or 8. When the graphite part satisfies formula I, the graphite part is free from cracks and powder shedding after carbonization. When the amorphous carbon coating does not satisfy formula I, the graphite part will produce cracks or powder shedding after carbonization. Q=Y×Δρ×(Ra^0.5) / d≥4.0 Formula I Where: Y is the energy dissipation factor of the coating, Y=H / μ; H is the Vickers hardness of the coating, and the unit of Vickers hardness is HV; μ is the coefficient of friction of the coating; Δρ is the gradient densification factor of the substrate, Δρ=ρ1-ρ0, ρ0 is the volume density of the graphite substrate before impregnation, ρ1 is the volume density of the graphite substrate after impregnation, and the unit of volume density is g / cm³. Ra is the numerical value of the surface roughness of the substrate, and the unit of surface roughness is μm; d represents the thickness of the coating, with the unit of thickness being μm.

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