Method for eliminating carbon adsorbed on surface of carbide coating

Abstract

The invention discloses a method for eliminating carbon adsorbed on the surface of a carbide coating, which comprises the following steps: carrying out plasma activation treatment on a matrix containing a defective carbide coating, then coating the surface of the matrix containing the defective carbide coating with repair slurry to obtain a repair slurry layer, drying, and sintering, according to the method, the stoichiometric ratio of C / M on the surface can be recovered to 0.9-1.03 through quantitative reaction of the coated slurry and adsorbed carbon on the surface of the coating, meanwhile, the coating is compact and free of defects, the method is particularly suitable for coating repairing of a graphite matrix thermal field component for semiconductor crystal growth, and the crystal growth quality can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic coating surface treatment, and in particular relates to a method for eliminating carbon adsorbed on the surface of a carbide coating. Background Art

[0002] Carbide ceramic coatings (such as SiC, TaC, and HfC) are widely used in thermal field components for semiconductor single crystal growth due to their high-temperature performance and chemical inertness. However, when carbide coatings are prepared using processes such as CVD, equipment contamination or incomplete decomposition of process gases can lead to changes in the carbon potential in the thermal field, which can easily form non-stoichiometric adsorbed carbon (such as free carbon) on the coating surface. This adsorbed carbon can lead to uneven emissivity on the coating surface, affecting the temperature gradient distribution at the crystal growth interface and increasing crystal defects. Traditional high-temperature annealing or mechanical polishing can also cause problems such as grain coarsening and brittle damage.

[0003] Therefore, it is urgent to develop a surface treatment method that can restore the surface stoichiometric ratio of carbide coatings while maintaining the integrity of the coating. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide a method for eliminating carbon adsorbed on the surface of carbide coatings. The method of the present invention can restore the surface C / M (M=Si, Ta, Hf, etc.) stoichiometric ratio to 0.9-1.03 through quantitative reaction between the applied slurry and the adsorbed carbon on the coating surface. At the same time, the coating is dense and defect-free. The method of the present invention is particularly suitable for coating repair of graphite-based thermal field components used for semiconductor crystal growth, and can significantly improve the quality of crystal growth.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for eliminating carbon adsorbed on the surface of a carbide coating, wherein a substrate containing a defective carbide coating is subjected to plasma activation treatment, and then a repair slurry is applied to the surface of the substrate containing the defective coating to obtain a repair slurry layer, which is then dried and sintered.

[0007] The repair slurry is composed of the following components by weight: 60-70 wt% carbide powder, 1-2 wt% oxide powder, 0.5-1.5 wt% binder, 0.5-1.5 wt% dispersant, 1-3 wt% sintering aid, 0.1-0.3 wt% pH adjuster, and the balance is a composite solvent.

[0008] The carbides in the carbide powder are the same as the carbides in the defective carbide coating;

[0009] The carbide obtained by the thermal reduction reaction between the oxide in the oxide powder and carbon is the same as the carbide in the defective carbide coating;

[0010] The binder is selected from at least one of PVB and PVA;

[0011] The dispersant is selected from at least one of Tween-80 and BYK-306;

[0012] The sintering aid is selected from at least one of Co and Ni;

[0013] The composite solvent is selected from at least two of butanediol, ethanol, and benzyl alcohol; The thickness of the repair slurry layer is 15 - 25 μm.

[0014] In the preparation method of the present invention, first, the substrate with a defective carbide coating is treated by plasma to obtain polar groups on the surface of the substrate with a defective carbide coating, enhancing its wettability with the repair slurry, making it easier for oxides to contact and adsorb carbon, and increasing the synergistic effect of surface activation and reaction with the repair slurry; during the sintering process, the oxides in the repair slurry can not only react in situ with the adsorbed carbon to form carbides and fill the surface defects of the original coating in an epitaxial growth manner, but also the unreacted trace oxides during the heat treatment of the new coating are uniformly distributed at the grain boundaries, and their continuous reaction with the residual carbon can inhibit the re-adsorption of carbon, and the added carbides can compensate for the cracking caused by the volume shrinkage after the reduction of oxides, and the synergistic effect of the two ensures the integrity of the coating; at the same time, during the sintering process, the sintering aid of the present invention has a eutectic temperature with the carbide (such as the Co-TiC eutectic point of 1280 °C) 300 - 500 °C lower than the sintering temperature of pure carbide. Therefore, during the sintering process, a liquid phase is formed to promote particle rearrangement and inhibit abnormal grain growth of the carbide coating, ensuring that the performance of the original coating is not affected. The added binder can form a three-dimensional network skeleton at a low temperature stage. When pyrolyzed, it can not only form controllable nanopores (pore diameter 20 - 50 nm) to provide an escape channel for the CO gas generated by the subsequent carbothermal reduction reaction, but also the pyrolytic carbon reacts with the oxides to form nanocarbides (such as SiO2 + C → SiC), further filling the microscopic defects of the coating, thereby restoring the surface C / M (M = Si, Ta, Hf, etc.) stoichiometric ratio to 0.9 - 1.03, and at the same time, the coating is dense and defect-free.

[0015] Of course, for the above sintering effect, the uniform dispersion of carbides and oxide particles in the slurry is also crucial. Therefore, first, in the present invention, at least one selected from Tween-80 and BYK-306 is used as a dispersant. The dispersant can ensure the uniform dispersion of carbides and oxide particles through a stabilization mechanism. When Tween-80 is used as a dispersant in an organic slurry system, the hydrophobic end of Tween-80 is a long oleic acid chain, which can physically adsorb on the surfaces of carbides and oxides by forming coordination bonds, and the hydrophilic PEO chain extends into the solvent to form steric hindrance, realizing the uniform dispersion of particles. Second, a composite solvent is used to achieve good compatibility with the dispersant and binder, so as to ensure the effective adsorption of the dispersant on the surfaces of carbides and oxides to ensure uniform dispersion of particles without agglomeration, and the binder is uniformly dispersed to form a network skeleton, so that the particles in the obtained green body are orderly stacked. Moreover, the composite flux of the present invention is combined with high-boiling and low-boiling points, which can prevent cracks from occurring due to too fast volatilization during drying. Third, controlling the proportion of each component in the slurry within the scope of the present invention is also the key to ensuring the uniform dispersion of the two kinds of carbides and oxide particles. Through the synergistic effect of each component, when the particles are uniformly dispersed without agglomeration, they are uniformly covered on the surface of the defective carbide coating by a coating method, and a coating green body with high packing density is obtained after slow drying. Finally, the particles uniformly dispersed in the green body are combined with a low-temperature sintering aid, and the diffusion distance will be shortened during heat treatment, promoting densification dominated by grain boundary diffusion. If the proportion of each component is not within the scope of the present invention, it will cause agglomeration or insufficient dispersion of particles, and the oxide cannot fully play its role during heat treatment, and there will still be a small amount of adsorbed carbon on the surface. In addition, although the main purpose of adding the oxide is to remove the adsorbed carbon by carbothermal reduction, the crystal structure changes after the phase change, resulting in a smaller atomic spacing, and thus the volume shrinks. As the amount of oxide added increases, more oxides are reduced to carbides, resulting in more severe volume shrinkage. Therefore, only when an appropriate amount of oxide is added can the carbides compensate for the cracking caused by the volume shrinkage after the reduction of the oxide, and a dense and defect-free coating can be obtained.

[0016] In addition, in the present invention, only when the thickness of the repair slurry layer is controlled within the above range can the surface C / M stoichiometric ratio be better restored, and the coating is dense and defect-free. If the coating is too thin, it will cause incomplete removal of the adsorbed carbon on the surface, and the stoichiometric ratio on the coating surface cannot be restored during heat treatment. If the repaired coating is too thick, it may hinder the escape of gases (such as CO, etc.), resulting in an increase in internal porosity or residual unreacted oxides, and there will be a small amount of defects in the repair layer, affecting the service performance.

[0017] In a preferred embodiment, the carbide in the substrate with a defective carbide coating is selected from one of SiC, TaC, and HfC.

[0018] In a preferred embodiment, the substrate with the defective carbide coating is first ultrasonically cleaned in ethanol for 5 - 10 minutes, then ultrasonically cleaned in deionized water for 5 - 10 minutes, and then placed in an oven and dried at 80 - 120 °C for 60 - 100 minutes. Subsequently, the dried substrate with the defective carbide coating is subjected to plasma activation treatment.

[0019] In a preferred embodiment, the plasma activation treatment is carried out in an oxygen atmosphere or an argon atmosphere. The power of the plasma activation treatment is 200 - 400 W, and the time of the plasma activation treatment is 1 - 5 minutes.

[0020] Experiments have found that after the plasma activation treatment, polar groups can be obtained on the surface of the substrate with the defective carbide coating, thereby enhancing the wettability between the surface of the substrate with the defective carbide coating and the slurry, making it easier for the oxide to contact and adsorb carbon, and promoting the complete reaction of carbon.

[0021] In a preferred embodiment, the particle size D50 of the carbide powder is ≤ 1.5 μm, and the particle size D50 of the oxide powder is ≤ 1.5 μm.

[0022] In the present invention, the carbide in the carbide powder is the same as the carbide in the defective carbide coating (for example, TaC powder is selected to repair the defective TaC coating).

[0023] In a preferred embodiment, the binder is PVB.

[0024] In a preferred embodiment, the dispersant is Tween - 80.

[0025] In a preferred embodiment, the sintering aid is Co.

[0026] In a preferred embodiment, the pH regulator is selected from at least one of TMAH (tetramethylammonium hydroxide), ammonia water, and citric acid, and ammonia water is preferred.

[0027] In the present invention, through pH regulation, two stable mechanisms, namely the double - layer electric effect and the steric - hindrance effect, can act synergistically to promote the effective adsorption of the dispersant on the particle surface and give full play to the role of the dispersant. When the dispersant is Tween - 80, its ester bond hydrolyzes rapidly in a weak alkaline medium (pH ≈ 8), exposing more - COOH groups to enhance the adsorption on the particle surface and further play the role of the dispersant.

[0028] In a preferred embodiment, the process for obtaining the repair slurry is as follows: Carbide powder, oxide powder, sintering aid, composite solvent, and dispersant are weighed according to the designed ratio and placed in a ball mill. First, ball - mill at a speed of 400 - 600 rpm for 2 - 3 hours, then add the binder and ball - mill at a speed of 80 - 120 rpm for 0.5 - 1 hour. Finally, add the pH regulator to adjust the pH to obtain the repair slurry.

[0029] In the process of preparing the slurry of the present invention, carbides, oxides, sintering aids, solvents, and dispersants are sequentially added first, followed by high-speed ball milling, and finally a binder is added for low-speed ball milling to prevent the binder and the dispersant from competing for adsorption on the powder surface and ensure that each component plays its full role.

[0030] Further preferably, a ball mill and ball beads made of silicon nitride or tungsten carbide are used during the ball milling.

[0031] In a preferred embodiment, the particle size D50 of the solid-phase particles in the repair slurry is 0.6 - 1 μm, the viscosity is 100 - 150 mPa·s, the pH = 5 - 10, preferably 7 - 8.5.

[0032] By controlling the conditions of the repair slurry within the above range, the final repair effect is optimal. If the solid-phase particle size is too large, the slurry stability will be insufficient due to the particle weight and it is easy to settle; if the particle size is too small, the specific surface area will increase, resulting in a thicker slurry, which is not conducive to subsequent coating implementation.

[0033] In a preferred embodiment, the coating method is one of spraying, brushing, and dipping. In the present invention, different coating methods can be selected for different structures, as long as the uniformity of the coating thickness is ensured.

[0034] In a preferred embodiment, the coating method is spraying. During spraying, the nozzle diameter is controlled to be 0.5 - 0.8 mm, the compressed air pressure is 0.2 - 0.6 Mpa, the spraying distance is 15 - 25 cm, the moving speed of the spray gun is 50 - 200 mm / s, and the spray gun angle is 70 - 90°. 90° means the spray gun angle is perpendicular to the surface to be sprayed.

[0035] In a preferred embodiment, the drying process is as follows: first, heat up to 40 - 60 °C and keep warm for 2 - 4 h, then heat up at a heating rate of 5 - 10 °C / min to 80 - 100 °C and keep warm for 3 - 4 h, and finally heat up at a heating rate of 1 - 3 °C / min to 120 - 150 °C and keep warm for 3 - 6 h.

[0036] In the present invention, through the segmented drying process, solvents with different boiling points can be removed gradiently, preventing stress concentration in the green body due to too fast volatilization and generating cracks.

[0037] In a preferred embodiment, the sintering is carried out in a protective atmosphere. The sintering process is as follows: heat up at a heating rate of 5 - 7 °C / min to 250 - 350 °C and keep warm for 0.5 - 1 h, then heat up at a heating rate of 5 - 7 °C / min to 350 - 450 °C and keep warm for 1 - 2 h, then heat up at a heating rate of 6 - 10 °C / min to 1200 - 1400 °C and keep warm for 2 - 3 h, and finally heat up at a heating rate of 5 - 7 °C / min to 1600 - 1800 °C and keep warm for 3 - 5 h, and the vacuum degree is 5 - 7 mbar.

[0038] In the present invention, through the synergy of the components in the repair slurry, a slurry with uniformly dispersed particles and no agglomeration is obtained. After uniformly coating the part to be repaired and combining with the gradient drying process, a green coating blank with a certain thickness and no defects such as cracks and pores is obtained. Then, through the above sintering process, the surface C / M (M = Si, Ta, Hf, etc.) stoichiometric ratio is finally restored to 0.9 - 1.03, and at the same time, the coating is dense and defect-free. During the above sintering heat treatment process, polymers such as binders and dispersants are gradually removed in a gradient manner at a low temperature section to form controllable nanopores. As the temperature rises, the uniformly dispersed oxides will preferentially react with the adsorbed carbon in-situ to form carbides and fill the surface defects of the original coating in an epitaxial growth manner. While the reaction is proceeding, the re-adsorption of the adsorbed carbon is inhibited. Along with the formation of a liquid phase by the uniformly distributed low-temperature sintering aids, the diffusion distance between carbide particles is shortened, promoting densification dominated by grain boundary diffusion.

[0039] Experiments have found that after the polymers such as binders and dispersants are gradually removed in a gradient manner at a low temperature section by low-temperature gradient heat preservation, it is necessary to further heat preserve at 1200 - 1400 °C and then rise to the highest temperature to make the density of the coating the highest. Because when heat preserving at 1200 - 1400 °C, the liquid phase fills the particle gaps, enhances the mass transfer through capillary action, and promotes densification. When the temperature is not in this range, it is not conducive to diffusion, ultimately affecting densification.

[0040] Further preferably, the protective atmosphere is Ar gas.

[0041] Principle and Advantage

[0042] The method of the present invention first treats the substrate with defective carbide coating by plasma to obtain polar groups on the surface of the substrate with defective carbide coating, enhance its wettability with the repair slurry, make it easier for oxides to contact and adsorb carbon, and increase the synergistic effect of surface activation and reaction with the repair slurry; during the sintering process, the oxides in the repair slurry can not only react with the adsorbed carbon in situ to form carbides and fill the surface defects of the original coating in an epitaxial growth manner, but also the trace unreacted oxides in the heat treatment process of the new coating are evenly distributed at the grain boundaries, and their continuous reaction with the residual carbon can inhibit the re-adsorption of carbon, and the added carbide can compensate for the cracking caused by the volume shrinkage after the reduction of oxides, and the synergistic effect of the two ensures the integrity of the coating; avoid the degradation of the substrate coating performance; at the same time, during the sintering process, the sintering aid of the present invention has a eutectic temperature with the carbide (such as the Co-TiC eutectic point of 1280 °C) 300-500 °C lower than the sintering temperature of pure carbide. Therefore, during the sintering process, a liquid phase is formed to promote particle rearrangement and inhibit abnormal grain growth of the carbide coating, ensuring that the performance of the original coating is not affected. The added binder can form a three-dimensional network skeleton at the low temperature stage. During pyrolysis, it can not only form controllable nanopores (pore diameter 20-50 nm) to provide an escape channel for the CO gas generated by the subsequent carbothermal reduction reaction, but also the pyrolytic carbon reacts with the oxides to form nanocarbides (such as SiO2 + C → SiC), further filling the microscopic defects of the coating, thereby restoring the surface C / M (M = Si, Ta, Hf, etc.) stoichiometric ratio to 0.9-1.03, and at the same time the coating is dense and defect-free.

[0043] The method provided by the present invention has simple process and low cost, and is particularly suitable for the surface repair of large-sized and complex-shaped components. By quantitatively reacting the applied slurry with the adsorbed carbon on the coating surface, the surface C / M (M = Si, Ta, Hf, etc.) stoichiometric ratio is restored to 0.9-1.03, and at the same time the coating is dense and defect-free. Brief Description of the Drawings

[0044] Figure 1 is the process flow chart of the present invention.

[0045] Figure 2 are the SEM comparison pictures of the tantalum carbide coating before and after treatment in Example 1, where Figure 2 (a) is the SEM image of the defective tantalum carbide coating before treatment, Figure 2 (b) is the SEM image of the tantalum carbide coating obtained after treatment in Example 1, Figure 2 In (a), 1 is the marking point of the first energy spectrum diagram (EDS), Figure 2 In (b), 2 is the marking point of the second energy spectrum diagram (EDS).

[0046] Figure 3 are the SEM pictures of different positions on the surface of the tantalum carbide coating after surface treatment in Comparative Example 1, whereFigure 3 (a), Figure 3 (b) are SEM images of different positions on the surface of the tantalum carbide coating after surface treatment in Comparative Example 1. Figure 3 In (b), 3 is the marking point of the third energy spectrum diagram (EDS), and 4 is the marking point of the fourth energy spectrum diagram (EDS). Specific Embodiments

[0047] Example 1

[0048] This example provides a method for eliminating adsorbed carbon on the surface of a carbide coating. The specific repair process is as follows:

[0049] Step S1: Ultrasonically clean a tantalum carbide coating part with a size of 50×50×10 mm (graphite substrate with a defective tantalum carbide coating) successively with ethanol and deionized water for 8 minutes each. Then place the coating part in an oven and dry it at 100 °C for 100 minutes to ensure no moisture remains on the surface. Perform plasma activation treatment on the coating part in an oxygen atmosphere with a power of 200 W and a treatment time of 5 minutes.

[0050] Step S2: Add 100 g of TaC powder (particle size D50 ≤ 1.5 μm), 2.85 g of Ta2O5 (particle size D50 ≤ 1.5 μm), 2 g of Co powder, 6.2 ml of butanediol, 32 ml of ethanol, 4.8 ml of benzyl alcohol, and 1.4 g of Tween-80 into a silicon nitride ball mill jar in sequence. The grinding balls are silicon nitride, the ball-to-material ratio is 2:1, the rotation speed is 400 rpm, and the ball milling time is 3 hours. Then add 1.1 g of PVB to the mixed suspension, with a rotation speed of 100 rpm and a ball milling time of 1 hour. Finally, add 0.3 g of ammonia water and mix evenly to obtain a repair slurry.

[0051] Step S3: Uniformly spray the repair slurry prepared in S2 on the surface of the tantalum carbide coating part. The spraying parameters are: nozzle 0.5 mm, air pressure 0.4 MPa, spraying distance 18 cm, moving speed of the spray gun 150 mm / s, spray gun angle 90° (perpendicular to the surface to be sprayed), and spraying thickness 15 - 18 μm.

[0052] Step S4: Dry the sprayed part prepared in S3 according to the following process. Keep it at 45 °C for 2 hours, then heat it to 100 °C at a rate of 5 °C / min and keep it for 4 hours, and then heat it to 150 °C at a rate of 3 °C / min and keep it for 5 hours.

[0053] Step S5: Under an Ar atmosphere, heat it to 250 °C at a rate of 5 °C / min and keep it for 1 hour, then heat it to 350 °C at a rate of 5 °C / min and keep it for 2 hours, heat it to 1200 °C at a rate of 8 °C / min and keep it for 2 hours, heat it to 1800 °C at a rate of 6 °C / min and keep it for 4 hours, with a vacuum degree of 5 - 7 mbar; then cool it to room temperature with the furnace, and that's it.

[0054] After testing, the particle size D50 of the solid-phase particles in the prepared repair slurry is 0.72 μm, the viscosity is 122 mPa·s, the pH is 8.1, and the coating thickness after the final heat treatment is 5 - 7 μm. According to Figure 1 The SEM pictures before and after the tantalum carbide coating treatment in Example 1 are shown, where Figure 2 (b) is the SEM image of the tantalum carbide coating obtained after being treated in Example 1. It can be seen from Figure 2 (b) that almost all the adsorbed carbon on the coating surface has been removed after repair, and the coating completely covers without crack defects being found. For Figure 2 the first energy spectrum diagram (EDS) marked point 1 in (a) and Figure 2 the second energy spectrum diagram (EDS) marked point 2 in (b) are subjected to EDS analysis as shown in Table 1. The C / TaC atomic ratio on the coating surface is reduced from 7.84 to 0.96, realizing the restoration of the surface stoichiometry.

[0055]

[0056] Example 2

[0057] This example provides a method for eliminating the adsorbed carbon on the carbide coating surface. The specific repair process is as follows:

[0058] Step S1: Ultrasonically clean the tantalum carbide coating parts with dimensions of 50×50×10 mm successively in ethanol and deionized water, and the ultrasonic cleaning time is 10 min for both; then put the coating parts into an oven and dry them at 120 °C for 100 min to ensure that there is no moisture residue on the surface; perform plasma activation treatment on the coating parts in an oxygen atmosphere, with a power of 400 W and a treatment time of 3 min.

[0059] Step S2: Add 100 g of TaC powder (particle size D50 ≤ 1.5 μm), 2.65 g of Ta2O5 (particle size D50 ≤ 1.5 μm), 2.2 g of Co powder, 7.2 ml of butanediol, 33.6 ml of ethanol, 5.8 ml of benzyl alcohol, and 1.2 g of Tween-80 into a silicon nitride ball milling tank in sequence. The grinding balls are silicon nitride, the ball-to-material ratio is 2:1, the rotation speed is 400 rpm, and the ball milling time is 2.5 hours. Then add 1.2 g of PVB to the mixed suspension, with a rotation speed of 100 rpm and a ball milling time of 1 hour. Finally, add 0.2 g of ammonia water and mix evenly to obtain the repair slurry.

[0060] Step S3: Uniformly spray the repair slurry prepared in S2 on the surface of the tantalum carbide coating parts. The spraying parameters are: nozzle 0.5 mm, air pressure 0.4 MPa, spraying distance 18 cm, the moving speed of the spray gun is 150 mm / s, the spray gun angle is 90° (perpendicular to the surface to be sprayed), and the spraying thickness is 15 - 18 μm.

[0061] Step S4: Dry the sprayed parts prepared in S3 according to the following process. Keep them at 45°C for 2 hours, then heat them up to 100°C at a rate of 5°C / min and keep them at this temperature for 4 hours, and then heat them up to 150°C at a rate of 3°C / min and keep them at this temperature for 6 hours.

[0062] Step S5: Under an Ar atmosphere, heat them up to 250°C at a rate of 5°C / min and keep them at this temperature for 1 hour, heat them up to 350°C at a rate of 5°C / min and keep them at this temperature for 2 hours, heat them up to 1200°C at a rate of 8°C / min and keep them at this temperature for 2 hours, heat them up to 1750°C at a rate of 6°C / min and keep them at this temperature for 4.5 hours, with a vacuum degree of 5 - 7 mbar; then cool them down to room temperature in the furnace, and thus obtain the product.

[0063] After testing, the particle size D50 of the solid-phase particles in the prepared repair slurry is 0.85 μm, the viscosity is 145 mPa·s, the pH is 7.8, and the coating thickness after the final heat treatment is 5 - 7 μm. The surface morphology of the coating in Example 2 is basically the same as that in Example 1. After the surface of the coating is repaired, the adsorbed carbon is basically completely removed. The coating completely wraps without cracks or defects being found. The C / TaC atomic ratio on the coating surface decreases from 4.65 to 0.91.

[0064] Example 3

[0065] This example provides a method for eliminating the adsorbed carbon on the surface of the carbide coating, and its specific repair process is as follows:

[0066] Step S1: Ultrasonically clean the tantalum carbide coating parts with dimensions of 50×50×10 mm successively with ethanol and deionized water, and the ultrasonic cleaning time is 10 minutes for both. Then put the coating parts into an oven and dry them at 120°C for 100 minutes to ensure that there is no moisture residue on the surface. Carry out plasma activation treatment on the coating parts in an oxygen atmosphere, with a power of 300 W and a treatment time of 5 minutes.

[0067] Step S2: Add 100 g of TaC powder (particle size D50 ≤ 1.5 μm), 2.77 g of Ta2O5 (particle size D50 ≤ 1.5 μm), 2.4 g of Co powder, 5.3 ml of butanediol, 30.2 ml of ethanol, 4.1 ml of benzyl alcohol, and 1.3 g of Tween-80 into a silicon nitride ball milling tank in sequence. The grinding balls are made of silicon nitride, the ball-to-material ratio is 2:1, the rotation speed is 400 rpm, and the ball milling time is 3 hours. Then add 1.2 g of PVB into the mixed suspension, with a rotation speed of 100 rpm and a ball milling time of 1 hour. Finally, add 0.2 g of ammonia water and mix them evenly to obtain the repair slurry.

[0068] Step S3: Spray the repair slurry prepared in S2 evenly on the surface of the tantalum carbide coating parts, and the spraying parameters are as follows: nozzle 0.5 mm, air pressure 0.4 MPa, spraying distance 18 cm, the moving speed of the spray gun is 150 mm / s, the angle of the spray gun is 90° (perpendicular to the surface to be sprayed), and the spraying thickness is 23 - 25 μm.

[0069] Step S4: Dry the sprayed parts prepared in S3 according to the following process. Keep them at 45°C for 2 h, then heat them up to 100°C at a rate of 5°C / min and keep them at this temperature for 4 h, and then heat them up to 150°C at a rate of 3°C / min and keep them at this temperature for 5 h.

[0070] Step S5: Under an Ar atmosphere, heat them up to 250°C at a rate of 5°C / min and keep them at this temperature for 1 h, then heat them up to 350°C at a rate of 5°C / min and keep them at this temperature for 2 h, then heat them up to 1200°C at a rate of 8°C / min and keep them at this temperature for 2 h, and then heat them up to 1800°C at a rate of 6°C / min and keep them at this temperature for 4 h. The vacuum degree is 5 - 7 mbar. Then cool them down to room temperature in the furnace, and thus obtain the product.

[0071] After testing, the particle size D50 of the solid-phase particles of the prepared repair slurry is 0.77 μm, the viscosity is 132 mPa·s, the pH is 8.2, and the coating thickness after the final heat treatment is 8 - 10 μm. The surface morphology of the coating in Example 3 is basically the same as that in Example 1. After the surface of the coating is repaired, the adsorbed carbon is basically completely removed. The coating completely wraps without cracks or defects being found. The C / Ta atomic ratio on the coating surface decreases from 6.71 to 0.92.

[0072] Comparative Example 1

[0073] This comparative example is exactly the same as Example 1 in other conditions, and the difference lies in that: Ta2O5 powder is not added during the preparation of the slurry in Step S2.

[0074] After testing, the particle size D50 of the prepared tantalum carbide slurry is 0.70 μm, the viscosity is 145 mPa·s, the pH is 8.0, and the coating thickness after the final heat treatment is 5 - 7 μm. The ceramic material obtained in this Comparative Example 1 is as Figure 3 shown in the SEM pictures of different positions on the surface of the tantalum carbide coating after surface treatment. From Figure 3 (a), Figure 3 (b), dark gray parts can be seen, indicating that adsorbed carbon still exists locally on the coating surface. Perform EDS analysis on the third energy spectrum (EDS) marked point 3 and the fourth energy spectrum (EDS) marked point 4 in Figure 3 (b). The results are shown in Table 2. The surface stoichiometric ratio does not reach C / TaC = 0.9 - 1.03 because the non-addition of oxide powder will cause the adsorbed carbon to not fully react, and the re-adsorption of carbon cannot be further inhibited during heat treatment.

[0075]

[0076] Comparative Example 2

[0077] This Comparative Example 2 is exactly the same as Example 1 in other conditions, and the difference lies in that: 0.8 g of Ta2O5 powder is added during the preparation of the slurry in Step S2.

[0078] After testing, the particle size D50 of the prepared tantalum carbide slurry is 0.78 μm, the viscosity is 121 mPa·s, the pH is 8.1, and the coating thickness after the final heat treatment is 5 - 7 μm. The surface morphology of the coating is basically the same as that of Comparative Example 1. There is still adsorbed carbon locally on the coating surface, and the surface stoichiometry does not achieve C / TaC = 0.9 - 1.05. This indicates that the addition of oxide powder undergoing carbothermal reduction during the slurry preparation process should be strictly carried out in accordance with the requirements of the present invention. If the addition amount of tantalum pentoxide powder is not within the above requirements, it cannot restore the surface stoichiometry of the coating.

[0079] Comparative Example 3

[0080] This comparative example is exactly the same as Example 1 in other conditions, and the difference lies in that: during the coating preparation in step S3, the spraying thickness is 35 - 40 μm.

[0081] After testing, the coating thickness after the final heat treatment is 18 - 22 μm. There are a small number of defects such as microcracks and small holes on the coating surface, and there is still adsorbed carbon locally on the surface. The surface stoichiometry does not achieve C / TaC = 0.9 - 1.05. When the repaired coating is too thick, it may hinder the escape of gases (such as CO, etc.), resulting in an increase in internal porosity or the residue of unreacted oxides, and a small number of defects in the repair layer will affect the service performance.

Claims

1. A method for eliminating adsorbed carbon on the surface of a carbide coating, characterized in that: The substrate with a defective carbide coating is subjected to plasma activation treatment, and then a repair slurry is coated on the surface of the substrate with the defective coating to obtain a repair slurry layer. After drying, sintering is carried out to obtain the product; The repair slurry, by mass percentage, is composed as follows: carbide powder 60-70wt%, oxide powder 1-2wt%, binder 0.5-1.5wt%, dispersant 0.5-1.5wt%, sintering aid 1-3wt%, pH regulator 0.1-0.3wt%, and the balance is a composite solvent; The carbide in the carbide powder is the same as the carbide in the defective carbide coating; The carbide obtained by the thermal reduction reaction of the oxide in the oxide powder with carbon is the same as the carbide in the defective carbide coating; The binder is selected from at least one of PVB and PVA; The dispersant is selected from at least one of Tween-80 and BYK-306; The sintering aid is selected from at least one of Co and Ni; The composite solvent is selected from at least two of butanediol, ethanol, and benzyl alcohol; The thickness of the repair slurry layer is 15-25μm.

2. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 1, characterized in that: First, the substrate with the defective carbide coating is successively subjected to ultrasonic cleaning with ethanol for 5-10 minutes, ultrasonic cleaning with deionized water for 5-10 minutes, then placed in an oven and dried at 80-120°C for 60-100 minutes, and then the dried substrate with the defective carbide coating is subjected to plasma activation treatment.

3. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 1, characterized in that: The plasma activation treatment is carried out in an oxygen atmosphere or an argon atmosphere. The power of the plasma activation treatment is 200-400W, and the time of the plasma activation treatment is 1-5 minutes.

4. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 1, characterized in that: The particle size D50 of the carbide powder is ≤1.5μm, and the particle size D50 of the oxide powder is ≤1.5μm.

5. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 1, characterized in that: The process for obtaining the repair slurry is as follows: Carbide powder, oxide powder, sintering aid, composite solvent, and dispersant are weighed according to the designed ratio and placed in a ball mill. First, ball milling is carried out at a rotation speed of 400-600 rpm for 2-3 hours, then the binder is added, and ball milling is carried out at a rotation speed of 80-120 rpm for 0.5-1 hour. Finally, the pH regulator is added to adjust the pH to obtain the product; During the ball milling, a ball tank and ball beads made of silicon nitride or tungsten carbide are used.

6. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 1, characterized in that: The particle size D50 of the solid-phase particles in the repair slurry is 0.6-1μm, the viscosity is 100-150 mPa·s, and the pH is 5-10; The coating method is one of spraying, brush coating, and dip coating.

7. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 6, characterized in that: The coating method is spraying. During spraying, the nozzle diameter is controlled to be 0.5-0.8 mm, the compressed air pressure is 0.2-0.6 Mpa, the spraying distance is 15-25 cm, the moving speed of the spray gun is 50-200 mm / s, and the spray gun angle is 70-90°.

8. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 1, characterized in that: The drying process is as follows: First, the temperature is raised to 40-60°C and kept warm for 2-4 hours, then the temperature is raised at a rate of 5-10°C / min to 80-100°C and kept warm for 3-4 hours, and finally the temperature is raised at a rate of 1-3°C / min to 120-150°C and kept warm for 3-6 hours.

9. A method for eliminating adsorbed carbon on the surface of a carbide coating according to claim 1, characterized in that: The sintering is carried out under a protective atmosphere. The process of the sintering is as follows: heating is carried out at a heating rate of 5 - 7 °C / min to 250 - 300 °C and holding for 0.5 - 1 h, then heating at a heating rate of 5 - 7 °C / min to 350 - 450 °C and holding for 1 - 2 h, then heating at a heating rate of 6 - 10 °C / min to 1200 - 1400 °C and holding for 2 - 3 h, and finally heating at a heating rate of 5 - 7 °C / min to 1600 - 1800 °C and holding for 3 - 5 h, with a vacuum degree of 5 - 7 mbar.

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