A plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating and its preparation method

Abstract

This invention provides a plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating and its preparation method, relating to the field of surface-protective functionalized coating preparation technology. The preparation method includes: combining graphene nanosheets with Al2O3-20wt%TiO2 ceramic powder to form a composite powder; and using a plasma spraying process, under specific process conditions, spraying the composite powder onto a pretreated substrate surface. Under this process, molten ceramic droplets can effectively coat the graphene nanosheets, forming a "ceramic-coated graphene" composite structure. The graphene nanosheets act as a reinforcing phase, synergistically improving the microhardness and fracture toughness of the coating. This invention solves the problem of traditional ceramic coatings being unable to simultaneously achieve both hardness and toughness, resulting in a coating with excellent overall performance.

Description

Technical Field

[0001] This invention relates to the field of surface protective functional coating preparation technology, and in particular to a plasma-sprayed graphene nanosheet reinforced Al2O3-20wt%TiO2 coating and its preparation method. Background Technology

[0002] While plasma-sprayed Al2O3-20wt%TiO2 coatings possess high hardness and good chemical stability, their limited fracture toughness and decreased wear resistance with increasing TiO2 content restrict their application under harsh working conditions. Introducing graphene nanosheets (GNPs) as a reinforcing phase is considered an effective approach to synergistically improve the coating's hardness, toughness, and wear resistance. GNPs, with their two-dimensional structure, ultra-high strength, and self-lubricating properties, can theoretically significantly improve the mechanical and tribological properties of coatings. However, during the high-temperature, high-speed plasma spraying process, GNPs are highly susceptible to thermal ablation or structural damage, and their reinforcing effect heavily depends on the precise control of the spraying heat input and particle melting behavior.

[0003] Researchers have attempted to introduce carbon-based nanomaterials, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and graphene nanosheets (GNPs), into ceramic coatings as reinforcing phases. Among these, graphene nanosheets are considered highly promising reinforcing materials due to their unique two-dimensional structure, ultra-high specific surface area, excellent mechanical properties (such as high elastic modulus and tensile strength), outstanding thermal conductivity, and self-lubricating properties. However, translating the theoretical advantages of GNPs into improvements in the actual performance of coatings faces severe challenges posed by plasma spraying processes. The plasma jet center temperature is extremely high (reaching 10,000-15,000°C), and the particles are in an extreme non-equilibrium process of high-speed melting-impact-solidification. Under these conditions, GNPs are highly susceptible to oxidation, structural collapse, or amorphization due to high-temperature thermal corrosion, severely weakening or even completely losing their reinforcing effect.

[0004] In view of this, it is necessary to design an improved plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating and its preparation method to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating and its preparation method.

[0006] To achieve the above-mentioned objective, in a first aspect, the present invention provides a method for preparing a composite powder for plasma spraying, wherein the composite powder comprises Al2O3-20wt%TiO2 ceramic powder and graphene nanosheets uniformly dispersed therein, and the preparation method includes the following steps:

[0007] The composite powder was prepared by adding Al2O3-20wt%TiO2 ceramic powder to a graphene nanosheet suspension, followed by ball milling and drying.

[0008] Preferably, in the process of mixing graphene nanosheet suspension with Al2O3-20wt%TiO2 ceramic powder, the amount of graphene nanosheets used is 1-3wt% of the total mass of graphene nanosheets and Al2O3-20wt%TiO2 ceramic powder.

[0009] Preferably, the ball milling process uses zirconia or agate grinding balls as the milling medium, the milling speed is 200-400 rpm, and the milling time is 2-4 hours.

[0010] Preferably, the average diameter of the graphene nanosheets is 3-10 μm.

[0011] Preferably, the drying process is carried out at a temperature of 100-200°C for 12-24 hours.

[0012] Secondly, the present invention provides a plasma spraying method for composite powder, including the step of spraying composite powder onto the surface of a substrate using a plasma spraying method; the process parameters of the plasma spraying process are as follows: spraying current of 500-600 A, spraying voltage of 60-70 V, spraying distance of 80-120 mm, main gas flow rate of 50-60 L / min, auxiliary gas flow rate of 5-10 L / min, and powder feeding rate of 9-15 g / min.

[0013] Preferably, the substrate needs to be pretreated before spraying. The pretreatment is carried out as follows: after degreasing and derusting the substrate surface, ultrasonic cleaning is performed using acetone or ethanol. After drying, roughening treatment is performed using sandblasting. After the roughening treatment is completed, the substrate is heated and held at 180-220℃ for 30 minutes.

[0014] Thirdly, the present invention provides a graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating, which is formed by plasma spraying of composite powder, and the content of graphene nanosheets in the coating is 1-3wt% of the total mass of the coating.

[0015] Fourthly, the present invention provides a coated component comprising a substrate and a graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating attached to the surface of the substrate.

[0016] Preferably, the substrate is made of metal.

[0017] The beneficial effects of this invention are:

[0018] 1. The coating preparation method provided by this invention introduces an appropriate amount of graphene nanosheets (GNPs) as a reinforcing phase into Al2O3-20wt%TiO2 ceramic powder, and effectively retains the structure of the graphene nanosheets and achieves stable coating under a specific plasma spraying process window. The resulting coating achieves simultaneous improvement in multiple properties (hardness, toughness, and wear resistance). GNPs not only improve the microhardness of the coating through grain refinement and load-bearing effects as a hard second phase, but their unique two-dimensional structure also significantly improves the fracture toughness of the coating through mechanisms such as crack deflection, bridging, and interface slip. At the same time, the inherent excellent lubrication properties of GNPs help reduce the coefficient of friction, thereby fundamentally and synergistically optimizing the hardness, toughness, and wear resistance of the coating, enabling it to adapt to more complex and harsh mechanical service environments.

[0019] 2. The coating preparation method provided by this invention, under optimized process conditions, allows molten ceramic powder droplets to fully wet and tightly encapsulate GNPs, forming stable "ceramic-coated graphene" micro-composite units. During the deposition process, these structural units effectively embed GNPs between the layers of the coating, enhancing not only the mechanical interlocking and bonding force between the layers but also effectively filling the micropores within the coating and terminating microcracks. This significantly reduces the overall porosity of the coating, providing a solid microscopic foundation for achieving excellent mechanical properties. Furthermore, the optimized process conditions ensure that the AT20 ceramic powder is fully melted for good spreading and bonding, while precisely controlling the thermal process to minimize oxidation, ablation, and structural damage to GNPs. This ensures that the high performance of the coating does not depend on accidental process adjustments but possesses high process controllability, stability, and repeatability, providing a solid and reliable technical foundation for the industrial application of high-performance coatings. Attached Figure Description

[0020] Figure 1 A schematic flowchart illustrating the preparation method of the plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating provided by the present invention;

[0021] Figure 2 This is a schematic diagram of the atmospheric plasma spraying system used in an embodiment of the present invention;

[0022] Figure 3 This is a SEM image of the composite powder prepared in Example 1 of the present invention;

[0023] Figure 4 This is a cross-sectional SEM image of the coating obtained in Example 1 of the present invention;

[0024] Figure 5 The wear rate results are for the coatings obtained in Examples 1 to 3 and Comparative Example 1 of the present invention.

[0025] Figure 6 The microhardness results of the coatings obtained in Examples 1 to 3 and Comparative Example 1 of this invention are shown.

[0026] Figure 7 The fracture toughness results of the coatings obtained in Examples 1 to 3 and Comparative Example 1 of the present invention are shown.

[0027] Figure 8 The porosity results are for the coatings obtained in Examples 1 to 3 and Comparative Example 1 of this invention.

[0028] The attached figures are labeled as follows:

[0029] 1. Composite powder; 2. Inert gas; 3. Spray gun; 4. Cathode; 5. Anode; 6. Plasma jet; 7. Coating; 8. Substrate. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0032] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0033] Please see Figure 1 As shown, this invention provides a method for preparing a plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating, which includes the following steps:

[0034] S1. After adding Al2O3-20wt%TiO2 ceramic powder to a graphene nanosheet suspension, the composite powder is obtained after ball milling and drying.

[0035] S2. Using plasma spraying, the composite powder obtained in step S1 is sprayed onto the surface of the pretreated substrate to obtain an Al2O3-20wt%TiO2 coating on the substrate surface.

[0036] In the above technical solution, graphene nanosheets are used as a reinforcing phase and composited with Al2O3-20wt%TiO2 ceramic powder, followed by plasma spraying to form a coating. During the spraying process, the high-temperature plasma jet rapidly melts or semi-melts the composite powder, depositing it on the substrate surface to form a layered structure. During deposition, the graphene nanosheets are distributed between the coating layers and in local defect areas, forming interfacial contact or partial coverage with the ceramic phase. The introduction of graphene nanosheets helps improve interlayer bonding and plays a synergistic reinforcing role in crack deflection, bridging, and pull-out during crack propagation, thereby improving the coating's hardness, toughness, density, and wear resistance.

[0037] In some embodiments, in step S1, the graphene nanosheet suspension is prepared by dispersing graphene nanosheets in an organic solvent and ultrasonically dispersing for 30-60 minutes. It should be noted that the organic solvent in the above steps can be anhydrous ethanol, added solely for dispersing the graphene nanosheets; as long as the dispersion purpose is achieved, the amount added is not strictly limited. Preferably, the average diameter of the graphene nanosheets is 3-10 μm. This is because when the diameter of the graphene nanosheets is less than 3 μm, they are more prone to ablation or structural damage in the high-temperature environment of plasma spraying, and the bridging effect is insufficient; while when the diameter is greater than 10 μm, they are prone to agglomeration or breakage during spraying, which is not conducive to uniform dispersion.

[0038] In some embodiments, in step S1, the particle size distribution of the Al2O3-20wt%TiO2 ceramic powder satisfies: D10 is 12-18μm, D50 is 22-28μm, and D90 is 32-38μm, which is determined by laser diffraction. In the mixing process of graphene nanosheet suspension and Al2O3-20wt%TiO2 ceramic powder, the amount of graphene nanosheets used is 1-3wt% of the total mass of graphene nanosheets and Al2O3-20wt%TiO2 ceramic powder. In the above technical solution, by selecting Al2O3-20wt%TiO2 ceramic powder with a given particle size and blending it with graphene nanosheets to prepare the coating, it is possible to ensure that the ceramic powder has a good melting state and spreading behavior during plasma spraying. Secondly, the ceramic powder within the above particle size range can better match the size of the graphene nanosheets, which is conducive to the stable existence and uniform distribution of the graphene nanosheets during the spraying deposition process, thereby helping to improve the hardness, wear resistance, toughness, and density of the coating. In addition, by controlling the amount of graphene nanosheets added, not only can their physical properties (electrical conductivity / thermal conductivity, etc.) and structural characteristics (reinforcement and toughening) be fully utilized, but also the agglomeration of graphene nanosheets can be avoided, which would affect the spraying process and coating performance.

[0039] In some embodiments, in step S1, the ball milling process is carried out in an inert atmosphere or air environment, using zirconia or agate grinding balls as the milling medium, with a milling speed of 200-400 rpm and a milling time of 2-4 hours. It should be noted that the ball milling process has no special requirements for the milling medium or the milling ratio, and these can be selected according to needs during the preparation process; therefore, no further restrictions are imposed here.

[0040] In some embodiments, in step S1, the drying process is carried out at a temperature of 100-200°C for 12-24 hours.

[0041] In some embodiments, in step S2, the substrate material can be metal, and its pretreatment is performed as follows: after degreasing and derusting the substrate surface, ultrasonic cleaning is performed using acetone or ethanol. After drying, a sandblasting process is used to roughen the surface. After roughening, compressed air or ultrasonic cleaning is used to remove residual sand particles and dust from the surface. The substrate is then heated and held at 180-220℃ for 30 minutes to remove moisture adsorbed on the substrate surface, reduce the temperature difference between the substrate and the coating material, thereby reducing internal stress in the coating, preventing cracking, and improving bonding strength. In some embodiments, the roughening treatment uses alumina with a particle size of 20μm as abrasive particles, and the substrate surface is treated by sandblasting. The purpose is to clean and intentionally create a rough, clean, and active surface. It should be noted that in this step, the degreasing and derusting steps can be performed using chemical or physical methods as needed, and there are no excessive restrictions on this. In the above technical solution, a rough and activated surface is formed on the pretreated substrate, which effectively increases the mechanical anchoring force between the substrate and the coating and reduces thermal stress.

[0042] In some embodiments, during step S2, the plasma spraying process features a spraying current of 500-600 A, a spraying voltage of 60-70 V, a spraying distance of 80-120 mm, a main gas flow rate of 50-60 L / min, an auxiliary gas flow rate of 5-10 L / min, and a powder feeding rate of 9-15 g / min. The main gas can be Ar, and the auxiliary gas can be H2. In the above technical solution, by precisely controlling the spraying current within the range of 500-600 A, the plasma can provide sufficient and stable thermal energy, ensuring that the Al2O3-20wt% TiO2 powder reaches a fully molten state, avoiding excessive vaporization or unmelted defects. Simultaneously, limiting the spraying distance to 80-120 mm allows the molten particles to obtain a suitable cooling rate during flight, maintaining optimal temperature and kinetic energy upon impact with the substrate, promoting effective interaction with the graphene nanosheets. Combined with an optimized powder feeding rate, this achieves uniform and continuous injection of powder into the plasma flow, ensuring thorough mixing of the molten ceramic droplets and the graphene nanosheets. Under these conditions, molten Al2O3-20wt%TiO2 droplets can wet and tightly encapsulate graphene nanosheets, forming a stable core-shell coating structure. In this structure, the ceramic composite powder provides high microhardness and load-bearing capacity, significantly improving the wear resistance of the coating. Meanwhile, the graphene nanosheets, as a toughening reinforcing phase, effectively absorb and disperse stress and inhibit crack propagation through mechanisms such as crack deflection, bridging, and interfacial slip, thereby simultaneously improving fracture toughness and ultimately achieving a synergistic enhancement of coating hardness, wear resistance, and toughness. However, when the spraying current is below 500A, the Al2O3-20wt%TiO2 particles do not melt sufficiently in the plasma jet, making it difficult for the graphene nanosheets to be effectively encapsulated by the molten ceramic, thus hindering their reinforcing and lubricating effects in the coating. When the spraying current is above 600A, the heat input of the plasma jet is too high, causing significant ablation or even structural damage to the graphene nanosheets, which in turn reduces the overall performance of the coating. When the spraying distance is less than 80mm, the residence time of the powder particles in the high-temperature, high-energy plasma flame is too short. When impacting the substrate, the temperature is too high and the velocity is too high, which can easily lead to molten droplet splashing and severe ablation of graphene nanosheets, resulting in a decrease in coating density and structural stability. When the spraying distance is greater than 120mm, the powder particles suffer severe heat loss during flight, and the ceramic particles are prone to being in an incompletely molten state, which leads to a decrease in interlayer bonding force and makes it difficult for graphene nanosheets to form a stable interface distribution structure.

[0043] The following specific embodiments further illustrate the plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt% TiO2 coating and its preparation method provided by the present invention:

[0044] Example 1

[0045] This embodiment provides a method for preparing a plasma-sprayed graphene nanosheet-reinforced Al2O3-20wt% TiO2 coating, comprising the following steps:

[0046] S1. Graphene nanosheets (GNPs) were dispersed in anhydrous ethanol and sonicated for 45 min to obtain a uniform suspension. Al2O3-20wt% TiO2 ceramic powder (hereinafter referred to as AT20) was added to the above suspension. The resulting mixture was transferred to a planetary ball mill, using zirconium oxide as the ball milling medium, with a ball milling ratio of 3:1. The mixture was ball milled at 400 rpm for 4 h in an air atmosphere. After ball milling, the slurry was dried at 180℃ for 18 h to completely remove the solvent, and a composite powder was obtained, denoted as AT20-2wt%GNPs. The average diameter of the graphene nanosheets was 5 μm, the average particle size of the Al2O3-20wt% TiO2 ceramic powder was 25 μm, and the mass ratio of graphene nanosheets to Al2O3-20wt% TiO2 ceramic powder was 2:98.

[0047] S2. Using 316 steel plate as the base material, it is successively ground, degreased, ultrasonically cleaned with acetone, and thoroughly dried. Then, the substrate surface to be coated is roughened by sandblasting with alumina sand with a particle size of 20μm. After sandblasting, the cleaned substrate is placed in a preheating furnace and heated to 200℃, and kept at that temperature for 30 minutes to obtain the pretreated substrate material.

[0048] An atmospheric plasma spraying system is used to feed the composite powder obtained in step S1 into a spray gun and spray it onto the surface of the pretreated substrate material to form a coating layer. The spraying parameters are set as follows: spraying current 550A, spraying voltage 65V, main gas (Ar) flow rate 52L / min, auxiliary gas (H2) flow rate 6L / min, spraying distance 100 mm, and powder feed rate 10 g / min. During the spraying process, the spray gun and the substrate surface are kept moving at a relatively uniform speed. In practical applications, the coating can be sealed or finished (e.g., ground, polished) as needed. It should be noted that, unless otherwise specified, the reagents and raw materials used in this embodiment of the invention are all obtained through commercial purchase.

[0049] The structure of the atmospheric plasma spraying system used in this embodiment is as follows: Figure 2 As shown in the figure, 1 represents composite powder, 2 represents inert gas, 3 represents spray gun, 4 represents cathode, 5 represents anode, 6 represents plasma jet, 7 represents coating, and 8 represents substrate. The coating system is a commonly used device structure in this field, so its specific structure will not be described in detail here.

[0050] The SEM image of the composite powder obtained in step S1 is shown below. Figure 3As shown, the results indicate that the powder particles exhibit an irregular polygonal or blocky structure. This structure is beneficial for increasing the heated surface area of ​​the particles during plasma spraying, promoting heat conduction, and achieving more complete melting. The cross-sectional SEM image of the coating is shown below. Figure 4 As shown in the figure, the coating has a relatively dense internal structure, exhibiting a typical lamellar stacking structure, melt profile, and a small number of pores. The distinct angular morphology of the original powder has largely disappeared, indicating that the Al2O3-20wt% TiO2 particles underwent sufficient melting and spreading during the spraying process. This may be because, during the melting and spreading process, a tight interfacial contact was formed between the ceramic phase and the graphene nanosheets. The graphene nanosheets may have been surrounded or embedded in the ceramic matrix by the molten ceramic droplets, thus forming a relatively stable composite structure.

[0051] Example 2

[0052] The only difference between this embodiment and Example 1 is that in step S1, the amount of graphene nanosheets used is 1wt%, and the other experimental parameters are the same as in Example 1, which will not be repeated here. The resulting composite powder is denoted as AT20-1wt%GNPs.

[0053] Example 3

[0054] The only difference between this embodiment and Example 1 is that in step S1, the amount of graphene nanosheets used is 3wt%, and the other experimental parameters are the same as in Example 1, which will not be repeated here. The resulting composite powder is denoted as AT20-3wt%GNPs.

[0055] Comparative Example 1

[0056] The only difference between this comparative example and Example 1 is that graphene nanosheets are not added in step S1. The other experimental conditions are the same as in Example 1, and will not be repeated here. The resulting composite powder is denoted as AT20.

[0057] Comparative Example 2

[0058] The only difference between this comparative example and Example 1 is that the Al2O3-20wt% TiO2 ceramic powder in step S1 is replaced with an equal amount of Al2O3-13wt% TiO2 composite powder. The other experimental conditions are the same as in Example 1, and will not be repeated here. The resulting composite powder is denoted as AT13-2wt%GNPs.

[0059] To evaluate the wear resistance of the coatings prepared in Examples 1 to 3 and Comparative Example 1 (tested using a ball-disc dry sliding wear tester, with a test load of 15 N, a sliding speed of 0.1 m / s, a test time of 30 min, and a Si3N4 bearing ball (6 mm in diameter) as the mating material), the wear rate results of the coatings in the examples and the comparative example were measured under the same dry sliding wear conditions as follows: Figure 5As shown, the results indicate that the wear rate of the coatings in Examples 1 to 3 was 1.5 × 10⁻⁶ compared to Comparative Example 1. -4 mm 3 The wear resistance was reduced by approximately 10-30% (N·m), and the coating exhibited optimal wear resistance when the amount of graphene nanosheets added was 2wt%. Furthermore, under the same spraying process parameters, the wear rate of the coating in Example 1 (AT20-2wt% GNPs) was 1.18 × 10⁻⁶. -4 mm 3 The N·m value was also lower than that of the 1.31 × 10⁻⁶ coating (AT13-2wt%GNPs) in Comparative Example 2. -4 mm 3 / (N·m).

[0060] The microhardness of the coatings prepared in Examples 1 to 3 and Comparative Example 1 was tested using a Vickers microhardness tester. The test load was 200g, the holding time was 15s, and 5 points were measured for each sample and the average value was taken. The results are as follows: Figure 6 As shown, the results indicate that the microhardness of the coatings in Examples 1 to 3 is higher than that of the coating in Comparative Example 1 (AT20) at 953 HV. Furthermore, under the same spraying current and other process parameters, the microhardness of the coating in Example 1 (1286 HV) is higher than that of the coating in Comparative Example 2 (1141 HV). The fracture toughness of the coatings obtained in the examples and comparative examples is as follows: Figure 7 As shown in the figure, the fracture toughness of the coatings in Examples 1-3 is 5.08 MPa·m. 1 / 2 3.57 MPa·m 1 / 2 4.25 MPa·m 1 / 2 Overall, it is higher than the 2.5 MPa·m of the coating in Comparative Example 1 (AT20). 1 / 2 Furthermore, the fracture toughness of the coating in Example 1 is 5.08 MPa·m. 1 / 2 Superior to 4.16 MPa·m of the coating in Comparative Example 2. 1 / 2 .

[0061] The porosity of the coatings obtained in the examples and comparative examples is as follows: Figure 8 As shown, the results indicate that the porosities of the coatings in Examples 1 to 3 were 2.03%, 3.5%, and 2.96%, respectively, which were lower than the 4.7% of the coating in Comparative Example 1 (AT20). Under the same spraying conditions, the porosity of the coating in Example 1 was also lower than the 3.27% of the coating in Comparative Example 2. These results suggest that graphene nanosheets are mainly distributed between the layers and at the microcrack termination sites, thus having a certain filling and bridging effect on the pores.

[0062] The characterization results above confirm that the addition of graphene nanosheets significantly improves the overall performance of the coating. This is fundamentally due to a multi-faceted synergistic effect: In terms of wear resistance, the increased microhardness of the coating (originating from the second-phase strengthening and grain refinement of graphene) enhances its resistance to plastic deformation and abrasive cutting. Simultaneously, the excellent lubricating properties of graphene itself can form a lubricating film on the wear surface, reducing the coefficient of friction, thus collectively leading to a decrease in wear rate, achieving an optimal balance at a 2wt% addition level. In terms of mechanical properties, graphene effectively dissipates fracture energy through mechanisms such as crack deflection, bridging, and pull-out, significantly improving the coating's toughness. Furthermore, as a hard phase, it directly contributes to hardness. In addition, graphene nanosheets can fill the spaces between layers and bridge micropores during spraying, thereby reducing the overall porosity of the coating and making the structure more compact. Example 1 exhibits the best performance across all properties, demonstrating that its 2wt% graphene addition achieves the optimal synergy between reinforcement, toughening, densification, and lubrication effects.

[0063] Comparative Example 3

[0064] The only difference between this comparative example and Example 1 is that in step S2, the spraying current is adjusted to 450 A, while the other spraying parameters are the same as in Example 1.

[0065] The wear rate of the obtained coating was tested to be 1.39 × 10⁻⁶. -4 mm 3 The coating exhibits a microhardness of 1075 HV, a fracture toughness of 3.16 MPa·m¹ / ², and a porosity of 4.1%. Compared to Example 1 (550 A), the coating shows a significant decrease in microhardness and fracture toughness, and an increase in porosity. This indicates that when the spraying current is below 500 A, the ceramic particles do not melt sufficiently, resulting in reduced interlayer bonding and hindering the acquisition of a dense coating structure.

[0066] Comparative Example 4

[0067] The only difference between this comparative example and Example 1 is that in step S2, the spraying current is adjusted to 650 A, while the other spraying parameters are the same as in Example 1.

[0068] The wear rate of the obtained coating was tested to be 1.35 × 10⁻⁶. -4 mm 3 The microhardness is 1126 HV, the fracture toughness is 3.51 MPa·m¹ / ², and the porosity is 3.7%. Compared with Example 1, when the spraying current is higher than 600 A, the graphene nanosheets undergo varying degrees of thermal damage in the high-temperature plasma jet, resulting in a weakened reinforcing effect and a decline in the overall performance of the coating.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite powder for plasma spraying, characterized in that, The composite powder comprises Al2O3-20wt%TiO2 ceramic powder and graphene nanosheets uniformly dispersed therein, and the preparation method includes the following steps: The composite powder was prepared by adding Al2O3-20wt%TiO2 ceramic powder to a graphene nanosheet suspension, followed by ball milling and drying.

2. The preparation method according to claim 1, characterized in that, The process of mixing graphene nanosheet suspension with Al2O3-20wt%TiO2 ceramic powder, wherein the amount of graphene nanosheets used is 1-3wt% of the total mass of graphene nanosheets and Al2O3-20wt%TiO2 ceramic powder.

3. The preparation method according to claim 1, characterized in that, The ball milling process uses zirconia or agate grinding balls as the milling medium, with a milling speed of 200-400 rpm and a milling time of 2-4 hours.

4. The preparation method according to claim 1, characterized in that, The average diameter of graphene nanosheets is 3-10 μm.

5. The preparation method according to claim 1, characterized in that, The drying process is carried out at a temperature of 100-200℃ for 12-24 hours.

6. A plasma spraying method for the composite powder according to any one of claims 1-5, characterized in that, The process includes the step of spraying composite powder onto the substrate surface using plasma spraying. The process parameters of the plasma spraying process are as follows: spraying current of 500-600 A, spraying voltage of 60-70 V, spraying distance of 80-120 mm, main gas flow rate of 50-60 L / min, auxiliary gas flow rate of 5-10 L / min, and powder feeding rate of 9-15 g / min.

7. The plasma spraying method according to claim 6, characterized in that, Before spraying, the substrate needs to be pretreated. The pretreatment is carried out as follows: after degreasing and derusting the substrate surface, use acetone or ethanol for ultrasonic cleaning. After drying, use sandblasting to roughen the surface. After roughening, heat and keep warm at 180-220℃ for 30 minutes.

8. A graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating, characterized in that, The composite powder prepared by any one of claims 1-5 is formed by plasma spraying, and the content of graphene nanosheets in the coating is 1-3 wt% of the total mass of the coating.

9. A coated component, characterized in that, The coating comprises a substrate and a graphene nanosheet-reinforced Al2O3-20wt%TiO2 coating attached to the surface of the substrate, as described in claim 8.

10. The coated component according to claim 9, characterized in that, The substrate is made of metal.

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