Fundamental Research On Plasma Spraying Process For Bevel Coating

Plasma spraying technology is commonly used to prepare wear-resistant,high-temperature and corrosion-resistant coatings,which can be used to strengthen the surface of mechanical parts and improve the service life of industrial machinery parts.The Al₂O₃/TiO₂ series powders used in plasma spray ceramics are the most widely used.Researches on Al₂O₃/TiO₂ series coatings mainly focus on Al₂O₃-based coatings such as AT8,AT13 and AT40.The study of TiO₂-based coatings is relatively rare,the titanium oxide coating has high deposition efficiency,and the coating is dense and has good wettability with the matrix metal.The spray powder material used in this paper is TiO₂ based composite powder（80%TiO₂+20%Al₂O₃）,the coating is prepared for different process parameters,and the process parameters are optimized by analyzing the performance of the coating.When the spraying angle is 90°,an orthogonal test is designed for different process parameters to study the characterization and mechanical properties of the coating,in conjunction with the temperature change of the substrate in the spraying process,the influence of spraying current,spray distance and main gas flow on the microstructure and properties of the coating is studied,and the parameters of the process are optimized.The effects of plasma spraying parameters on the comprehensive performance of the coating are spraying current,spray distance and main gas flow.The optimum spraying parameters are:spraying current 350A,spraying distance 110mm,main gas flow rate 2100L/H.The coating with the spray angle of 90°,80°,70°,60°and50°were prepared with the optimum spraying angle of 90°,the microstructure,thickness,hardness and erosion resistance of the coating were detected.The results showed that the quality of the coating decreased with the decrease of spraying angle,especially when the spraying angle was lower than 70°,the quality is rapidly reduced,and spraying angle should be less than 70°in actual spraying.The VOF model and the solidification melting model were used in FLUENT to set up a mathematical model for spreading and solidifying the sprayed powder droplets on the substrate at different spray angles,the droplet spread,the temperature and morphology of the solidification process were obtained.The numerical simulation results showed that the spray angle was 90°,during the process of solidification of the droplets,the temperature of the droplets continuously decreases from the inside to the surface layer,becoming low on both sides of the middle,resembling a hump-like shape,and the molten droplets are symmetrically distributed.When the spraying angle is reduced,the droplets are initially dropped.The temperature and liquid distribution are similar to the spraying angle of 90°.As the time goes by,the center of the temperature field and the droplet’s liquid phase move downwards in the direction of the tilt of the substrate,and the solidification time becomes longer,formed surface is longer and thinner,the coating thickness increases from the top edge to the bottom edge and presents a"wedge"structure.