The Study on Flow Field Simulation and WC-12Co Multi-layer Coating Growth in High-Velocity Oxygen-Fuel (HVOF) Thermal Spraying

HVOF has unique advantages as spraying metal carbides and alloys and is widely used in the aerospace, national defense industry, iron and steel metallurgy, petrochemical industry and other fields. The WC-Co coating prepared by HVOF has the characteristics of low oxide content, high bonding strength, low porosity and high temperature resistance and is the most ideal surface strengthening technology to replace surface chrome plating. In this study, a three-dimensional model of HVOF spraying was established and the flame flow characteristics in the spraying were analyzed. Combined with the discrete phase model (DPM), the influence of spraying distance, particle size and O/F ratio on temperature and velocity for particle flight were revealed. Based on the birth and death unit method, a three-dimensional thermodynamic coupling model of multi-layer coating growth was established. The stress-strain law of each coating unit in the growth process of WC-12Co coating was explored. The optimal particle parameters were obtained by calculating the flow field. The calculation shows that the optimal temperature and velocity of the sprayed particles are 1402 K and 535 m/s, respectively. The temperature of each coating unit gradually increases from the center to the outer ring and decreases under the action of air cooling with the spread time. The difference of temperature is obvious between the coating and the substrate, resulting in a relatively large stress value at the junction of the two and a relatively concentrated stress between adjacent elements. The maximum tensile stress in the X-axis direction reaches 1908 MPa and distributes in an elliptical shape at the center position of the coating unit. The shear stress in the XY direction is concentrated at the edge of each element for the coating, and the maximum reaches 1285 MPa.