Numerical and Experimental Investigation Gas-Particle Two Phase Flow in Cold Spraying Nanostructured HA/Ti Composite Particle

Abstract

HA composite coatings added reinforcement phases could improve the mechanical properties and bonding strength of the coatings. Cold spraying is a feasible surface technology for preparing HA composite coatings. In order to investigate the influence of cold spraying parameters on the deposition behavior of a single HA/Ti composite particle, numerical and experimental investigation of gas-particle two-phase flow in cold spraying nanostructured HA/Ti composite particle were investigated in this study. The results show that the influence of different temperatures and pressures on static pressure was not significant. The effects of gas pressure on the static temperature were tiny under the same inlet temperature and different pressure conditions; however, the static temperature in the entire spray gun cavity increased as the inlet temperature increased under the same pressure and different inlet temperature conditions. There is little effect of gas pressure on the axial velocity of gas flow in the spray gun cavity; however, the axial velocity of gas flow increased with the increase in gas temperature. Meanwhile, the axial velocity of gas flow gradually increases throughout the spraying process. At a gas temperature of 573 K and 973 K, the maximum axial velocities of a gas flow at gas pressure of 2.2 MPa were 778 m/s and 942 m/s, respectively. There is little effect of gas pressure on the axial velocity of HA/30 wt.% Ti particles under the same gas temperature. The axial velocity of HA/30 wt.% Ti particles increased with the increase in gas temperature under the same gas pressure condition. The axial velocity of composite particles decreased with the increase in the particle size under the same gas pressure and gas temperature. At a gas temperature of 573 K and 973 K, the minimum axial velocity of HA/30 wt.% Ti particles with a particle size of 30 μm at a gas pressure of 2.2 MPa was 435 m/s and 467 m/s, respectively. A certain deformation of splats occurred after impacting the substrate, and the splats adhered to the surface of the Ti6Al4Vsubstrate, clearly presenting a flat shape with a central hump surrounded by a ringy band. At a gas temperature of 973 K, particles generated more severe deformation with more cracks and ejecta phenomenon. The splats attached to the substrate were increased as the gas temperature increased.