Critical Velocities for High Speed Particle Deposition in Kinetic Spraying

Abstract

During kinetic spraying (or cold gas dynamic spraying), small solid particle can be deposited onto the substrate by a supersonic velocity impaction. A critical velocity of flying particle was found for the minimum deposition speed. Generally, it was thought that higher impact velocity caused higher deposition efficiency. However, some different phenomena were observed during spraying processing in laboratory.In this study, individual particle impact tests have been carried out to probe the effect of impact velocity. Instead of deposition efficiency (DE) of coatings, ratio of bonds, which was defined as the number fraction of attached particles to total impact particles (Craters + Bonds) in unit area of impact surface, was measured in our test. A maximum velocity for particle deposition was observed, because of which a high fraction of rebounded particles occurred at a high impact velocity. A model considering the adhesion and rebound energy was built up to estimate the particle/substrate interaction. The particle deposition behavior was a result of the competition between adhesion and rebound energies during the impact process. Only when the adhesion energy was higher than the rebound energy, the impacting particles could be attached onto the substrate.