In the kinetic spraying process, the critical velocity is an important criterion which determines the deposition of feedstock particle onto substrate. It was experimentally proved that the critical velocity is determined by the physical properties of materials and the state of materials such as initial temperature, size and especially oxidation. Comparing with un-oxidized feedstock, oxidized feed stock would need more kinetic energy of in-flight particle to break away the oxide film during impact.

The oxide film formed on the surface of particle and substrate is of relatively higher brittleness and hardness than those of general metals. Because of its physical characteristics, the oxide did affect significantly the deposition behavior and critical velocity as well.

The effects of oxidation on the critical velocity and deposition behaviour of feedstock were investigated and evaluated by individual particle impact test in this study. And the velocity of pure Al particles was measured with spray watch for wide range of process gas condition.