Coating deposition by the kinetic spray process

This paper describes the deposition of metallic coatings using the kinetic spray process (also referred to as cold spray or cold gas dynamic spray). This coating process is a relatively new process that involves using high velocity metallic particles to generate surface coatings. In the coating process, metallic particles (~ 50–150 μm) are injected into a de-Laval nozzle and propelled by a supersonic gas stream to high velocity (> 300 m/s) to impinge upon a substrate. The coatings are formed subsequently as the metallic particles are severely deformed plastically and bonded to both the substrate and to one another. The kinetic spray process is a rapid coating process; its deposition rates can be favorably compared to most known coating processes such as PVD, CVD and thermal sprays. In this study, the kinetic spray process is utilized to deposit several types of coatings, including metal coatings of Zn and Al, and the composite coatings of Zn + Al, Zn + Al + Si and Zn + (Al–Si). Several aspects of the coatings, including the coating formation, surface morphology and microstructure, were characterized. The coating formation by the kinetic spray process was studied through examinations of the mass loadings of the coatings as functions of the dwell time (i.e. the inverse of the traverse speed at which the substrate moves in front of the spray nozzle). For the composite coatings, the composition dependence on the starting powders was investigated and interpreted in the light of loading characteristics of each type of the involved metal particles.