Aluminum coatings via kinetic spray with relatively large powder particles

Coatings have been produced by entraining relatively large diameter metal powders in a supersonic airflow. For the first time, most of the particles in the powders have diameters >50 μm. Substantial plastic deformation is involved in the conversion of the particle's kinetic energy into heat and strain energy in this kinetic spray process. As suggested by simple estimates and confirmed by coating grain structures, the particles are not melted or thermally softened in this coating process. These coatings have a relatively low oxide content, low thermal stress, high adhesion, low porosity and hardness somewhat higher than those of corresponding bulk materials. Threshold or critical velocities for coating formation are discussed. Critical velocities for the relatively large particles were observed to be substantially less than have been reported earlier for smaller diameter (