Mechanical Properties of Cold Sprayed Al Coatings Reinforced by Ceramics

This work investigates the effect of feedstock size on the hardness and wear resistance of metal-matrix composite coatings produced by cold spraying. Feedstocks consisting of Al and Al₂O₃ powders were prepared for the study. The feedstocks, which differ in regard to Al₂O₃ particle size (100, 50, 10 µm) and composition (25-50 vol%), were accelerated by compressed air through a Delaval-type nozzle positioned 10 mm from the target substrate. The morphology of the coating resembled that of an Al matrix with embedded Al₂O₃ particles. Optical microscopy showed that large Al₂O₃ particles (> 50 µm) fractured into small pieces and embedded in the matrix. It is likely that some of the fragmented particles bounced off, rather than adhering. These collisions (tamping effect) increase coating hardness and density. In the case of the feedstock with 10 µm Al₂O₃, particle sizes were unchanged during spraying and the benefits of work hardening were not achieved.