Microstructure and tribological behavior of copper and composite copper+alumina cold sprayed coatings for various alumina contents

Cold-sprayed metal-ceramic composite coatings are candidates for wear-critical applications such as applications in the automotive and aircraft fields. In the present study, the microstructure and tribological behavior of Cu and Cu+Al2O3 cold sprayed coatings were investigated. Al2O3 powders having two different particle size ranges were used, each of which was blended with copper powder at concentrations of 10, 20 and 30 wt%. Non-lubricated pin-on-disk sliding friction and wear tests using alumina pins were conducted. Cross sectional examination revealed thick and dense coatings, in which there was no evidence for either oxidation or phase transformation during cold spraying. Addition of Al2O3 particles in the copper matrix resulted in a slight increase in the Vickers microindentation hardness. The sliding coefficients of friction were of the order of 0.4-0.5. The presence of hard Al2O3 particles in the composite coatings increased their wear resistance, compared with a Cu coating alone. Also, the wear rates of composite coatings containing fine Al2O3 particles were lower than those containing coarse Al2O3 particles. Observation of the wear tracks indicated that the main wear mechanism was micro‐ploughing. Plastic deformation as well as oxidation of copper particles also took place on the wear tracks.