Investigation of high temperature oxidation behavior and tribological performance on cold sprayed nickel-alumina composite coating

Cold spraying shows a great potential in the fabrication of metal matrix composites. In this study, a nickel-coated Al₂O₃ powder produced with the hydrothermal hydrogen reduction method was employed aiming to increase the volume fraction of ceramic particles in the cold sprayed composites. The effect of oxidation temperatures on the microstructure and microhardness of as-cold-sprayed and vacuum heat-treated Ni/Al₂O₃ composite coatings was characterized. In addition, the high temperature oxidation behaviors of as-sprayed and heat-treated coatings were compared and discussed. Eventually, the tribological performance of as-sprayed coating was examined at 25°C and 400°C. Results show that the oxidized coatings are denser compared with the as-sprayed coating. The oxide films morphologies of as-sprayed coatings are obviously different under different oxidizing temperatures. Moreover, the as-sprayed coating has a similar oxide film feature to the heat-treated coating when oxidized at 850°C, which may suggest the direct use of coating after deposition without any heat-treatment. The microhardness values of the oxidized coatings are comparable with the as-sprayed coating and even the heat-treated coating. Finally, friction tests indicate that the as-sprayed coating shows a good tribological performance at elevated working temperatures.