Microstructure and mechanical properties of alumina coatings plasma-sprayed at different substrate temperatures

Alumina coatings are prepared by atmospheric plasma spraying through controlling the substrate temperature during spraying. The changes in microstructure and mechanical properties ol the coatings prepared at different substrate temperatures are examined. The hardness and the elastic modulus of the coatings are measured by indentation methods. The results show that interlamellar bonding in the coatings is significantly improved with increasing the substrate temperature. Moreover, long through-thickness columnar grains form in the coatings when the substrate temperature reaches above 430°C. As a result, the cross-sectional hardness and the elastic modulus perpendicular to the coating surface increase with increasing the substrate temperature.