High temperature treatment effects on the microstructure and properties of a plasma sprayed 25 mol% AI2O3-25 mol% Cr2O3-50 mol% TiO2 coating

In this study, the influence of heat treatments up to 1200°C in vacuum on coatings prepared by atmospheric plasma spraying (APS) from a blend of 25 mol% Al2O3, 25 mol% Cr2O3 and 50 mol% TiO2 on microstructure, porosity, hardness and sliding wear resistance was investigated. The well-known transformation from a-Al2O3 to g-Al2O3 occurred as a result of the spray process, as well as small amounts of titanium were found in Cr2O3 splats due to an interaction between the feedstock particles. No significant changes were found after a heat treatment at 400°C or 800°C. Heat treatment at 1200 °C led to complete coating delamination. Besides the retransformation of g-Al2O3 to a-Al2O3, interactions between Cr2O3 and TiO2 splats and the formation of CrTi2O5 was observed. The formation of Al2Ti7O15 was observed in result of a reaction at the outer regions of the Al2O3 splats. At the same time, a reduction in porosity and healing of microcracks were observed as a result of sintering processes, which leads to an increase of the coating hardness to 1170 HV0.2.