Effect of long-term heat-treatment at 1150 °C on the microstructure and properties of thermal barrier coatings based on ZrO2-4 mol.% Y2O3-1 mol.% Gd2O3-1 mol.% Yb2O3

In this study, thermal barrier coatings of ZrO2-4 mol.% Y2O3-1 mol.% Gd2O3-1 mol.% Yb2O3 containing two different grades of porosity were produced using a conventional spray powder as well as a special spray powder prepared by high energy ball milling by means of a three-cathode plasma generator TriplexPro™-210. The coating deposited using the milled powder exhibited a significantly more porous microstructure than the conventional coating. Both coatings were heat-treated in a furnace at 1150 °C for 100 h, 200 h and 500 h to investigate the effect of sintering on the microstructure and properties of the coatings. The coatings were characterized in terms of their microstructure and phase stability. Their microhardnesses were measured and their thermal diffusivities were determined. Results revealed that both coatings were sintered by the heat-treatment which resulted in densification of their microstructures, increase of their microhardnesses and thermal diffusivities. Because of its special microstructure, the coating based on the milled powder remained highly porous despite sintering and exhibited significantly lower microhardnesses and thermal diffusivities in as-sprayed condition as well as after the heat-treatment compared to the conventional coating. Both TBCs showed high phase stability at 1150 °C.