Microstructure and properties evolution of plasma sprayed Al2O3-Y2O3 composite coatings during high temperature and thermal shock treatment

Al2O3-Y2O3 composite powder with TiO2 additive was plasma sprayed to prepare Al2O3-Y2O3 composite coatings. The microstructure and properties evolution of the Al2O3-Y2O3 coatings during high temperature and thermal shock resistance were investigated. The results show that the microstructure of the Al2O3-Y2O3–TiO2 coating is more uniform than that of the Al2O3-Y2O3 coating. Meanwhile, amorphous phase is formed in the two coatings. The Al2O3-Y2O3(–TiO2) coatings were heat treated for 2 h at temperatures of 800, 1000 and 1200 °C, respectively. It is found that the microstructure and properties of the two coatings have no obvious change at 800 °C. Some of the amorphous phase is crystallized at 1000 °C, and meanwhile Y2O3 and Al2O3 react to form YAG phase and YAM phase. At 1200 °C, all of the amorphous phases are crystallized. After heat treatment, the microhardness of the two coatings is increased. The thermal shock resistance of the Al2O3-Y2O3 system coatings can be improved by using TC4 titanium alloy as substrate and with NiCrAlY bonding layer. Moreover, the Al2O3-Y2O3-TiO2 coating exhibits better thermal shock resistance due to the addition of TiO2.