Constructing self-supplying Al2O3-Y2O3 coating for the γ-TiAl alloy with enhanced oxidation protective ability

The failure of the ceramic coating usually occurs at high temperatures due to the appearance of the cracks, which are caused by the accumulation of thermal stress. Here a self-supplying Al2O3-Y2O3/Al-Y coating was prepared by magnetron sputtering on the gamma-TiAl alloy. After oxidation, the coating cross-section showed that three layers were formed, and the main phases consisted of Al2O3, Y2O3, and Y3Al5O12 (YAG). The isothermal oxidation test revealed that the coating efficiently prevented gamma-TiAl alloy from degeneration for 100 h with a mass gain of 0.34% compared to the uncoated sample with a mass loss of 1.51% for 60 h at 950 degrees C. The study focused on the microstructure evolution of the coating during the oxidation process. We found that the improvement of oxidation resistance primarily could be attributed to three reasons: 1) the Y2O3 phase was more stable than Al2O3 and TiO2 at elevated temperature. 2) Al-Y layer, as the intermediate layer, can compensate for the element consumption of the ceramic layer caused by oxidation. 3) the Al3Ti layer efficiently suppressed the outward diffusion of Ti.