Influence of Y addition on the long time oxidation behaviors of high Nb containing TiAl alloys at 900 °C

Influence of Y addition on the long time isothermal and cyclic oxidation behaviors of Ti45Al8Nb alloys containing 0.1-1.0 at.% Y with full lamellar microstructure was investigated in air at 900 °C. Only a proper amount of Y addition (0.3 at.%) can improve the long time oxidation resistance under both isothermal and cyclic oxidation. Either excessive or deficient addition of Y was detrimental to the oxidation resistance. Under isothermal oxidation, much thinner oxide scale was formed on 0.3 at.% Y-added alloy than it on Y-free alloy. Meanwhile, Y addition can effectively suppress the outmost TiO2 layer and enhance the protective Al2O3 layer on the sample surface. Under cyclic oxidation, different from the oxide scale formed on Y-free and Y-lean (0.1 at.%) alloys, the oxide scales on higher Y-added alloys were not typical layered structure and oxide pegs protruding into the substrate were formed at the oxide scale/substrate interface. As a result, no spallation was observed in the higher Y-added alloys even after 1000 cycles while spallation occurred on Y-free alloy after 280 cycles and 0.1 at.% Y added alloy after 460 cycles. However, high Y added alloys (>0.3 at.%) suffered severe internal oxidation. Therefore, the oxidation rate on high Y added alloys was significantly high.