Isothermal oxidation behavior and microstructure evolution of heat-treated TiAl alloys

In this work, Ti-44Al-5Nb-1Cr-0.3C alloy was heat treated by two processes (labeled as WQ and FC samples, respectively), and the isothermal oxidation behavior and oxide layer evolution of the heat-treated samples at 800 °C were studied in detail. Experimental results revealed that compared with FC sample, the rapid cooling of the WQ sample refined the inter-lamellar spacing and caused destruction to local lamellae. With the increase of oxidation duration, the oxidation kinetics of both samples changed from linear to parabolic law. The short-term oxidation resistance of WQ sample was better, while the FC sample showed more advantages in resisting long-term oxidation. The extension of oxidation time not only increased the size of oxide particles and the thickness of oxide scale, but also promoted the transformation of the mono-layer oxide scale composed of Al₂O₃ and TiO₂ to a multi-layer structure. Moreover, the specific component of the multi-layer oxide varied with oxidation duration. The dissolution and re-precipitation of Al₂O₃ and diffusion of various atoms along lamellar interfaces and cracks in the interlayer were responsible for differences in the specific component of the multi-layer structure of WQ and FC samples.