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 degrees 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 longterm 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.