Effects of microstructure on oxidation behavior of lamellar TiAl alloys

The oxidation behavior of Ti-48Al-2Cr-2Nb alloys with fully lamellar and nearly lamellar microstructure achieved by different heat treatments was investigated by a thermogravimetric method at 800℃ for 100 h. The morphology, phase composition and element distribution of the specimens were analyzed by OM, SEM, TEM, XRD and EDS. It is found that oxidation kinetic curves of the TiAl alloys with nearly lamellar and fully lamellar microstructures accord with the parabolic curve law. And nearly lamellar microstructure has better oxidation resistance than fully lamellar microstructures, when the specimens are at 800℃ in air. Based on the analysis of oxidation kinetic, microstructure of substrate, microstructure of scale, surface morphology and phase of the sample, it is concluded that the microstructure of TiAl alloy castings has a significant influence on the oxidation behavior.