Oxidation behavior of TiAl alloys during thermal cycling

Oxidation behaviors of Ti-50Al, Ti-48Al, Ti-52Al, Ti-48Al-1Cr and Ti-48Al-4Cr during 100 thermal cycles from 800 °C for 1 hour in static air to room temperature for 10 minites were studied by the TGA method. Mass gain (ΔM) of ternary TiAl-Cr is a magnitude larger than that of binary TiAl. Unlike interrupted oxidation of TiAl at the same condition, cyclic oxidation shows linear kinetic law. It is shown that the deterioration in oxidation resistance of the TiAl alloys with increasing the cycling number results from the thermal stresses among TiO₂, Al₂O₃ and TiAl phases, and the micro-cracks introduced by the thermal shock, which lead the short-way diffusion of oxygen. The typical oxidation stratification of TiAl was identified as the surface TiO₂ layer/the (TiO₂+Al₂O₃) mixture layer with alternate rich Ti or rich Al sub-layers/diffusion zone/TiAl matrix.