High temperature oxidation behaviour of compositionally complex Ta‒Mo‒Cr‒Ti‒Al alloy in steam atmosphere

The oxidation behaviour of TaMoCrTiAl in steam at 900-1100 degrees C has been investigated by thermogravimetric analysis of oxidation kinetics and detailed cross-sectional SEM and TEM characterization of the multilayered oxide scales formed during exposure. Experiments point to the significance of both outward diffusion of metal cations and inward transport of oxidizing species, whereas the latter becomes increasingly dominant with increasing exposure times. Based on these findings, a mechanistic oxidation model for TaMoCrTiAl in steam is proposed and compared with the oxidation behaviour in air. In contrast to oxidation in synthetic air, the (Cr, Ta, Ti)O$_2$ layer typical for TaMoCrTiAl is absent, but formation of (Ti, Ta)O$_2$ observed, with impact on both formation of external oxide and internal corrosion.