Intermediate and high-temperature oxidation behavior of an equiatomic TaTiCr RCCA from 800 °C to 1400 °C

Abstract

This study explores the oxidation behavior of a TaTiCr refractory complex concentrated alloy (RCCA) in the temperature regime of 800–1400 °C. The oxidation kinetics were found to be proportional with temperature. However, a mechanistic shift from linear oxidation kinetics at 800 °C and 1000 °C to sub-parabolic kinetics at 1200 °C and 1400 °C was observed. This was attributed to the establishment of continuous external scales of TiO2 and Cr2O3, with fairly continuous underlying complex oxide layers at the higher temperatures. While there were morphological differences in the oxide scales depending on exposure temperature, the oxide species were all similar, primarily consisting of an outer layer of TiO2, an intermediate layer of Cr2O3, and an inner layer of rutile-structured (Cr,Ta,Ti)O2. Internal nitridation was observed in all cases, with a severe degree of internal reaction at 1400 °C, reaching a depth of 750 μm. Overall, the best performance was observed at 1200 °C, where a favorable balance of kinetics and thermodynamics promoted the most continuous oxide layers, thereby enhancing oxidation resistance.