Effect of Nb content on the oxidation of NbxTiAlCrSi light-weight refractory high-entropy alloys

Abstract

The oxidation of NbxTiAlCrSi light-weight refractory high-entropy alloys (RHEAs) (where x = 0, 0.5, 1.0, and 1.5 mol) was investigated at 950 degrees C in various He-O2 mixed gases. The oxidation kinetics of all alloys followed the parabolic-rate law, with their oxidation rates increasing with increasing Nb content and oxygen content. The scales formed on the alloys strongly depended on Nb content. TiO2 intermixed with Al2O3 and SiO2 was observed on the Nb-free alloy, while Nb2O5 was additionally detected on Nb-containing alloys, whose amount strongly increased with Nb content. The formation of highly defective Nb2O5 in the 1 Nb and 1.5 Nb alloys was responsible for the significantly faster oxidation rates compared to Nb-free and 0.5 Nb RHEAs.