Oxidation response of a vacuum arc melted NbZrTiCrAl refractory high entropy alloy at 800–1200 °C

Abstract An equimolar refractory high-entropy alloy NbZrTiCrAl was prepared by vacuum arc melting, the microstructure and oxidation response of the alloy at 800 °C, 1000 °C and 1200 °C were investigated. The alloy mainly consists of BCC single-phase solid solution and shows an inhomogeneous microstructure with dendritic and inter-dendritic regions. The oxidation of the alloy at 800 °C and 1000 °C follows parabolic rate law, and the protection performance can be attributed to the formation of dense and homogenous complex oxides scale composed of CrNbO4, ZrO2, TiO2, Al2O3 and ZrNb2O7. The linear oxidation kinetics of the alloy at 1200 °C is observed, the scale composed of similar oxide products but with layered structure is probably the reason of the poor resistance to long-term oxidation at higher temperatures. The formation of the oxide scale and the oxidation-resistant mechanism of the alloy at different temperatures have been discussed.