Oxidation properties and microstructure evolution of oxidation layer for Cr NbMoTiV refractory high entropy alloys at elevated temperature

Oxidation resistance at elevated temperature is one of the important parameters to evaluate high temperature of materials. To study effect of chromium on oxidation resistance of refractory high entropy alloy, Cr x MoNbTiV ( x = 0.2, 0.4, 0.6, 0.8 and 1.0) refractory high entropy alloys with different addition of chromium were prepared. The high temperature oxidation properties of different alloys at 800 °C are tested, and the phase constitution, microstructure characteristics and evolution of oxidation film were investigated. Results show that after oxidation at 800 °C for 100h, weight gains of Cr x MoNbTiV alloys are decreased with increasing of chromium, and the weight gain is from 59.2 mg/cm 2 to 8.8 mg/cm 2 with increasing chromium from 0.2 to 1.0. The thickness of the oxidation film is decreased with increasing of chromium, and that of C 0.2 rMoNbTiV and CrMoNbTiV alloy is 310 μm and 65 μm, respectively. The surface of oxidation film gets smoother with increasing of chromium, and the amount of dense products CrVNbO 6 and Ti 4 Cr 3 Nb 3 O 2 increases with increasing of chromium, while that of porous products Nb 9 VO 25 and V 2 Nb 6 O 19 decreases with increasing of chromium, consequently, the oxidation properties of Cr x MoNbTiV alloys is improved. The porous products of CrMoNbTiV with addition of chromium by 1.0 disappear, and the oxidation film of CrMoNbTiV is consisted of compact TiO 2 , Ti 4 Cr 3 Nb 3 O 2 and CrVNbO 6 , which can protect the inner microstructure of alloy, therefore the oxidation resistance is significantly improved.