Oxidation behaviour of eutectic refractory high-entropy alloys at 800–1000 °C

Herein, we investigated the oxidation behaviour of B2/C14 Laves phase hypoeutectic Al 23 Cr 20 Nb 15 Ti 32 Zr 10 , eutectic Al 28 Cr 20 Nb 15 Ti 27 Zr 10 , and hypereutectic Al 33 Cr 20 Nb 15 Ti 22 Zr 10 (at%) refractory high-entropy alloys (RHEAs) at 800–1000 °C. An increase in the Al/Ti ratio reduced the mass gain, but induced an oxide scale spallation. Before spallation, the studied alloys demonstrated better oxidation resistance than the current Al-Cr-Nb-Ti-(V)-Zr RHEAs at 800 °C. An analysis of the Al 23 Cr 20 Nb 15 Ti 32 Zr 10 alloy with near-parabolic oxidation kinetics revealed the formation of an external oxide layer with a dominant TiO 2 and an internal reaction zone comprised O-rich products and TiN. The oxidation mechanisms and suggestions for improving the oxidation/spallation resistance were discussed. • Oxidation behaviour of eutectic B2/C14 Laves phase RHEAs at 800–1000 °C was studied during the interrupted tests in the air. • A hypoeutectic Al 23 Cr 20 Nb 15 Ti 32 Zr 10 (at%) alloy showed better spallation resistance than eutectic and hypereutectic alloys. • A dominant TiO 2 and additional Al 2 O 3 , CrO 2 , Ti 0.4 Al 0.3 Nb 0.3 O 2 , Zr 0.5 Al 0.5 O 2 oxides were formed. • Outward diffusion of Ti and inward diffusion of O controlled the growth of the oxide layer. • Before spallation, the alloys were the most oxidation-resistant at 800 °C among the current Al-Cr-Nb-Ti-(V)-Zr RHEAs