The Effect of Al on the Formation of a CrTaO4 Layer in Refractory High Entropy Alloys Ta-Mo-Cr-Ti-xAl
Steven Schellert, Bronislava Gorr, H.‐J. Christ, C. Pritzel, Stephan Laube, Alexander Kauffmann, Martin Heilmaier
Abstract
Abstract In this study, the effect of Al on the high temperature oxidation of Al-containing refractory high entropy alloys (RHEAs) Ta-Mo-Cr-Ti-xAl ( x = 5; 10; 15; 20 at%) was examined. Oxidation experiments were performed in air for 24 h at 1200 °C. The oxidation kinetics of the alloy with 5 at% Al is notably affected by the formation of gaseous MoO 3 and CrO 3 , while continuous mass gain was detected for alloys with the higher Al concentrations. The alloys with 15 and 20 at% Al form relatively thin oxide scales and a zone of internal corrosion due to the formation of dense CrTaO 4 scales at the interface oxide/substrate. The alloys with 5 and 10 at% Al exhibit, on the contrary, thick and porous oxide scales because of fast growing Ta 2 O 5 . The positive influence of Al on the formation of Cr 2 O 3 followed by the growth of CrTaO 4 to yield a compact scale is explained by getter and nucleation effects.