Oxidation mechanism of refractory high entropy alloys Ta-Mo-Cr-Ti-Al with varying Ta content

The effect of Ta on the oxidation resistance of the alloys Ta-x-(Mo-Cr-Ti-Al)(1-x) (x=0; 5; 10; 15; 20 at%) in air at 1200 degrees C was examined. The oxidation behavior improves continuously with the increasing Ta concentration. Alloys with Ta concentrations Ta <= 10 at% exhibit poor oxidation. Severe evaporation of MoO3 occurred which was quantitatively estimated. The evaporation of MoO3 is drastically reduced in alloys with the higher Ta concentrations. At 15 and 20 at% Ta, protective CrTaO4 scales are found. The CrTaO4 scale formed on Ta2O-(Mo-Cr-Ti-Al)(80) grows according to the parabolic rate law as a result of oxygen inward diffusion.

Automated summary

The oxidation resistance of alloys Ta-x-(Mo-Cr-Ti-Al)(1-x) in air at 1200 degrees C is improved with increasing Ta concentration. However, alloys with Ta concentrations less than or equal to 10 at% exhibit poor oxidation behavior. Protective CrTaO4 scales are found in alloys containing 15 and 20 at% Ta.