Influence of the Cr to Ti Ratio on the High‐Temperature Oxidation Behavior of TaMoCrTiAl Complex Concentrated Alloys in Nitrogen‐Free Atmospheres

ABSTRACT Refractory high‐entropy alloys (RHEAs) offer high strength at extreme temperatures but suffer from poor oxidation resistance. The Ta‐Mo‐Cr‐Ti‐Al system shows promising oxidation resistance due to protective (Cr,Ti,Ta)O₂ scale formation. This study investigates how varying Cr:Ti ratios (2:1, 1:2, and equimolar) affect microstructure and oxidation behavior in Ar‐5 vol.%H₂O and Ar‐2.5 vol.%O₂ atmospheres at 1000°C. Titanium influences oxide defect structure through its valence state, controlling oxygen transport kinetics. Results demonstrate strong atmosphere‐dependent performance: Cr‐rich alloys excel in dry oxygen due to continuous chromia formation and reduced oxygen diffusion zones, while Ti‐rich alloys perform superior in humid conditions, likely due to hydrogen uptake effects and reduced chromium volatilization. The study reveals that optimal oxidation resistance requires atmosphere‐specific compositions, with microstructural factors (Laves phase distribution) playing equally important roles as oxide defect chemistry in determining overall performance.