Effect of Re or W Addition on the Oxidation Behaviour of a Compositionally Complex Ta–Mo–Cr–Ti–Al Alloy in Air at 1000°C

Presuming that doping of protective (Cr,Ta,Ti)O$_2$ with cations of +5 or higher valence further improves the oxidation resistance of Ta–Mo–Cr–Ti–Al, the effect of 3 at.% of Re or W in otherwise equimolar Ta–Mo–Cr–Ti–Al is investigated in oxidation tests performed at 1000°C in air. Both minor additions indeed decrease the parabolic mass gain (72 h), which for W also manifests in reduced thickness of oxide layers and zone of internal corrosion that persists for at least 100 h. Besides the hypothesised doping, other factors that may explain the effect of Re or W are discussed. A general finding of the analytical work is the identification of (Ti,Ta)O$_2$ with Mo inclusions underneath the inward growing (Cr,Ta,Ti)O$_2$ layer.