Improving high temperature oxidation resistance via tungsten modification in FeCr2V-based low activation medium entropy alloys

The high-temperature oxidation behavior of FeCr2VWx (x = 0, 0.1, 0.3, 0.5) low activation medium-entropy alloys (LAMEAs) was investigated in air at 650 °C. Using systematic post-mortem microstructural analysis and in-situ confocal microscopy, the oxidation kinetics were found to follow a parabolic law. Compared to conventional nuclear-grade P91 steel, FeCr2VWx LAMEAs exhibited superior oxidation resistance. The diffusion rate constants of solute elements in the FeCr2VWx alloys were determined to be 0.68, 0.529, 0.522, and 0.538 mg2·cm−4·h−1 for x = 0, 0.1, 0.3 and 0.5, respectively, significantly lower than the value of 0.704 mg2·cm−4·h−1 observed for P91. Notably, the W0.3 alloy demonstrated a 1.35× lower diffusion rate constant than P91. The enhanced oxidation resistance is primarily attributed to two mechanisms: (1) the addition of W increases the melting point of the oxide scales, preventing liquefaction and promoting the rapid formation of a denser, more protective oxide layer, thereby delaying oxidation, and (2) the formation of a WO3 inter-oxide layer, which effectively impedes element diffusion and further improves oxidation resistance.