Microstructure, Mechanical Properties, and High-Temperature Oxidation Behavior of Al_0.3CoCrFeNiW_x High Entropy Alloys

A series of Al_0.3CoCrFeNiW_x (x=0, 0.2, 0.3, and 0.5) high entropy alloys were designed. The effect of W addition on microstructure, mechanical behavior, and high-temperature oxidation was systematically investigated. It is indicated that the addition of W element promoted the structural transformation of as-cast Al_0.3CoCrFeNiW_x HEAs from single FCC to FCC + μ, and the volume fraction of μ phase increased as the W content increased. The yield strength of the alloys was enhanced with increasing W content, which could be attributed to solid solution and second phase strengthening. Oxidation studies were performed on the HEAs at 800 °C for 100 hours. Protective external Cr₂O₃ layer and internal Al₂O₃ formed in the investigated HEAs. With increasing W content, a higher mass gain was obtained. This could be explained by the relatively decreased Cr content in the as-cast alloy as well as the depletion of Cr element in the underlying alloy caused by μ phase. The results in our work could provide clues for the development of new HEAs.