Effect of iron content on wear behavior of AlCoCrFexMo0.5Ni high-entropy alloys

A new high-entropy alloy system, AlCoCrFeMoNi, was designed based on the AlCoCrCuFeNi, by replacing Cu with Mo to improve strength and thermal stability. The effect of iron content on hardness and wear behavior of AlCoCrFexMo0.5Ni alloys is related to the microstructural change. As the iron content is increased, the microstructure changes from “dendritic” for Fe0.6 and Fe1.0 alloys to “polygrain” for Fe1.5 and Fe2.0 alloys. The two constituent solution phases are BCC and σ, but the volume fraction of the BCC phase increases with the iron content. The hardness declines correspondingly because the σ phase is harder than the BCC phase. The wear resistance also declines as the Fe content increases, but the wear resistance of Fe2.0 is much lower than that of Fe1.5, which result is inconsistent with their similar hardness levels. Composition analysis of the worn surface and worn debris indicates that, the major wear mechanism of all these HE alloys is abrasion. The oxidation test at the pin/disk interface flash temperature, 500 °C, indicates that the oxidation rate of Fe2.0 markedly exceeds that of Fe1.5, indicating more oxides abrade the surface resulting lower wear resistance.