Abstract:In this study, the microstructure, phase assemblages, hardness and wear properties of Al0.5CoCrCuFeNiBx (x=0-1) high-entropy alloys were investigated. The parameters representing simple solid-solution formation ability in Al0.5CoCrCuFeNiBx alloys were estimated. Without boron addition, the alloy was composed of simple FCC solid solution structure. With the addition of boron, the alloys were composed of borides and simple FCC solid solution matrix phase. Boron precipitated as borides instead of entering the crystal structure and thus there is no change in the lattice constant of the matrix FCC phase. Borides precipitation significantly hardens the alloy and the hardness showed a strong correlation to the boron content. There was no distinct difference in the wear resistance of the alloys with x?0.4, but the wear resistance showed a strong relation to the boron content in the alloys with x?0.6. With increasing boron content, the wear mechanism changes from delamination wear to oxidative wear. The great enhancement in the hardness and wear resistance is attributed to the combination of the large hard borides and relatively ductile and tough FCC matrix.