Effect of Boron on the Microstructure, Phase Assemblage and Wear Properties of Al0.5CoCrCuFeNi High-Entropy Alloy

The microstructure, phase assemblages, hardness and wear properties of Al0.5CoCrCuFeNiBx (x = 0∼1) high-entropy alloys were investigated. The results show that without boron addition, the alloy is composed of simple fcc solid solution structure. In the alloys with boron additions, boron precipitates 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 alloys and the hardness shows strong correlation with the boron content. There is no distinct difference in the wear resistance of the alloys with x ≤ 0.4, but the wear resistance increases linearly with the boron content increasing in the alloys with x ≥ 0.6. With the boron content increasing, 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 ductile and tough fcc matrix.