Effect of yttrium on phase composition and microstructure of FeCoNiAlCrB high entropy alloys

The effects of yttrium (Y) addition on phases, microstructure, Vickers hardness, nanohardness and modulus, and fracture toughness of the FeCoNiAlCrB alloy were investigated in this study. Results show that, the fracture toughness of the Y-contained alloy was improved by ∼50%, but with only ∼10% decrease in Vickers hardness. With the addition of Y, no obvious changes can be differentiated from the main phases of the FeCoNiAlCrB alloy, but the continuous network-structured borides are much refined and dispersed. The significantly increased fracture toughness could be probably due to the microstructure refinement and uniform dispersion of brittle borides. In addition, high-speed mapping at the micro-nano scale revealed that the decrease in hardness could be possibly attributed to the local variations in the composition and phase separation resulting from the Y addition.