High entropy alloy borides prepared by powder metallurgy process and the enhanced fracture toughness by addition of yttrium

High entropy alloy borides FeCoNiAlCrBx (x = 0.5 and 1.0 in molar ratio) were prepared by high energy ball milling and spark plasma sintering (SPS). Pure high entropy alloy FeCoNiAlCr was prepared for comparison. The effect of boron content on alloying behavior, phase composition, microstructure, micro hardness, and fracture toughness of the as-prepared samples were studied. The results showed that, with the increase of boron content, the hardness of FeCoNiAlCr alloy increased significantly in the cost of embrittlement due to decrease/disappear of FCC phase as well as the formation/increase of borides enriched in Fe and Cr elements. The borides were found to be distributed uniformly at the grain boundaries. The toughness of FeCoNiAlCrB was found to be increased by about 40% with only small sacrifice of hardness when 0.1 molra ratio of Yttrium (Y) was introduced. The enhanced fracture toughness could be probably attributed to the more uniformly distribution of brittle borides phases and the increase of the solid solution of boron in the alloy.

Automated summary

Increasing boron content significantly enhances the hardness of high entropy alloy FeCoNiAlCr, but also increases its brittleness. Introducing a small amount of Yttrium (Y) can improve the fracture toughness of the alloy with only a slight sacrifice of hardness, possibly due to the more uniform distribution of brittle borides phases and the increase of boron solid solution in the alloy.