Grain Refinement of an As-Cast CoCrNi Multi-principal Element Alloy by Inducing Solute Segregation: Solute Design and Effects.

Multi-principal element alloys (MPEAs) have been extensively studied in recent years. However, the as-cast MPEAs usually possess coarse columnar grains with undesirable properties, thus columnar-to-equiaxed transition (CET) and grain refinement are of great significance. According to the interdependence theory, increasing the constitutional supercooling (CS) and limiting the diffusion of solutes will result in a refined structure. Therefore, the effect of boron (B) element on grain refinement of the as-cast CoCrNi MPEAs was evaluated: B element accumulates in the region ahead of the solid–liquid (S–L) interface during solidification and has such a strong affinity with the Cr element that it can induce the segregation of Cr element and restrict the diffusion of Cr element. The results indicate that B element induces CET and grain refinement significantly. The grain refinement is attributed to CS ahead of the S–L interface caused by the interaction of solutes and the slower diffusion rate induced by the concentration of B element. This work proposed a new method to refine the microstructure of the MPEAs. [ABSTRACT FROM AUTHOR]