Boronizing of CoCrFeMnNi High-Entropy Alloys Using Spark Plasma Sintering

In this study, we investigated the formation of a protective coating on a face-centered cubic high-entropy alloy (HEA). The coating was formed by a diffusion coating method. In the conventional diffusion coating method, the degradation of the mechanical properties of the base material owing to prolonged high-temperature treatment is a major issue. Therefore, we formed a ceramic layer using spark plasma sintering (SPS), which suppresses grain growth with rapid heating and enables fast, low-temperature processing. The objective of this study was to form borides on the surface of CoCrFeMnNi HEAs using the SPS method and to investigate their properties. A CoCrFeMnNi HEA prepared by the casting method was used as the base material, and a powdered mixture of B4C and KBF4 was used as the boron source. The analysis of the surfaces of the SPS-treated samples revealed the formation of M2B, MB, and Mn3B4-type borides on the HEA surface. The surface hardness was 2000-2500 HV owing to the formation of a ceramic layer on the HEA surface, and elemental analysis showed that certain elements exhibited characteristic diffusion behaviors.