Abstract
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.
Highlights
High-entropy alloys (HEA) are multi-component alloys obtained by blending five or more metal elements in equiatomic fractions (5–35%) [1]
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
Various studies have been conducted on HEA [9–11], including research on hardening by surface modification treatment, which has been actively pursued [12–15]
Summary
High-entropy alloys (HEA) are multi-component alloys obtained by blending five or more metal elements in equiatomic fractions (5–35%) [1]. HEA, the hardness is as low as, or lower than, those of general steel materials [7,8], which hinders its practical applications To overcome these disadvantages, various studies have been conducted on HEA [9–11], including research on hardening by surface modification treatment, which has been actively pursued [12–15]. The diffusion coating method involves the formation of a hard layer by thermochemically diffusing various elements from the surface into the base material, which simultaneously react with it. Using this method, a hard layer with excellent adhesion can be formed. We formed a boride layer on a HEA using the SPS method and evaluated the properties of the HEA boride layer
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