Boronizing of CoCrFeMnNi High-Entropy Alloys Using Spark Plasma Sintering

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.

An Overview of High-Entropy Alloys Prepared by Mechanical Alloying Followed by the Characterization of Their Microstructure and Various Properties

“…The higher temperature of SPS shows the degradation of the M2B and Mn3B4-type, and only the MB ceramic layer will remain. Nakajo et al concluded that increases in sintering time and temperature do not affect the thickness of the ceramic layer [43].…”

“…Alloys 2022, 2, FOR PEER REVIEW 13 Nakajo et al consolidated CoCrFeMnNi HEAs by an SPS technique at temperatures of 973, 1073, and 1173 K, and formed a thin ceramic layer on the top to improve the mechanical properties of the HEA [43]. Surface analysis of the SPS-consolidated HEA layer revealed the presence of a different variety of boride layers, such as M2B-, MB-, and Mn3B4-type borides, which considerably improved their mechanical properties.…”

“…The higher temperature of SPS shows the degradation of the M2B and Mn3B4-type, and only the MB ceramic layer will remain. Nakajo et al concluded that increases in sintering time and temperature do not affect the thickness of the ceramic layer [43]. Alvi et al prepared W0.5(TaTiVCr)0.5 HEAs followed by consolidation by SPS at 1000, 1200, and 1400 °C sintering temperatures [44].…”

Modeling the mechanism of micro / nanostructured surface formation in Al-Co-Cr-Fe-Ni and Co-Cr-Fe-Mn-Ni high-entropy alloys treated with a high current pulsed electron beam

“…The methods of surface modification also play an important role in the design of HEAs since they allow eliminating some defects as pores or microcracks and increasing durability. For example, the HEA surface can be modified by plasma nitriding [7], laser remelting [8], boronizing [9], gaseous carburization [10], ultrasonic nanocrystal surface modification [11] and high current pulsed electron beam treatment (HCPEB) [12,13]. The latter method introduces high energies into the surface layers and forms a cellular microstructure with a grain size of 100 -500 nm, leading to better mechanical and tribological characteristics.…”

Electron-ion-plasma boriding of a multilayer nanostructural high-entropy alloy

“…One of the options for improving the service characteristics of HEA is to saturate them with boron atoms. Various methods of HEA boriding are used: using nanosized borating powders [19,20], plasma borating [21], using laser technologies [22] and plasma spark sintering technologies [23], and many others.…”