Abstract
High-entropy alloys (HEAs) were fabricated by powder metallurgy using gas-atomized powder and spark plasma sintering (SPS) followed by surface modification (plasma nitriding) of the sintered sample. Plasma nitriding forms nitride and induces solid-soluting of N; it enables the diffusion of N atoms by removing the passive film formed on the surface of alloys such as stainless steel, Al alloys, and Ti alloys, via the sputtering of cations during glow discharge. Therefore, plasma nitriding has the potential to process HEAs that contain strong oxidizing elements such as Cr, Al, and Ti. In this work, a sintered CoCrFeMnNi HEA was plasma-nitrided and its properties were subsequently evaluated. A uniform microstructure without segregation was obtained in the SPS sample, and its hardness and wear resistance were found to have improved. Analysis of the sample surface after nitriding revealed that an expanded face-centered cubic phase formed on the surface plasma-nitrided at 673 K and that a CrN phase formed on the surface plasma-nitrided at temperatures greater than 723 K. The surface hardness of the plasma-nitrided sample was 1200 HV or greater, and the wear resistance and pitting corrosion resistance were improved compared with those of the untreated sample.
Highlights
High-entropy alloys (HEAs) have recently become a subject of extensive research because they are expected to be used in applications such as molds, tools, and functional coatings [1,2]
CoCrFeMnNi alloy powder prepared by gas atomization (Sanyo Special Steel Co., Ltd., Hyogo, Japan)CoCrFeMnNi was used as aalloy starting material and was μm by sieving
A secondary electron image (SE image) of the CoCrFeMnNi alloy powder prepared by gas atomization is shown in
Summary
High-entropy alloys (HEAs) have recently become a subject of extensive research because they are expected to be used in applications such as molds, tools, and functional coatings [1,2]. HEAs are composed of at least five major elements with concentrations in the range 5–35 at% [2]. Because of their simple microstructure, HEAs possess a unique combination of properties not found in traditional metallic materials, such as high strength at elevated temperatures, ductility, and corrosion resistance [3,4,5]
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