Comparison of Plasma Nitriding Characteristics of High-Entropy Sintered Alloys Using Several Ni-Containing Auxiliary Cathode Screens

CoCrFeMnNi high-entropy alloys (HEAs) have recently attracted considerable attention owing to their excellent tensile strength and ductility at low temperatures. However, regardless of the fabrication method, conventional CoCrFeMnNi HEAs generally exhibit lower hardness compared with that of traditional steels. To address this limitation, surface-modification techniques have been employed as an effective approach to enhance the surface hardness of CoCrFeMnNi HEAs. In this study, CoCrFeMnNi HEAs were sintered and subsequently treated by screen-assisted direct current plasma nitriding (S-DCPN) using a Ni-containing multi-screen; the properties of the nitrided samples were then systematically evaluated. During S-DCPN, three types of auxiliary cathode screens, namely stainless steel (SUS316L), Ni-based superalloy (Alloy 600), and pure Ni, were employed to ensure uniform heating and enhanced nitrogen activation. The nitrided samples were characterized by X-ray diffraction, scanning electron microscopy, glow discharge optical emission spectroscopy, and surface hardness and wear tests. Compared with the untreated specimens, all nitrided samples exhibited a significant increase in surface hardness and wear resistance, confirming the effectiveness of the S-DCPN process for strengthening CoCrFeMnNi HEAs.