Nitriding CoCrNi medium-entropy alloy with atmospheric pressure plasma jet: Enhancements in wear performance

Abstract

In this study, the surface of a CoCrNi medium-entropy alloy (MEA) was modified via atmospheric pressure plasma jet (APPJ) nitriding with a 2% H2/N2gas mixture, aiming to enhance its hardness and wear resistance. The influence of APPJ nitriding on nitride layer development, tribological properties, and mechanical performance was systematically investigated. Plasma species analysis confirmed the presence of only nitrogen-hydrogen species, with excitation intensity increasing with increasing power. Elevated plasma power enhanced plasma dissociation, nitrogen diffusion, and nitride layer thickness, leading to CrN precipitation that promoted surface hardening. Materials characterization of APPJ-nitriding MEA samples showed that the substrate retained its FCC solid-solution structure, the surface evolved from single-crystal to polycrystalline diffraction. The untreated CoCrNi MEA primarily exhibited adhesive and abrasive wear, whereas APPJ-nitriding specimens showed a transition toward abrasive and fatigue wear. Contact angle measurements indicated decreasing wettability with rising power, alongside increased surface free energy. These results highlight APPJnitriding process as a rapid and effective method for tailoring the surface properties of CoCrNi MEAs, offering strong potential for applications requiring enhanced durability.