High power impulse magnetron sputtering plasma nitriding of biomedical grade CoCrMo alloy

Abstract

Medical implants are requested to meet stringent requirements to ensure their safety and efficacy over extended periods within the human body. The use of surface modification techniques, such as nitriding, is essential in advancing the performance and lifetime of implant materials. The innovative use of High Power Impulse Magnetron Sputtering (HiPIMS) discharge for nitriding represents a significant advancement in surface treatment technologies for medical implants. In this work, a CoCrMo alloy underwent a low-pressure plasma nitriding process by using four different target materials to sustain the plasma: Ti, Cr, Mo and Ta. Among them, the molybdenum target leads to the best overall performance, since it achieves the formation of the desired γ_N phase without secondary phases or surface particles and provides enhanced mechanical properties and chemical stability. The hardness achieved after the nitriding process is significantly higher than that of untreated CoCrMo, reaching up to 18 GPa. All nitrided samples exhibit a positive shift in corrosion potential values in Ringer’s solution, indicating improved corrosion resistance and demonstrate reduced wear rates and smoother wear scars compared to pristine samples, especially the Mo-treated one offers improved tribocorrosion behaviour, balancing wear and corrosion resistance effectively.