Surface modification of a medical grade Co-Cr-Mo alloy by low-temperature plasma surface alloying with nitrogen and carbon

Cobalt-chromium (Co-Cr) alloys are one of the best materials for biomedical applications owing to their fairly good wear resistance, high mechanical properties, adequate corrosion resistance and acceptable bio-compatibility. However, recently, there are concerns over the wear behaviour of metal-on-metal artificial hip joints and the formation of numerous nano-sized wear debris from the articulating Co-Cr surfaces. This is mainly because such extremely fine wear debris could release chromium and cobalt ions into the host body, which can cause potential toxicity. Therefore, how to improve the wear resistance of Co-Cr alloys is a scientifically interesting and clinically important research topic. This study aimed to improve the hardness, wear, corrosion and corrosion-wear properties of medical grade Co-Cr by plasma surface alloying with nitrogen and with both nitrogen and carbon at very low temperatures (between 300 and 400. °C). The metallurgy, mechanical, chemical and wear properties of the surface alloyed layers were characterised and the results demonstrate that the optimised treatment conditions have produced very promising surface layers on Co-Cr alloy for biomedical applications.