A novel plasma surface engineering process has been developed for engineering the surfaces of austenitic stainless steels to achieve combined improvements in wear and corrosion resistance. The process employs carbon as the major alloying species in the glow discharge of a plasma, facilitating the diffusion of carbon into the surfaces of various austenitic stainless steels and forming a precipitate free layer supersaturated with carbon at relatively low temperatures. This low temperature plasma surface alloying process produces a surface engineered layer several tens of micrometres thick, which has a high hardness together with excellent wear and corrosion resistance. The present paper describes various aspects of the novel process, concerning processing, structures, properties, and applications to engineering components.

A low temperature plasma carburising process has recently been developed to engineer the surfaces of austenitic stainless steels to achieve combined improvements in wear and corrosion resistance. The present paper discusses the structural characteristics of the carburised layers produced on AISI type 316 steel at temperatures between 400 and 600°C. It was found that at low temperatures (<520°C), the carburised layers produced were precipitation free and comprised a single phase, which had a face centred cubic structure and was identified as expanded austenite owing to the supersaturation of carbon in austenite. The carburised layer was in a deformed and distorted state. High densities of twins, stacking faults, and dislocations were found in the expanded austenite. The degree of lattice expansion was estimated and was found to vary with processing temperature and depth in the layer. Precipitation of carbides (mainly Cr₇ C₃ ) occurred when the carburising temperature was relatively high (for example 550 and 600°C). In addition, stress induced martensite was found, particularly in the carburised layers produced at relatively high temperatures.

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