Production of nitrogen and carbon S phases in austenitic stainless steels by hybrid plasma surface alloying

The discovery of the S phase phenomenon during low temperature nitriding of austenitic stainless steels by Tom Bell and others in the 1980s has stimulated significant international interest not only in the research but also in the industrial community. This has led to the intensive research on the S phase technology during the past two decades and the development and industrial acceptance of several important low temperature techniques to enhance the tribological and biological properties of austenitic stainless steels and related materials without compromising their corrosion resistance. These include low temperature nitriding by various methods, low temperature carburising and the hybrid surface alloying process combining nitriding and carburising. The present paper discusses the recent development in the hybrid plasma surface alloying process, which involves incorporating both nitrogen and carbon in the surface region of austenitic stainless steels to form a dual layer structure comprising a nitrogen S phase layer on top of a carbon S phase layer. This paper is presented to highlight the seminal contribution of Professor Tom Bell to the S phase technology.