Effects of rare earth additions on nitriding of EN40B by plasma immersion ion implantation

Reports over the last two decades have shown the potential for improving existing thermochemical surface engineering processes by rare earth (RE) additions. Some theories for the mechanism by which RE additions have an effect suggest that they can act as catalysts for the reactions that take place in the treatment atmosphere. In plasma nitriding, this is reported to provide an increased supply of nitrogen to the component surface. Thus, there is better nitrogen uptake by the component material. Therefore, treated component properties can be improved, attributed to enhanced diffusion of nitrogen. Here, the effects of small lanthanum RE additions to PI3 treatment of steels are discussed. It is shown that RE addition in the form of a small solid piece in the centre of the negatively biased work table results in increased nitrogen concentrations in the near surface regions of steel specimens coupled with improved surface hardness properties. The same small piece of RE can be reused for several consecutive PI3 treatments, making this potentially a cost-effective method for improving the treatment of steels by PI3.