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 ex isting thermochemical surface engineering processes by rare earth (RE) addi tions. 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 i n the treatment atmosphere. In plasma nitriding, this is reported to provid e an increased supply of nitrogen to the component surface. Thus, there is better nitrogen uptake by the component material. Therefore, treated compon ent properties can be improved, attributed to enhanced diffusion of nitroge n. Here, the effects of small lanthanum RE additions to PI3 treatment of st eels are discussed. It is shown that RE addition in the form of a small sol id piece in the centre of the negatively biased work table results in incre ased 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 poten tially a cost-effective method for improving the treatment of steels by PI3 . (C) 2001 Elsevier Science B.V. All rights reserved.