THE EFFECTS OF LOW-ENERGY-NITROGEN-ION IMPLANTATION ON THE TRIBOLOGICAL AND MICROSTRUCTURAL CHARACTERISTICS OF AISI-304 STAINLESS-STEEL

The effects of nitrogen implantation conditions (ion energy, dose rate, and processing time) on the thickness and wear behavior of N-rich layers produced on 304 stainless-steel surfaces are examined. Surfaces implanted at elevated temperatures (approximate to 400 degrees C) with 0.4 to 2 keV nitrogen ions at high dose rates (1.5 to 3.8 mA/cm(2)) are compared to surfaces implanted at higher energies (30 to 60 keV) and lower current densities (0.1 to 0.25 mA/cm(2)). The most wear-resistant surfaces are observed when the implanted-ion energy is near 1 keV and the dose is very large (>2x10(19) ions/cm(2)). Typically, surfaces implanted under these optimum conditions exhibit load-bearing capabilities at least 1000 times that of the untreated material. Some comparisons are also made to surfaces processed using conventional plasma-nitriding. Samples treated using either process have wear-resistant surface layers in which the nitrogen is in solid solution in the fee phase. It is argued that the deep N migration ( >1 mu m) that occurs under low-energy implantation conditions is due to thermal diffusion that is enhanced by a mechanism other than radiation-induced vacancy production.