Low energy, high current density ion implantation of materials at elevated temperatures for tribological applications

Low energy, high current density ion implantation at elevated temperatures has been shown to improve significantly the tribological properties of various materials. This paper summarizes the results published previously in this research area and presents some new results. Comparisons of this technique are made with ion nitriding and high energy ion implantation conducted under similar conditions (treatment temperature, treatment time and so on) on austenitic stainless steel and tool steel materials. The microstructural analyses and tribological evaluations presented here show that all three techniques generate almost identical microstructures on each metal studied, but low energy ion implantation produces treated layers with higher nitrogen concentrations and deeper diffusion, leading to higher wear resistance. A physical model is proposed to explore the mechanisms for these advantageous phenomena. The analysis suggests that a high current density is the primary mechanism responsible for the formation of deep nitrogen-containing layers. The ion energy is of secondary importance, as long as it is sufficiently high to overcome certain surface barrier potentials, to allow the removal of native oxide layers, to prevent surface oxidation and to allow the build-up of a high concentration of atomic nitrogen on the top of the treated surface to facilitate subsequent fast diffusion. Some applications and limitations of this technique are also addressed. It seems evident that low energy implantation (slightly higher than for ion nitriding, but much lower than for high energy ion implantation) at high current densities (much higher than those used in both ion nitriding and high energy implantation) generates superior nitrogen-containing layers on many materials, and hence the superior tribological performance compared to the other two techniques.