On the Inhibition of Metal Transfer by Ion Implantation

Metal transfer is a phenomena associated with adhesive wear during dry-sliding, boundary lubrication, and elastohydrodynamic lubrication. Coatings, lubricants, and proper wear couple selection are traditionally implemented to reduce metal transfer. Ion implantation is a surface modification technique that has been studied for over 30 years with the goal of improving tribosurfaces. It has the following advantages over traditional techniques: it is a non-equilibrium process in that any element can literally be implanted into a surface, is non-evasive in that bulk material chemistry, structure, dimensionality is unaltered, and coating adhesion is not a factor. The goal of this study was to attempt to study the reduction in metal transfer by ion implantation using a single-pass, 1100-O Al pin on implanted ISF steel disk wear test. Characterization/analysis was performed with electron microscopy, surface analysis, profilometry, and Density Function Theory. We have shown that ion implantation of nitrogen, carbon and sulfur reduces metal transfer through the combination of mitigating two independent processes: a two-body processes involving adhesion at the surface and a complicated three-body process, known as the Mutual Material Transfer mechanism, which is affected by the amount of debris tribooxidation. The reduction in adhesion results from the weakening of a mixed layer between the aluminum and implanted surface through the incorporation of the implanted impurities in that layer. The incorporation of implanted material wear particles into the wear debris mitigates the three-body process because these particles lose their metallicity through implantation and subsequent oxidation during wear-testing resulting in “less metallic” debris. With this contribution, it is hoped that a better understanding of metal transfer and the effect of ion implantation on the tribology of surfaces will be put forth