Surface analysis, ion implantation and tribological processes affecting steels

Abstract

An analytical approach is presented for investigating surface processing treatments used to improve the friction and wear (i.e., tribological) behavior of engineering alloys, with specific examples cited for ion implantation of steels. Surface composition techniques such as scanning Auger microscopy, energy dispersive X-ray analysis and secondary ion mass spectroscopy and microscopies such as transmission electron microscopy (TEM), secondary electron microscopy and interferometry have eluciated the microstructure and chemistry of a variety of implant species (N, C, Ti and Ta) found to affect the tribological behavior of surfaces. Novel combinations of these techniques, along with metallography of ion-etched surfaces or TEM of ion-beam-etched foils, are shown to be useful methods for establishing microstructures of ion-implanted and worn surfaces. The tribological behavior of the thin implanted layer (∼ 200 nm) is examined by two devices: a stickslip machine and a polishing wear apparatus, the latter having wear rate versus depth resolution of 10 to 20 nm. Tribology studies of two implanted steels, 304 stainless steel and 52100 bearing steel, are presented, and analytical investigations which have led to models for their improved wear behavior are described. A process by which implanted metal ions can react with residual gases in the vacuum chamber to “carburize” steel and produce superior tribological surfaces is also discussed.