Tribological effects of nitrogen implantation on hard chromium coatings

Nitrogen implantation at optimum doses improved the wear resistance under high loads by a factor of four. A parallel enhancement of about 40% in hardness was also achieved when determined using a Vickers indentor at 5 g load. Auger spectroscopy revealed a maximum 47 at% nitrogen at the optimum dose for wear resistance improvement. X-ray photoelectron spectroscopy indicated that most of the nitrogen was bound to chromium as a nitride; however, chromium spectra showed that less than 50% of the chromium is bound to nitride at a depth close to the maximum of the nitrogen distribution. This suggests that implantation creates a dispersion of nitrides with the chromium matrix, which explains the benefits in wear resistance. Nitrogen implantation introduces compressive stress but these stresses are not suficiently high to close the inherent microcracks of the deposit. Nitride precipitation improves the load bearing capacity of the surface, reducing abrasion and running-in friction. Steel H-13 was the substrate.