The effect of nitrogen ion implantation on the impact wear of several metals and alloys with different hardnesses was studied. An impact testing machine was built for this study. In this machine, bullet-shaped projectiles are bounced against a metal surface which is either stationary or rotating. Wear was determined by weight loss measurements. Scanning electron microscopy pictures were taken to study the surface damage. It was found that nitrogen ion implantation improved the impact wear of most of the materials studied. With sliding motion added during the impact, nitrogen ion implantation has little effect. © 1985.