Microstructure and wear behaviour of chromium nitride films formed by ion-beam-enhanced deposition

Chromium nitride films were deposited on AISI 52100 steel substrates by chromium evaporation and simultaneous nitrogen ion beam irradiation, either by varying the arrival ratio of Cr to N atoms at the substrate while keeping the N ion beam current constant, or by varying the ion beam current while keeping the Cr/N arrival ratio constant. Glow discharge spectroscopy analyses show that the Cr/N ratio of the films is strongly affected not only by the Cr/N arrival ratio but also by the N ion beam current. X-ray diffraction analyses show that the crystalline structure of the films changes from CrN for a film with low Cr/N ratio to Cr 2N for a film with high Cr/N ratio. Although the friction coefficient of the films against an untreated AISI 52100 steel pin does not decrease much from that of the untreated substrate, the wear characteristics are greatly improved. Regarding the influence of the process conditions on the wear characteristics, a small amount of wear is achieved for the films with Cr/N arrival ratios of 1/1 and 1.5/1, which have both high hardness and good adhesion to the substrate.