Comparative study of CrN coatings deposited by ion plating and vacuum arc evaporation. Influence of the nature and the energy of the layer-forming species on the structural and the mechanical properties

Abstract

CrN coatings are obtained by ion plating (IP) and by vacuum arc evaporation (VAE) in identical deposition chambers. The parameters governing the growth mechanisms are systematically controlled and measured during the deposition process, i.e. the nitrogen pressure p N2, the bias voltage V s, and the substrate temperature T s During all the deposition time, T s is kept constant. A comparison of the substrate ionic current densities and the corresponding deposition rate allows to specify the nature and electrical state of the layer forming species: molecular nitrogen ions and chromium atoms with low energy for IP, molecular nitrogen and chromium ions for VAE. The nitrogen pressure governs the phase composition of the film. A mixture of β-Cr 2N and CrN phases and a pure CrN phase are successively observed when p N2 is increased. In both cases the structure and morphology of the films depend on the deposition temperature. However, this dependence is more important for VAE deposited films than for those obtained by IP. The structure and texture appear to be very sensitive to V s, in particular in VAE. This is due to the sputtering effect by the chromium ions. As a consequence, the internal stress level and the mechanical properties depend more strongly on V s in VAE than in IP. The grain size of the films obtained by VAE (about 10 nm) is lower than that of the IP deposited films (about 15 nm). As a consequence the microhardness of the films obtained by VAE (30 GPa) is greater than that of the IP deposited films (21 GPa). The two kinds of coatings exhibit a high wear resistance.