COMPARATIVE-STUDY OF CRN COATINGS DEPOSITED BY ION PLATING AND VACUUMARE EVAPORATION - INFLUENCE OF THE NATURE AND THE ENERGY OF THE LAYER-FORMING SPECIES ON THE STRUCTURAL AND THE MECHANICAL-PROPERTIES

CrN coatings are obtained by ion plating (IP) and by vacuum are evapor ation (VAE) in identical deposition chambers. The parameters governing the growth mechanisms are systematically controlled and measured duri ng the deposition process, i.e. the nitrogen pressure p(N2), the bias voltage V-s, and the substrate temperature T-s. During all the deposit ion time, T-s is kept constant. A comparison of the substrate ionic cu rrent densities and the corresponding deposition rate allows to specif y the nature and electrical state of the layer forming species: molecu lar 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 beta-Cr2N 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 th e deposition temperature. However, this dependence is more important f or VAE deposited films than for those obtained by IP. The structure an d texture appear to be very sensitive to V-s, in particular in VAE. Th is is due to the sputtering effect by the chromium ions. As a conseque nce, the internal stress level and the mechanical properties depend mo re strongly on V-s in VAE than in IP. The grain size of the films obta ined 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 obtain ed 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. (C) 19 97 Elsevier Science S.A.