CUBIC NITRIDES OF THE 6TH GROUP OF TRANSITION-METALS FORMED BY NITROGEN ION IRRADIATION DURING METAL CONDENSATION

Nitrogen-containing phases of chromium, molybdenum and tungsten were f ormed by evaporation of the metal under simultaneous nitrogen ion irra diation. With gradually increasing ion irradiation intensity, chromium forms initially Cr and Cr2N phase mixtures, then additionally CrN app ears, and at the highest intensities pure CrN films are formed. Molybd enum also forms pure nitride MoN under intense ion bombardment. Howeve r, in this case two different crystal structures are found, the stable hexagonal phase and the metastable cubic high-temperature phase. The latter is favoured under intense ion irradiation. In the case of tungs ten, even at the highest intensities, only phase mixtures of W and W2N were formed. These observed differences can be explained by the low r eactivity of these metals towards nitrogen and the low chemical stabil ity of the nitrides, particularly of WN. The metastable high-temperatu re structure of MoN is formed under the particular conditions of ion b ombardment with rapid energy dissipation.