PHYSICOCHEMICAL INTERACTION AND STRUCTURE DEVELOPMENT DURING THE FORMATION OF METAL GAS-TRANSPORT COATINGS ON DIAMOND (REVIEW) .2. MECHANISM

Formation of chromium, titanium, molybdenum, vanadium, and tungsten coatings on diamond under various metallizing conditions and with different phase compositions of the metal sprays is studied. In the initial stages this process is controlled by the interaction of the diamond (carbon) surface with metal oxides through the gas phase as well as by diffusion of the metal spray. After formation of a continuous layer further coating growth is controlled by carbon diffusion. A reduction in the rate of mass transfer to the reaction surface and the rate of carbon yield from it are factors which limit coating growth. The former is connected with depletion of the metal spray; with a decrease in volatile phase flow, and reduction of MoO3, V2O5, and WO3, as well as with their removal during pumping; a reduction of the dissociation and disproportioning rate of the oxides; retardation of metal ion diffusion in the metal spray and appearance of oxides (V2O3, VO, Ti2O3, TiO, etc.) in it which interact weakly with carbon. Emergence of carbon at the surface is specified by its inhibition under diffusion in the growing layer of the coating, filling of carbon vacancies in carbide (TiC, VC) lattices, carbidization of metal, and transformation of lower carbides into higher forms.