Features of the Formation of an Interface Zone Structure during Thermal Diffusion Metallization of Diamond by Transition Metals

Abstract

The features of the morphology and chemical and structural-phase compositions of the diamond–metal interface zone formed in the process of thermal diffusion metallization of diamond by chromium, titanium, iron, nickel, and cobalt powders under the same temperature–time mode of the vacuum furnace operation that corresponds to the mode of sintering of diamond-containing WC–Co matrix with copper impregnation are studied. In the process of thermal diffusion metallization by chromium and titanium, a metalized coating is formed on the diamond surface, consisting of a phase mixture of carbides, metals, and graphite of variable composition. The small content of graphite formations and their discontinuous character of location in the diamond–metal interface zone ensure a strong adhesion of the metalized coating to the diamond through the carbides of the corresponding metals. During thermal diffusion metallization by iron, the intermediate layer strongly adhering to the diamond is also formed in the diamond–metal interface zone. The intermediate layer has a complex structural-phase composition comprising a mixture of iron phases, a solid solution of carbon in iron, and graphite of variable composition. An assumption is made that the intermediate layer could be formed on the surface of diamond grains by solidification of the liquid phase with eutectic composition, resulting from the eutectic melting of the diamond–iron contact pairs. However, the confirmation of this assumption requires performing special experiments using highly sensitive methods of research. Under the heating conditions specified in the experiment, the nickel–cobalt and cobalt–diamond interaction causes intense catalytic graphitization of diamond followed by the formation of numerous traces of erosion on its surface. The observed weak adhesive interaction of these metals with diamond is likely to be determined by the high melting temperatures of the Ni–C and Co–C eutectics, which does not allow the metals to react with diamond actively under the specified experimental conditions.