We report the formation and development of the interface between diamond and nickel in partially densified compacts obtained from powder mixtures by Spark Plasma Sintering, hot pressing and conventional sintering at 700 and 900 degrees C - temperatures, which are well below the melting point of nickel and even below that of the nickel-graphite eutectic. The nickel particles sintered among themselves and formed joints with facets of the diamond crystals. Most of these joints fractured cohesively leaving Ni-containing patches on the diamond facets. The microstructure of the patches adhered to the diamond surface in compacts sintered at 900 degrees C and their geometry and orientation relative to the edges of the diamond facets suggest that the formation and development of the nickel/diamond interface are associated with melting and solidification of the melt according to certain directions of the diamond crystalline lattice. A possible explanation of the formation of a liquid at such a low temperature is contact melting of a metastable eutectic between nickel and diamond.
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