Phase Composition and Distribution of Ni-, Co-, Fe-, Mn-, and Cr-Based Inclusions in Carbonado Polycrystals

The phase composition and distribution of inclusions of the Ni, Co, Fe, Mn, and Cr metal catalysts in carbonado polycrystals 8 mm in diameter were studied. The polycrystals (>90 wt % diamond) were found to contain inclusions of solid solutions of carbon in Ni and Co and the carbides Fe₃C, Mn₅C₂, and Cr₃C₂. The concentration of inclusions was shown to increase with distance from the catalyst insert. The results are interpreted in terms of the model for the growth of polycrystalline diamond via corrugation of graphite layers, their dissolution in the catalyst melt owing to structural matching with its fcc lattice, and stabilization of the diamond structure at high supersaturations in the p–T stability region of diamond.