Selective Deposition of Mo2C-Containing Coatings on {100} Facets of Synthetic Diamond Crystals

Abstract

An efficient way to improve the properties of metal–diamond composites (mechanical strength, wear resistance, thermal conductivity) is the preliminary modification of the diamond surface to improve its wettability by the metal matrix. In the present work, Mo2C-containing coatings were deposited on the diamond crystals under different conditions: hot pressing (atmosphere of argon), spark plasma sintering (forevacuum), and annealing in air. The influence of the sintering parameters on the morphology and phase composition of the coatings deposited on diamond was studied. Mo2C-containing coatings were selectively deposited on the facets of synthetic diamond microcrystals by annealing of the latter with a molybdenum powder. Experiments were carried out to deposit coatings under different conditions: during hot pressing (argon atmosphere), spark plasma sintering (forevacuum), and annealing in air. The process parameters were the temperature, holding time, and concentration of molybdenum in the initial mixture. Experiments with a pre-oxidized molybdenum powder were also conducted. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The deposition was enabled by the gas phase transport of molybdenum dioxide, MoO2, contained in the starting powder. The following sequence of the coating formation stages was proposed. First, MoO2 sublimes and is adsorbed mainly on the {100} facets of diamond. Then, it is reduced to metallic molybdenum by carbon of the diamond, which further reacts with carbon to form the Mo2C carbide phase. These processes occurred during treatment of the mixtures in the hot press and the spark plasma sintering facility. When the mixture was annealed in air, no selective deposition was observed. During annealing, MoO3 particles adhered to the diamond surface.

The Influence of the Carbide-Forming Metallic Additives (W, Mo, Cr, Ti) on the Microstructure and Thermal Conductivity of Copper–Diamond Composites

“…It appears possible that the SPS conditions of consolidation can promote a homogeneous distribution of Ti in the copper matrix, which can facilitate uniform wetting of diamonds by the copper matrix. For example, in the study of the formation of Mo-containing coatings on diamond [29], it was found that, under the SPS conditions, a more homogeneous coating was deposited on the surface of diamond particles than under the HP conditions. This can be influenced both by the passage of electric current and by the atmosphere (vacuum in the SPS and argon in the HP).…”

Selective deposition of silver particles on {111} or {100} diamond facets

“…The carbide phases formed in the coatings during annealing of diamond crystals with these metals. 26,27 The studies presented in ref. 28 and 29 should also be mentioned in this context.…”