Morphological features and phase composition of W-containing coatings formed on diamond via its interaction with WO3

Abstract

In the present work, W-containing coatings were deposited on the surface of diamond microcrystals. The coatings formed as diamond reacted with a WO3 powder in the die of a hot press at elevated temperatures. The morphology and phase composition of the coatings were studied as functions of the treatment temperature and treatment time. The coated diamond crystals were investigated by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. After treatment of the mixture at 850 °C for 15 min, WO2 and W18O49 were found on the diamond surface. After treatment at 950 °C (15 min), tungsten was the dominant phase of the coating. Treatment at 1150 °C (15 min) led to the formation of the WC and W2C phases; no metallic tungsten was present in the coating obtained at this temperature. The reaction sequence describing the coating formation process was proposed. During the coating formation, the deposition selectivity with regard to the diamond facet was observed. The {100} facets of diamond were preferentially coated. The coating developed through the formation and coalescence of islands, which were of square shape on the {100} facets and of triangular shape on the {111} facets of diamond.