High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W2C–WC. The average roughness, R a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m−1 K−1 are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 107 W m−2 K−1. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.