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A simple process for depositing a coating of silicon carbide (SiC) crystallites ∼10 nm in size onto diamond particles has been developed. SiO powders react with diamond in a vacuum at 1350°C to form a uniform β‐SiC polycrystalline layer ∼60 nm thick. The SiC coating improves the oxidation resistance of the diamond. A cemented carbide material containing 20‐vol%‐SiC‐coated diamond particles was sintered to a relative density of 99.5% by pulsed‐electric‐current sintering. A Vickers hardness and indentation fracture toughness of 15 GPa and 16.3 MPa·m1/2, respectively, were obtained. This toughness is two times higher than that of cemented carbide containing no particles. The higher toughness is attributed to deflection and blockage of crack propagation by the diamond particles.

Diamond particles were coated with a thin SiC layer by the reaction of SiO vapor with diamond, and the growth mechanism of SiC as well as the oxidation resistance of the SiC‐coated diamond were studied. The growth process of the SiC layer can be separated into two steps. In the first step, a thin layer of SiC with a thickness of about 15 nm is formed due to the reaction between SiO vapor and diamond. In the second step, nanometer‐sized SiC granules are deposited on the SiC layer by the reaction between SiO vapor and CO. The apparent activation energy for the formation of SiC layer on diamond was found to be 100 kJ/mol. This value suggests that the SiC coating process occurred mainly by vapor‐phase reaction. The oxidation resistance of the SiC‐coated diamond was improved depending on the thickness of the SiC layer. Oxidation of the SiC‐coated diamond particles began at 950°C, which was 400°C higher than that of uncoated diamond.