Unveiling the formation of Mo2C coating on diamond particles along with anisotropic etching by Mo powder

Diamond has been widely used as reinforcing phases in diamond tools and thermal management materials owing to its high hardness and thermal conductivity. However, the surface inertness of diamond inhibits the formation of tight bonding between diamond and matrix, leading to performance of diamond-reinforced composites significantly declined. However, the formation of carbide coatings with good wetting on the diamond may serve as a bridge for optimizing the interfacial bonding of composites. Accordingly, Mo2C coatings were prepared by the molten salt method. Key parameters influencing the coating quality were investigated systematically to shed light on the growth mechanism. Using Mo powder as the Mo source, triangular and square etching pits were formed on diamond (111) and (100) surfaces, serving as nucleation sites for carbides. Mo2C grains nucleated and grew to gradually fill the pits. After simultaneous etching and growth, Mo2C coatings completely covered the surface of the diamond, with thicknesses estimated to 410–420 and 550–600 nm for (111) and (100) surfaces, respectively. Features like the growth rate of carbide, as well as the structure of the etching pits and Mo2C coatings, were found all crystal orientation dependent. The thermal shock and oxidation tests confirmed the effectiveness and affinity of as-prepared Mo2C coatings. The paper provides novel insights into the growth mechanism of Mo2C coating on the diamond from Mo powder source, promising for future syntheses.