MPCVD diamond coating of Si3N4–TiN electroconductive composite substrates

A study of microwave plasma (MPCVD) diamond deposition on Si3N4–TiN composites with different TiN amounts (0–30 vol.% TiN) is performed. These ceramic composites are requested in order to obtain a suitable material to be cut by electrodischarge machining (EDM), aiming their use as substrates for cutting tools and tribological components. TiN is an electrical conductor, contrarily to Si3N4, but it is characterized by a higher thermal expansion coefficient value than Si3N4 and diamond. The estimated thermal stresses are found to be low and tensile (0.90 GPa) when using the monolithic Si3N4 substrate, but compressive for the Si3N4–TiN composites, and even relatively high in magnitude (− 1.9 GPa) for the Si3N4–30 vol.% TiN composite. Brale indentation assessed the adhesion strength of diamond on the different substrate grades. Optimal behaviour (very low residual stress; no film delamination under 1000 N) is observed for the Si3N4–9 vol.% TiN substrate, corresponding to the lowest thermal mismatch and minimal residual stress magnitude.