MPCVD diamond coating of Si 3N 4–TiN electroconductive composite substrates

Abstract

A study of microwave plasma (MPCVD) diamond deposition on Si 3N 4–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 Si 3N 4, but it is characterized by a higher thermal expansion coefficient value than Si 3N 4 and diamond. The estimated thermal stresses are found to be low and tensile (0.90 GPa) when using the monolithic Si 3N 4 substrate, but compressive for the Si 3N 4–TiN composites, and even relatively high in magnitude (− 1.9 GPa) for the Si 3N 4–30 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 Si 3N 4–9 vol.% TiN substrate, corresponding to the lowest thermal mismatch and minimal residual stress magnitude.