Bilayered coatings of BN/diamond grown on Si3N4 ceramic substrates

Cubic boron nitride (c-BN) is a well known material to be used in machining of ferrous metallic alloys, namely as a coating. However, in most practical cases, there is a lack of adhesion to the substrate material. In this work, BN coatings were deposited by magnetron sputtering on silicon nitride (Si3N4) ceramic substrates using an intermediate layer of CVD microcrystalline (MCD) or nanocrystalline diamond (NCD). The goal was to improve the c-BN content by using diamond interlayers, and to optimize film adhesion to the substrate by employing such ceramic, which is known to provide very high adhesion strength to CVD diamond. The BN/NCD/Si3N4 combination demonstrated to be unique regarding the absence of delamination at both the BN/diamond and diamond/substrate interfaces, also providing the highest c-BN phase content.

Research Highlights
► BN coatings were successfully grown by magnetron sputtering from a h-BN target.
► The c-BN phase content is highly enhanced by a CVD nanocrystalline diamond underlayer.
► Nanocrystalline diamond offers higher BN adhesion than microcrystalline underlayers.