Nano to micrometric HFCVD diamond adhesion strength to Si3N4

In the present study, hot filament chemical vapour deposition technique was used to grow diamond films from nanometric to microcrystalline grain sizes. Their adhesion levels to a silicon nitride ceramic were compared after Brale tip indentation testing. The best behaviour was attained by the microcrystalline diamond (MCD) grade due to its higher crystallinity and superior hardness. In contrast, nanocrystalline diamond (NCD) coatings showed the less effective chemical bonding to the ceramic substrate due to the higher degree of sp2 content. The MCD coating supported a normal load of 1600 N without spalling-off and presented an interfacial crack resistance of 12.0 N μm−1, much better than that reported until the present. This behaviour may be attributed to the CF4 plasma pre-treatment of the substrate.