Adherent nanocrystalline diamond coatings deposited on Ti substrate at moderate temperatures

Microwave plasma enhanced CVD deposition of adherent nanocrystalline diamond coating on pure Ti substrate was studied at a moderate temperature and with a wide range of CH4 concentrations. Under low CH4 concentrations, the adhesion failure of diamond coatings is primarily observed at the titanium carbide–substrate interface. Under higher CH4 concentrations, the diamond coating debonding occurs both at the diamond–carbide interface and carbide–substrate interface. On the whole, the nucleation density, nucleation rate and adhesion strength of diamond coatings grown on Ti substrate are enhanced with increasing CH4 concentrations. Synchrotron X-ray Laue micro-beam diffraction characterization of the underlying Ti substrate reveals that a microstructure coarsening occurs after hydrogen plasma etching, whereas the hydrogen penetration is effectively mitigated under super high CH4 concentrations.