Effect of TiAl-based interlayer on the surface morphology and adhesion of nanocrystalline diamond film deposited on WC–Co substrate by hot filament CVD

The effect of various interlayers of TiAl, TiAl/TiAlN, and TiAl/TiAlN/TiAl on the surface morphology and adhesive strength of nanocrystalline diamond (NCD) film on WC–Co substrate was investigated in this study. NCD film was deposited on WC–6 wt.% Co substrate by hot filament CVD (HFCVD) technique with H2–5 vol.% CH4 gas mixture. In contrast to the NCD film deposited on the TiAl terminated interlayers (TiAl and TiAl/TiAlN/TiAl) showing flat surface morphology, hump structure (like cauliflower) was observed for the NCD film deposited on the TiAlN terminated interlayer (TiAl/TiAlN). The surface morphology and adhesion behavior of NCD film deposited on WC–Co substrate with various TiAl(N)-based interlayers were closely related to the nucleation density of NCD and Co diffusion from the substrate. The seed density was observed to be higher when we adopted the TiAl-terminated interlayer, whereas the Co diffusion from the WC–6 wt.% Co substrate was much more retarded by the incorporation of TiAlN into the interlayer. As a result, the adhesion improvement of NCD film was noticeable for the TiAl/TiAlN/TiAl-coated WC–Co substrate.