Effects of surface pretreatments on the deposition of adherent diamond coatings on cemented tungsten carbide substrates

Well-adhered microcrystalline diamond (MCD) coatings have been deposited on WC–Co substrates by the microwave plasma enhanced chemical vapor deposition (MPECVD) method. A multi-interlayer system Cr/CrN/Cr was deposited on the cemented carbide substrate before diamond deposition to act as a diffusion barrier. The interlayer-coated substrate was shortly peened by friable diamond powders with an average size of 150 μm to roughen the surface. Diamond coatings deposited on short peened substrates show higher nucleation density and stronger adhesion properties. The X-ray diffraction (XRD) pattern showed that an additional carbide compound layer (Cr3C2 and Cr7C3) was formed during the CVD diamond deposition to work as an intermediate bonding layer for better adhesion. Rockwell indentation tests with a load of 1470 N were conducted to investigate the coating's adhesion. No delamination outside of the indentation zone was observed for the diamond coating deposited on the roughened sample. Electron probe microanalysis (EPMA) results showed that the delamination in the indentation zone occurred mainly at the diamond/Cr interface and very little Co (less than 1 wt.%) was detected on the Cr failure surface. This suggests that during the CVD process Co/C inter-diffusion was successfully prevented by the Cr/CrN/Cr buffer layers.