Lattice disorder and texture in diamond coatings deposited by HFCVD on Co-cemented tungsten carbide

Diamond coatings were deposited by hot filament chemical vapour deposition on 5.8 wt.% Co-cemented tungsten carbide (WC-Co). Under the same deposition conditions, two sets of samples were produced by varying the CH4 percentage (0.5 and 1.0%) in the H-2 atmosphere, and changing the substrate temperature in the range 650-950 degrees C. The effect of different CH4 percentage and of temperature on diamond microstructure was investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). In particular, pole figure measurement and line profile analysis (LPA) were used to study diamond texture and lattice disorder, respectively. Diamond grains were not preferentially oriented for deposition temperatures below 800 degrees C. Above this temperature, a [111] fibre texture developed in samples deposited with 0.5% CH4 in H-2. The XRD profile broadening indicated a marked increase of lattice disorder in the diamond him with increasing deposition temperature. This observation was correlated with the Raman peak broadening, also attributed to lattice disorder effects. A detailed LPA showed a decrease of crystallite mean size and a corresponding microstrain increase with raising temperature, although SEM morphological observations indicated a progressive grain coarsening at higher deposition temperatures.