Si and Cr doping effects on growth and mechanical properties of ultrananocrystalline diamond/amorphous carbon composite films deposited on cemented carbide substrates by coaxial arc plasma deposition

Si and Cr doped ultrananocrystalline diamond/amorphous carbon composite films were deposited on cemented carbide (WC-Co) substrates by using coaxial arc plasma deposition with Si and Cr blended graphite targets. The undoped films deposited at room temperature and a repetition rate of arc discharges of 1 Hz have the maximum hardness of 51 GPa and Young’s modulus of 520 GPa. With increasing substrate temperature and repetition rate, the hardness and modulus are degraded, which might be because the growth of sp² bonds is thermally enhanced. The doping of Cr and Si degrades the hardness and modulus. From energy-dispersive X-ray spectroscopic measurements, the diffusion of Co atoms from the substrates into the films were observed for the Si-doped films. Since the Co diffusion induce the graphitization due to the catalytic effects, the degraded hardness and modulus of the Si doped films should be attributable to the catalytic effects of Co. For the Cr-doped films, the degraded hardness and modulus might be because of the Co catalytic effects being enhanced by the bombardment of Cr atoms whose atomic weight is much larger than that of C and the formation of chromium carbide.