Masatoshi Sakurai

Room-temperature hard coating of ultrananocrystalline diamond/nonhydrogenated amorphous carbon composite films on tungsten carbide by coaxial arc plasma deposition

Ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite films were deposited on unheated WC containing Co by coaxial arc plasma deposition. The hardness of the film is 51.3 GPa, which is comparable with the highest values of hard a-C films deposited on nonbiased substrates. The deposited film is approximately 3 µm thick, which is one order larger than that of hard a-C films. The internal compressive stress is 4.5 GPa, which is evidently smaller than that of comparably hard a-C films. The existence of a large number of grain boundaries in the UNCD/a-C film might play a role in the release of the internal stress.

Fabrication of ultrananocrystalline diamond/nonhydrogenated amorphous carbon composite films for hard coating by coaxial arc plasma deposition

Ultrananocrystalline diamond (UNCD)/nonhydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were deposited on cemented carbide (WC-Co) substrates by coaxial arc plasma deposition (CAPD). To suppress the graphitization induced by Co in the WC-Co, the film deposition was carried out on unheated substrates. The hardness and Young’s modulus were 51.3 GPa and 520.2 GPa, respectively. These values are comparable or rather larger than those of UNCD/a-C films deposited on other substrates such as Si, which implies that the graphitization of UNCD/a-C hardly occurs. Surprisingly, UNCD/a-C films could be deposited at the maximum film thickness of approximately 3 μm in spite of the room temperature growth. The internal compress-stress of the film is approximately 4.5 GPa, which is evidently smaller than that of comparably hard a-C films. The existence of a large number of grain boundaries in the films, which is structural specific to UNCD/aC, might play an important role in the release of an internal stress in the film. It was experimentally demonstrated that UNCD/a-C films prepared by CAPD are potential hard coating materials for WCCo.

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 Sidoped 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. It was found that the doping of Si and Cr for the deposition of UNCD/a-C films deposited on WC-Co by CAPD is not effective for the improvement of the hardness and modulus