Negative bias effects on deposition and mechanical properties of ultrananocrystalline diamond/amorphous carbon composite films deposited on cemented carbide substrates by coaxial arc plasma

Abstract

Ultrananocrystalline diamond/amorphous carbon composite (UNCD/a-C) films were deposited on negatively biased cemented carbide (WC-Co) substrates by coaxial arc plasma deposition. The deposition rate is increased to be 0.9 nm/s, which is approximately 3 times larger than that of films deposited under no bias condition. In addition, the critical load in scratch tests was enhanced to be 31 N, which is 4 times more than that of the no bias films. On the other hand, the hardness was slightly degraded by employing the negative bias. From electrical diagnostics of the bias application, it was found that the negative bias is immediately compensated by the arrival of highly-dense positive carbon ions at the substrate and the substrate is weakly positively charged after the compensation. This might be the main reason for the degraded hardness by the bias application, Since the positive bias deaccelerate carbon ions, which facilities the formation of sp2 bonds.