Synthesis of ultra-smooth and ultra-low friction DLC based nanocomposite films on rough substrates

Abstract

Rough TiC/a-C films were intentionally grown on smooth surface to simulate a rough finishing of industrial substrates. Surface roughness and growth dynamics of TiC/a-C nanocomposite films deposited on such rough surfaces by non-reactive pulsed-DC (p-DC) sputtering of graphite targets at 350 kHz pulse frequency were studied using atomic force microscopy, cross-sectional scanning electron microscopy. Intensive concurrent ion impingement during the film growth at higher pulse frequency of p-DC sputtering leads to rapid smoothing of such initial rough surfaces. It was shown that rapid smoothing of initially rough surfaces with RMS roughness ~ 6 nm to < 1 nm can be effectively achieved by 350 kHz p-DC sputtering. These films exhibit dense and glassy microstructure. The surface roughness strongly influences the frictional behavior of TiC/a-C nanocomposite films where the rougher surfaces yielded higher steady state friction coefficient (CoF). The observed dynamic smoothing phenomenon was applied to obtain ultra-smooth and ultra-low friction (μ ~ 0.05) TiC/a-C:H nanocomposite films on industrial polished steel substrates by 200 and 350 kHz p-DC sputtering of Ti-targets in an argon/acetylene atmosphere.