Se Jun Park

Effect of environment on the tribological behavior of Si-incorporated diamond-like carbon films

An experimental study was performed to discover the effect of environment on the tribological behavior of Si-incorporated diamond-like carbon (Si-DLC) film slid against a steel ball. The films were deposited on Si (1 0 0) wafers by a radio frequency glow discharge of mixtures of benzene and dilute silane gases. Experiments using a ball-on-disk test-rig were performed in vacuum, dry air and ambient air. It was observed that coefficient of friction decreased as the environment changed from vacuum to dry air. Results also showed that low and stable friction related closely to the smoothening of track surfaces and the formation of silicon-rich oxide debris.

Microstructure and mechanical properties of WC–C nanocomposite films

WC–C nanocomposite film was prepared by using a hybrid deposition system of r.f.-PACVD and DC magnetron sputtering. W concentration in the film was varied from 5.2 to 42 at.% by changing the CH fraction of the mixture sputtering gas of Ar and 4 CH . Hardness, residual compressive stress and electrical resistivity were characterized as a function of W concentration. Raman 4 spectroscopy, XRD and high resolution TEM were employed to analyze the structural change in the film for various W concentrations. In the present W concentration range, the film was composed of nano-sized WC particles of diameter less than 5 nm and hydrogenated amorphous carbon matrix. Content of the WC particles increased with increasing W concentration. However, the mechanical properties of the film increased only when the W concentration was higher than 13 at.%. Structural analysis and electrical conductance measurements evidently showed that the increase in hardness and residual stress occurred as the WC particles were in contact with each other in the amorphous carbon matrix. 2002 Elsevier Science B.V. All rights reserved.

Humidity dependence of the tribological behavior of diamond-like carbon films against steel ball

Diamond-like carbon (DLC) films deposited on Si(100) wafer by r.f.-plasma assisted chemical vapor deposition were friction tested by ball-on-disk type tribometer in various test environments. The friction tests were performed in an ambient air of relative humidity ranging from 0 to 90% or dry oxygen environment. We focused on the tribochemical reactions by analyzing the chemical composition, chemical bond structure and agglomerated shape of the debris. High and unstable frictional behavior was observed in both humid air and dry oxygen environment. In these environments, Auger spectrum analysis showed that the debris contained large amount of Fe. Significant incorporation of Fe in the debris resulted from the wear of the steel ball, which might be enhanced by the surface oxidation of the ball. However, a very low frictional coefficient was observed against the sapphire ball even in dry oxygen environment. These results show that the increased frictional coefficient of the DLC film is closely related with the increased Fe concentration in the debris. Hence, the humidity dependence of the frictional coefficient is not an inherent tribological property of DLC film but results from the surface reaction of the steel ball with humid environment. Two possible reasons for the Fe rich debris to affect the frictional behavior were suggested.

Tribological and electrochemical characteristics of DLC coatings with bias voltage

Diamond-like carbon (DLC) coatings were deposited on a STS 316L substrate by means of R.F plasma-assisted chemical vapor deposition (R.F PACVD) technique using benzene (C6H6) as a reaction gas. The tribological and electrochemical characteristics of the DLC coatings were investigated by a tribological technique (wear test) and by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy). Surface analyses of the DLC coatings were conducted by means of scanning electron microscopy and atomic force microscopy. This study provides reliable and quantitative data for an assessment of the effect of bias voltage on tribological and electrochemical characteristics in a simulated body fluid environment (0.89 wt.% NaCl of pH 7.4 at 37°C). From the results of the tribological and electrochemical techniques, wear and corrosion resistance of the DLC coatings were improved owing to the low surface roughness, low porosity and good adhesion strength. Among all DLC coatings in this experiment, the DLC coating with a bias voltage of −800 V showed better wear and corrosion resistance than did other coatings