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Abstract: Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH4/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp2 carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus. [Copyright &y& Elsevier]

Abstract: Diamond-like carbon (DLC) films were deposited on Si (100) wafers by a plasma enhanced chemical vapor deposition (PECVD) technique using CH4 plus Ar as the feedstock. The friction and wear behaviors of the resulting film sliding against Si3N4 balls were investigated on a ball-on-disk test rig in air and nitrogen environments at a relative humidity from 5% to 100%. The worn surface morphologies of the DLC film and the Si3N4 counterpart were observed on a scanning electron microscope (SEM), while the chemical states of some typical elements thereon were investigated by means of X-ray photoelectron spectroscopy (XPS). It was found that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity in air. It showed linearly increased friction coefficient with increasing relative humidity in nitrogen, in this case the wear rate sharply decreased and reached the minimum at a relative humidity of 40%, which was followed by an increase with further increase of the relative humidity. The interruption of the transferred carbon-rich layers on the Si3N4 balls, and the friction-induced oxidation of the films in higher relative humidity were proposed to be the main reasons for the increases of the friction coefficient and wear rate. Moreover, the oxidation and hydrolysis of the Si3N4 ball in higher relative humidity, leading to the formation of a tribochemical film that mainly consists of silica gel on the wearing surface, were also thought to have effects on the friction and wear behaviors of the DLC films. [Copyright &y& Elsevier]

Abstract: Friction and wear behaviors of diamond-like carbon (DLC) film sliding against steel ball were investigated on a ball-on-disk test rig at different relative humidity (RH) in a nitrogen environment. The worn surface morphology of the steel ball was observed on a scanning electron microscope (SEM), while the chemical states of some typical elements on the worn surface of DLC film were investigated by means of X-ray photoelectron spectroscopy (XPS). The result showed that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity from 5% to 100%. In dry nitrogen (RH<5%), thick and compact transferred carbon-rich layer was observed covering on the worn surface of steel ball, while the chemical states of the original and worn film surface showed no obvious change. In humid nitrogen, distinct changes of the chemical states on the worn surface of DLC film took place, indicating that tribochemical reactions such as the oxidation of DLC film and the interactions between DLC film and steel ball were involved in the friction process. Therefore, it was proposed that the friction and wear behaviors of DLC film were dependent on the friction-induced physical and chemical interactions among DLC film, steel ball and water and/or oxygen molecules. The roles of environment in the friction and wear behaviors of DLC film were discussed in terms of the friction-induced physical and chemical interactions. [Copyright &y& Elsevier]