Abstract
The purpose of the present work is to probe the friction mechanism of hydrogenated diamond-like carbon (H-DLC) film in air by varying sliding velocity (25–1000 mm/s). Friction tests of Al2O3 ball against H-DLC film were conducted with a rotational ball-on-disk tribometer. As the sliding velocity increases, both the friction coefficient and the surface wear of H-DLC film decrease, reach the minimum values, and then increase in the high sliding velocity region. Based on the observed results, three main friction mechanisms of H-DLC film—namely graphitization mechanism, transfer layer mechanism, and passivation mechanism—are discussed. Raman analysis indicates that the graphitization of worn surface on the H-DLC film has a negligible contribution to the variation of the friction coefficient and the surface wear. The origin of the sliding velocity dependence is due to the synergistic interaction between the graphitized transfer layer formation and the surface passivation. The present study will not only enrich the understanding of friction mechanism of H-DLC films in air, but will also help to promote their practical engineering applications.
Highlights
Over the past few decades, energy and material losses caused by friction and wear in machine elements have given rise to the huge economic and environmental burdens for all countries [1].lots of low-friction materials, coatings, and lubricants have been prepared and discovered to regulate the process of friction and wear in machine elements [2,3]
It is noted that the friction coefficient of the diamond-like carbon (DLC) films increased from 0.07 to 0.22 with increasing of sliding velocity in air, and the reason is due to the entrapment of more debris particles at the sliding interface [18]
Previous studies [27,28] reported that the hydrogenated diamond-like carbon (H-DLC) material beneath worn surface could be graphitized under shear and compression stresses, and the higher graphitization degree resulted in a lower friction coefficient
Summary
Over the past few decades, energy and material losses caused by friction and wear in machine elements have given rise to the huge economic and environmental burdens for all countries [1].lots of low-friction materials, coatings, and lubricants have been prepared and discovered to regulate the process of friction and wear in machine elements [2,3]. The effect of sliding velocity on the friction characteristics of DLC films has been extensively studied, giving rise to a large amount of diverging findings [15,16,17]. It is noted that the friction coefficient of the DLC films increased from 0.07 to 0.22 with increasing of sliding velocity in air, and the reason is due to the entrapment of more debris particles at the sliding interface [18]. Some studies reported that the friction coefficient of H-DLC film decreased from 0.13 to 0.007 with the increase of sliding velocity, and the reason was attributed either to the removal of adsorbed water layer or the increase of the graphitization degree at the sliding interface [19,20]. Based on the above research, the effects of sliding velocity on the friction and wear characteristics of DLC films are still not well understood
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