Two different low friction mechanisms of diamond-like carbon with silicon coatings formed by plasma-assisted chemical vapor deposition

Abstract

Diamond-like carbon with silicon (DLC-Si) coatings formed by plasma-assisted chemical vapor deposition showed low friction coefficients of the order of 0.01 against steel without a lubricant, not only in dry atmosphere but also in humid atmosphere, where conventional DLC coatings showed higher friction coefficients of 0.1-0.2. DLC-Si coatings with 1 fim thickness deposited on steel were slid against steel using a conventional ball-on-disk type of apparatus to compare with a low friction mechanism of DLC-Si in dry and humid atmospheres. Analyses of wear scars indicated that formation and/or transfer of graphite-like carbon including hydrogen that originated in a DLC-Si coating occurred in dry atmosphere, while oxidation of contained silicon with water vapor formed silica-sol by sliding in humid atmosphere. The latter, peculiar to DLC-Si, was considered to cause the low friction coefficient in humid atmosphere through adsorbed water on silica.

Repressing oxidative wear within Si doped DLCs

“…This increased friction for the Si,O,F doped DLC could be indicative of the formation of a mechanically hard tribofilm (37). The Si,O doped DLC does not show the reduced friction that may have been expected when compared to the a-C:H, as seen in dry sliding experiments (3,4). This however is in-line with literature precedents concerning Si-DLCs in lubricated contacts where SiDLCs friction reducing properties are markedly reduced (8,9).…”

“…The main mechanism for reduced friction in Si-DLC contacts is identified as being caused by production of SiOx species. These are often referred to as silicon rich oxide debris (2,4,11,38). This debris represents oxidative destruction and removal of Si within the coating which in turn amplifies wear of the DLC as a whole.…”

Small amplitude reciprocating wear performance of diamond-like carbon films: dependence of film composition and counterface material

“…DLC films are synthesized by ion-or plasma-47 based processes using hydrocarbon precursor gases and 48 therefore contain substantial amounts of hydrogen 49 (usually 10-50 atomic%). Techniques for DLC film 50 deposition include direct ion beam processes, plasma-51 enhanced chemical vapor deposition, and electron 52 cyclotron resonance CVD processes [1,[9][10][11]. DLC films 53 are amorphous with no long-range order, and the car-54 bon is present in both the hybridized sp 3 (diamond) and 55 sp 2 (graphite) bonding configurations, although sp 1 56 (polymeric) configuration has also been observed.…”

An Electrochemical Impedance Evaluation and Laser Irradiation Effects on the Electronic Structure of Silicon Containing Diamond-Like Carbon Coating

“…The friction coefficient of unlubricated DLC films in dry gases can be as low as 0.01, but this value can reach values as high as 0.10 and 0.20 when measured in a 10% relative humidity [1][2][3]. Various researchers [2][3][4] have shown that conventional DLC films doped with elements such as Si and Ti exhibit low pin-on-disk friction coefficients in humid environments. Amorphous DLC coatings have shown extremely smooth and dense surface morphology.…”

“…DLC films containing Si (Si-DLC) exhibit friction coefficients as low as 0.04 [2][3][4] at ambient humidity and temperature and are therefore highly promising for tribological applications. It has been also shown repeatedly that the adhesion of the Si-DLC coating on various substrates, including steel has been excellent [4].…”