Tribological Performance of Alternating-Layered Si-DLC/DLC Films Under Humid Conditions

Abstract

The tribological behavior of alternating-layered diamond-like carbon (DLC) films was examined under a variety of humid conditions. Alternating deposited layers with Si-incorporated DLC (Si-DLC) and DLC films were prepared using a hybrid coating system. The residual stress of the alternating-layered films was reduced while the hardness was relatively less dependent on the number of alternating-layered sets. A ball-on-disk type tribological test was carried out under the following humid conditions: dry, 50% and 90% relative humidity. The friction coefficient for higher number of alternating-layered sets decreased with increasing humidity conditions but there was no dependency on the wear rate.

Effect of Humidity on Friction and Wear—A Critical Review

“…There are several models to explain this superlubricity; the most highly cited mechanism assumes that the hydrogen-termination of the carbon surfaces leads to little or no chemical or physical interactions during sliding contacts [48][49][50]. However, the superlow COF cannot be maintained in humidity conditions and COF generally increases as the water vapor pressure rises, regardless of the chemistry or type of the counter friction material: a-C:H film [47][48][49]51,52], steel [41,45,[53][54][55][56][57][58][59][60][61][62][63] or ceramics [40,57,61,[64][65][66][67].…”

“…At early times, there are mainly two hypothesizes proposed to explain Since moisture has a negative effect on the friction and wear of a-C:H films, some efforts have been made to decrease the humidity dependence. The most widely used method is to produce Si-doped or Ti-doped DLC films [67][68][69][70][71]. The humidity dependence can be decreased with the additional elements, but superlubricity has not been achieved in ambient or humid conditions.…”

Origin of temperature-induced low friction of sputtered Si-containing amorphous carbon coatings

“…structural (sp 3 -sp 2 transition) and mechanical changes during thermal annealing [23][24][25]. Besides this structure stabilization, Si addition affects the film surface chemistry, in particular the surface energy [26], and consequently tribological characteristics [27,28]. Previously published experimental findings [29] showed that less than 5 at.% Si [30] added to hydrogen-free (H <2 at.%) amorphous carbon thin films significantly improves their tribological properties at temperatures above 200°C.…”

Influence of modulation periods on the tribological behavior of Si/a-C: H multilayer film

“…Jin et al investigated the tribological properties of alternatinglayered Si-DLC/DLC films under various humidity conditions (dry air, 50% RH, 90% RH) compared to single layered DLC or Si-DLC films. The alternating-layered films showed a relatively lower friction coefficient than the single layered films in different humid conditions, as well as a reduced residual stress [11]. As is known, the composition of the sublayer which determines the interface bonding structure has a great effect on the multi-environmental lubrication performance of the film.…”

“…Amongst them, multilayer films with different sublayers alternatively deposited usually contain a soft layer to allow easy sliding and a hard layer to provide bearing capacity. It can not only reduce the internal stress and improve the toughness of the a-C: H film, but also improve the multi-environmental lubrication performance [10,11]. Zhang et al compared multilayer films combined by soft and hard a-C: H to the monolayer (hard or soft) a-C: H film, and found that multilayers have lower hardness, friction coefficient and wear rate [12].…”