Mechanical and tribological properties of Si and W doped diamond like carbon (DLC) under dry reciprocating sliding conditions

Mingwen Bai,Liuquan Yang,Jiayu Li,Lun Luo,Shikuan Sun,Beverley Inkson

doi:10.1016/j.wear.2021.204046

Mingwen Bai, Liuquan Yang + Show 4 more

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https://doi.org/10.1016/j.wear.2021.204046

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The mechanical and tribological properties of three types of diamond like carbon (DLC) coatings, i.e., non-doped, Si-doped, and W-doped DLC, are evaluated. Dry reciprocating sliding wear tests were performed to evaluate the effect of sliding frequency/velocity on friction, adhesion, and wear. The degree of graphitization of non-doped and W-doped DLC increases with sliding velocity, which results in a lower coefficient of friction (COF), and a decrease in wear rate. Si-doped DLC, however, exhibits distinct friction behaviour, with increasing COF and severe fluctuations in friction at higher sliding velocities. In Si-DLC frictional heating drives the formation of an oxide-rich tribofilm and large amounts of Si-rich oxide wear debris that are both adhesive and abrasive. The oxide-rich tribofilm, and lack of surface graphitization, result in the severe fluctuations of Si-DLC friction via stick-slip and surface fracture/wear mechanisms, and significantly increased COF and wear rates at higher sliding velocities.

Highlights

Solid lubricant coatings have been widely applied in real industrial applications to improve tribological performances of machine compo nents, in conditions such as clean environments, severe load, slow relative velocity between mating surfaces, and high working temperatures where fluid lubricant films cannot be used or formed [1]
The three diamond-like carbon (DLC) nano-composite coatings are all fully amorphous with no crystalline peaks detected by grazing incidence X-ray diffraction (GIXRD; PANalytical model X’Pert PRO diffractometer, Cu Kα radiation at 1◦ angle)
For the DLC, Si-DLC and W-DLC coatings investigated, a decrease of hardness and H/Er was observed in Si-DLC coatings (Fig. 4) that was due to the change in sp3/sp2 ratio compared to non-doped DLC

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Introduction

Solid lubricant coatings have been widely applied in real industrial applications to improve tribological performances of machine compo nents, in conditions such as clean environments, severe load, slow relative velocity between mating surfaces, and high working temperatures where fluid lubricant films cannot be used or formed [1]. Amongst such coatings, diamond-like carbon (DLC) coatings have attracted a lot of interest because of their low friction, high hardness, good wear resistance and protection of the uncoated counter surface [2,3,4]{Tyagi, 2019 #32}. Metallic dopants, including Ti and W [15], are often used with the aim to increase the surface activity to oil additives, improving coating/substrate adhesion and altering carbon bonding within the DLC [1]

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