Effects of Si content in DLC films on their friction and wear properties

Abstract

Diamondlike carbon (DLC) has been well known as a very hard and very low-friction material. The most critical issue of DLC is to improve its adhesion. To improve the adhesion, some other elements, such as Si, have been included in DLC films. We have studied the effects of Si content on friction and wear properties of DLC films made by our bipolar pulse PBII system. The content of Si was changed by varying the flow rates of tetramethylsilane (TMS) from 0.0 to 3.5 sccm while the flow rate of toluene and the total pressure was kept constant. Friction coefficients (FCs) were measured with a JIS-SUJ2 (AISI 52100) ball of 3-mm diameter. The length of sliding was 2 mm, the speed was 10 mm/s, and the load was 4.9 N for 40-min tests. Without TMS flow, the friction coefficients (FCs) were the largest, 0.35, and the DLC film came off easily. With the increase of TMS flow up to 1.0 sccm, the FC decreased to 0.14, and there was almost no peeling off. For 2.0 sccm, the FC was 0.18, and there was a lot of debris on the DLC surface. Hardness gradually decreased with the increase of TMS flow up to 1.0 sccm, and it decreased drastically for high flow rates or high Si content. Internal stress (compressive) of the films decreased with the increase of TMS flow. Si content in the film corresponded almost linearly to the TMS flow rate. One to two percent of Si doping is very suitable for improving the adhesion of films and reducing internal stress while maintaining the surface hardness of DLC films.