Influence Of Chromium Content And Friction Conditions On Friction Coefficient And Wear Resistance Of Cr-doped DLC Films

Diamond-like carbon (DLC) films, which have excellent friction-reduction and anti-wear properties, have been widely applied in tribological field. Cr-doped DLC films were prepared by hybrid technique of ion beam deposition and magnetron sputtering to improve the performance of DLC films. Cr content is controlled by adjusting the sputtering current of Cr target. The correlation between Cr content, the microstructure and mechanical properties of DLC films was studied, and the influence of Cr content and friction conditions on the friction coefficient and the wear rates of Cr-doped DLC films were investigated also. The results as followed were found:(1) Cr-doped DLC films prepared by hybrid technique of ion beam deposition and magnetron sputtering have the typical structure of diamond-like carbon and the high adhesion between the films and their substrates. Cr content of DLC films is increased with the sputtering current. The content of sp~2-C in the films is increased and the nano-hardness and elastic modulus are decreased with the rise of Cr content.(2) Under the unlubricated conditions, there exists a run-in period for the Cr-doped DLC films with a Cr content less than 16.0%. With the increase of load, the run-in period is shortened and the friction coefficient is decreased. Sliding velocity has a less obvious effect on the friction coefficient and wear rate of the films than load. The friction coefficient of DLC films is increased with the increase of Cr content; but the wear rate of DLC films is decreased firstly and then increased with the rise of Cr content, and when the Cr content is 2.4%, the wear rate is lowest.(3) Under lubricated conditions, the types of basic oil and additives, the Cr content of DLC films have an obvious influence on the friction coefficient and wear rate of DLC films. Under both PAO and 150SN lubricated conditions, the friction coefficient of DLC films can be obviously reduced by the addition of MoDTC into base oil; the action duration and efficiency of MoDTC is attributed to the species of base oil and Cr content of DLC films; when Cr content is 0.2%, the friction-reduction and wear-resistant properties were the best. ZDDP and T307 have good anti-wear properties for undoped DLC films, and when cooperated with 150SN, and T307 shows lower friction coefficient and wear rate than ZDDP; when lubricated by PAO+T307 or 150SN+T307, the introduction of Cr into the films is harmful to the friction coefficient and wear rate.