Preparation And Tribological Properties Of Composited Diamond-like Carbon Films

Doped diamond-like carbon (DLC) films and DLC/MoS2were prepared to improve the friction and wear performance under high vacuum by a combination of magnetron sputtering and plasma enhanced chemical vapor deposition techniques. The correlations of deposition conditions, composition, microstructure, mechanical and tribological properties of the films were investigated systematically. Superlubricity performances in high vacuum environments were obtained and the corresponding lubrication mechanisms were examined. The major conclusions of the thesis are drawn as follows:1. Effects of deposition parameters on the structure of TiC/a-C:H films were investigated. The MF power should be kept about2.0A, otherwise, a higher power would produce incident species with excessive energy and lead to the graphitization of the films, thus resulting in a drastic deterioration of the mechanical property. In addition the optimum CH4/Ar ratio should be kept about40/120. A lower ratio would produce poor toughness, while a higher ratio wold aggravate the "target poisoning" and inhibit the target atoms from being sputtered out, thus affecting the doping efficiency. The content of the doped metallic elements should not be too high, the doped metal atoms resolved in the carbon matrix and formed solid solution, which can retain the inherent lubrication performance of the films and enhance the mechanical property. The prepared TiC/a-C:H films show low friction coefficient and wear rate in air, and superlow friction coefficient in high vacuum, however, the friction lifetime was only about600cycles.2. We prepared DLC films in a highly hydrogenated plasma. The films contained high hydrogen content and showed superlow friction coefficient in high vacuum, owing to the elimination of the possibility of strong covalent interactions at sliding interface. While the lifetime was about900cycles, longer than TiC/a-C:H films. 3. The duplex doped TiC(Ag)/a-C:H nanocomposite films were prepared. The introduction of Ag caused a significant reduction in the residual compressive stress without considerable decrease of the hardness. The nanocomposite films show a reduction of friction coefficients and wear rates with increment of Ag concentration. Under high vacuum condition, the nanocomposite films presented superlow friction coefficient, where the friction coefficient was reduced to0.005, and the lifetime increased to1500cycles. The significant improvenment in tribological properties was mainly attributed to the low shear strength of Ag clusters on the surface as well as Ag diffusion to the surface and wear track of coatings.4. Alternate hard and soft multilayers of DLC/MoS2films integrated the high wear resistance of hard diamond-like carbon, and the excellent friction-reducing property of soft MoS2films. Furthermore, the multilayer coating exhibited the superlow friction behavior where the friction coefficient was0.001and the lifetime was more than300K cycles under high vacuum environment. These excellent trobological properties make DLC/MoS2films suitable for numerous potential applications in high-technology as triboligical materials.