Study On Tribological Behavior Of Ti-doped DLC Coatings

Diamond-like carbon (DLC) films have been used in many fields for their excellent properties, thus, they are focus of new materials research. The hardness and elastic modulus of Ti-doped in DLC (Ti-DLC) can be increased, and the tribological performance can be improved. Ti-DLC films were prepared by hybrid technique of ion beam deposition and magnetron sputtering. The Ti content in the films was controlled by changing the sputtering current of titanium target. The correlation between Ti content and microstructure and mechanical properties of DLC films, the influence of Ti content and the friction conditions on the friction coefficients and wear rates of Ti-DLC films were discussed. The results as followed were shown:(1) Ti-DLC films prepared by hybrid technique of ion beam deposition and magnetron sputtering exhibit the typical structure of diamond-like. The surface of Ti-DLC films with different Ti content, on which there exist some defects with a dimension of hundreds nanometer. When the sputtering current is lower than 3.5A, the Ti content in the films is slowly increased with the rise of the sputtering current, and then a obvious rise of Ti content is observed when the sputtering current excess 5A. The influence of Ti content on sp3-C content is unobvious for the DLC films with a Ti content lower than 0.68at%; however when Ti content is higher than 5.81at%, the sp3-C content is decreased with the rise of Ti content, and TiC appears in the films. The nanohardness and the elastic modulus of Ti-DLC films is grandually increased with the augment of Ti content, and the fracture toughness can be improved by the introduction of Ti into DLC films at an optimum level.(2) Under the unlubricated conditions, the friction coefficient of Ti-DLC films is decreased with the rise of load; the wear rate of the films with a Ti content lower than 0.68at% is increased with the rise of load, while the wear rate of Ti-DLC films with a Ti content higher than 23.3at% is decreased with the rise of load. The friction coefficient and the wear rate of Ti-DLC films are decreased with the rise of velocity. The friction coefficient and the wear rate are decreased with the introduction of Ti into DLC films at an optimum level, but when Ti content were higher than 0.28 at%, the wear rate of the films is increased with the rise of Ti content.(3) Under PAO and 150SN lubricated conditions, the wear rate of Ti-DLC films is increased with the rise of Ti content. Under MoDTC solution lubricated conditions, the change of the friction coefficient and wear rate of Ti-DLC films are unobvious with the rise of Ti content. Under ZDDP and T307 solution lubricated conditions, the lowest friction coefficient and wear rate of the Ti-DLC can be found for the films with an optimum Ti content level.For un-doped DLC films, the addition of lubricant oil additives is harmful for the tribological properties. For Ti-doped DLC films, the friction coefficient and wear rate can be obviously decreased by introducing the additives into lubricant oil, especially for the Ti-DLC films with a high Ti content. The friction coefficient and wear rate of Ti-DLC films lubricated by T307 solution is the lowset compared the films lubricated by MoDTC or ZDDP.