Friction and Wear Properties of Multilayer Films Designed on Tantalum Substrate

In this paper, a titanium nitride film (TiN) monolayer film was deposited on a pure Tantalum (Ta) substrate with Ti as an intermediate layer by magnetron sputtering technique, and a Ta/Ti/DLC (diamond-like carbon)/Ti/TiN/DLC multilayer film was designed. Raman spectroscopy and scanning electron microscopy were used to observe the film structure and morphology. Friction and wear properties of Ta/Ti/TiN monolayer film and Ta/Ti/DLC/Ti/TiN/DLC multilayer film were analyzed by UMT-3 tester. The results show that the surface of multilayer film is denser and better bonded than TiN monolayer film. Under dry friction conditions, the friction coefficient of TiN monolayer film is stable at about 0.45. In contrast, the friction coefficient of DLC multilayer film remains around 0.15 with very small fluctuation during the whole friction process. This is determined by the inherent characteristics of DLC film, which is composed of sp2-C graphite structure and sp3-C diamond structure. From the analysis of the wear mechanism, the Ta substrate mainly undergoes adhesive wear and abrasive wear, however, the TiN monolayer film and Ta/Ti/DLC/Ti/TiN/DLC multilayer films mainly undergo abrasive wear mechanism. The friction coefficient of TiN monolayer fluctuates more than that of dry friction conditions in the body-liquid environment, and finally stabilize at about 0.5. The friction coefficient of DLC multilayer films does not differ much from those of dry friction conditions. This is because the TiN monolayer film generates a large amount of abrasive chips to fill the scratches in the body fluid environment, accompanied by the peeling and flaking of the compacted abrasive chips, thus the friction coefficient fluctuates greatly. The DLC multilayer films also undergoes graphitization transfer. In addition, the free hanging bonds of DLC film are passivated, which reduces the degree of adhesive wear. In summary, the DLC multilayer film has better biocompatibility, wear resistance, and stronger bonding.