Structural investigation and wettability of PVD TiN caoted CoCrMo orthopedic alloy

Abstract

Wettability, defined as the ability of any solid surface to be wetted when in contact with a liquid, is one of the most important properties of biomaterials since highly wettable surfaces are expected to disclose better adhesion of the cells.The wettability characteristics of a biomaterial.s surface can be improved by surface modification techniques.In this study, wettability characteristics of TiN coated CoCrMo orthopedic alloy materials were investigated. CoCrMo alloys were coated with TiN using physical vapor deposition (PVD) technique at 550 C for 6 h. The TiN coated layer microstructure,roughness, thickness, and composition were studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscope (SEM). Wetting studies involved contact angle and surface tension measurements using distilled water and simulated body fluid (SBF) as test liquids. The contact angles of the coated and uncoated CoCrMo alloys were investigated by the sessile drop method and the surface tension of the test liquids was measured by the ring method. The XRD results show the PVD coated TiN films had (111) preferred orientation, while the SEM analysis indicated quite uniform TiN coated layers (about 3 m thick) with a columnar growth mode. The AFM results indicated much higher roughness values for the TiN coated surfaces compared to the uncoated ones. The experimental results show the contact angle values for the TiN coated samples is lower than the uncoated ones suggesting better wetting for the coated layer. Based on the contact angle and the surface tension values, the work of adhesion values were estimated and it was found that the TiN coated layers has better adhesion ability compared to the uncoated CoCrMo alloy. The lower contact angles for the TiN coated samples were attributed mainly to the rougher surfaces associated with the TiN coated surfaces in comparison with the relatively smooth surface of the uncoated samples. Also, based on the EDX analysis results, the surface oxygen content on the coated surface may be another factor contributing to the better wettability characteristics of the TiN coated CoCrMo alloy compared to the uncoated alloy.