SYNTHESIS AND CHARACTERIZATION OF TANTALUM AND DIAMOND-LIKE CARBON THIN FILMS ON CoCrMo ALLOY SHEETS
In the present research study, Tantalum (Ta) and Diamond-like Carbon (DLC) thin films were deposited on a biomedical Cobalt-Chromium-Molybdenum alloy (CoCrMo alloy) and investigated to improve the surface functionality of this alloy as femoral heads for artificial hip joints. Ta thin films were deposited on the CoCrMo alloy sheets by magnetron sputtering and the effect of deposition parameters on the formation of different phases of Ta was studied using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and X-ray Absorption Spectroscopy (XAS). By choosing appropriate processing conditions, adherent α- and β-Ta thin films were developed on the CoCrMo alloy sheets and their adhesion, mechanical, and surface properties were characterized using Rockwell C indentation, nanoindentation, optical profilometry, and a contact angle goniometer. The tribological and corrosion behavior of the Ta coated and uncoated CoCrMo alloy sheets were studied using a ball-on-disk tribo tester and a potentiostat. The results demonstrate that adherent Ta thin films (α-Ta or β-Ta) can be applied to improve corrosion and wear behavior of the CoCrMo alloy, and possibly the performance of the alloy in orthopedic implant applications. Specifically, fcc Ta thin film formation, its structure and stability were investigated and its XRD pattern was obtained and reported for the first time. DLC thin films were deposited on the CoCrMo alloy sheets using Ta interlayers by ion beam deposition and characterized using Raman spectroscopy, XPS, and SEM. Severe delamination of DLC coatings was observed on the samples. The results show that the delamination is not just related to the energy level of ion bombardment, which induces intrinsic stress into the film during DLC deposition, but also related to the interfacial layer formation between Ta and DLC films. Furthermore, a simple nondestructive method was evaluated for DLC stress measurement. For this purpose, DLC thin films on Si wafers with different shapes and sizes were synthesized and the internal stress of the thin films were measured with the aid of Zygo optical profiler using the Stoney equation. The results show that this simple method is appropriate and reliable for DLC stress determination.
Tantalum, Diamond-like Carbon, Thin Film
Doctor of Philosophy (Ph.D.)