Improvement of Diamond-Like Carbon Adhesion on CoCrMo by Microdiamond and Nitrogen Incorporation for Wear Resistant Applications

Abstract

Coating the joint surfaces with diamond like carbon (DLC) is a promising way to increase the service lifetime of hip joints made of CoCrMo alloy. DLC thin films have been attracted the most interest because of its extreme smoothness, low coefficient of friction, high hardness and excellent biocompatibility. One of the key issues that limit the use of DLC is its poor adhesion to commonly used biomedical alloys like CoCrMo. The low adhesion has been attributed to the high internal stress, and Nitrogen (N) doping is one of main approaches to minimize it. Nevertheless Nitrogen incorporation is being investigated due to the complex mechanism behind the formation of different chemical species in the amorphous DLC network by using different deposition techniques. In the present thesis work, micro-diamond particles were synthesized on CoCrMo alloy sheets by Microwave Plasma Enhanced Chemical Vapor Deposition (MPCVD) and nitrogen doped DLC thin films were then deposited on them by Inductively Coupled Plasma assisted Chemical Vapor Deposition (ICP-CVD) to improve DLC adhesion on CoCrMo sheets. The effect of nitrogen doping and nanodiamond incorporation on the film adhesion was investigated by Rockwell indentation. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to analyze the chemical structure of the coatings. Morphology of the films was observed by Scanning electron microscopy (SEM) and optical profilometry. The mechanical properties of the films were measured by nanoindentation testing. Results showed that Nitrogen doping and diamond incorporation could improve the film adhesion significantly. Raman and XPS spectra showed an increase in sp2 bonding in N-DLC films with a consequent decrease in hardness according to nanoindentation measurements. Surface roughness decreased while nitrogen content increased according to optical profilometer images. The results have demonstrated that the modified DLC films are promising for total hip joint replacement application.