CVD diamond coated titanium alloys for biomedical and aerospace applications

Abstract

The titanium alloys Ti-6Al-4V and Ti-6Al-7Nb, which are commonly used in aerospace and biomedical applications, were coated with diamond films using a Microwave-Plasma-CVD process. The internal compressive stresses of these films may reach −8 GPa, strongly depending on the substrate temperature during deposition. The stresses can be effectively lowered by grit-blasting of the substrates prior to deposition to values of −2 GPa. This measure is expected to improve the adhesion of the diamond coatings even further. The solid particle erosion of diamond thin films on Ti-6Al-4V substrates grown with various methane concentrations in the process gas was compared with a commercial TiAlN PVD hard coating. Under an incidence angle of 90 °, a superior erosion resistance of diamond coatings with 4% and 8% methane was demonstrated. The biocompatibility of diamond films was tested in vitro using the human osteoblastic cell line hFOB 1.19. The performance of the coatings was comparable to that of pure titanium, i.e. diamond coatings are very suitable for medical applications. Retarded cell proliferation as observed in some cases is attributed to the high surface roughness due to grit-blasting and the hydrophobic character of the diamond films.