CVD DIAMOND-COATED TITANIUM-ALLOYS FOR BIOMEDICAL AND AEROSPACE APPLICATIONS

The titanium alloys Ti-6Al-4V and Ti-6Al-7Nb, which are commonly used in aerospace and biomedical applications, were coated with diamond fil ms using a Microwave-Plasma-CVD process. The internal compressive stre sses of these films may reach -8 GPa, strongly depending on the substr ate temperature during deposition, The stresses can be effectively low ered by grit-blasting of the substrates prior to deposition to values of -2 GPa. This measure is expected to improve the adhesion of the dia mond coatings even further. The solid particle erosion of diamond thin films on Ti-6Al-4V substrates grown with various methane concentratio ns in the process gas was compared with a commercial TiAlN PVD hard co ating, Under an incidence angle of 90 degrees, a superior erosion resi stance of diamond coatings with 4% and 8% methane was demonstrated. Th e biocompatibility of diamond films was tested in vitro using the huma n osteoblastic cell line hFOB 1.19. The performance of the coatings wa s comparable to that of pure titanium, i.e. diamond coatings are very suitable for medical applications. Retarded cell proliferation as obse rved in some cases is attributed to the high surface roughness due to grit-blasting and the hydrophobic character of the diamond films. (C) 1997 Elsevier Science S.A.