Improved adhesion of titanium oxide film to titanium-base alloy by Ti/O compositional gradient using reactive sputter-deposition

Abstract

This chapter presents a study in which the effects of Ti/O compositional gradient on adhesion of the film at the interface to the alloy substrate are investigated by comparing the adhesion of Ti-O compositionally gradient films at the interface boundary with that of Ti-O compositionally constant films at the interface. Coating of Ti-6A1-4V alloy substrates with Ti/0 compositional gradient films is carried out by reactive DC sputtering, not only to improve the biocompatibility and the surface hardness of the alloy but also to relax the stress concentrated at the interface between the film and the alloy substrate. The compositional gradient is realized by continuously varying the oxygen content in Ar-O2 sputter gas during depositing. Under SEM, the surface of the deposited film is found to have fine particles dispersed on a smooth accumulated deposit. Under AES, the oxygen concentration in the film decreases gradually in depth direction from the surface toward the substrate, confirming that a Ti/O compositional gradient film has formed on the alloy. A specific increase of the oxygen concentration was detected in the vicinity of the interface, concluding that the oxygen atoms, which had concentrated in the surface layer of the alloy substrate diffused into the titanium layer in the compositional gradient film. Based on indentation-fracture tests, it is concluded that this depositing method improved the adhesion of the coated film to the alloy substrate and the toughness of the film.