Thermal activation of Ti(1-x)Au(x) thin films with enhanced hardness and biocompatibility.

Abstract

The lifetime of orthopaedic implants can be extended by coating the softer Ti₆Al₄V alloy with harder biocompatible thin films. In this work, thin films of Ti_(1-x)Au_(x) are grown on Ti₆Al₄V and glass substrates by magnetron sputtering in the entire x = 0-1 range, before their key biomechanical properties are performance tuned by thermal activation. For the first time, we explore the effect of in-situ substrate heating versus ex-situ post-deposition heat-treatment, on development of mechanical and biocompatibility performance in Ti-Au films. A ∼250% increase in hardness is achieved for Ti-Au films compared to bulk Ti₆Al₄V and a ∼40% improvement from 8.8 GPa as-grown to 11.9 and 12.3 GPa with in-situ and ex-situ heat-treatment respectively, is corelated to changes in structural, morphological and chemical properties, providing insights into the origins of super-hardness in the Ti rich regions of these materials. X-ray diffraction reveals that as-grown films are in nanocrystalline states of Ti-Au intermetallic phases and thermal activation leads to emergence of mechanically hard Ti-Au intermetallics, with films prepared by in-situ substrate heating having enhanced crystalline quality. Surface morphology images show clear changes in grain size, shape and surface roughness following thermal activation, while elemental analysis reveals that in-situ substrate heating is better for development of oxide free Ti₃Au β-phases. All tested Ti-Au films are non-cytotoxic against L929 mouse fibroblast cells, while extremely low leached ion concentrations confirm their biocompatibility. With peak hardness performance tuned to >12 GPa and excellent biocompatibility, Ti-Au films have potential as a future coating technology for load bearing medical implants.