Year

2017

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials, Mechatronic and Biomedical Engineering

Abstract

Titanium alloys are used extensively in orthopaedic implants because of their high strength to weight ratio, resistance to corrosion, and biocompatibility, but the poor wear resistance of Ti-based implants and the stress at the articulating surfaces releases wear debris and metal ions. As the average life expectancy of the world population increases, the development of long lasting implants is essential. The aim of this thesis is to modify the surface of titanium alloys by depositing a highly adherent thin film using physical vapour deposition methods to enhance its wear and corrosion resistance in a biological environment.

The effect that a titanium buffer layer has on the structure of sputtered Ta films and coating-to-substrate adhesion was investigated. Since Ta films have a dual-phase structure with a body centred cubic (α-Ta) and tetragonal (β-Ta), the amount of alpha phase in the Ta film increased when titanium was introduced because the lattice match between α-Ta and α-Ti becomes closer. This titanium buffer layer also reduces the residual stress of the films by 25% compared to pure Ta film on a Ti6Al4V substrate, which also improve adhesion between the coating and substrate interface. Ta films also enhance the corrosion resistance of Ti6Al4V substrate by presenting a stable surface layer with negligible capacitive behaviour ...

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