Investigation of the corrosion and tribocorrosion behaviour of metallic biomaterials

Abstract: Metals are commonly used in various biomedical applications due to their excellent mechanical properties, such as high strength, ductility and toughness. However, the main drawback of metallic biomaterials is their high reactivity, which makes them especially susceptible to corrosion when exposed to aqueous environments such as body fluids. In addition to the corrosiveness of body fluids, metallic biomaterials can be exposed to mechanical loading and wear. The combined effect of corrosion and wear, also known as tribocorrosion, can lead to enhanced release of metallic ions and particles into the surrounding fluids and tissue, which can cause different adverse biological reactions and limit the lifetime of metallic implants. The overall goal of this study was to investigate the tribocorrosion behaviour of different metallic biomaterials. Firstly, the corrosion and tribocorrosion resistance of a novel candidate material, hafnium, have been studied and compared with titanium. Secondly, the tribocorrosion behaviour of Cobalt-Chromium-Molybdenum alloys has been investigated. The study of the corrosion and tribocorrosion behaviour of hafnium and titanium revealed that both metals form a stable oxide layer that provides high protection to corrosion. Although the oxide layer can be damaged due to fretting and wear, it rapidly reforms when the mechanical damage ceases. However, hafnium showed a tendency to suffer from pitting, especially when the material was subjected to fretting, which could be a major drawback that might limit the application of hafnium in biomedical applications. The behaviour of CoCrMo alloys was also investigated. The analysis of the repassivation kinetics of CoCrMo revealed that a second order exponential decay can be used to model the current transient after wear damage. This suggests that the repassivation process can be divided in two phases, first the depassivated area is rapidly recovered by an oxide layer; then, the thickness of the oxide film grows and stabilises. In addition, it was observed that the chemical composition of the environment can affect not only the corrosion but also the tribological performance of the system. This work has provided an insight into the degradation processes and the parameters affecting the corrosion and tribocorrosion behaviour of different metals in simulated body fluids.