Tribological Behaviour of Mg–3Zn–xZr–1Y Alloys for Biomedical Implant Applications

Abstract

Magnesium (Mg) alloys are promising biodegradable materials for orthopaedic implants because of their bone-like mechanical properties and biocompatibility. However, their clinical application is limited by rapid degradation, caused by the combined effects of wear and corrosion in physiological environments. Understanding the tribological behaviour of these alloys is essential for improving both the design and performance of medical implants. This paper studies recently developed Mg–3Zn–xZr–1Y alloys with a focus on the influence of zirconium (Zr) additions (0.25–1.00 wt%) on the tribological performance for biomedical applications. The developed alloys were tested under dry and physiological conditions simulated by phosphate-buffered saline (PBS) using a customised reciprocating ball-on-disc tribometer. The normal loads of 6, 17.5 and 30.8 N were selected to mimic a range of typical contact pressures experienced by relevant medical implants. The surface damage of the tested alloys was characterised using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), and material loss was determined by confocal microscopy. Volume loss analyses showed that PBS significantly reduced material loss as a result of the lubrication effect and the possible formation of tribochemical films. The effect of Zr content on the material loss was found to be highly coupled with the effect of both normal load and the testing environment. SEM characterisations showed that abrasive wear, primarily ploughing and localised cutting, was the dominant degradation mechanism under dry conditions; whereas, in PBS conditions, the dominant degradation mechanism was found to change from abrasive wear to a combination of moderated abrasive wear and oxidation/corrosion.