Bio-tribocorrosion behaviour of spark plasma sintered titanium composites in simulated body fluid

Abstract : The aim of this work was to investigate the fretting corrosion behaviour of zirconia reinforced Ti-6Al-4V composites in simulated body fluid for potential use in load-bearing hip implant applications. The current challenge with pure Ti-6Al-4V alloy in these applications is the low wear resistance and poor tribological properties of Ti-6Al-4V, which make the alloy susceptible to early failure. Additionally, the introduction of wear particles and metal ions around the area of the implant resulting from the degradation of the implant material can have detrimental effects on the human body. Furthermore, the alloying elements of Ti-6Al-4V such as aluminium and vanadium may induce inflammatory effects when introduced into the body in large quantities; through metal ion release at the onset of implant degradation as in the case of fretting corrosion. Thus, reinforcing Ti-6Al-4V with an inert and very wear resistant ceramic material like ZrO2 is expected to counteract the drawbacks of pure Ti-6Al-4V. Composites of Ti-6Al-4V were manufactured by introducing different volume fractions of ZrO2 (5 and 10 wt. %) into Ti-6Al-4V matrix via powder metallurgy techniques, using the spark plasma sintering technique. The main focus of the current work is to investigate the bio-tribocorrosion properties of the composites for potential use in load bearing implants; and thus the sintering process of the composites is beyond the scope of this work. The as-received spark plasma sintered composites were examined using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) to evaluate the resulting microstructures formed and the composition of various phases. Thereafter, fretting corrosion tests were conducted for each material composition with a special device used for fretting corrosion investigations using a cylinder-on-flat contact configuration. The tests were done in foetal bovine serum maintained at ambient temperature. Open circuit potential, dissipated energy and coefficient of friction were monitored throughout the experiments. The post wear analysis of the samples was done using optical profilometry and scanning electron microscopy equipped with EDS. The microstructures produced after zirconia additions were very different from those observed in pure Ti-6Al-4V. The presence of zirconia promoted the formation of globular zirconia-rich agglomerates throughout the matrix. The wear profiles showed that zirconia greatly improved the wear and corrosion behaviour of Ti-6Al-4V. The Ti-6Al-4V composite having 10% zirconia exhibited the lowest wear rate, while Ti-6Al-4V with 5 wt.% ZrO2 exhibited the worst tribological properties. Mixed slip and partial slip regimes were promoted at a higher applied normal load, and this had an effect on the wear behaviour and degradation characteristics of the various compositions.M.Tech. (Metallurgical Engineering