In vitro degradation and dry sliding wear characteristics of AZ31/TiO₂ nanocomposites for biomedical application

Abstract

This study concentrated on the degradation and wear characteristics of nanocomposites reinforced with (0, 0.5, 1.5 and 2.5 wt.%) titanium dioxide (TiO2) nanoparticles on the AZ31 Mg alloy fabricated by the stir casting method. Optical microscopy and FESEM images showed that the TiO2 nanoparticles were distributed uniformly and the intermetallic phase Mg17Al12 observed along the grain boundaries. The surfaces of the nanocomposite samples was gradually covered with a magnesium hydroxide (Mg(OH)2) protective layer after 48 h of immersion in simulated body fluid (SBF). The immersed composite samples contained several white hydroxyapatite and magnesium phosphate particles. The addition of up to 1.5 wt.% TiO2 nanoparticles reduced the degradation rate of the nanocomposites in SBF, while further addition increased it. FESEM images of the immersed samples revealed the presence of corrosion pits and cracks on the AZ31 alloy and its nanocomposites. Under dry conditions with varying loads, the wear characteristics of fabricated nanocomposites were studied using computerised pin-on-disc equipment. The addition of TiO2 nanoparticles up to 1.5 wt.% improved the wear resistance of the nanocomposites. However, the further addition increased the coefficient of friction (COF) and wear loss due to agglomeration and porosity in the nanocomposites. The FESEM morphology of the worn surface revealed that abrasion was the primary wear mechanism at low loads, and abrasion with severe plastic deformation was dominant at higher loads.