Microstructure, mechanical and tribological characteristics of AZ91D-HAp-TiB₂ hybrid nanocomposites synthesized through the stir casting route

The aim of this study is to develop a novel magnesium-based nanohybrid composite for potential orthopaedic bioimplant applications. The hybrid nanocomposites were fabricated with AZ91D magnesium alloy as the matrix and hydroxyapatite (HAp) and TiB 2 nanoparticles as reinforcements, through the stir casting route. The nanocomposites were synthesized with a fixed concentration of HAp (5 wt%) and different concentrations of TiB 2 (2, 4 and 6 wt%). The microstructure of the fabricated composites revealed that the grains are significantly refined with the addition of nanoparticles. The AZ91D-5wt%HAp-2wt%TiB 2 hybrid nanocomposite is observed with relatively low porosity, without significant agglomeration of the reinforcement particles, and exhibited the highest tensile and compressive strength with considerably higher ductility than the base AZ91D alloy and the nanocomposites with 4 and 6 wt% TiB 2 (about 21% and 34% improvement in compressive and tensile strengths, respectively, compared to the AZ91D alloy). The refinement of grains due to the addition of nanoreinforcements and the alleviation of micro-strain up to a certain extent due to the presence of HAp nanoparticles together with the negligible porosity and agglomeration are the major reasons for the superior strength and ductility. The wear test results showed that the nanocomposite with 2 wt% TiB 2 has superior tribological properties. The studies revealed that the AZ91D-5 wt% HAp-2 wt% TiB 2 hybrid nanocomposite is a potential material for temporary orthopaedic bioimplants due to its superior strength, ductility, and tribological properties together with the possible enhanced biocompatibility and corrosion resistance due to the presence of HAp particles.