Influences of multi-pass friction stir alloying on characterization of AZ91D alloy-based dual reinforcement bio-ceramic nano-composites.

In current study, microstructural, mechanical and corrosion behaviour were investigated with incorporation of dual reinforced AZ91D surface composites. This research was carried out for enhancement of the bio-degradability in biological environment. The surface composites were successfully fabricated by friction stir processing method with a rotation speed of 800 rpm, travel speed of 80 mm/min and 2.5° tilt angle at multi-passes. The surface properties were characterized via optical, SEM, EDS, XRD and EBSD techniques. The microstructure showed that the reinforcements were equally distributed into the surface matrix after 3-passes for sets of composites. After 3-passes FSP average grain diameter of the composite C (1.61 μm) was smaller than that of composite A (1.86 μm) and composite B (1.63 μm), because of the strong shear deformation and generated friction heat, which occurred via dynamic recrystallization between grains in the processed zones. The microhardness of Composite C (162 Hv) has a higher than the composite A (125.2 Hv) and composite B (146.2 Hv). The ultimate tensile strength of composite A (152.7 MPa) was greater than that of composite B (133 MPa) and composite C (111.3 MPa). Furthermore, the corrosion resistance at 7, 15 and 30 days of immersion of composite C was higher than that of composite A and composite B, because of the domino effects and better bio-mineralization with the addition of Y₂O₃ and ZrO₂ particles. The typically worn surface revealed reduced deep pits, pits and cracks due to better ionization of the hydrogen generated during immersion. Finally, this research was carried out for treatment of bone defects and fractures as well as improving corrosion resistance of the mg-containing biocompatible implants.