3D printed silicon nitride, alumina, and hydroxyapatite ceramic reinforced Ti6Al4V composites - Tailored microstructures to enhance bio-tribo-corrosion and antibacterial properties

This study utilized directed energy deposition (DED) as a metal additive manufacturing (AM) technique to create ceramic-reinforced composites of Ti6Al4V (Ti64) with hydroxyapatite (HA), alumina (Al2O3), and silicon nitride (Si3N4). The resulting composites had tailored microstructures designed to improve bio-tribological and antibacterial properties simultaneously. A total of 5-wt % ceramic reinforcement were used in Ti64 in four different composites – (1) only Si3N4 (5S), (2) only Al2O3 (5A), (3) 3 wt % Si3N4 and 2 wt% HA (32SH) and (4) 3 wt % Al2O3 and 2 wt% HA (32AH). Microstructural observations revealed that martensite transformation between α and β-Ti in composites resulted in compressive residual stress at the matrix. Coherency is observed between the ceramic particles and Ti64 matrix, preventing cracking, debonding, or porosity. Vicker's hardness of the composite samples increases by 50% over the Ti64 matrix. Various strengthening mechanisms are discussed in detail, representing the reason behind the reduction of compound wear in 5S and 5A composites. Si3N4-added composites demonstrated an antibacterial response against gram-positive Staphylococcus aureus. The multifunctional performance of ceramic-reinforced Ti64 composites makes them suitable for articulating biomedical devices such as femoral heads in hip implants.