Microstructure evolution and enhanced bioactivity of Ti–Nb–Zr alloy by bioactive hydroxyapatite fabricated via spark plasma sintering
The crystalline phases and bioactivity of materials play crucial factors in determining the biological interactions and osseointegration process of orthopaedic replacements or implants. In this study, (Ti–13Nb–13Zr)–10hydroxyapatite (HA) composites were fabricated by spark plasma sintering (SPS) process at different sintering temperatures (950–1150 °C) with the synergistic effects of Ti–13Nb–13Zr and HA. The effects of the sintering temperature on the microstructure evolution, mechanical properties, corrosion behaviour and in vitro bioactivity in simulated body fluid of the composites were investigated. The results show that the composites consist of (α + β)-Ti and HA matrix, and reaction products of metal–ceramic phases (CaO, TCP, CaZrO3, Ti3P5 etc.). With the sintering temperature increasing, the α-Ti phase gradually decreases, while the β-Ti phase and metal–ceramic phases gradually increase. The relative density, elastic modulus, compressive strength and yield strength of the composites increase with increasing sintering temperature. However, when the sintering temperature exceeds 1050 °C, metal–ceramic phases rapidly increase due to the violent reaction between Ti metal and HA ceramic, which leads to the elastic modulus increasing intensely. At the same time, the surface of the composites after soaking in SBF spontaneously nucleated and precipitated diverse bone-like apatite layers, indicating that the composites exhibit high bioactivity and that the surface activity is enhanced by the sintering temperature. The results demonstrate that (Ti–13Nb–13Zr)–10HA composites sintered between 1000 and 1050 °C are potential biomaterials for orthopedic replacement or implants.