Toward Novel Porous Boronized Ti6Al4V/FHA Composite Implants by Combined Microwave Sintering and Temporary Space Alloying

Titanium alloys are unsuitable implants for patients with low bone quality due to their high moduli and bioinertness. In this study, porous boronized Ti6Al4V/fluorohydroxyapatite (FHA) composites are synthesized via microwave sintering of mixed Ti6Al4V, FHA and TiB 2 powders at 1050 °C for 30 min, with 0–10 wt% urea as a space holder material. It is shown that increasing urea addition leads to higher porosity, promoting microwave penetration and microwave “lens effect”, which improves boronization and restrains degradation of mechanical properties of the composites caused by the increased porosity. With the urea addition of 0–3 wt%, the compressive strength and modulus decrease from 380.3 MPa and 14.5 GPa to 134.4 MPa and 3.26 GPa, respectively, while the Vickers microhardness declines from 360.3 to 300.0 HV. The increased exposure of FHA improves chemical and biological properties of the composite, with water contact angle decreased by nearly half and osteogenesis increased by sixfold. By adding more urea, the microhardness decreases evidently, with poorer wettability and biocompatibility due to looser structure and FHA decomposition. By adding 3 wt% urea, the composite achieves an optimal balance between ultralow modulus and enhanced bioactivity, making it ideal for rapid osseointegration in patients with poor bone conditions.