Fabrication of Boronized Ti6Al4V/HA Composites by Microwave Sintering in Mixed Gases

The effect of atmosphere on the fabrication of boronized Ti6Al4V/hydroxyapatite (HA) composites was investigated by microwave sintering of the mixture of Ti6Al4V alloy, HA, and TiB₂ powders at 1050 °C for 30 min in the mixed gases of Ar + N₂, Ar + CO, and Ar + H₂, respectively. The presence of N₂, CO, and H₂ in the atmosphere caused formations of TiN, TiC, and TiH₂ in the composites, respectively, together with evident microstructural changes that determined the mechanical properties (compressive strength, compressive modulus, and Vickers microhardness) and wettabilities of the composites after sintering. It was found that the composite exhibited the best mechanical performance with compressive strength of 148.59 MPa, compressive modulus of 13.9 GPa, and Vickers microhardness of 300.39 HV by microwave sintering in the mixed gas of Ar + H₂, followed by those obtained in the mixed gases of Ar + N₂ and Ar + CO. All of the composites possessed desirable wettabilities, irrespective of the sintering atmosphere, as demonstrated by their very low water contact angles (≤31.9°). The results indicated that it is critical to control the extents of nitration and carbonization for maintaining the performance of the composites, especially the mechanical properties, whereas there is no strict requirement for the same objective using the mixed gas of Ar + H₂ in which qualified composites could be obtained for implant applications.