Hydroxyapatite–Ti functionally graded biomaterial fabricated by powder metallurgy

A functionally-graded biomaterial (FGM) in a hydroxyapatite (HA)–Ti system was developed by an optimized powder metallurgical process and investigated by microstructural analysis and mechanical tests. The constituents in sintered HA–Ti FGM distribute gradually with the variation in chemical composition, eliminating the macroscopic interfaces, such as that in HA–Ti direct joint. Partial decomposition of HA phase was found in interlayers of the FGM due to the co-existence of Ti during sintering. Mechanical properties in HA–Ti FGM also exhibit gradient distributions. Vickers hardness and Young’s modulus are strongly affected by the porosity. However, bending strength and fracture toughness increase remarkably with the rise of Ti content, especially in the Ti-rich region. Maximum strength and toughness (971.96 Mpa and 29.691 MPam1/2 respectively) were reached in the pure Ti layer, which are far higher than those of human bone. In addition, the strengthening and toughening mechanism was discussed. In summary, HA–Ti FGM is a promising biomaterial for use as a hard-tissue replacement implant, considering its mechanical behaviors.