Mechanical characteristics of porous hydroxyapatite/oxide composites produced by post-sintering hot isostatic pressing

Porous hydroxyapatite and hydroxyapatite/oxide composites, with 10 wt% addition of Y2O3, ZrO2 or TiO2 have been prepared by hot isostatic pressing after pressureless sintering, and their phase composition, mechanical properties and microstructure investigated. The quantitative X-ray diffraction analyses reveal that the addition of Y2O3 inhibits the hydroxyapatite decomposition completely during the consolidation processes as a result of the Y ion dissolution into the hydroxyapatite lattice. On the contrary, it is found that the addition of ZrO2 or TiO2 enhances the decomposition of hydroxyapatite into Ca3(PO4)2, which causes the transformation of the starting oxides. The mechanical characterization of the materials has been accomplished by three-point flexure tests, and nanoindentation and microhardness measurements. Post-sintering hot isostatic pressed pure hydroxyapatite, which resulted in a porous biphasic material with 13.2 wt% β-Ca3(PO4)2, exhibited the best mechanical properties. The failure of hydroxyapatite-10Y2O3 during the flexure tests was no catastrophic in contrast to the catastrophic behaviour found in the other materials.