Hydroxyapatite ceramics with tetragonal zirconia particle dispersion prepared by HIP post-sintering

Hydroxyapatite (HAp) powders with dispersed tetragonal zirconia particles were synthesized hydrothermally at 200°C under 2MPa for 10h. Transmission electron microscopy (TEM) demonstrated that the homogeneous mixture of ultra-fine HAp single crystals and zirconia particles could be obtained by the hydrothermal technique. The mixture with the volume ratio of HAp: zirconia=90:10 was hot-pressed at 1050°C under 30MPa for 1h in Ar, then post-sintered by HIP at the same temperature under 200MPa of Ar for 1h. The product had almost pore free microstructures consisting of HAp matrix and tetragonal zirconia particles. Its fracture toughness was 2.5 times as large as that of the transparent pure HAp ceramics. This ceramic was toughened by the crack deflection toughening mechanism and probably by the transformation toughening mechanism due to tetragonal zirconia particles dispersed in the matrix. Furthermore, the reactivity between HAp and zirconia was examined. The decomposition of HAp to β-tricalcium phosphate (β-TCP) was accelerated by zirconia, and CaO was not detected in every temperature. Thus the decomposition was taken place by dissolution of Ca components in zirconia in the first step, then HAp decomposed to β-TCP subsequently.