The phase stability, mechanical and in vitro bioactivity properties of hydroxyapatite/alumina composite with and without yttria were investigated. Hydroxyapatite without additives decomposed at 1300 oC to beta- and alpha-tricalcium phosphate and calcium oxide phases. Although alumina contributed to the mechanical properties of hydroxyapatite, it not only decreased the decomposition temperature of hydroxyapatite from 1200 oC to 900 oC and it's in vitro bioactivity property but also increased the decomposition ratio of hydroxyapatite. An improvement in the properties of hydroxyapatite/alumina composite was provided by yttria via inhibiting the solid-state reactions between hydroxyapatite and alumina via the formation of yttrium aluminum oxide and calcium yttrium trialuminum oxide phases. The maximum fracture toughness of 2.178 ± 0.251 MPam1/2, microhardness of 4.947 ± 0.191 GPa, a compressive strength of 227.75 ± 27.87 MPa, and a three-point bending strength of 90.15 ± 6.93 MPa were achieved for hydroxyapatite/alumina composite containing 1.5 wt% yttria at the sintering temperature of 1200 oC. The relative density of 92.94 ± 0.11% was also attained. This ternary composite can potentially be used in the human body for load-bearing applications because of its sufficient mechanical and in vitro bioactivity properties with a decomposition ratio of 9.4%.

Keywords: Hydroxyapatite, Alumina, Yttria, Sintering