Effect of a novel sintering process on mechanical properties of hydroxyapatite ceramics

Two-step sintering (TSS) has been applied, in the present work, to suppress the accelerated grain growth of hydroxyapatite (HA) nanopowder compacts in the last sintering stage. The average grain size of near full dense (>98%) specimens made via conventional sintering (CS) was around 1.7 μm. By using novel two-step sintering, however, the final grain size (∼190 nm) dropped 9 times less than that for the specimens produced by the CS method. Regarding the reduction of the grain size from 1.7 μm (CS method) to 190 nm (TSS method), the fracture toughness of samples increased 95% from 0.98 ± 0.12 to 1.92 ± 0.20 MPa m1/2. Due to the lower second step sintering temperature, the phase analysis shows no HA phase decomposition in TSS method.