Fracture toughness of an α-Al2O3 ceramic for joint prostheses under sinter and sinter-HIP conditions

The densification of submicron alumina powders by sinter and sinter-HIP to obtain specimens with submicron grain size has been investigated. The minimum temperature to obtain close porosity has been determined by pressureless sintering in air. Green compacts were obtained by uniaxial pressing at compaction pressures of 50–150 MPa with relative densities of 54% TD. Temperature of 1350 °C and pressures of 150 MPa were used to obtain relative densities >98% by sinter-HIP. Resulting microstructures were observed from polished surfaces by scanning electron microscopy (SEM). Submicron grain size was obtained in pressureless and sinter-HIPed samples. The cracks induced by Vickers indentations showed a more tortuous path in sinter-HIPed samples which lead to higher fracture toughness compared with only pressureless sintered samples. The maximum Vickers hardness (HV) and fracture toughness values reached 19 GPa and 5.2 MPa m1/2, respectively, with the sinter-HIP treatment. The observed crack deflection was an important mechanism in improving fracture toughness in sinter-HIPed samples. On the other side, the grain size and remain porosity seem to be responsible to obtain this high hardness and fracture toughness.