Spark plasma sintering and in vitro study of ultra-fine HA and ZrO2–HA powders

Spark plasma sintering (SPS) was employed to sinter RF suspension plasma sprayed HA ultra-fine powders and ZrO₂–HA nano-composite powders. The powders were sintered at 1000 °C for 5 min at 11.1 MPa and 1100 °C for 5 min at 11.1 MPa, respectively. After sintering, the samples were ground and polished for subsequent indentation and microscopy studies. The as-sintered compacts of the HA–CaP powders were studied in vitro by immersion in simulated body fluid (SBF). The in vitro studies indicated that a bio-active apatitic layer was formed as early as 1 week after immersion. Optical microscopy and SEM investigation revealed negligible porosity and dense microstructure suggesting liquid phase sintering to have taken place. Phase composition was calculated with the aid of XRD and the Rietveld method. The results indicated that the mechanical properties of the as-sintered compacts were improved in the presence of nano-ZrO₂. The Young’s modulus increased to 130 MPa and the fracture toughness was 1.6 MPa m^1/2 for ZrO₂ loading lower than 3 vol.% indicating greater enhancement of properties than that suggested by the rule of mixtures.