Microstructure and mechanical properties of spark plasma sintered zirconia-hydroxyapatite nano-composite powders

ZrO2-hydroxyapatite composites spark plasma sintered (SPS) at 1075 ± 25°C involve inter and intra particle porosities. The porosity level in the compacts (<3–42%) varied with sintering pressure (4.5–17.3 MPa), and apparently contributed to the increase in indentation fracture toughness. Rietveld phase analysis revealed that the powders and SPS compacts composed of HA, tricalcium phosphate (TCP), zirconia (t- and c-ZrO2) and CaZrO3. The indentation toughness increased in tandem with porosity to about 20 vol% after which little or no cracking was observed in the compacts (even at loads up to 1 kgF). Possible reasons for this exceptional toughness are discussed. A 2-D model is proposed to describe the increase in toughness, which agrees with the experimental results. Thus, SPS compacts of nanoZrO2-HA composite powders could be considered for load-bearing orthopaedic implants because of its unique fracture toughness and high porosity.