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.