Hydroxyapatite/Hydroxyapatite‐Whisker Composites without Sintering Additives: Mechanical Properties and Microstructural Evolution

Hydroxyapatite/0%‐30% hydroxyapatite‐whisker (HAp/0%‐30%HAp(w)) composites have been fabricated by pressureless sintering, hot pressing, and hot isostatic pressing (HIP). Composites that were HIPed at 1000°‐1100°C (2 h, 190 MPa) exhibited the best properties: relative densities of 97.0‐99.5%, fracture toughness of 1.4‐2.0 MPa·m 1/2 (as compared with 1.0 MPam 1/2 for the nonreinforced HAp matrix). Compressive pre‐stressing and crack deflection contributed mostly to the increase of fracture toughness. Depending on processing conditions, grain growth in the HAp matrix and/or Rayleigh instability of the HAp whiskers were probably responsible for microstructural changes in the composites. The HAp/HAp(w) composites exhibited improved toughness, attaining the lower fracture‐toughness limit of bone without a decrease of bioactivity and biocompatibility.