Hot Isostatic Pressing (HIPing) of FeCralloy®-Reinforced Hydroxyapatite

The goal of this study was to produce hydroxyapatite (HAp), a bioactive biomaterial, in a decomposition-free form with fracture toughness comparable to bone by metal fibre-reinforcement. This goal was ultimately achieved. Glass encapsulation of FeCralloy®-reinforced HAp was an unsuccessful technique due to the excessive low-temperature volatilisation, which aerated the glass. Therefore a graphite/stainless steel encapsulation system was used in the present study. Hot isostatic pressing enabled the production of fully dense decomposition-free HAp with toughness improvements of 14 times (FeCralloy® fibres, optimally 15 vol%), comparable to cortical bone. Further, it was found that the HAp decomposition temperature was higher at 100 MPa (the HIPing pressure) than for pressureless sintering. Addition of the FeCralloy® fibre additive induced significant plastic deformation and ductile fracture of the hydroxyapatite.