Hydroxyapatite-316L fibre composites prepared by vibration assisted slip casting

To prepare hydroxyapatite (HA, or HAp)-stainless steel 316L fibre composites with up to 30 vol% 316L fibres (∼1 mm long and 50 μm in diameter), slip casting assisted by vibration (frequency: ∼55 Hz; amplitude: ∼5 mm) was carried out, followed by both cold isostatic pressing (CIPing) and hot isostatic pressing (HIPing). With the addition of around 0.5 wt% sodium carboxymethylcellulose (Na-cmc), solids loadings up to 44 vol% were obtained in calcined HA powder-derived slips, which were castable only under the vibration. The slips were concentrated and viscous so that the preferential sedimentation of the dense and large 316L fibres could be avoided. Subsequent CIPing was able to increase the relative density of the cast and dried green compacts from 46% after casting to 60% after CIPing. With the dense and uniform green compacts of the HA-316L mixtures, final HIPing at 950 °C resulted in HA-316L fibre composites of 99% relative density. The HA-316L fibre composites had improved fracture toughness of 3.6 ± 0.3 MPa.m0.5, due to the bridging effect of the ductile 316L fibres. However, the mechanical strength of the composites was limited by the presence of residual thermal stresses and circumferential microcracks. The HA-316L fibre composites were biocompatible and exhibited favourable bone-bonding characteristics.