An Investigation Into Machinability of Sintered Nanocrystalline Hydroxyapatite

Close physical properties with human bone make sintered hydroxyapatite (HAP) a suitable bioceramic material for hard tissue replacement. When being used as implant devices in the human body, the HAP bioceramic needs to be machined to the closest possible configuration with minimal surface roughness. This study investigates the machinability of a newly developed, fully dense nanocrystalline hydroxyapatite (nHAP) bioceramic in turning operations. Efforts are focused on the effects of various machining conditions on surface integrity. Surface roughness is measured using a surface profilometer and the machined surface is observed using a scanning electron microscope (SEM). Chip morphology and tool wear are examined using an optical microscope. Cutting forces are measured using a three-component dynamometer. Based on the experimental results, it is found that the nHAP bioceramic is not very difficult to machine because the tool wear and cutting forces are small. However, the big challenge is how to obtain a smooth and strong surface without chipping or fracturing the material. Two machining strategies are proposed for improving the surface integrity of the sintered nHAP bioceramic in the future.