Characterisation of calcium phosphate coating on investment cast 316L stainless steel

Medical grade 316L stainless steel (316L-SS) was coated with hydroxyapatite (HA) using investment casting technique. The molten metal was poured into a HA coated ceramic mould at 1650°C under vacuum. The coated samples were vacuum sintered in a furnace at three different temperatures for 1 h. The cast and sintered coated samples were characterised using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. A uniform layer of HA was formed on ceramic mould by dipping method. The cast samples showing good HA coating and bonding and form of a complex calcium-chromium oxide layer at the interface between HA and 316L-SS. The results confirmed increased crystallinity of the coating with increasing sintering temperature. Ca/P atomic ratio was found to decrease from 1·98 in the as cast coated sample to 1·69 and 1·61 for samples sintered at 800 and 1000° C respectively, which are close to that of human bone