Analysis of the interface between plasma-sprayed calcium phosphate coating and Ti-6Al-4V

Plasma sprayed calcium phosphate coatings on Ti(alloy) have been considered advantageous over the uncoated Ti as dental implants or orthopedic prostheses due to their abilities to decrease healing time, attach firmer to the bone, and inhibit ion release from the Ti substrate. However, the coating was found not to adhere well to the Ti substrate, presumably because there is no or little chemical bonding between the calcium phosphate coating and the Ti substrate. The interfacial bond strength relies almost entirely on the mechanical locking of calcium phosphate splats onto the roughened Ti surface. In this study, the interfacial area between the calcium phosphate coating and the Ti-6Al-4V substrate was characterized using SEM and TEM. The results revealed the presence of amorphous calcium phosphate layer at the interface, which is believed to be responsible for the low bond strength. Also small particles were observed which were embedded in the amorphous phase near the interface. The presence of the amorphous phases is very important since they are more easily attacked by the physiological solution than crystalline phases are.