Residual stress evaluation of hydroxyapatite coating Ti implant

Bio-active ceramics which have the capability for bonding to bone have been developed as one of the most effective implant materials. Because these materials consist of brittle hydroxyapatite, their mechanical reliability and workability are much lower than those of metal. Therefore, hydroxyapatite ceramics are used as coating materials. During or after the coating process, cracking and tearing often occur in the coating layer of the implant. These defects are caused by the residual stress in the vicinity of the coating interface. It is important to evaluate the residual stress in this region. The purpose of work is to present a method for measuring simultaneously and nondestructively three-dimensional distribution of residual stress in both the hydroxyapatite coating layer and the titanium substrate, using polychromatic X-rays. From this method, the steep stress gradient in the coating layer and the increase in tensile residual stress on the surface of the substrate were confirmed.