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. Becaus e these materials consist of brittle hydroxyapatite, their mechanical reliability and workability are much lower than those of metal. Theref ore, hydroxyapatite ceramics are used as coating materials. During or after the coating process, cracking and tearing often occur in the coa ting layer of the implant. These defects are caused by the residual st ress in the vicinity of the coating interface. It is important to eval uate the residual stress in this region. The purpose of work is to pre sent 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 substrat e were confirmed.