Effect of Intermediate Layer on Residual Stress Occurred in Hydroxyapatite Coating Implant.

Abstract

Hydroxyapatite (HAp) is one of the most effective biomaterials used in an artificial bone and a dental designed implant. Since its mechanical reliability and workability are much lower than those of metal, it is often used as a coating material. However, cracking and delamination at the coating interface are induced by the residual stress which occurs in the coating process. In our previous report, the steep stress gradient in the coating layer and the increase in tensile residual stress on the surface of the substrate were obtained using the polychromatic X-ray diffraction. Therefore, an additional intermediate layer between the coating and the substrate material may decrease the residual stress in the coating layer. In this work, we describe the method to measure nondestructively three dimensional residual stress generated in the coating implant with the intermediate layer, using the polychromatic X-ray diffraction. As a result, the compressive residual stress in the coating layer of the hydroxyapatite coating titanium implant with the titania intermediate layer, made by atmospheric plasma-spray processing, was smaller than that of the implant coated only with hydroxyapatite.