The structural characteristics and mechanical behaviors of nonstoichiometric apatite coatings sintered in air atmosphere

Two types of nonstoichiometric apatite coatings on Ti6Al4V substrates were prepared in our laboratory by electrodeposition and hydrothermal synthesis. One was composed of highly pure needle-like calcium-deficient hydroxyapatite, and the other consisted of needle-like calcium-deficient hydroxyapatite and plate-like brushite. In this paper, the morphology, phase transition, and bonding strength of these coatings sintered at 450°~980°C in an air atmosphere were studied. In addition, the residual stresses in pure calcium-deficient hydroxyapatite coatings and coatings sintered at 800°C were measured by a hole-drilling method. The results show that after being sintered at a higher temperature, the coating/Ti6Al4V samples exhibited structural characteristics such as biphasic [hydroxyapatite + β- Ca₃(PO₄)₂] coatings and dense TiO₂ film/Ti6Al4V in which the residual stresses in the coatings slightly increased. In addition, the results indicate that bonding strength was improved.