An investigation into the processing procedure and mechanical properties of hydroxyapatite/tetragonal zirconia bilayer structure has been carried out. The investigation consists of two parts. In the first part, the green compacts of hydroxyapatite/tetragonal zirconia bilayer structure have been formed by using sigle-end die press. Then they are sintered at a suitable temperature. To form a strong interface between the top and the bottom layer of the obtained bilayer specimens. However, numerous flaws are found in the hydroxyapatite layer. Accordingly, the obtained bilayer structure specimens are not appropriate to be used for an investigation of their mechanical response. In the second part, an alternative processing procedure is employed. Monolithic hydroxyapatite and tetragonal zirconia specimens are separately prepared and their surfaces are bonded together by a thin adhesive polymer interlayer. By using the indentation technique together with the bonded-interface technique in investigating their mechanical response, it is found that the mechanical properties of the hydroxyapatite layer of the bilayer with thin hydroxyapatite layer are influenced by the presence of the adhesive polymer interlayer or the tetragonal zirconia substrate. Its fracture toughness is higher than that of the monolithic hydroxyapatite whereas its hardness is lower. However, the mechanical properties of the hydroxyapatite layer of the bilayer with thick hydroxyapatite layer are not different from those of the monolithic hydroxyapatite.
