STRUCTURAL CHARACTERIZATION OF PULSED LASER-DEPOSITED HYDROXYAPATITE FILM ON TITANIUM SUBSTRATE

Pure, crystalline hydroxyapatite (HA) films with thicknesses of roughl y 10 mu m have been deposited on titanium substrate using the pulsed l aser deposition (PLD) technique. Experimental results indicate that th e structure and properties of the PLD-HA films varied with deposition parameters. The PLD process used in the present study did not induce s ignificant amounts of calcium phosphate phases other than apatite, or significant changes in the behaviour of hydroxyl or phosphate function al groups. Broad face scanning electron microscopy showed that HA coat ing was comprised of numerous essentially spheroidal-shaped particles of different sizes, while the lateral morphology indicated that column ar and dome-shaped structures both existed in the film. Many pinholes and crevices observed on coating surfaces were linked to the original substrate surface crevices/craters. The adhesion strength of the coati ng, mostly in the range of 30-40 MPa, was found to be closely related to the fractography of the tested specimen. The fracture surfaces of s pecimens with higher bond strengths were usually accompanied by a high er degree of deformation and coating-substrate debonding, while the fr acture of specimens with lower bond strengths occurred more frequently within HA coatings in a more brittle manner. The energy dispersive sp ectroscopy-determined Ca/P ratios of raw HA powder (1.78) and sintered HA target for PLD (1.79) were Very close, indicating that the sinteri ng process used in the present study essentially did not change the Ca /P ratio of HA. After the PLD process, the Ca/P ratio of the HA film i ncreased to 1.99. Cross-sectional scanning electron microscopy-energy dispersive spectroscopy point analysis indicated that the value of the Ca/P ratio was significantly higher in the region near the surface, p articularly near the coating-substrate interface, than in the coating interior. (C) 1997 Published by Elsevier Science Limited. All rights r eserved.