Amorphous calcium phosphate coatings on the order of 1 μm thick were deposited onto titanium and silicon substrates using an ion-beam sputtering technique. The target material utilized for sputter deposition was plasma-sprayed fluorapatite [Ca10(PO4)6F2; FA]. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to analyze the coatings. The amorphous as-deposited coatings were annealed in air (at 500 °C or 600 °C) to a crystalline state consisting of a polycrystalline FA matrix with a small amount of microcrystallites of a different composition. The higher annealing temperature (600 °C) tended to produce coarser FA and microcrystallite grains; however, the coatings buckled on the titanium substrates as a result of the heat treatment. Attempts to form the FA phase by in situ annealing in the vacuum chamber at a substrate temperature of 500 °C were not successful. The average bond strength for the as-deposited and 500 °C post-annealed coatings was comparable, while the lowest bond strength was observed in the 600 °C post-annealed coatings. The results suggest that the 500 °C post-annealed coatings have a suitable structure and possess sufficient adherence to be acceptable for use in certain medical and dental implant applications, and further tests under physiologic conditions will be conducted.
Thermal Spraying of Functionally Graded Calcium Phosphate Coatings for Biomedical Implants
