Crystallization of ion beam deposited calcium phosphate coatings

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.