Immersion behavior of RF magnetron-assisted sputtered hydroxyapatite/titanium coatings in simulated body fluid

The focus of the present study was on the dissolution/degradation behavior of a series of magnetron-sputtered, single-layered HA/Ti coatings on Ti-6Al-4V substrate immersed in SBF. Changes in coating morphology, crystal structure, and adhesion strength with immersion time are characterized. XRD, FTIR, and LVSEM results consistently indicate that highly crystalline monolithic HA coating is very dissolvable in SBF. The monolithic HA coating is largely delaminated in 3 weeks and entirely peeled off the substrate in 7 weeks. The dissolution is even greater for 95HA/5Ti coating, which severely disintegrated in only 1 week. The amorphous-like coatings sputtered from targets comprising 10 vol % or more Ti, however, appeared almost intact, and their adhesion strengths, which were all higher than 60 MPa, did not change much (within 10%) even after 14 weeks of immersion. The coatings from targets comprising roughly 10-50 vol % Ti combine advantages of high and nondeclining adhesion strength, high resistance to SBF attack, and possibly much higher bioactivity (with large amounts of Ca, P, etc., dissolved in the coatings) than that of Ti.