Properties and immersion behavior of magnetron-sputtered multi-layered hydroxyapatite/titanium composite coatings

A new biocompatible multi-layered coating was developed by alternately depositing Ti and HA layers on Ti6Al4V substrates using radio frequency magnetron-assisted sputter processing to improve the interface properties between the coating and the substrate. The multi-layered coating consisted of an underlying Ti bond coat, the alternating layer, and an HA top-layer. Between the bond coat and the top layer, an alternating layer was created by means of gradually increasing Ti content with increasing depth from the HA top-layer. The experimental results indicated that the as-sputtered coating had quite uniform thickness and well bonded to the substrate. The multi-layered coating exhibited a better electrochemical behavior than monolithic HA coating. The XRD and low vacuum SEM results consistently indicated that highly crystalline coating was not appreciably dissolvable in simulated body fluid. The adhesion strength higher than 60 MPa did not change much even after 14 weeks of immersion. The multi-layered composite coatings had the advantages of high and non-declining adhesion strength and high resistance to SBF attack.