Sol-gel-derived zirconia thin film coatings for titanium - 6-aluminum - 4-vanadium and 316L stainless steel implant applications: A study of zirconia microstructure and the response of the coating-substrate system to applied deformation

In vivo ageing of {dollar}sim{dollar}100nm alkoxide-sol-gel-derived zirconia films on Ti-6Al-4V was performed to assess low-temperature degradation of the film and interface. Morphology and crystal structure were unchanged after ageing for up to 12 weeks. Calcium phosphate precipitated onto samples aged in HBSS. Adhesion was investigated using a shear-lag protocol. At {dollar}sim{dollar}1.5% strain, cracks in the film were initiated from substrate slip bands. Gross delamination of the coating was not observed. This response was unchanged by ageing. Similarly, cracking of zirconia films on 316L stainless steel was associated with slip bands in the substrate. Delamination of the film was not observed, implying good adhesion. A model was proposed which examines microscopic-scale stress transfer across the film-substrate interface, and suggests why slip-band-induced cracking may occur instead of the transversely oriented cracks predicted by shear-lag analysis. TEM imaging showed that the film was crystalline, composed of {dollar}sim{dollar}50nm clusters of {dollar}sim{dollar}5nm subgrains.