Buried interfaces – A systematic study to characterize an adhesive interface at multiple scales

Highlights: • Laser pretreatment generates a network of open porous nanostructures on Ti15-3-3-3. • TEM and serial sectioning show a nanostructure layer of ∼150 nm thickness. • The functional nanostructure is infiltrated by the polymer PEEK. • Ptychography allows differentiating between different materials in the buried interface. • Neither 2D nor 3D imaging shows channels in the buried interface down ∼3 nm. A comparative study of a model adhesive interface formed between laser-pretreated Ti15-3-3-3 and the thermoplastic polymer PEEK has been carried out in order to characterize the interfaces' structural details and the infiltration of the surface nano-oxide by the polymer at multiple scales. Destructive approaches such as scanning and transmission electron microscopy of microsections prepared by focused ion beam, and non-destructive imaging approaches including laser scanning and scanning electron microscopy of pretreated surfaces as well as synchrotron computed tomography techniques (micro- and ptychographic tomographies) were employed for resolving the large, μm-sized melt-structures and the fine nano-oxide substructure within the buried interface. Scanning electron microscopy showed that the fine, open-porous nano-oxide homogeneously covers the larger macrostructure features which in turn cover the joint surface. The open-porous nano-oxide forming the interface itself appears to be fully infiltrated and wetted by the polymer. No voids or even channels were detected down to the respective resolution limits of scanning and transmission electron microscopy.