TEM Characterization of the Coating-Substrate Interface in Vacuum Cold-Sprayed Nano-TiO₂ Coating

This study investigates the microstructure of coating-substrate interfaces formed by vacuum cold spraying. Commercially available TiO₂ nanopowder was deposited on SnO₂-glass substrates using a lab-developed vacuum cold spray system. For comparison, TiO₂ coatings were also prepared by screen printing followed by mechanical pressing. Coating surfaces and interfaces were evaluated by means of TEM and SEM imaging and XRD analysis. SEM images show that screen-printed coatings have a crack-rich morphology, while mechanical pressed and vacuum cold sprayed coatings have no obvious cracks. TEM images, on the other hand, show the extent of bonding between TiO₂ nanoparticles and the glass substrate. Very little interface bonding was observed in screen-printed coatings in contrast to their vacuum cold sprayed and mechanical pressed counterparts. The difference is attributed to the higher pressures achieved by mechanical pressing and the high-velocity impact of vacuum cold spraying.