Formation of Cold-Sprayed Ceramic Titanium Dioxide Layers on Metal Surfaces

Titanium dioxide (TiO2) coatings have potential applications in biomedical implants or as photo-catalytic functional systems. Cold spraying is a well-established method for metal on metal coatings. In cold spraying, the required heat for bonding is provided by plastic deformation of the impacting ductile particles. In contrast, few authors have investigated the impact phenomena and layer formation process for spraying brittle ceramic materials on ductile metal surfaces. In this study, the formation of TiO2 coatings on aluminum, copper, titanium, and steel substrates was investigated by SEM, TEM, XRD, and Raman spectroscopy. The results show that the deposition efficiency depends on spray temperature, powder properties, and in particular on substrate ductility, even for impact of ceramic particles during a second pass over already coated areas. Ceramic particles bond to metallic substrates showing evidence of shear instabilities. High-resolution TEM images revealed no crystal growth or phase transitions at the ceramic/metal interfaces.