A preliminary study into the effect of oxide chemistry on the bonding mechanism of cold-sprayed titanium dioxide coatings on SUS316 stainless steel substrate

Current attention has focused on the preparation of thick ceramic coating of nano­structured materials as feedstock material using the thermal spray process. The cold spray method has appeared as a promising process to form ceramic nanostructured coating without significantly changing the microstructure of the initial feedstock materials due to its low processing temperature. However, deposition of ceramic powders by cold spray is not easy due to the brittle characteristics of the material. In this study, TiO2 coatings were deposited on unannealed stainless steel substrates and substrates that were annealed from room temperature to 700 °C prior to spraying. The adhesion strength was evaluated to investigate the bonding mechanism. The influence of the remaining surface oxide layer of chromium oxide, Cr2O3, which is thermodynamically preferred for stainless steel, on the bonding mechanism involved was investigated. The results showed that by increasing the annealing substrate temperature of stainless steel, the adhesion strength of the coatings (thicker oxide) is also increased. As a result, the bonding between the cold-sprayed TiO2 particle and the steel substrate is given by the chemical bonding of an inter-oxide reaction.