Understanding the Adhesion Mechanism of Cold Sprayed TiO2 Coatings

We have shown the fabrication of ceramics titanium dioxide (TiO2) coating via cold spray process. Cold spraying of any hard ceramics coating is considered to be difficult, including TiO2. However, we could obtain a coating with thickness greater than 100 µm. The adhesion mechanism of this cold sprayed TiO2 coating needs to be clarified. The effects of process gas parameters and substrate materials on coating's adhesion strength were studied. It was found that adhesion strength did not vary significantly with the change of process gas parameters, indicating that mechanical embedment is not the sole factor of coating¡¦s adhesion. The study of changing substrate materials reveals the degradation of adhesion strength due to surface oxide layer and that TiO2 shows better adhesion on bare metal surface. Hence, by altering the surface chemistry, the adhesion of TiO2 is varied, indicating the possibility of physical or chemical bonding between cold sprayed TiO2 and substrate.