Optimization of Fe- doped TiO2/Al2O3 solution precursor plasma spray coatings for corrosion mitigation of heat exchangers

Thermal spray coatings can be tailored to possess multiscale features that increase surface area as well as mechanical and thermal properties. Thermal spray is therefore a promising technology to enable higher performance heat exchangers. The properties of these coatings can be controlled by varying the deposition parameters. Solution precursor plasma spray (SPPS) is a recently evolved plasma spray process that deposits thin coatings with micro- and nano-scale structures, and offers better control over the coating properties than the conventional plasma spray. In SPPS, droplets of precursor feedstock undergo a series of thermo-physical and thermo-chemical transformations leading to the formation of semi- or fully- molten particles, which form the coating. Since the solution precursor interacts with the energy source differently, as compared to the suspension plasma spray, it is essential to understand and optimize the operational parameters of SPPS. In this study, we have developed Fe-doped TiO₂/Al₂O₃ composite coatings through SPPS, by varying different parameters like standoff distance, plasma current and feedstock flow rate. The effects of different spray parameters on microstructures and elemental compositions were compared through scanning electron microscopy (SEM) and qualitative energy dispersive X-ray (EDX) spectroscopy. Corrosion behaviour of deposited coatings was analysed using electrochemical testing and SEM/EDX.