Development of suspension-based plasma and HVOF spray TiO2 coatings

Thermal spray is a versatile process that produces high-quality coatings possessing diverse properties like superhydrophobicity, wear resistance, corrosion resistance, dielectric properties etc. Conventionally, powder feedstock is used in thermal spray, and this process is commercialised in numerous industrial processes. However, liquid feedstock based thermal spray is still in its development phases, due to limited information available on process parameters. Various parameters like plasma/fuel gas, plasma current, feedrate, feeding angle, feedstock (type, concentration, viscosity, and solvent) etc. significantly influence the thermal and kinetic energy exchange between plasma/flame and feedstock material. Suspension plasma spray and suspension high velocity oxy-fuel spray (SHVOF), once optimised, can give rise to coatings with multi-scale features. An in-depth understanding of the complex interaction between feedstock solution/suspension chemical-physical properties and plasma/flame jet characteristics is essential to understand its specific impact on coating properties and their application. This paper presents comparisons between two different TiO₂ coatings, deposited by SPS and SHVOF, and obtained by varying some of the fundamental spray deposition parameters. The crystallographic phases and pore architectures of the coatings were compared through XRD analysis and SEM/EDX, respectively. Surface topographical information was collected through a profilometer and wetting properties were analysed through measuring the contact angles.