Deposition of TiO2 Coatings: Comparison Between High Velocity Suspension Flame Spraying (HVSFS), Atmospheric Plasma Spraying (APS) and HVOF-Spraying

The innovative High-Velocity Suspension Flame Spraying (HVSFS) process, whereby a conventional gas-fuelled HVOF torch is modified in order to allow the processing of liquid feedstock, was employed in order to spray a TiO₂ nanopowder suspension. Three different sets of parameters were employed. The structure, microstructure, nanohardness, tribological properties and photocatalytic activity of the resulting coatings were studied and compared to conventional atmospheric plasma sprayed (APS) and HVOF-sprayed TiO₂ coatings, manufactured using commercially available feedstock.

Compared to the APS and HVOF techniques, HVSFS enabled the deposition of thinner (20 μm – 60 μm thick), yet high-quality layers.

Moreover, it was found that the HVSFS process leaves a fairly large freedom to adjust coating properties (thickness, porosity, anatase content, hardness, etc…) according to the desired objective. Layers with higher anatase content and higher porosity can be produced, in order to achieve higher photocatalytic efficiency than conventional APS and HVOF TiO₂.

Alternatively, it is possible to deposit dense layers, with lower porosity and pore interconnectivity and better hardness and wear resistance than as-deposited APS and HVOF coatings.