HVSFS Deposition of TiO2 Coatings Using A Kerosene-Fueled Torch

HVOF-spraying of suspension feedstock, also known as High Velocity Suspension Flame Spraying (HVSFS), is a very promising technique for the deposition of thin (10 – 100 µm), dense ceramic coatings. Up until now, all experiments have been carried out using (suitably modified) gas-fueled HVOF torches, where the liquid stream is injected axially, upstream of the expansion nozzle. Liquid (kerosene)-fueled torches could improve further the denseness and mechanical strength of the coatings, because of their comparatively higher gas flow velocities, but they still haven't been used for suspension spraying, out of concern for insufficient heating of the feedstock, radially injected in a region of lower gas temperature.

This work anyway demonstrates that suspension spraying of a relatively low-melting ceramic material such as TiO₂ is possible using a kerosene-fueled GTV K2 HVOF torch. The coatings contain very little unmelted material and consist of tightly superimposed splats coming from molten droplets of micrometer and sub-micrometer size. Even the smallest ones flatten upon impact, thanks to their high in-flight velocity. Under ball-on-disk sliding wear conditions, the coatings undergo micro-scale plastic deformation, an ability that is enhanced with increasing temperature, so that, at 450 °C, negligibly small wear rates are obtained.