High velocity flame spraying of highly-filled ceramic — Polymer filaments (F-HVOF)

A novel technique of spraying fine and ultra-fine powders via high velocity oxy fuel flame spraying (HVOF) is presented based on a highly filled filament as feedstock material – F-HVOF. The polymer material is used as a solid dispersion medium for the desired coating material, similar to the liquid dispersion medium in a suspension. Thus, the polymer works as a transportation medium only and is burned upon entering the combustion zone, thereby releasing the powder material. Within this study two filaments are fabricated and sprayed using Al2O3 and Al2O3-TiO2 87/13 ceramic powders in combination with low-density Polyethylene and Polybutylenadipat-Terephthalat, respectively. The filaments are characterized using TGA and electron as well as light microscopy. Compared to suspension spraying, filament spraying offers several benefits especially from a manufacturing and handling point of view as it is geared similar to a wire flame spraying method. In order to evaluate the potential of the new process, the coatings are characterized with regard to their microstructure, topography, microhardness, surface roughness and phase composition. The obtained results are compared to suspension sprayed samples and literature data.