Abstract
Thermal spraying is a material processing technique, which is based on the combination of thermal and kinetic energy. The used feedstock is melted in a hot flame and the melt is atomized and accelerated by means of atomization or process gases. The formed particles are rapidly solidified and consolidate to form splats as they hit a pre-treated substrate. The splats pile one-on-top-of-other forming lamellas and creating the final coating. In the work presented here a combination of cored wire (WC as filling powder) and massive wire (copper) were simultaneously sprayed using the twin wire arc spraying (TWAS) process. 3D micro tomography was used in order to gain knowledge about splat formation and layer build-up. Due to the high attenuation coefficient of tungsten in comparison with copper and carbon tungsten-rich particles and splats can easily be spotted in the tomogram of the coating layer. It turns out that besides irregular formed flat splats also ball-shaped particles exist in the coating layer which suggests that the spherical particles impacted on the substrate in an un-molten state. By 3D data processing tungsten-rich particles were visualized to analyze their spatial distributions as well as their geometric parameters were quantified. This work aims at contributing to the understanding of spraying processes.
