The influence of the substrate topography on the plasma jet flow and particle deposition as a determining factor of Thermal Barrier Coatings (TBCs) build-up mechanisms in plasma spraying

Surface micro-texturing prior spraying is aimed to obtain the controlled columnar structure of Thermal Barrier Coatings and then improving thermal insulation properties. In this work, the flat substrates were first laser micro-textured and different pattern geometries were produced. Then, numerical model plasma jet hitting against such textured substrates with corresponding topographies were developed. Numerical modeling included turbulent flow models, such as transition SST model and Reynolds Stress Model, as well as a volumetric heat source that generates plasma jet flow while maintaining the thermophysical plasma properties throughout the process. The motivation for this investigation was to determine the influence of substrate micro-texture geometry on the behavior of the plasma jet flow in a substrate boundary layer. It opens the possibility of predicting the feedstock movement and its deposition on the substrate, which is essential in understanding the coating build-up mechanism as a whole. The numerical studies were then supported and verified experimentally by microstructural studies of TBCs deposited on substrates with a geometry corresponding to the numerical models.

Keywords: plasma spraying, thermal barrier coatings, micro-texturing, plasma jet modelling, substrate boundary layer, coating build-up