Numerical analysis of the plasma-induced self-shadowing effect of impinging particles and phase transformation in a novel long laminar plasma jet

Currently, the self-shadowing effect of impinging particles is recognized as a vital factor to form columnar-like coating in the manufacture of thermal barrier coatings. Most of these quasi-columnar coatings are usually prepared under a very low-pressure condition. This paper investigates a novel quasi-columnar yttria stabilized zirconia (YSZ) coating using an atmospheric plasma spray-physical vapor deposition method. The microstructures of the coating present a quasi-columnar structure that is distributed along the cross-section of the coating within certain intervals with a large number of cluster-like structures on the top surface of the coating. A lower particle velocity that contributes to the generation of a mass of vapor YSZ materials is studied via experimental and numerical analyses and these results are compared with other current plasma spray methods. The mechanism of the self-shadowing effect from impinging particles that leads to the formation of a quasi-columnar feature at the boundary layer of the substrate is demonstrated by a three-dimensional numerical simulation and experimental observation. Furthermore, the hybrid growth model of the vapor and droplet co-deposited coating is clarified in this paper.