Understanding the impacting phenomena of yttria-stabilized zirconia (YSZ) particles and following coating formation in plasma spraying process is of importance to control and design the microstructure of coatings such as thermal barrier coatings. To this aim, recently, the authors have developed a novel in situ monitoring system for particle impacts under atmospheric dc plasma spraying conditions. This system utilized a high-speed video camera coupled with a long-distance microscope and was capable of capturing the particle-impinging phenomena at one million frames per second. To understand the coating formation mechanism, two approaches were attempted, that is, observation of the single splat formation and the following coating formation as the integration of splats. In the former case, the deformation and cooling processes of YSZ droplets impinging on substrates were captured successfully. In the latter case, multiple-droplet-impacting phenomena were observed as an ensemble treatment. Representing coating process, the tower formation (1- dimensional) and bead formation (2-dimentional) were observed under typical plasma spray conditions for thermal barrier coatings. By using a triggering system coupled with the motion of a robot, impact events were recorded for every pass. The obtained images clearly showed the coating formation resulted by the integration of single splats.

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