Evolution of Agglomerate Yttria Stabilized Zirconia Particles During Flight in Suspension Plasma Spray

Suspension plasma spraying (SPS) is a powerful coating technique for depositing high-quality thermal barrier coatings with promising mechanical and physical properties while taking advantage of the well-established Atmospheric Plasma Spray (APS) process. In this process, fine ceramic powders are suspended in fluids like water or ethanol before injection into a plasma jet. The heat from plasma evaporates the carrier fluid and leads to agglomeration of the particles. The optimum condition is that all particles arriving at the substrate are molten. However, some particles are semi-molten or unmolten upon impacting on substrate due to operating conditions. In order to optimize the coating performance especially for solid agglomerates, the evolution of suspension during flight in plasma jet should be investigated. In this study, agglomeration and sintering of yttria stabilized zirconia (YSZ) submicron particles in SPS has been studied. The transient and final agglomerate structures formed during the process has been studied. Various stages of the submicron particles agglomeration have been identified: formation of doughnut/cup-like microstructure, formation of polycrystalline and the final structure of an amorphous. A numerical model has been developed which allows us to predict and visualize the observed agglomeration stages during the evaporation of the liquid phase.