Aging Behavior of Water-Based YSZ Suspensions for Plasma Spraying of Thermal Barrier Coatings

Suspension stability is a key parameter that should be considered in any coating process utilizing a suspension as the main feedstock. Application of water as the liquid phase for suspension preparation is promising due to its availability, low cost and no toxicity. In the present study, the effects of three surfactants, polyethyleneimine (PEI), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) and α-Terpineol, on the functional stability of yttria-stabilized zirconia (YSZ) water-based suspensions were investigated. The changes in the suspensions' zeta potential, pH, viscosity and Turbiscan Stability Index (TSI) were monitored over their aging time of 1 to 7 days. The results showed that α-Terpineol is the most effective surfactant to produce functionally stable suspensions with low viscosity and surface tension values. Plasma spraying of such stable suspensions results in the formation of thermal barrier coatings (TBCs) with columnar morphology having porosity in the range of 17 to 18 vol.%.