Drying stress of yttria-stabilized-zirconia slurry on a metal substrate

Aqueous yttria-stabilized-zirconia (YSZ) nano-particle slurries (termed as nano-slurries later) were cast on metal substrates to form wet coatings. Stress development was measured using a substrate reflection method, coupled with drying kinetics measurements and coating structure examination. Lateral drying occurred and was controlled by the viscosity of the slurry. Tensile stress was generated due to constrained shrinkage of the wet coating when the slurry became saturated with water, starting from the coating edge when the solid concentration reached a certain level. As the saturated region extended to the centre, the stress increased to the maximum, then dropped quickly to zero due to cracking and delamination. Addition of micro-sized particles to the nano-slurry resulted in reduction of the peak stress while no apparent cracks were formed during drying. In addition, non-zero residual stress remained after drying, suggesting good bonding between the coating and the substrate.