Tensile properties and statistical analysis of freestanding YSZ thin films with and without stress concentrations

Yttria-stabilized zirconia (YSZ) is used as a top coat in the thermal barrier coating system on superalloy components of aircraft engines, for its low thermal conductivity and superior thermal insulation properties. To avoid premature failure due to excessive operating temperatures, turbine blades and some engine components are provided with holes for cooling purposes. Therefore, in this study, the effect of stress concentrations on the tensile properties of freestanding YSZ thin films of ~300 μm was studied using samples with an inherent circular hole of Ø1 mm at the centre of the tensile sample, devoid of any machining. The effect of the presence of a circular hole on the tensile strength was studied and compared to that of continuous YSZ films using a custom-built uniaxial microtensile setup in conjunction with digital image correlation. A drop in fracture strength from 16 ± 4 MPa in continuous samples to ~11 ± 3 MPa in samples with a circular hole was observed. The cracks initiated at the circumference of the hole and perpendicular to the loading direction. Weibull statistical analysis was performed on tensile strength of continuous and hole containing samples. It was observed that the three-parameter method is more accurate for YSZ films than for two-parameter analysis. The properties reported in this current study could contribute to the design database for modelling the mechanical behaviour of YSZ.