Mechanical behavior of freestanding 8YSZ thin films under tensile and bending loads

Thermal barrier coatings (TBCs) with yttria stabilized zirconia (YSZ) as topcoat, are used to provide thermal insulation for the hot sections of gas turbine engines and other high temperature components. The aim of the present study is to evaluate the in situ tensile properties of plasma sprayed freestanding ZrO2 8 wt% Y2O3 top coat of similar to 250 mu m thickness. Air plasma sprayed films were prepared, using pre-fabricated templates, in the form of tensile specimens. Digital image correlation with optical imaging was used to obtain full-field deformation, and a strain resolution less than 0.01% was achieved. Further, the probability of failure in these coatings was investigated using Weibull analysis. The tensile stress vs. Strain curves of the coatings exhibited a non-linear behavior, with an elastic modulus of 12 +/- 4 GPa, and failure strength of similar to 16 +/- 4 MPa with a Weibull modulus (m) of 5. The bending strength and flexural modulus of these coatings were higher, and found to be similar to 69 +/- 12 MPa with 'm' of 10 and 37 +/- 8 GPa, respectively. Successive unloading-reloading experiments indicated the absence of non-linearity in tensile behavior with increase in number of cycles demonstrating the inhibition of frictional sliding of microcracks. Furthermore, fractography indicated intersplat shear and decohesion as probable failure mechanisms.