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Plasma sprayed ceramics exhibit nonlinear stress-strain behaviour under tension and compression due to porosity and microcracks existing in their microstructure. The modelling done in the previous works, was reported under compression and tensile loading of YSZ. In the present study, it was extended to the effect of microstructural parameters on tensile behaviour of YSZ and validates the experimental results and introduces the variation of stress with microstructural parameters. In this paper, the nonlinear tensile behaviour of YSZ plasma sprayed material is modelled phenomenologically by obtaining a relationship between microcrack density and tensile strength. The governing equations in this model are used from the previous works done on compression behaviour of plasma sprayed materials. In the present work, an empirical relationship between tensile stress and crack density is proposed based on the experimental stress strain curves obtained from the uniaxial tensile tests on freestanding YSZ coating. The variations in maximum strength corresponding to a strain and elastic modulus were also studied for different microcrack densities and porosity. Further, the effect of porosity and crack density on mechanical behaviour of YSZ coatings is extrapolated at different combinations of porosity and crack densities ranging from 0.1–0.5 per unit volume. The result obtained using the proposed numerical model was found to be in good agreement with the obtained experimental results and the non-linear tensile behaviour of YSZ could be modelled phenomenologically.

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 ~250 μm 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 ~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 ~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.