Effects of pores and interfaces on effective properties of plasma sprayed zirconia coatings

It is difficult to establish structure-property relationships in plasma sprayed coatings because of their unique and intermingled splat microstructures incorporating networks of various intrinsic process-dependent microdefects. In this paper, these coatings are characterized using two distinctly different approaches, both based on novel experimental techniques and computational modeling tools. In each approach, detailed finite element models are illustrated to represent the porous coatings fabricated with four different types of zirconia feed powder. One approach is based on small-angle neutron scattering (SANS) studies carried out to quantify microstructure. In this approach, the pore morphology is idealized by artificially rebuilding, based on the collective microstructural information obtained in terms of component porosities of three pore systems, their opening dimensions and orientation. The other method relies on image analysis of real microstructural images obtained using scanning electron microscopy (SEM). The finite element mesh for the actual cross-sectional model, generated by thresholding the SEM images, is constructed with the object oriented finite (OOF) element method. Through these two approaches, the effective thermal conductivity and elastic modulus along the spray, as well as the transverse directions are estimated for thermally sprayed yttria-stabilized zirconia (PSZ) coatings. Our results show the effectiveness of these computational approaches for estimating material properties with each approach having its strength and weakness. However, in comparison with experimentally measured properties, there exist some limitations in both approaches. To further probe the source of discrepancy within the measurements, the coatings are thermal cycled to reduce the effect of splat boundaries on properties. Additional models are constructed for these coatings and their analysis is carried out. For the first time, the influence of the splat interfaces on the effective properties of sprayed coatings is quantified