Microstructural characterization of porous thermal barrier coatings by laser flash technique

An inversion procedure has been developed to obtain microstructural parameters describing the porosity morphology of porous thermal barrier coatings (TBCs) from the thermal diffusivity measured in different environments by a laser flash technique. The model base for the inversion procedure combines the Knudsen effect (i.e. the thermal conductivity variation of gases within a pore as a function of pore size and shape) with the asymmetric Bruggeman model that describes the effect of porosity on the thermal conductivity of a porous medium in terms of pore shape, orientation and content. A simplified approach in the inversion procedure has been proposed, and the reliability has been checked by simulating different microstructures within the TBC. The inversion procedure has been also applied to experimental thermal diffusivity values of a TBC which were obtained by filling pores with He, N2, Ar and in vacuo.