Thermal conductivity determinations of thermal barrier coatings

The thermal diffusivity and conductivity of several free-standing thermal barrier coatings (TBCs) and coatings bonded to superalloy substrates were investigated using the laser flash technique. The results show good agreement between conductivity values for the free-standing and bonded TBC layers when certain parameters are within acceptable ranges. The results of a sensitivity analysis to identify the critical parameters are presented. It was shown that layered samples consisting of many alternate layers can be treated as though they are homogeneous with conductivity values equivalent to those calculated from rules of mixtures. The effects of heat treatment on the conductivity of plasma-sprayed TBCs are discussed.