Experimental and analytical evaluation of damage processes in thermal barrier coatings

Progressive damage evolution was evaluated using microscopy on samples subj ected to a series of different thermal cycle profiles. Fick's law was used to describe the thermally grown oxide (TGO) buildup during early cycles. A correlation of damage thickness and oxide thickness for different thermal c ycle profiles was established. The importance of this correlation is that, for a given thermal cycle profile and number of cycles, the oxide thickness can be calculated analytically using Fick's law, and from this thickness o ne can determine the interlayer separation (damage thickness). Both oxidati on kinetics and interlayer separation (delamination) appear to have signifi cant roles with respect to spallation. As early microcracks coalesce to for m major delamination cracks or interlayer separation, the susceptibility fo r coating buckling is increased. The delamination cracks finally consume th e TGO layer. Progressive microcrack linking is a possible mechanism to deve lop such critical delamination crack lengths. Physical evidence of buckling was found in specimens prior to complete spallation. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.