MICROCRACK MORPHOLOGY OF AN ADHERENT COATING ON A THERMALLY MISMATCHED SUBSTRATE

It is well known that thermal expansion mismatch between a coating and a substrate often results in a microcracked coating. Depending on the degree of adhesion to the substrate, the coating can fracture at the interface (leading to coating spalling) or the coating can fracture no rmal to the plane of the interface. The latter is given attention in t his paper. A better understanding of the mechanics and the performance of coatings requires an improvement in the quantification of the coat ing crack morphology. This work proposes and implements a variety of c oating crack morphology measurements. Characterization has been accomp lished via section and plan views. Specimen preparation techniques and digital image processing approaches have been developed to make measu rements feasible. A data set from a chemically vapor deposited SiC-coa ted carbon-carbon composite substrate is given. The data obtained are used to propose two simplified models of the coating crack morphology.