High-temperature delamination mechanisms of thermal barrier coatings: In-situ digital image correlation and finite element analyses

Through in-situ high-temperature digital image correlation (DIC) and finite element simulation, we unveil new, critical delamination and fracture mechanisms of dense vertically cracked thermal barrier coatings (DVC TBCs). Full-field DIC strain maps of cross-sectioned TBCs during thermal cycling up to 1200 degrees C reveal the coupled formation mechanisms of vertical and horizontal cracks, which showed that horizontal cracks were formed by vertical crack deflection/branching. Horizontal crack growth was characterized by crack bridging, crack shielding, and crack deflection. Internal defects and weak interfaces such as pre-existing voids and inter-splat boundaries promoted crack formation. Finite-element simulations revealed that the interaction between the vertical and horizontal cracks produced favorable strain energy release rates (ERR) for horizontal crack initiation and propagation on the interior of the coating compared to along the bond coat interface, which contrasts with conventional delamination mechanisms. These results indicate that high-temperature DIC is a powerful tool for in-situ measurement of microstructure-processing-deformation-failure relationships that are otherwise unobtainable. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.