Study of the mechanics of the delamination of ceramic functional coatings

Delamination experiments were performed on composite materials consisting o f a thick ceramic coating on a metallic substrate as is common in thermal b arrier coatings (TBC). TBCs consist of a ceramic coating (200-400 mu m thic k) deposited on a metallic substrate. Failure and delamination of the ceram ic can be initiated by transverse cracks caused by sintering processes, the rmal stresses and internal oxidation during prolonged exposure to high temp eratures. Although these transverse cracks do not the function of the therm al barrier coatings, they may induce important stresses at the interface be tween substrate and coating, and delamination is initiated. The cracking an d delamination after continued loading of ceramic plasma sprayed ZrO2 coati ngs with a thickness ranging from 250 to 400 mu m was studied by four-point bending experiments. The estimation of the stress distribution and concent ration at the interface during these experiments allows the failure stress of the ceramic and of the toughness of the interface coating-substrate to b e evaluated. The interfacial toughness of a ZrO2 (Y) coating deposited on s and blasted Inconel 617 substrates was about two times higher than the same coating deposited on a polished CMSX4 substrate (K-1 = 3.0 and 0.9 MPa m(1 /2), respectively). (C) 1999 Published by Elsevier Science S.A. All rights reserved.