EFFECTS OF MORPHOLOGY ON THE DECOHESION OF COMPRESSED THIN-FILMS

Residually compressed thin films are susceptible to spalling from subs trates. A prerequisite for this to occur is that a separation develop at the interface large enough to allow buckling. Thereafter, the mecha nisms of spalling are well-established, In this article, the mechanics of formation of the initial separation are addressed. Perturbations o n the interface ale deemed responsible for this process. Calculations of energy release rates for various interface morphologies have reveal ed that aperiodic perturbations can initiate and extend the separation s to a length sufficient for buckling. Conversely, periodic perturbati ons trap separations at dimensions too small to buckle. Illustrations are given for an alumina film (scale) on Ni-based superalloys. Implica tions for life prediction models are explored. (C) 1998 Elsevier Scien ce S.A. All rights reserved.