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 develops at the interface large enough to allow buckling. Thereafter, the mech anisms of spalling are well-established. In this article, the mechanic s of formation of the initial separation are addressed. Perturbations on the interface are deemed responsible ibr this: process. Calculation s of energy release rates for various interface morphologies have reve aled that aperiodic perturbations can initiate and extend the separati ons to a length sufficient for buckling. Conversely, periodic perturba tions trap separations at dimensions too small to buckle. illustration s are given for an alumina film (scale) on Ni-based superalloys. Impli cations For life prediction models are explored.