Project Leader: Dr. Megan J. Cordill

Abstract

In most applications, thin films are cyclically loaded and fail through specific fatigue mechanisms. Sub-micrometric thin metal films behave, and thus fail, differently than bulk materials. This has been attributed to the prominent presence of an interface to a substrate and to the free surface, which strongly affects the dislocation processes pertaining to bulk fatigue. What has not yet been examined is how the type of interface controls the fatigue behavior of thin films. Interfaces can be considered as hard, created with a rigid ceramic or metal substrate, soft, next to a polymer substrate, or films can have no interface and be free‐standing. It is believed that the interface type is a dominant parameter that controls the deformation mechanisms and final failure of the thin metal films as a function of the microstructure, yield strength and cyclic stress amplitude. 

In order to obtain deformation and failure information on thin films and their specific interface, a thorough and systematic investigation is required. We are using advanced in‐situ micro-mechanical testing methods to examine the role of the interface type, hard, soft, or no interface, on the damage formation and failure of thin metal films. Of note is the use of sophisticated in‐situ bulge testing, X‐ray diffraction techniques and transmission electron microscopy with cyclic mechanical testing to observe film deformation, possible grain growth, extrusion formation, film cracking or delamination. Direct observations enable the decoupling of the microstructural response from the interface induced mechanisms.