Adhesive Failure of a Thin Epoxy Film on an Aluminized Substrate
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Adhesive Failure of a Thin Epoxy Film on an Aluminized Substrate N. R. Moody, D. F. Bahr*, M. S. Kent**, J. A. Emerson**, E. D. Reedy, Jr. ** Sandia National Laboratories, Livermore CA 94550 *Washington State University, Pullman, WA 99164 **Sandia National Laboratories, Albuquerque, NM 87185 ABSTRACT In this study we used nanoindentation to determine mechanical properties and combined nanoindentation with stressed overlayers to determine interfacial fracture energy of a 164 nm thick film of Epon 828/T403 on an aluminized glass substrate. The combination of nanoindentation and a tungsten overlayer was required to trigger delamination of the epoxy film from the aluminized substrate. Mechanics-based models for circular blister formation were then used to determine residual stresses and interfacial fracture energies. This approach showed that the tungsten overlayer had a compressive residual stress of 1.9 GPa which drove blister formation at a fracture energy of 1.9 J/m2 with a phase angle of loading equal to –62Û INTRODUCTION Determining adhesion of thin polymer films as well as their mechanical properties has become increasingly important as some applications shift from hard metallic and ceramic films to more cost effective polymeric films. These softer films have found a variety of uses, from surface protective coatings to functional layers with special magnetic and electric properties. Nevertheless, applications are limited by large thermal mismatchs between film and substrate which can lead to delamination and device failure. Quantitative measures of fracture energies are limited by a lack of established test techniques for very thin layer systems. Traditional test techniques such as double cantilever beam sandwich samples [1] often require relatively thick films while peel tests are dominated by plastic energy contributions as the film is bent. [2] The work of Bagchi et al. [3,4], and more recently the work by Bahr et al. [5] and Kriese and coworkers [6,7], shows that these limitations can be overcome for testing thin ductile metal films by deposition of a hard highly stressed overlayer. Zhuk et. al [8] extended this technique to the study of thin polymer films. In this study, we combined stressed overlayers with nanoindentation to study interfacial fracture of a thin epoxy film where the additional stresses from nanoindentation were required to trigger delamination. MATERIALS AND EXPERIMENTS The film system used in this study was created by first sputter depositing 200 nm of aluminum onto a microscope glass slide substrate. The aluminized substrate was plasma cleaned and spin coated with a 100:46 ratio of Epon 828/T403 to a thickness of 164 nm. The film system was then given a 50Û&KÛ&KFXUH The elastic modulus and hardness values of the film were measured using the continuous stiffness measurement option on a Nano Indenter II™ with a Berkovich diamond indenter. Ten indentations were made at an excitation frequency of 45 Hz and displacement of 3 nm 50 µm apart. [9,10] All tests were conducted in air a
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