The elastic biaxial modulus of Ag–Pd multilayered thin films measured using the bulge test

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Abstract
Analysis and sample preparation techniques for the bulge test have been improved to the point where the test can provide reliable and accurate measurements of the mechanical properties of thin films. Ag-Pd multilayer films of variable bilayer period were prepared for this study and characterized by cross-section transmission electron microscopy and by x-ray methods. The films were tested in the bulge test to determine their biaxial moduli. The data show no peak in biaxial modulus at a critical composition wavelength and no nonlinear elastic behavior. They do show a slight trend toward increasing elastic modulus with increasing strength of (111) crystallographic texture. These findings refute a previous report of the “supermodulus” effect in this system and add to the evidence that the effect is caused by artifacts of the mechanical testing technique. Methods for eliminating such artifacts are discussed.