Elastic modulus in composition-modulated copper-nickel foils

Abstract

The biaxial elastic modulus Y[111] was measured by bulge testing on Cu-Ni thin foils containing short-wavelength composition modulations produced by vapor deposition. In the wavelength range of 1.3–3.0 nm, we observed a twofold increase in the modulus as compared with homogeneous foils. The increase was proportional to the square of the composition amplitude. The maximum modulus occurred at a wavelength of 1.7 nm and an average composition of 45 at. % Cu. The stress-strain curves of the modulated foils were reversible but non-Hookean, while homogeneous foils displayed a Hookean behavior with moduli in good agreement with those calculated from the single-crystal elastic constants of bulk Cu-Ni alloys.