Mechanical behavior of nanoscale Cu/PdSi multilayers

Abstract Berkovich nanoindentation and uniaxial microcompression tests have been performed on sputter-deposited crystalline Cu/amorphous Pd 0.77 Si 0.23 multilayered films with individual layer thicknesses ranging from 10 to 120 nm. Elastic moduli, strengths and deformation morphologies have been compared for all samples to identify trends with layer thicknesses and volume fractions. The multilayer films have strengths on the order of 2 GPa, from which Cu layer strengths on the order of 2 GPa can be inferred. The high strength is attributed to extraordinarily high strain hardening in the polycrystalline Cu layers through the inhibition of dislocation annihilation or transmission at the crystalline/amorphous interfaces. Cross-sectional microscopy shows uniform deformation within the layers, the absence of delamination at the interfaces, and folding and rotation of layers to form interlayer shear bands. Shear bands form where shear stresses are present parallel to the interfaces and involve tensile plastic strains as large as 85% without rupture of the layers. The homogeneous deformation and high strains to failure are attributed to load sharing between the amorphous and polycrystalline layers and the inhibition of strain localization within the layers.