Large strain deformation of bimodal layer thickness Cu/Nb nanolamellar composites

Nanolayered composites have garnered much attention due to their ability to withstand deformation to large strains, shock deformation, and irradiation induced microstructural damage. These behaviors have been attributed to high densities of bimetal interfacial content. Although they exhibit yield strengths approaching theoretical limits, multilayered materials with layer thicknesses less than 10 nm have shown limited ductility in rolling. In this study, bimodal 4 nm/40 nm Cu/Nb multilayers are rolled to 30% thickness reduction without the onset of shear instability. The stacking order used allows focus to be drawn specifically to the ductility by the boundary crossing mechanism exhibited in multilayered materials with layer thicknesses below 10 nm. Through the geometric constraint offered by alternating 4 nm and 40 nm layer thickness modes, the onset of localized shear is avoided and the 4 nm layers can be rolled to large strains.