High strength and ductility in a heterostructured nanotwinned Ni film

We report the synthesis and mechanical behavior of two nanotwinned (NT) Ni films with different distributions of twin widths along the film growth direction. The NT Ni films, deposited on Si (111) substrates with an Ag buffer layer, are composed of two crystallographic variants with (111) out-of-plane orientation, which results in the formation of twin boundaries at their interfaces. The uniaxial stress-strain response of the freestanding NT Ni films was measured using MEMS tensile testing stages. While both films exhibited high strength, the film with a larger mean and broader distribution of twin widths exhibited significant strain hardening as well, which led to uniform elongation of ∼10%. These results suggest that by controlling the twin width distribution it is possible to realize a synergistic combination of strength and ductility in NT metal films.