Mechanical behavior of heterostructured iron films with precisely defined bimodal architectures

Heterostructured metals exhibit a superior combination of strength, ductility and toughness compared to both nanocrystalline (NC) and coarse-grained metals with homogeneous microstructures. However, despite considerable advances in characterizing their mechanical behavior and deformation mechanisms, only limited progress has been made in synthesizing heterostructured metals with robust microstructural control. Here, we utilize a novel technique to synthesize heterostructured Fe films with precisely defined bimodal architectures wherein the NC (grain size ∼ 50 nm) and single crystal (SC) domains (> 1000 nm) are explicitly configured to be in parallel, series and wave-like architecture. As anticipated, the films with parallel architecture exhibited the highest strain to failure due to the co-deformation of NC and SC domains. But contrary to expectation, the wave-like architecture led to lower strength and strain to failure compared to the series architecture. This discrepancy arises due to the formation of larger dislocation pile-ups in the SC domains of films with wave-like architecture, which increases the local stress concentration and leads to early yielding and premature failure. These results demonstrate that the interplay between the geometry of dislocation slip and the spatial orientation of SC (coarse) domains is a key factor in determining the mechanical behavior of heterostructured metals. This synthesis method provides a route to systematically probe the relationship between the microstructural architecture and mechanical behavior of heterostructured metals, and tailor their mechanical properties in a reproducible manner.