Enhanced strength-ductility synergy in pure Cu through the design of alternating coarse-grained and nanostructured layers

Heterogeneous micro/nano laminated structure (HM/NLS) design has emerged as a promising strategy for circumventing the strength-ductility trade-offs in nanostructured metals. However, most of reported HM/NLSed metals is mainly prepared from two dissimilar metals, which make it challenging to fully understand the deformation mechanisms of HM/NLS due to the complicated coupling of microstructural and compositional difference between component layers. Here, a series of HM/NLSs, consisting of alternating coarse-grained (CGed) and nanostructured (NSed) layers with varied thickness ratio (RCGed/NSed) of CGed layers to NSed layers, have been designed and introduced into pure Cu, which aim to exclude the influence of compositional difference between component layers and investigate the effect of microstructural difference on the deformational behavior of HM/NLSed metals independently. The effects of RCGed/NSed on the mechanical property of HM/NLSed Cu were investigated and an optimized strength-ductility synergy was achieve when RCGed/NSed = 2:3. Loading-unloading-reloading tests and in situ EBSD characterization reveal that the huge microstructural discrepancy between the neighboring CGed and NSed layers promotes dislocations accumulation and produces strong back stress strengthening during plastic deformation, thereby achieving a high yield strength ~296 MPa and large uniform elongation of ∼18%. The results of this work will provide a viable approach for fabricating high-performance HM/NLSed metals and deepen the understanding of the underlying deformation mechanisms of HM/NLSed metals.