Abstract
Generally, strength and ductility are mutually exclusive in homogeneous metals. Nanostructured metals can have much higher strength when compared to their coarse-grained counterparts, while simple microstructure refinement to nanoscale generally results in poor strain hardening and limited ductility. In recent years, heterogeneous nanostructures in metals have been proven to be a new strategy to achieve unprecedented mechanical properties that are not accessible to their homogeneous counterparts. Here, we review recent advances in overcoming this strength–ductility trade-off by the designs of several heterogeneous nanostructures in metals: heterogeneous grain/lamellar/phase structures, gradient structure, nanotwinned structure and structure with nanoprecipitates. These structural heterogeneities can induce stress/strain partitioning between domains with dramatically different strengths, strain gradients and geometrically necessary dislocations near domain interfaces, and back-stress strengthening/hardening for high strength and large ductility. This review also provides the guideline for optimizing the mechanical properties in heterogeneous nanostructures by highlighting future challenges and opportunities.
Highlights
High strength in metals is always favorable in industry, while the elevation in strength is usually accompanied with the drastic loss in ductility [1,2,3,4,5,6]
In 1999, a concept of surface nanocrystallization on metals and alloys was introduced for the first time [35], a gradient structure was produced by surface mechanical attrition treatment (SMAT) and nanostructured (NS) grains were formed at the surface layer by repetitive severe plastic deformation (Figure 4a)
Using the same SMAT technique, we have produced a gradient structure in an IF steel and large tensile ductility was achieved in the NS surface layer of IF steel without apparent grain growth when confined by the coarse grains (CGs) substrate [14]
Summary
High strength in metals is always favorable in industry, while the elevation in strength is usually accompanied with the drastic loss in ductility [1,2,3,4,5,6]. The strain gradients should produce geometrically necessary dislocations (GNDs) and extra-hardening for better performance in mechanical properties [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30] In this regard, we will present a review in recent advances for heterogeneous nanostructures, and the addressed points are focusing on mechanical properties, microstructure characterization, and deformation physics. In this type of materials, the interplays between different adjoining microdomains with different grain sizes, phase constitutes, and/or dislocation substructures are crucial to understand the mechanical behaviors and guide the designing of ultra-strong materials with good tensile ductility [2,3,11,12,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
