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The effect of back stress on the mechanical behaviors of heterogeneous material is studied in two modeled heterogeneous laminates, i.e. laminated structure with a nanostructured (NS) Cu-Zn alloy layer sandwiched between two coarse-grained (CG) pure Cu layers. The improved tensile ductility of NS layer is revealed and attributed to the constraint from the stable CG layers. It is found that the elastic/plastic interaction between NS and CG layers is capable of significantly improving the back stress, which makes a significant contribution to the synergetic strain hardening in low strain stage. Furthermore, a higher mechanical incompatibility permits stronger and longer mutual interaction between layers, i.e. coupling effect, which contributes to a higher back stress. These results improve our understanding about the role of back stress on mechanical behaviors of heterogeneous laminate materials. [ABSTRACT FROM AUTHOR]

The low strength of pure Ti significantly limits its biomedical applications, although its biocompatibility is the best. Here, by controlled annealing and cryogenic drawing after rolling, we synthesize a set of pure Ti combining the strength of ultrafine-grained Ti and the ductility of coarse-grained Ti. The microstructure is characterized with fine grains (a few microns), abundant twins, and high dislocation density, which enable both short dislocation-slip path for strengthening and enough defects accumulation room for work hardening. Twins provide strengthening due to the subdivision effect of twin lamella on grains and dislocations accumulation near the twin boundaries. High flow stress helps to activate FCC phase transformation at large-strain stage. The excellent ductility is originated from the sustained work hardening enabled by the initial texture, fine grains, the interaction among dislocations, FCC lamellae, and twins. [ABSTRACT FROM AUTHOR]

Here the combination of synergistic strengthening and strain delocalization effects is realized in high-manganese steel by gradient microstructure designing, which results in an excellent strength-ductility synergy. Specifically, the gradient structure consists of two gradient surface layers sandwiching a coarse-grained center. Hardness and microstructure examinations reveal that the synergistic strengthening is originated from the enhanced twinning behavior and extra work hardening in gradient layers. The formation of dispersed strain concentration bands is found in the nanostructured surface layer, which evolves steadily and undertakes large applied strain, thereby leading to delocalized straining response. The formation and stabilization mechanisms of strain concentration bands are analyzed in depth with respect to the microstructure gradient. These findings shed light on the deformation fundamentals of gradient structure, especially on the hetero-deformation induced effects. [ABSTRACT FROM AUTHOR]