Stabilizing defective coherent twin boundaries for strong and stable nanocrystalline nanotwinned Cu.

Manipulating coherent twin boundaries (CTBs) opens an avenue to design strong nanostructured materials. However, below a critical TB spacing, these inherently defective CTBs decorated with kink-like steps (abbreviated by kinks) and intersected with grain boundaries (GBs) will suffer from the thermal/mechanical instability, leading to the degradation of material properties. Here, utilizing Cr-segregation at kinks and GBs via a minor (1 at.%) Cr-doping, we report the nanocrystalline-nanotwinned (NNT) Cu-Cr alloy manifests continuous strengthening reaching 1.2 GPa at extremely fine TB spacing of ∼ 2 nm, associated with excellent structural-mechanical stability after high-temperature (0.5 T m of Cu) annealing. The underlying mechanism mainly originates from the highly stabilized defective CTBs controlled by Cr-segregation at kinks and TB-GB junctions, which facilitates the plastic deformation mode transition: from detwinning dislocation nucleation to stacking faults (SFs) accumulation for ultrahigh strength. Under elevated temperature, the stabilized TBs inhibit GB motion and therefore result in enhanced thermal stability of NNT Cu-Cr alloys, which is quantitatively explained via a modified Zenner pinning model. Our findings not only deepen the understanding of deformation mechanisms in nanotwinned metals, but also provide a new perspective to design plainified Cu alloys with high performances. [Display omitted] Take nanocrystalline-nanotwinned Cu with minor Cr addition as an example, we synthesis a class of plainified, strong and stable Cu alloys and meanwhile demonstrate a novel alloy-designing concept, that the highly stabilized defective TBs controlled by grain boundary segregation can render ultrahigh strength and impart high thermal/mechanical stability to nanostructured metals. [ABSTRACT FROM AUTHOR]