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

GY Li and Y Yang and BY Gou and JY Zhang and J Li and YQ Wang and LF Cao and G Liu and XD Ding and J Sun, ACTA MATERIALIA, 241, 118368 (2022).

DOI: 10.1016/j.actamat.2022.118368

Manipulating coherent twin boundaries (CTBs) opens an avenue to design strong nanostructured ma-terials. 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 similar to 2 nm, associated with excellent structural-mechanical stability after high-temperature (0.5Tm of Cu) an-nealing. 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. Un-der 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.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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