Rejuvenation as the origin of planar defects in the CrCoNi medium entropy alloy

Yang Yang (), Sheng Yin, Qin Yu, Yingxin Zhu, Jun Ding, Ruopeng Zhang, Colin Ophus, Mark Asta, Robert O. Ritchie and Andrew M. Minor ()
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Yang Yang: National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory
Sheng Yin: Materials Sciences Division, Lawrence Berkeley National Laboratory
Qin Yu: Materials Sciences Division, Lawrence Berkeley National Laboratory
Yingxin Zhu: The Pennsylvania State University
Jun Ding: Xi’an Jiaotong University
Ruopeng Zhang: University of California
Colin Ophus: National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory
Mark Asta: Materials Sciences Division, Lawrence Berkeley National Laboratory
Robert O. Ritchie: Materials Sciences Division, Lawrence Berkeley National Laboratory
Andrew M. Minor: National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory

Nature Communications, 2024, vol. 15, issue 1, 1-9

Abstract: Abstract High or medium- entropy alloys (HEAs/MEAs) are multi-principal element alloys with equal atomic elemental composition, some of which have shown record-breaking mechanical performance. However, the link between short-range order (SRO) and the exceptional mechanical properties of these alloys has remained elusive. The local destruction of SRO by dislocation glide has been predicted to lead to a rejuvenated state with increased entropy and free energy, creating softer zones within the matrix and planar fault boundaries that enhance the ductility, but this has not been verified. Here, we integrate in situ nanomechanical testing with energy-filtered four-dimensional scanning transmission electron microscopy (4D-STEM) and directly observe the rejuvenation during cyclic mechanical loading in single crystal CrCoNi at room temperature. Surprisingly, stacking faults (SFs) and twin boundaries (TBs) are reversible in initial cycles but become irreversible after a thousand cycles, indicating SF energy reduction and rejuvenation. Molecular dynamics (MD) simulation further reveals that the local breakdown of SRO in the MEA triggers these SF reversibility changes. As a result, the deformation features in HEAs/MEAs remain planar and highly localized to the rejuvenated planes, leading to the superior damage tolerance characteristic in this class of alloys.

Date: 2024
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DOI: 10.1038/s41467-024-45696-z

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