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; Andrew M Minor

doi:10.1038/s41467-024-45696-z

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

Nat Commun. 2024 Feb 16;15(1):1402. doi: 10.1038/s41467-024-45696-z.

Authors

Yang Yang^{1

2}, Sheng Yin³, Qin Yu³, Yingxin Zhu⁴, Jun Ding⁵, Ruopeng Zhang⁶, Colin Ophus⁷, Mark Asta^{3

6}, Robert O Ritchie^{3

6}, Andrew M Minor^{8

9}

Affiliations

¹ National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. yangyang@alum.mit.edu.
² Department of Engineering Science and Mechanics and Materials Research Institute, The Pennsylvania State University, University Park, PA, USA. yangyang@alum.mit.edu.
³ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁴ Department of Engineering Science and Mechanics and Materials Research Institute, The Pennsylvania State University, University Park, PA, USA.
⁵ Center for Alloy Innovation and Design (CAID), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, China.
⁶ Department of Materials Science and Engineering, University of California, Berkeley, CA, USA.
⁷ National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁸ National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. aminor@berkeley.edu.
⁹ Department of Materials Science and Engineering, University of California, Berkeley, CA, USA. aminor@berkeley.edu.

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.

Grants and funding

DE-AC02-CH11231/U.S. Department of Energy (DOE)