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

Y Yang and S Yin and Q Yu and YX Zhu and J Ding and RP Zhang and C Ophus and M Asta and RO Ritchie and AM Minor, NATURE COMMUNICATIONS, 15, 1402 (2024).

DOI: 10.1038/s41467-024-45696-z

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. High and medium-entropy alloys have shown excellent mechanical performance, yet the role of short-range order (SRO) on these properties has been unclear. Here, the authors demonstrate that the reduction of SRO by deformation leads to rejuvenation, explaining their remarkable damage tolerance.

Return to Publications page