Atomic-level study of twinning behaviors in metastable hexagonal high- entropy alloys

B Li and KS Ming and YC Zhang and N Zi and WQ Wu and J Wang, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 935, 148358 (2025).

DOI: 10.1016/j.msea.2025.148358

High-entropy alloy (HEAs) with a hexagonal close-packed (hcp) structure can be generated from the high-entropy face-centered cubic (fcc) matrix phase through martensitic transformation (MT) as deformed at low temperatures. 10 1 1 deformation twinning (DT) was widely observed in these deformation-induced hcp HEAs. Corresponding to local heating by plastic work, the deformation-induced hcp phase is generally metastable during plastic deformation. The metastability of the hcp phase facilitates the formation of high-density basal stacking faults (BSFs) and two types of fcc nano-bands with a 111 twinning relationship, significantly influencing 101 1 twin propagation and thickening. Using high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) simulations, we systematically investigated the behaviors of 101 1 DT and its interactions with BSFs and fcc nano-bands associated with reversible martensitic transformation (RMT) in the deformation-induced hcp phase. The dynamically coupled deformation mechanisms of RMT (fcc H hcp) and 111 DT generate complex structural evolutions within 10 1 1 twins, where kinematic paths of RMT are influenced by twin boundaries. Interactions between 101 1 twin and fcc nano-bands are categorized into "non-crossing" and "apparent crossing" mechanisms, depending on their crystallographic orientations. HRTEM characterizations and MD simulations reveal that 10 1 1 twin transmission through fcc nano-bands with low misorientation angles is facilitated by indirect slip transmission via re-nucleation of 101 1 twinning dislocations from the hcp/fcc phase boundaries. These findings provide an in-depth understanding of the deformation mechanisms in metastable hcp HEAs, highlighting the role of dynamically coupled DT and RMT mechanisms in governing microstructural evolutions during plastic deformation.

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