Local chemical order regulating dislocation behavior in CoCrFeNi high- entropy alloys: Suppressed dislocation nucleation and promoted pre- existing dislocation activation

ZC Li and X Jin and Q Zhang and AD Lan and JW Qiao, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 948, 149268 (2025).

DOI: 10.1016/j.msea.2025.149268

The influence of local chemical order (LCO) on the dislocation behavior remains a fundamental yet underexplored aspect in the design of high- performance high-entropy alloys (HEAs). In this study, the effects of LCO on the microplastic deformation behavior of CoCrFeNi HEAs are systematically investigated. Aberration-corrected scanning transmission electron microscopy provides direct evidence of LCO formed during furnace cooling. Nanoindentation pop-in analysis of load-displacement curves reveals that LCO decouples incipient plasticity, or micro- yielding, into both competing effects: suppressed dislocation nucleation and promoted slip activation of pre-existing dislocation. Statistical deconvolution of pop-in events, verified through the activation energy and defect density calculations, evaluates these dual roles. Atomic- scale molecular dynamics simulations combined with nudged elastic band calculations reveal that LCO increases the energy barrier for dislocation nucleation, thereby restricting dislocation formation during incipient plasticity. During subsequent loading, the LCO model displays increased intrinsic stacking fault energy, which inhibits the dissociation of pinned dislocations. Concurrently, the expanded plastic and shear strain zones, together with aligned high-stress regions beneath the indenter in the LCO model, imply enhanced activation of subsequent dislocation motion after initial dislocation passage through. This study provides atomic-to-nanoscale insights into how LCO governs dislocation behavior, offering a foundation for tailoring mechanical properties in HEAs.

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