4.7 Article

Dynamically reversible shear transformations in a CrMnFeCoNi high-entropy alloy at cryogenic temperature

期刊

ACTA MATERIALIA
卷 232, 期 -, 页码 -

出版社

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2022.117937

关键词

High-entropy alloy; Deformation twinning; Martensitic phase transformations; Mechanical properties; High-resolution electron microscope

资金

  1. National Natural Science Foundation of China [52002109, 51771201, 52071124]
  2. Natural Science Foundation of the Hebei province [E2020202088, E2021202135]
  3. Natural Science Foundation of Tianjin [20JCZDJC00440]
  4. Overseas Scientists Sponsorship Program by Hebei Province [C20210331]
  5. Open Research Fund from the State Key Laboratory of Rolling and Automation, Northeastern University [2020RALKFKT002]

向作者/读者索取更多资源

Under extremely low temperature, the CrMnFeCoNi high-entropy alloy exhibits dynamically reversible shear transformations, leading to the formation of dynamic nano-laminated dual-phase structures. These transformations enhance the strength, strain-hardening ability, and ductility of the alloy, providing a new approach to tackle the strength-ductility dilemma.
Shear transformation, such as twinning and martensitic phase transformation, is generally unidirectional under monotonic thermal or mechanical loading. Here, we report the dynamically reversible shear transformations in a CrMnFeCoNi high-entropy alloy (HEA) under uniaxial tension at the extremely low temperature of 4.2 K. Since stacking fault energy (SFE) of CrMnFeCoNi HEA with a face-centered cubic (fcc) structure is low and decreases with decreasing temperature, plastic deformation is accommodated by dislocation slips and shear transformation bands, such as {111} stacking faults (SFs), {111} nano-twins and fcc -> hcp (hexagonal close-packed structure) shear transformation bands. When deformed at 4.2 K, the lower SFE promotes fcc -> hcp shear transformation, forming hcp grains. Besides basal and non-basal dislocation slips in hcp grains, high-density {0 0 01} SFs and {1 0 1 over line 1} nano-twinning are activated to accommodate plastic deformation. More intriguingly, reverse hcp -> fcc shear transformations are stimulated by deformation-induced local dissipative heating. The reversible fcc <-> hcp shear transformations and both {1 0 1 over line 1} and {111} nano-twinning lead to dynamic nano-laminated dual-phase (NL-DP) structures, which advances the monotonic dynamic Hall-Petch effect in enhancing strength, strain-hardening ability, and ductility by dynamically tailoring the type and width of shear transformation bands. Our work provides a promising strategy for evading the strength-ductility dilemma via dynamically developing NL-DP structures through activating reversible shear transformations.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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