High-entropy alloy (HEA) microfibers exhibit promising prospects in microscale high-tech applications owing to their exceptional mechanical properties and stability. However, the strength-plasticity tradeoff largely hinders their further industrial applications. Heat treatment can optimize the mechanical properties of HEA microfibers. However, it should be noticed that conventional heat treatment (CHT) faces challenges in precisely regulating microstructures within short durations while being prone to grain coarsening that compromises performance. This study employs an electric current treatment (ECT) technique to finely modulate the properties of cold-drawn CoCrFeNi high-entropy alloy microfibers at the microscale (~70 μm diameter), systematically investigating the effects of thermal and athermal effects during ECT on microstructure and mechanical properties via electron back scatter diffraction, transmission electron microscopy, and synchrotron radiation. A recrystallization, nucleation, and growth model for HEA microfibers is established. Compared to CHT, the synergistic effects of electron wind force and Joule heating during ECT significantly accelerate recrystallization kinetics, yielding finer and more homogeneous grains with a great decrease in dislocation density, and finally lead to better mechanical properties. The ECT-processed HEA microfibers achieve a yield strength ranging from 400 to 2033 MPa and a tensile elongation reaching 53%, which are markedly higher than those of CHT samples. This work demonstrates that ECT is effective for optimizing the microstructure and properties of HEA microfibers. Meanwhile, the results obtained here can provide both a theoretical foundation and technical guidance for the fabrication of high-performance metallic microfibers.
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