Achieving superb mechanical properties in CoCrFeNi high-entropy alloy microfibers via electric current treatment

Metallic microfibers with high strength and ductility are highly desirable for engineering applications. In this work, electric current treatment (ECT) is applied to CoCrFeNi high-entropy alloy (HEA) microfibers prepared by a multi-process of heavy-drawing. A high yield strength (1.1 GPa) and large uniform elongation (43%) are obtained in the microfibers ECTed at a current density of 140 A /mm ² . In-depth microstructural characterization indicates that the high performance is derived from a combination of controlled structural homogeneity, grain size, and intragranular dislocation density by ECT. This process generates a number of microstructural features including homogeneous ultrafine grains, low dislocation density, and dense 9R phase within the HEA microfiber. Among them, the low dislocation density enables significant dislocation scarcity-induced hardening beyond grain boundary strengthening, which brings hardening accounting for 47% of the yield strength. After yielding, the sequential activation of stress-dependent multiple hardening mechanisms endows the microfibers with a sustained strain-hardening capability and thus a large ductility. This work offers a promising avenue for achieving strength-ductility synergy in metallic microfibers.