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

Abstract

<p>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 /mm2. 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.</p>