Anomalous precipitate-size-dependent ductility in multicomponent high-entropy alloys with dense nanoscale precipitates

Precipitates are known to be effective obstacles for dislocation gliding, which can substantially increase the strength of metallic materials. In particular, dense nanoscale precipitates under a peak-aged condition can achieve a favorable precipitate size for pronounced strengthening, which, however, often causes progressive stress localization and premature failure of alloys with reduced ductility. Here, we showcase an “unusual ductilization effect from the peak-aged state” in a high-entropy alloy (HEA) system with a medium-to-high stacking fault energy (SFE). Compared with the under-aged HEA, the peak-aged HEA with relatively large precipitates exhibits a pronounced increment in both the strength and the tensile ductility, distinguishing from the conventional wisdom. Such an anomalous precipitate-size-dependence of ductility is achieved by trigging a unique multi-staged strain-hardening mechanism from the activation of microbands, which is enabled through a delicate modulation of precipitate size, volume fraction, and SFE of the precipitate-hardened HEA. Specifically, the dynamically active microbands upon loading can simultaneously serve as dislocation obstacles for strengthening and also the origins of stress delocalization, leading to a sustainable strain hardening for balanced mechanical properties. These discoveries shed new insights into the innovative design of ultrastrong and ductile metallic materials for advanced structural applications.