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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. [Display omitted] [ABSTRACT FROM AUTHOR]

We developed a novel high-performance L1 2 -strengthened high-entropy alloy (HEA) in the multicomponent Ni-Co-Fe-Cr-Al-Nb system. The phase transformation, mechanical properties and associated deformation behaviors were systematically investigated through combinational analyses involving the three-dimensional atom probe tomography (3D-APT), transmission electron microscopy (TEM) and first-principles calculations. In contrast to conventional alloys that generally strengthened by Ni 3 (Al, Ti)-type precipitates, a high density of coherent L1 2 nanoprecipitates with a new chemical constitution of (Ni, Co, Fe, Cr) 3 (Al, Nb) can be controllably introduced via elaboratively tuning the content of Al and Nb, resulting in a large lattice misfit of ~0.78% that rarely achieved in previous HEAs. The newly developed (Ni 2 Co 2 FeCr) 92 Al 4 Nb 4 HEA enables excellent tensile properties at a large temperature window from room temperature to 870 °C. More remarkably, an anomalous growth in yield strength can be observed at the temperatures above 600 °C, showing a peak yield stress over 720 MPa when deformed at 760 °C, which surpasses most of the previous L1 2 -strengthened HEAs, as well as the commercial superalloys. Detailed TEM analyses revealed that the multicomponent L1 2 precipitates are mainly sheared by the super-partial dislocations, forming superlattice intrinsic stacking fault (SISF) loops coupled with antiphase boundaries (APBs). Such an interesting deformation substructure enables sustained work hardening and produces high tensile strengths at the high temperatures. The underlying mechanisms of those SISF loops were carefully discussed, which could be possibly ascribed to the local elemental segregation on the planner faults. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A series of Al–Fe–Mo–Si alloys with and without additions of Ti and Zr for elevated temperature applications have been produced by rapid solidification. These alloys are mainly strengthened by Al12(Fe,Mo)3Si dispersoids, exhibiting superior elevated temperature strengths and better damping capacity than conventional aluminum alloys. [Copyright &y& Elsevier]