Multiple mechanisms in Ni-rich high-entropy alloy for optimized strength and ductility across temperatures

High-entropy alloys (HEAs) have gained attention for their exceptional mechanical properties across a wide temperature range. At the same time, the alloys with sustained high strength and toughness across temperatures remain scarce. This study focuses on a Ni-rich HEA, Ni₄₄Fe₁₉Co₁₆Cr₉V₉Al₃, tailored specifically for elevated temperature applications. The alloy exhibits outstanding strength-ductility synergy at room temperature, low temperature (77 K), and high temperatures (873 and 1073 K). Its ultimate tensile strengths are about 1.59 GPa, 1.28 GPa, 1.03 GPa, and 619 MPa, respectively at 77, 293, 873, and 1073 K, accompanied by excellent ductility of 44.7%, 33.6%, 35.1%, and 13.7%, respectively. The exceptional mechanical behavior is realized by deliberate intervention reinforcement mechanisms at various temperatures, including back stress, dislocation, coherent precipitates, stacking faults, and TWIP effects. Furthermore, phase field simulation indicated that, besides the TWIP effect caused by the lower stacking fault energy, the subsequent deformation mechanisms, including the breakage of the wider twins into nanotwins to relieve the stress concentration, and the non-turning transfer of intracrystalline dislocations by the nanotwin boundaries, are important reasons for the high strength and high ductility of the alloy at 77 K. Conversely, at ambient temperatures, deformation is governed by hetero-deformation-induced hardening, driven primarily by the accumulation of geometrically necessary dislocations (GNDs). At elevated temperatures (873–1073 K), dynamic interactions between precipitates and dislocations dominate, involving mechanisms such as the Portevin-Le Chatelier effect and precipitate bypass (e.g., Orowan looping), with stacking faults further contributing to strengthening. This study presents a comprehensive understanding of the deformation mechanisms and can provide an efficient pathway for further enhancement of the alloy for broad temperature applications.