Nano-/Ultrafine Eutectic in CoCrFeNi(Nb/Ta) High-Entropy Alloys

The development of single-phase high-entropy alloys (HEAs) emerges as a new paradigm shift in material research society during the last decade. A strong rise in the demand for structural and functional applications leads to the design and fabrication of super-strong eutectic HEAs through solidification processing. We report on the evolution of eutectic microstructure in CoCrFeNiNb0.5 and CoCrFeNiTa0.4 HEAs synthesized by arc melting. The evolved microstructure consists of nanolamellae of FCC γ-Ni and hexagonal β (Fe2Nb or Co2Ta type) Laves phases of 150 nm lamellae thickness. These alloys exhibit high yield strength of 2 GPa, ultimate compressive strength up to 2.2 GPa and 20% plastic strain. The strain rate jump test and transmission electron microscopic studies of deformed specimens have been performed to explore the microscopic mechanism of deformation in these high-strength advanced eutectic alloys.