Microstructure and magnetic properties of SiO2/FeCoNiSi0.25 core-shell high-entropy alloys with nanotwinned structures

SiO2/FeCoNiSi0.25 core-shell high-entropy alloys (HEAs) containing nanotwinned structures combine good magnetic properties and bending ductility. This study successfully produced them by the combined mechanical alloying and spark plasma sintering method. The crystallization phase of the HEAs was a solid solution phase with a deformed twin face-centered cubic structure instead of a brittle intermetallic phase. In addition, the HEAs exhibited high yield strength (approximately 1365 MPa) and high plastic strain (about 22.5%). The magnetic intensity characteristics of the FeCoNiSi0.25 core-shell HEA significantly outperformed those of SiO2-shell-free HEAs. The improvement in mechanical properties and magnetic sensitivity can be attributed to the materials' strengthening and toughening by nanotwinned structures, while the excellent magnetic properties were due to the regulation of magnetic structure by grain boundaries and nanotwinned structures. These findings are instrumental in preparing HEAs with high magnetic sensitivity and an excellent combination of mechanical properties.