Unraveling the role of the BCC-B2 transition and V occupancies in the contradictory magnetism-ductility relationship of FeCoV alloys.

The contradictory relationship between magnetism and ductility restricts further applications of FeCoV alloys in high-performance electrical machines. The role of the BCC-B2 transition, accompanied by vanadium (V) site occupancies, in magnetic moments and ductility has been explored using first-principles calculations. The variations in magnetism and ductility of FeCoV alloys are attributed to the coupling of the BCC-B2 transition and V occupancies. When V replaces Fe atoms in the equiatomic B2-FeCo alloy, the superior magnetism observed in B2-Fe 50- c Co 50 V c alloys is a consequence of the enhanced local magnetic moment of Fe and the ferrimagnetic-ferromagnetic transition in the magnetic state. Moreover, due to the preferential V occupancy in the B2 phase, the B2-Fe 46 Co 50 V 4 alloy exhibits comparable ductility to the BCC-Fe 50 Co 46 V 4 alloy. The results indicate that the increased brittleness in the B2 phase arises from the raised Peierls stress and the enhanced covalent component in interatomic bonding, which is caused by the strong hybridization between Fe and Co atoms. Pearson correlation analysis illustrates that valence electron concentration (VEC) and V content are significant factors in the contradictory relationship between magnetization and ductility. The theoretical results demonstrate that tuning the V content and atomic occupancies is helpful to achieve a trade-off between magnetization and ductility in B2-FeCoV alloys. • The coupling effect of the BCC-B2 transition and V occupations on magnetic moment and ductility. • The underlying origins of magnetism-ductility contradictory relationship. • A trade-off between magnetic moment and ductility can be obtained in B2-Fe 46 Co 50 V 4 alloy. • the magnetization can be improved by adjusting VEC and V content. [ABSTRACT FROM AUTHOR]