Influence of Nb substitution for B on the microstructure, crystallization behavior and soft magnetic properties of FeBPCu alloys by two-step annealing

Alloying and annealing are essential approaches to optimize the soft magnetic performance of Fe-based amorphous/nanocrystalline alloys. This study systematically investigated the microstructure, crystallization behavior, and soft magnetic properties of Fe80.5B10-xP8Cu1.5Nbx (x = 0, 0.5, 1, & 1.5 at%) alloys prepared by substituting B with trace amount of Nb while maintaining a constant Fe content. The effects of Nb alloying on the Cu clustering process during pre-annealing were analyzed by Mo<spacing diaeresis>ssbauer spectra. The results indicate that the addition of trace amounts of Nb refines alpha-Fe nanocrystals and enhances the soft magnetic characteristics by promoting the formation of beneficial Cu clusters. However, excessive Nb content results in the coarsening of Cu clusters, which reduces the crystallization volume fraction and worsens the soft magnetic characteristics. The Fe80.5B9.5P8Cu1.5Nb0.5 nanocrystalline alloy possesses a saturation magnetic flux density of 1.81 T and a coercivity of 6.83 A/ m.