Kinetics of nanocrystallization in FeCoNbB(Cu) alloys

HITPERM alloys (FeCoMBCu; M=Nb, Zr, Hf...) have been recently developed and proposed as competitive soft magnetic materials for high-temperature applications. To our knowledge, this work contains the first results on nanocrystallization isothermal kinetics for these alloys. Analysis of nanocrystallization of the studied FeCoNbB(Cu) alloys in the frame of the Johnson–Mehl–Avrami theory shows a slowing-down of the kinetics and anomalously low values of the Avrami exponent, in a similar way to that reported for FeSiBNbCu (FINEMET)-type alloys. Compositional effects of Co substitution and Cu addition are considered. A more realistic kinetic model developed by Hermann et al. accounts for the experimental data.