Nanocrystallization Process of the Hitperm Fe-Co-Nb-B Alloys

Abstract

Crystallization behaviour, nanocrystallization kinetics and nanostructure characteristics of Nb containing HITPERM alloys are reviewed. The influence of the Fe/Co ratio in the alloy and the role of Cu as nucleant agent and refiner of the nanostructure are analysed. Clustering of Cu in the pre-crystallization stages is evidenced in these Nb-containing alloys from atom probe results. No difference in Co concentration between nanocrystals and the remaining amorphous phase has been found. The crystalline volume fraction at the end of the nanocrystallization process decreases for high Co content alloys and the mean size of nanocrystals decreases as the Co content increases for the Cu-free alloys whereas it is independent of Co content for Cu-containing alloys. A recrystallization process involving the bcc-Fe,Co phase occurs at the second crystallization stage and (FeCo) 23 B 6-type crystals form. An addition of Mn affects mainly the Curie temperature of the amorphous phase and Mn is rejected from nanocrystals and partitioned into amorphous residual phase.