Nanocrystalline Fe-M-B-Cu (M=Zr, Nb) alloys with improved soft magnetic properties (abstract)

Abstract

We have recently succeeded in producing good soft magnetic properties and high saturation magnetic density (Bs) for nanocrystalline Fe-M-B (M=Zr, Hf, or Nb) ternary alloys prepared by melt spun and sputtered technic. The alloys have the mixed structure consisting of α-Fe particles with 10–20 nm in size embedded in a remaining amorphous phase. The nanocrystalline bcc Fe90Zr7B3, Fe89Hf7B4 and Fe84Nb7B9 alloy ribbons subjected to the optimum annealing exhibit high Bs of 1.5–1.7 T as well as high effective permeability (μe) of 22 000–32 000 at 1 kHz. The soft magnetic properties of the nanocrystalline Fe-M-B alloys were found to be improved by adding small amounts of Cu and by optimizing the chemical composition. The addition of Cu to the alloys decreases the bcc grain size. The excellent soft magnetic properties (high μe of 100 000 at 1 kHz combined with high Bs of 1.53 T) can be achieved in the region where small grain size as well as nearly zero magnetostriction are obtained, which is attained in the compositional range around Fe84Nb3.5Zr3.5B8Cu1. The soft magnetic properties can be further improved by preannealing before crystallization treatment, probably resulting from the decrease in the distribution of the grain size at the crystallized state. Consequently, the μe reaches the maximum value of 120 000 for the nanocrystalline Fe84Nb3.5Zr3.5B8Cu1 alloy.