A. Kojima et al., SOFT-MAGNETIC PROPERTIES OF BULK NANOCRYSTALLINE FE-(NB,ZR,HF)-B ALLOYS PRODUCED BY EXTRUDING AMORPHOUS POWDERS, Journal of magnetism and magnetic materials, 162(1), 1996, pp. 95-102
Utilizing the softening phenomenon of amorphous alloys near the crysta
llization temperature, we have prepared bulk Fe84Nb7B9, Fe90Zr7B3 and
Fe89Hf7B4 alloys by extruding amorphous powders. The extruded bulk all
oys are composed of an amorphous phase containing a small amount of bc
c phase in the as-extruded state, and the structure changes to a mostl
y single bce phase with grain sizes of 10-25 nm by annealing at 923 K.
The soft magnetic properties of the bulk nanocrystalline alloys are b
etter for the alloys containing smaller volume fractions of bce phase
in the as-extruded state. This is presumably because the pre-existing
bcc grains in the as-extruded state cause an inhomogeneous nanostructu
re after annealing. Of the three alloys, Fe90Zr7B3 shows the best tend
ency to consolidate to the bulk form, with a high relative density abo
ve 99%, even by extrusion at a relatively low pressure P-e = 860 MPa.
This alloy exhibits the highest effective permeability mu(e) = 2350 at
300 Hz and flux density B-800, = 1.59 T, and the lowest H-c = 26 A/m.