MAGNETIC-PROPERTIES AND CORE LOSSES OF NANOCRYSTALLINE FE-M-B (M-EQUIVALENT-TO-ZR, HF OR NB) ALLOYS

A mostly single b.c.c. phase with nanoscale grain sizes of 10-20 nm was found to form by annealing amorphous Fe-Zr-B, Fe-Hf-B and Fe-Nb-B alloys prepared by the melt-spinning method for 3.6 ks in the temperature range 773-923 K. The highest mu(e) and B(s) values reach 22 000 and 1.63 T for Fe90Zr7B3, 32 000 and 1.59 T for Fe89Hf7B4 and 22000 and 1.49 T for Fe84Nb7B9 alloys. The low core loss of 0.066 W kg-1 at 1 T and 50 Hz was confirmed for the b.c.c. Fe89Hf7B4 alloy and is considerably smaller than that of a commercial Fe-based amorphous alloy being used in practical uses as core materials in transformer. The magnetostriction lambda(s) of Fe-M-B alloys shows a tendency to decrease with increasing annealing temperature and is as small as - 1 x 10(-6) for the b.c.c. Fe89Hf7B4 alloy. The small lambda(s) and the small grain size are concluded to be the reasons for the good soft magnetic properties. The residual existence of the amorphous phase with a large amount of solute elements in the grain boundaries of the b.c.c. phase was observed by high resolution transmission electron microscopy observations on the Fe84Nb7B9 alloy annealed for 3.6 ks at 923 K and is presumed to suppress the grain growth of the nanocrystalline b.c.c. phase.