SOFT-MAGNETIC PROPERTIES OF NANOCRYSTALLINE BCC FE-(NB, ZR)-B BULK ALLOYS CONSOLIDATED BY WARM EXTRUSION

We obtained Fe84Nb7B9 bulk alloys by extruding amorphous powders at temperatures (T-e) between 653 and 723 K and pressures (P-e) of 820 to 1210 MPa, and Fe90Zr7B3 bulk alloys by extruding al T-e of 673 to 698 K and P-e of 920 to 940 MPa. Subsequent annealing of these bulk alloys at 923 K for 3.6 ks causes the formation of a nanocrystalline bcc phase with grain sizes of 9 to if nm for Fe84Nb7B9 and 20 to 30 nm for Fe90Zr7B3. The bce Fe84Nb7B3 bulk alloy exhibits a magnetization (B-800) Of 1.40 T, a permeability (mu(e)) of 1120 at 300 Hz, and a coercive force (H-c) of 48 A/m in the extrusion condition of T-e = 698 K and P-e = 870 MPa. Similarly, the B-800 mu(c) and H-c of the bcc Fe90Zr7B3 bulk alloy prepared at T-e = 698 K and P-e = 923 MPa are 1.57 T, 1880 and 29 A/m, respectively. The soft-magnetic properties of the bcc Fe90Zr7B3 bulk alloy are superior to those of the bce Fe90Nb,B, bulk alloy, presumably because of the formation of a more homogeneous bce structure for the former alloy.