PRODUCTION OF NANOCRYSTALLINE BCC FE-NB-B BULK ALLOYS BY WARM EXTRUSION AND THEIR MAGNETIC-PROPERTIES

A bulky Fe84Nb7B, alloy was obtained by extruding the powders ground f rom amorphous ribbon, at temperatures T(e) between 563 K and 723 K at pressures P(e) between 824 MPa and 1208 MPa and at a speed of 5 mm s-1 . The bulk Fe84Nb7B9 alloy extruded at T(e) = 698 K and P(e) = 1208 MP a is in a fully consolidated state and has a density of about 99%. The bulk alloy is composed of a mostly single b.c.c. phase with a grain s ize of about 10 nm after annealing for 3.6 ks at temperatures between 873 K and 973 K, and its soft magnetic property tends to be better for the bulks extruded at lower pressures. The bulk alloy extruded at T(e ) = 698 K and P(e) = 824 MPa exhibits a high saturation magnetization B(s) of 1.40 T and a low coercive force H(c) of 64 A m-1 after anneali ng at 698 K.