Magnetic Properties of Extruded Nanocrystalline Fe-Nb-B Alloys

A bulk Fe84Nb7B9 alloy was produced by extruding amorphous powder at temperatures (Te) between 653 and 723K, at pressures (Pe) between 824 and 1208 MPa, and at a speed (Ve) of 5 mm/s. The subsequent annealing of the extruded bulk alloy for 3.6 ks at temperatures between 873 and 973K resulted in the formation of a (for the most part) single bec phase, with grain sizes near 10 nm. The bulk alloy, extruded at a Pe above 1000 MPa, has a high relative density of 99%. The soft magnetic properties are better for bulk materials extruded at lower pressures, and the bulk alloy extruded at Te=698K and Pe=870 MPa exhibits a magnetization (B800) of 1.40 T, a permeability of 1123, and a coercive force (Hc) of 47 A/m, values which are inferior to those of the bec ribbon alloy (1.49 T, 22000, 8 A/m). The difference between the soft magnetic properties of the bulk material and the ribbon forms is presumably due to the inhomogeneity of the microstructure, oxidation of the powder, and the remainder of a higher internal stress in the bulk alloy.