In this study, 1-roll melt spinning method has been utilized to produce a family of super sendust alloys with the nominal Nb content up to 0.6 at. %Nb, studies on magnetic properties, both optical and scanning electron microscope microstructure and X-ray diffraction have been performed under the conditions in which Nb content, annealing time and annealing temperature were chosen as variables. The alloy of $(Fe_{0.786} Si_{0.108} Al_{0.075} Ni_{0.0302})_{0.999} Nb_{0.001}$ was annealed at 1250℃ for 5 hour under hydrogen atmospheres, and then cooled to room temp. at a rate 1.7℃/S. Its magnetic properties were obtained as follows : Um=22,000, Hc=0.20e, $B_3=9,200$ Gauss.
Even though the grain size of super sendust alloys on the composition range from 0.03 at. %Nb to 0.3 at. %Nb annealed at 1250℃ was much smaller than that of super sendust alloy without Nb, the magnetic properties were improved by annealing. The magnetic properties tended to improve with both increasing annealing time and grain size in other alloys, too.
In the super-sendust alloy doped with relativiely large 0.4 at. % Nb to 0.6 at. % Nb, the grains grew slowly during the annealing process. However, the magnetic properties suffered. Both the slow grain growth and the worsened magnetic properties were ascribed to the precipitation of a new phase.
The magnetic properties of field cooled super sendust alloys of 0.03 at. % Nb to 0.6 at. % Nb were not greatly improved. This phenomenon is in contrast with the magnetic cooling effect of super sendust alloys without Nb, in with the magnetic properties were greatly improved.
