Study On Tensile Stress Annealing For Fe-based Nanocrystalline Alloys

A new way of stress annealing was carried out on the Fe-based nanocrystalline alloys in the dissertation. The effect of the annealing parameters, alloy composition and cooling rate on soft magnetic properties were systematically studied for toroidal cores of Fe73.5Cu1Nb3Si13.5B9 and (FeCo)₇3 5Cu₁Nb3(SiB)22 5 alloys with and without stress annealing. Crystallization temperature of the as-quenched alloys were measured by DSC. The microstructure of crystallized phase was investigated by X-ray diffraction. The static magnetization curves and hysteresis loops were measured by the ballistic galvanometer. In addition, the stress-induced magnetic anisotropy constant Ku was determined with magnetization work.The study shows that the alloys under stress annealing can obtain transversal induced magnetic anisotropy. The remanecne decreases with annealing temperature and reaches minimum value at 560 ℃ for Fe73.5Cu₁Nb₃Si 13.5B9 alloys under stress annealing, then it increases gradually as annealing temperature raises. The remanence decreases with annealing time and then remains unchanged as annealing time exceeds 20min for Fe73.5Cu1Nb3Si13.5B9 alloys with stress annealing. The alloys with stress annealing have a lower remanence, slightly higher coercivity and much higher core loss than that without stress annealing. With stress annealing alloy cooled in the furnace obtains a lower remanence than that cooled in the air. Under the same stress annealing conditions, the alloy of Fe73.5Cu1Nb3Si13.5B9 shows a more obvious stress-annealing effect with the stress-induced magnetic anisotropy constant Ku for the alloy of Fe₇3.5Cu₁Nb₃Si₁3.5B₉ and (FeCo)73.5Cu₁Nb₃(SiB)22.5 up to 87.2J/cm3 and 10.1 J/cm3, respectively.The magnetization curves for the alloys with stress annealing shows that it is difficult for alloys with stress annealing to be magnetized. The hysteresis loops for the alloys with stress annealing are flatter than that without stress annealing.Results of X-ray diffraction showed that the crystallized phase has almost the same microstructure for alloys with and without stress annealing under the same annealing conditions.