Study On Preparation And Properties Of Fe-based Amorphous/Nanocrystalline Soft Magnetic Materials

Fe-base amorphous/nanocrystalline alloys have been reported to exhibit good soft magnetic properties, such as high permeability and high electrical resistivity, low coercivity and low core loss, attributed to their unique structures. Such excellent performance makes Fe-base amorphous/nanocrystalline alloys widely used in power electronics industry, and thus have attracted extensive interest. For Fe-based amorphous alloys, the inherent character of high stress sensitivity determines their soft magnetic properties. Optimized heat treatment can drastically reduce the internal stress and to a large extent strengthen performance of amorphous alloys, thus the soft magnetic amorphous componets can be qualified for the application with higher requirements.Therefore,studies on the heat treatment of amorphous alloys are significant for both engineering and science. And for Fe-based nanocrystalline alloys, the preparation into the form of nanocrystalline soft magnetic composites enable them applicable in the occasion required good high-frequency property and components with complicated shape, and allows the substitution of hig flux (Fe-Ni) and MPP soft magnetic composites, both raw material of which are cost consuming. Such application is the outstanding advantage of nanocrystalline alloys when used as soft magnetic materials.Study on nanocrystalline soft magnetic composites at the present is stil early and the preparation process remains to be further optimized to fill the demand of high frequency.Powder morphology in powder preparation process,electrical insulation of powder and the control of stress relaxation and nanocrystallization behavior in the final heat treatment are significant to the achievement of good performance.In this paper, the work can be divided into two parts as follows: First, effect of annealing conditions, including the annealing temperature, heating and cooling rate, on the mechanical preformance and electromagnetic properties of Fe-Si-B amorphous alloys has been investigated through the stress relief in the process of structural relaxation And the optimized annealing process has been obtained when treated at 380 ? for 2 h with the heating rate of 10 K/min and tapping temperature of 250 ?.Second, for the preparation process of nanocrystalline soft magnetic composites,influence of embrittlement annealing, passivator content for poweder insulation and annealing temperature on the properties of Fe-Cu-Nb-Si-B nanocrystalline magnetic powder core, including density, tensile strength, coercive force, permeability and core loss. This part focuses on effect of realaxation of internal stress and nanocrystallization behavior on the soft magnetic propreties. And the optimized properties of high permeability (115), low total core loss (200 mW/cm~3 measured when f= 50 kHz and Bm = 0.1 T) and low coercivity (4.5 Oe) have been achieved for Fe-Cu-Nb-Si-B nanocrystalline powder core when finally annealed at 575 ? for 1 h.