Investigation On Properties Of Nanocrystalline FeCo-based Soft Magnetic Alloys At High Temperature And High Frequency

With the development of information technology and digitalization of electronic equipment, there are new demand to soft magnetic materials, such as high frequency, miniaturization and low core loss. Nanocrystalline soft magnetic alloy Fe_73.5Cu₁Nb₃Si_13.5B₉ has been studied widely because of its high permeability, high saturation induction and low coercive force. But high core loss and low working temperature define its applied field. On the base of nanocyrystalline Fe-Cu-Nb-Si-B, we added Co and got Fe-Co-Cu-Nb-Si-B alloys. Their properties at high temperature and high frequency were researched.1. The microstructure properties for Fe-Co-Cu-Nb-Si-B alloy annealed at different temperature of different alloy content were studied. Changing the alloy content and annealing temperature have great influence on microstructure of FeCo based soft magnetic material. Increasing the content of Cu and Co, the initial crystallization temperature of amorphous alloy decreased. Adding Cu decreased the clustering temperature of Cu, and Co restrained the formation of Cu cluster. Too higher or lower clustering temperature deteriorated the property of soft magnetic alloy. Microstructure and grain size of FeCo based alloy annealed at different temperature were analyzed by X-ray diffraction. Annealed above the initial crystallization temperature, a-FeCo soft magnetic phase in amorphous matrix was obtained. Along with the improvement of annealing temperature that ordered (FeCo)₃Si phase was obtained. Annealed above the crystallization temperature of hard magnetic phase, the formation of boride was observed, the soft magnetic property of alloy deteriorated.2. We studied the room temperature magnetic properties of Fe-Co-Cu-Nb-Si-B orbicular core samples at high frequency. Result indicated that changing alloy content and annealing temperature had effect on magnetic properties of FeCo based soft magnetic alloy at high frequency. For Fe_39.4-xCo₄₀Cu_xNb_2.6Si₉B₉ (x=0.5,1.0,1.5), when x=1.0, the highest complex permeability can be obtained. The frequency spectrum is relaxed. For (Fe_100-xCo_x)_78.4Cu₁Nb_2.6Si₉B₉ (x=0,35,50,65,100), increasing Co content, although the quality factor and cutoff frequency improved, the complex permeability reduced. This result is related to the restraint of Co for the formation of Cu cluster. Annealed above the initial crystallization temperature, the complex permeability of alloy improved at first and reached the peak value, then decreased. The grain size, crystallization volume fraction and the formation of hard magnetic phase had influence on this changing trend. Quality factor and cutoff frequency of alloy increased with improving the annealing temperature. Result indicated that we could expend the range of applied frequency of alloy by changing the annealing temperature.3. We conducted a investigation on high temperature magnetic properties of (Fe_100-xCo_x)_78.4Cu₁Nb_2.6Si₉B₉(x=0,35,50,65,100). Result showed that high temperature magnetic properties of alloy optimized by adding Co. When x=0, Curie temperature of amorphous alloy is 350℃, adding Co, during heating from room temperature to the 400℃, the magnetization of FeCo based amorphous alloy could keep stable. When Fe:Co=65:35, at the magnetic field of 64KA/m, the magnetization of amorphous alloy is maximum, 55.5emu/g. Increasing Co content, the variation of magnetization of amorphous alloy with temperature is slow, it showed good high temperature property. Crystallization improved the high temperature properties of alloy, it attributed to the formation ofα-FeCo phase with high saturation magnetization.