The Study Of Structure And Soft Magnetic Properties For Si-rich Finemet And Nanomet Alloys

The microstructure,crystallization behavior,soft magnetic properties for nanocrystalline Fe_74.5Cu₁Nb_2-xSi_17.5B₅P_x?x=0,1,2?,Fe_73.5Cu₁Nb_3-xSi_17.5B₅Ti_x?x=0,1,2,3?and Fe_85-xCo_xSi₂B₈P₄Cu₁?x=0,4,8?alloys were investigated.This thesis is mainly explored from two aspects.The first one is the influence of P and Ti on the high-temperature magnetic peroperties as well as the mechanism of improving high-temperature magnetic softness for high Si iron based nanocrystalline alloys.The second one is the influence of Co on the magnetic properties of Nanomet alloys at room-and high-temperatures.Experimental methods and instruments used include differential scanning calorimetry?DSC?,x-ray diffraction?XRD?,the static magnetic measurement system?NIM-2000S DC?,vibrating sample magnetometer?VSM,Lake Shore 7400?,high temperature magnetic permeability measuring instrument made by laboratory and small angle magnetization rotation?SAMR?method.In Fe_74.5Cu₁Nb_2-xSi_17.5B₅P_x?x=0,1,2?alloys,with the increase of P content,the Curie temperature(T_c^am)of amorphous phase increases gradually,and the first crystallization temperature(T_x1)decreases gradually.When the P is completely replaced by Nb,the crystallization temperature interval??T_x?decreases sharply,which leads to the deterioration of the high temperature magnetic performance.After annealing at 570°C,Fe_74.5Cu₁Nb₁Si_17.5B₅P₁ alloy shows the best soft magnetic properties at high temperature because of its larger volume fraction of crystallization phase and saturation magnetization,which strengthens the intergranular exchange coupling interaction at high temperature.In Fe_73.5Cu₁Nb_3-xSi_17.5B₅Ti_x?x=0,1,2,3?alloys,with the increase of Ti content,the amorphous phase Curie temperature(T_c^am)shows a decreasing trend.The first crystallization temperature(T_x1)decreases and the crystallization temperature interval??T_x?increases.After annealing at 550°C,Fe_73.5Cu₁Nb₂Si_17.5B₅Ti₁ alloy shows the highest permeability at room temperature of about 18000 and the minimum coercivity of about 0.54Oe.When Ti is completely replaced by Nb,the magnetic properties of these alloys have deteriorated at room-and high-temperatures,indicating that the role of Ti in preventing grain growth is far less than that of Nb.In Fe-Si-B-P-Cu?Nanomet?alloys,it is found that the Curie temperature(T_c^am)and the crystallization temperature interval??T_x?of amorphous phase increase gradually by replacing Fe with Co.After annealing at 550°C,the B_s of Fe₇₇Co₈Si₂B₈P₄Cu₁ alloy reaches up to 1.70T,which is superior to the previously reported Nanomet alloys containing Co.The initial permeability at room temperature has doubled,compared with that of the as-quenched ones.At the same time,the saturation magnetic induction intensity B_s is much higher than that of Co free alloy,which is due to the fact that the magnetic moment of the Fe-Co atomic pair is greater than that of the Fe-Fe atomic pair.It is found that the saturation magnetostriction costant?_s and the magnetocrystalline anisotropy constant K of Nanomet alloys increase with Co content,which leads to the decrease of initial permeability at room temperature.The application of Nanomet alloy at high temperature is greatly limited because of its lower amorphous forming ability and smaller crystallization temperature interval,but the magnetic properties at room temperature after annealing have been improved.