The Study Of Structure And Magnetic Properties For Si-rich Finemet-type Nanocrystalline Alloys Doped With Ge Or Co

Structure and magnetic properties of Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_3-xGe_x?x=0,0.2,0.4,0.6,0.8 and 1.0?and Fe_72.7-xCo_xAl_0.8Si_17.5B₅Cu₁Nb_3-yGe_y?x=0,4,8;y=0,0.4?alloys were majorly investigated.The main experimental methods in this paper we conducted were shown as follow:x-ray diffraction?XRD?,differential scanning calorimetry?DSC?,vibrating sample magnetometer?VSM?,transmission electron microscopy?TEM?,home-made apparatus for measuring permeability at elevated temperatures,equipment of isothermal treatment performed under vacuum atmosphere.The effects of adding Ge into the Finemet alloys on high-temperature soft magnetic properties were mainly analyzed and the origin of high-temperature magnetic softness for Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_2.6Ge_0.4.4 alloy was also studied.The structure and soft magnetic properties of doping Co into Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ and Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_2.6Ge_0.4.4 alloys were also studied.Curie point of amorphous phase,T_c^A,for Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_3-xGe_x?x=0,0.2,0.4,0.6,0.8 and 1.0?is enhanced by about 10-60°C compared with Ge-free alloy.For this family alloys,with Ge increasing,the primary crystallization temperature T_x11 and the second crystallization temperature T_x22 both decreases.And the crystallized interval temperature?T_x is also decreased.Even so the smallest?T_x is still 187°C which can also assure that single soft magnetic crystalline phase precipitates in a wide temperature ranges.The addition of Ge decreases the glass forming ability,so the higher wheel speed was required than non Ge-contained alloy but the activation energyislowerthanthatofFinemettypealloys.Forthe Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_3-xGe_x?x=0,0.2,0.4,0.6,0.8 and 1.0?alloys annealed at different temperature,570°C-annealed Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_2.6Ge_0.4 alloy shows the optimum high-temperature magnetic softness.This optimum high-temperature magnetic softness was attributed to the larger crystalline volume fraction?V_f?and the thinner intergranular amorphous layer???of Ge-doping alloy which guaranteed the stronger exchange interaction occurring at elevated temperature.Replacing Fe with small content Co in Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ and Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_2.6Ge_0.4 alloys enhances largely Curie temperature of amorphous phase T_c^A for the Fe_72.7-xCo_xAl_0.8Si_17.5B₅Cu₁Nb_3-yGe_y?x=0,4,8;y=0,0.4?alloys.Although the discrepancy trend of primary crystallization temperature T_x11 and the second crystallization temperature T_x2,the crystallized interval temperature?T_x weresmall.Annealedatdifferenttemperatureforthe Fe_72.7-xCo_xAl_0.8Si_17.5B₅Cu₁Nb_3-yGe_y?x=0,4,8;y=0,0.4?family,the 580°C-annealed Fe_64.7Al_0.8Si_17.5B₅Cu₁Nb_2.6Ge_0.4 alloy exhibits optimum high-temperature magnetic properties.The?_i could be maintained above 5000 from room temperature up to500°C,which is superior to the Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb_2.6Ge_0.4.4 and traditional FeCo-based nanocrystalline alloys ever reported.