The Study Of Structure And Magnetic Properties For Si-rich And Si-poor Co Content Nanocrystalline Alloys

Structure and magnetic softness of Fe_73.5-xAl_xSi_17.5B₅Cu₁Nb₃（x=0.6,0.8,1）,(Fe_1-xCo_x)_72.7Al_0.8Si_17.5B₅Cu₁Nb₃（x=0,0.5）and Fe₆₅Co₁₅Si₅Nb₃Cu₁B_11-xAl_x（x=0,1,2,3）alloys were majorly investigated.The main experimental methods we conducted were shown as follow: differential scanning calorimetry（DSC）,x-ray diffraction（XRD）,the static magnetic measurement system（NIM-2000 S DC）,vibrating sample magnetometer（VSM）,home-made apparatus for measuring permeability at elevated temperatures.The origin of high-temperature magnetic softness for Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ alloy,adding Co in Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ alloy,and replacing B with a small amount of Al in Fe₆₅Co₁₅Si₅Nb₃Cu₁B₁₁ alloy were mainly studied.Curie point of an amorphous phase,T_cA,for Fe_73.5-xAl_xSi_17.5B₅Cu₁Nb₃（x=0.6,0.8,1）alloys is almost the same as that of Fe_73.5Si_17.5B₅Cu₁Nb₃ alloy.For this family alloys,with Al increasing,the primary crystallization temperature T_x1 decreases,but the secondary crystallization temperature T_x2 increases,so the crystallized interval temperature ΔTx enlarged.For the Fe_73.5-xAl_xSi_17.5B₅Cu₁Nb₃（x=0.6,0.8,1）alloys annealed at different temperature,650 °C-annealed Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ alloy shows the optimum high-temperature magnetic softness.This optimum high-temperature magnetic softness was ascribed to the larger crystalline volume fraction(V_cry)and thinner thickness of intergranular amorphous layer（（?））which guaranteed the stronger exchange interaction occurring at elevated temperature.Replacing Fe with 50% Co in Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ alloy enhances Curie temperature of amorphous phase TcA largely and the secondary crystallization temperature T_x2.For(Fe_0.5Co_0.5)_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ alloy heating-cooling cycled at510-640 °C: The optimum high-temperature magnetic properties was found in550 °C-annealed sample,the μi could maintain above 1400 and shows roughly a horizontal linear correlation with T from room temperature up to 600 °C,which is superior to Fe_72.7Al_0.8Si_17.5B₅Cu₁Nb₃ and traditional Fe-based and Co-contained Finemet-type nanocrystalline alloys ever reported.In Fe₆₅Co₁₅Si₅Nb₃Cu₁B₁₁ alloy,replacing B with a small amount of Al decreases the Curie temperature of amorphous phase T_c^A and the primary crystallization temperature T_x1.T_x2 and ΔT_x exhibit general enlarged tendency compared with theFe₆₅Co₁₅Si₅Nb₃Cu₁B₁₁ alloy.It can be observed from μi-T curves of 550 °C-annealed Fe₆₅Co₁₅Si₅Nb₃Cu₁B_11-xAl_x（x=0,1,2,3）alloys that 550 °C-annealed Fe₆₅Co₁₅Si₅Nb₃Cu₁B₈Al₃ alloy shows the most stable value of μi and 550 °C-annealed Fe₆₅Co₁₅Si₅Nb₃Cu₁B₁₀Al₁ alloy exhibits the maximum room-temperature μi.For Fe₆₅Co₁₅Si₅Nb₃Cu₁B₈Al₃ alloys annealed 520-580 °C,it is found that although the μi is different at different annealed temperature,the μi-T curves of three annealed alloys show a similar decline rate.