Effect Of The C Element Addition And Annealing Treatment On The Properties Of Fe-Si-B-Cu Amorphous Nanocrystalline Alloys

Given the increasingly serious energy shortage and environmental pollution issues,Fe-based amorphous nanocrystalline alloys,as a new class of energy-saving functional materials,may replace silicon steel in power transmission and energy conversion domains such as distribution transformers and motors due to their excellent soft magnetic properties,which can promote the development of the devices in the direction of energy-saving,miniaturization,high efficiency,and high stability.However,Fe-based amorphous nanocrystalline alloys with high Fe content leading to insufficient glass formation ability（GFA）and poor thermal stability are difficult to be applied in commercial production.Therefore,it is of theoretical and practical significance to investigate the alloy composition and heat treatment to optimize the properties of Fe-based amorphous nanocrystalline alloy soft magnetic materials.In this thesis,Fe₈₅Si_6-xB₈Cu₁C_x（x=0,1,2,3,4,5,6）alloy ribbons were prepared by the single-roller melt spinning method,and the effect of C element substitution of Si element on their GFA,thermal stability,and soft magnetic properties was investigated.The influence of C element content and heat treatment on the phase composition,microstructure,and soft magnetic properties of Fe₈₅Si_6-xB₈Cu₁C_x amorphous nanocrystalline alloy ribbons were deeply discussed.The results show that the addition of the C element is beneficial to improve the GFA and thermal stability of Fe₈₅Si_6-xB₈Cu₁C_x alloy ribbons,in which the Fe₈₅Si₂B₈Cu₁C₄ alloy ribbon has the strongest GFA,and the temperature intervalΔT_x(ΔT_x=T_x2-T_x1)between the first crystallization peak onset temperature(T_x1)and the second crystalline peak onset temperature(T_x2)of this amorphous alloy is as high as 169°C,which widens the temperature window for further anneal and is conducive to control the grain size during the annealing process to obtain excellent soft magnetic properties.Further results show that the addition of the C element can improve the soft magnetic properties of Fe₈₅Si_6-xB₈Cu₁C_x amorphous nanocrystalline alloy ribbons,which are isothermally annealed at T_x1 for 10 min,and finally,the Fe₈₅Si₄B₈Cu₁C₂amorphous alloys ribbons precipitatedα-Fe phase with a volume fraction of 62.32%and a grain size of 20.39 nm,its saturation magnetic flux density（B_s）as high as 1.95 T and coercivity（H_c）as low as 3.9 A/m.To reduce the grain size of the precipitated phase,the final prepared Fe₈₅Si₂B₈Cu₁C₄ amorphous nanocrystalline alloy ribbons with a volume fraction of 66.54%,a grain size of 20.96 nm,the B_s as high as 1.96 T and H_c as low as 4.2 A/m after keeping the annealing temperature constant and shortening the annealing time.In summary,the Fe₈₅Si₂B₈Cu₁C₄ alloy ribbon has sufficient GFA and strong thermal stability and demonstrates excellent soft magnetic properties after isothermal annealing for 5 min.Therefore,the Fe₈₅Si₂B₈Cu₁C₄ amorphous nanocrystalline alloy has the advantages of sufficient GFA,strongest thermal stability,low cost,high B_s,and low H_c,which is expected to be applied in commercial production.