Research On Preparation And Magnetic Properties Of FeSiBPCu Amorphous/Nanocrystalline Alloys

Fe-based amorphous/nanocrystalline alloys possess excellent magnetic properties,simple preparation process,less energy consumption and low pollution,which is considered to have great applicational prospects as magnetic materials.However,low glass forming ability and poor thermal stability severely limit their wide engineering application.Therefore,the development of new Fe-based amorphous/nanocrystalline alloys with good glass forming ability,wide optimum annealing temperature range and excellent magnetic properties has been an active field of research in material science,and owning great application values and academic significance.In this thesis,the method of element substitution was used to design the alloy composition.A series of FeSiBPCu amorphous and nanocrystalline ribbons were prepared by single-roller melt spinning method followed by isothermal annealing.The organizational structure of as-spun alloy ribbons and ?-Fe crystallization process were identified by X-ray diffraction,and the thermodynamic properties of as-spun alloy ribbons were analyzed by differential scanning calorimetry.In addition,vibrating sample magnetometer was used to measure the soft magnetic properties of as-spun and annealed alloy ribbons.The effects of composition element and heat treatment on the organizational microstructure and soft magnetic properties of alloy ribbons were systematically investigated in order to obtain excellent magnetic Fe-based nanocrystalline alloys with low Hc and high Ms.The results show that Fe₈₃Si₄B₁₀P₂Cu₁ alloy has low glass forming ability and the alloy ribbons with completely amorphous structure were obtained only at copper roller speed of 45 m/s.There exist crystallized?200?textures of ?-Fe in melt-spun ribbons obtained at lower copper roller speed.The addition of Nb can effectively improve the glass forming ability and thermal stability of Fe83-xSi4B10P2Cu1 Nbx alloy,and increase the nucleation and growth activation energy too.It is found that appropriate Nb addition had a significant effect on retarding the growth of the ?-Fe nanocrystallines,thus improving the controllability of annealing process and prolonging annealing temperature range and effective annealing time.In Fe83-xSi4B10P2Cu1 Nbx alloy system,the soft magnetic properties of Fe82.1Si4B10P2Cu1Nb0.9 amorphous alloy after annealed are superior to others.Fe82.1Si4B10P2Cu1Nb0.9 nanocrystalline soft magnetic alloy with a grain size around 19.6 nm can be obtained after annealing the amorphous alloy at 753 K for 30 min,and it shows good soft magnetic properties with Hc = 7.6 A/m,Ms = 177.3 emu/g.In order to reduce costs,P was chosen to replace B to improve the content of P in the alloy.It is found that substitution B by P element decreases the glass forming ability of the Fe₈₃Si₄B_12-xP_xCu₁ alloy system.Meanwhile,the addition of P can decreases the crystallization temperature of ?-Fe phase and deteriorates the soft magnetic properties of this alloy system at as-quenched state.It is also found that the addition of P can suppress the grain growth during the crystallization process and thus decreasing the annealing temperature dependence sensitivity of Hc and prolonging annealing temperature range.When the content of P reach up to 8 at.% and 10 at.%,the effect on retarding the growth of the ?-Fe nanocrystallities was significant,and a large effective annealing temperature range was obtained,which was about 100 K and 80 K,respectively.After annealing by the same annealing process,the soft magnetic properties of Fe83Si4B4P8Cu1 nanocrystalline alloys are the best.Fe83Si4B4P8Cu1 nanocrystalline alloy exhibiting good soft magnetic properties with Hc = 7.6 A/m,Ms = 179.8 emu/g can be obtained after annealing the amorphous precursor at 753 K for 5 min.