Study On Soft Magnetic Properties Of Fe-Based Amorphous/Nanocrystalline Alloys By Applied Magnetic/Stress Field Heat Treatment

Fe-based amorphous/nanocrystalline alloys have attracted much attention because of their excellent properties such as high saturation magnetic flux density,high effective permeability,low coercivity and low high frequency loss.After decades of development,the comprehensive soft magnetic properties of Fe-based amorphous/nanocrystalline alloys have been greatly improved,which have become an important branch of soft magnetic materials.However,compared with the traditional Si-steel,relatively low saturation magnetic flux density of Fe-based amorphous/nanocrystalline alloys hinders their further development.In this context,the purpose of this paper is to improve the saturation magnetic flux density without deterioration of the soft magnetic properties by the special heat treatment and the appropriate addition of Co element.Firstly,based on FeSiBCu alloy system,Fe_82.65-xCo_xSi₂B₁₄Cu_1.35(x=0-20)amorphous ribbons were prepared by adding Co element.The soft magnetic properties and saturation magnetic flux density of amorphous ribbon samples were successfully improved by magnetic field annealing,and the maximum saturation magnetic flux density could reach to1.86 T.The addition of Co element not only improves the thermodynamic stability but also increases the Curie temperature of the alloys.The experimental results have shown that magnetic field annealing can adjust the internal domain structures,eliminate the magnetic anisotropy and reduce the pinning effects.It is also found that the magnetic field annealing can promote the precipitation of?-Fe grains and improve the ordering of the amorphous alloys,which enhancing the saturation magnetic flux density of the alloys.Based on the above experimental results,the amorphous ribbons of Fe_82.65-xCo_xSi₂B₉P₅Cu_1.35(x=0-20)were prepared by adding P element,combined with magnetic field annealing to study the soft magnetic properties of the Fe Co-based nanocrystalline systems.It is found that magnetic field annealing can effectively improve the permeability of samples without Co element or with low Co element.The samples with high Co element have significant differences in soft magnetic properties at different annealing temperatures.The transmission electron microscopy found that the difference in grain size leads to different sensitivity of the samples to the applied magnetic field.Because the addition of Co element reduces the ferromagnetic exchange length of the nanocrystalline sample,the low annealing temperature results in large grain size making it difficult for the sample to satisfy the necessary conditions for the effective random anisotropy model.Finally,Fe_82.65-xCo_xSi₂B₁₄Cu_1.35(x=0-20)amorphous ribbons were still used as the experimental research object in this work.The coercivity of amorphous ribbon samples with Co element or without Co element have benn successfully improved by tensile stress annealing The result shows that when the tensile stress is small,the improvement effect of the coercivity is obvious.As the tensile stress continues to increase,the effect tends to be gentle.It was found that the tensile stress can change the interatomic distance of the ribbon samples according to the synchrotron radiation results.And the thermal expansion behavior analysis of the tensile stress sample can find that the tensile stress sample has higher thermal expansion coefficient and rise rate compared with the normal annealing sample,which may be due to that the tensile stress annealing can effectively reduce the magnetostriction coefficient of the sample,while the"invar effect"occurs during thermal expansion of the normal annealing sample with large magnetostriction coefficient,resulting in a low thermal expansion coefficient and a slow rise rate.