Study On The Properties And Structural Relaxation Of FeNbB Amorphous Alloys

Due to their random packed atomic structure different from traditional crystalline metallic material,Fe-based amorphous soft magnetic alloys exhibit excellent soft magnetic properties,such as low coercive force?H_c?and high permeability??_e?,high magnetic saturation intensity?B_s?and good mechanical properties,such as high strength and hardness.Combined with the low cost,they have been widely used as a novel kind of structural and functional material for energy saving and environmental protection in the field of motors,transformers,reactors,inductors and coils.However,The Fe-based amorphous alloys generally have the disadvantages of low ductility or lack of ductility.Fe-based amorphous alloys are usually prepared by chill-quenching and rapid quenching methods.Therefore,there is a large casting thermal stress inside Fe-based amorphous alloys,which increases their magnetic anisotropy and seriously affects their soft magnetic properties.Fe-based amorphous alloys must be subjected to stress relief annealing before they can exert their excellent soft magnetic properties.However,amorphous alloys are different from crystalline alloys.After annealing treatment,their plastic toughness sharply decreases or even disappears,showing brittle mechanical characteristics,which severely limits their application in engineering.Therefore,it is of great engineering significance to prepare soft magnetic alloys with good magnetic and ductile toughness by adjusting the alloy composition,and to study the influence of annealing treatment on magnetic properties and mechanical properties.In this paper,FeNb B soft magnetic alloys are selected as the material research object,and the properties of the alloys under different composition conditions are studied.The structural relaxation induced by annealing is also discussed.This article mainly involves the following research content.?1?The effects of the content of Fe and Nb on the properties of FeNbB amorphous alloys were studied.The Fe_65+xNb₆B_29-x amorphous alloys were fabricated and the glass forming ability?GFA?,thermal stability,crystallization activation energy,magnetic and mechanical properties were studied.It was found that the thermal stability,GFA and crystallization activation energy of these amorphous alloys decreased with the increase of Fe content.Among these amorphous alloys,the Fe₇₁Nb₆B₂₃ amorphous ribbon exhibits the best soft magnetic properties with coercive force of 0.9 A/m and permeability more than 15000.The fully amorphous rod sample of Fe₇₁Nb₆B₂₃ with the diameter of 1 mm could be fabricated successfully and its yield strength is up to 4.2GPa with a certain ductility meanwhile.?2?The effects of different proportions of metal elements and metal elements on the properties of FeNb B amorphous alloys were explored.Based on the above results,the(Fe₇₁Nb₆)_1+x/77B_23-x alloys were designed and their glass forming ability,thermal stability,magnetic properties and mechanical properties were investigated.It is shown that their thermal stability and GFA decrease with increased B content,and that their strength and toughness deteriorated simultaneously.The increased Nb content although improved the permeability of the soft magnetic alloy,but reduced the saturation magnetic induction intensity.The 1mm crystal bar of x=12 possesses excellent comprehensive mechanical properties with yield strength of 1500 MPa and the plastic toughness as high as 5%.?3?The effects of minor addition of element yttrium?Y?in Fe₇₁Nb_6-xB₂₃Y_x alloys on GFA,thermal stability,magnetic and mechanical properties were studied.It is found that the minor addition of Y can improve the GFA,but the thermal stability decreases,and the coercive force and permeability deteriorate slightly.The minor addition of Y results in a great decrease in the ductility and toughness of the alloy.?4?The influence of annealing induced structural relaxation on the magnetic properties and mechanical properties of FeNb B amorphous alloy was studied by using Fe₇₁Nb₆B₂₃ amorphous alloy as a model material.The results showed that when the amorphous alloy was annealed during structural relaxation stage,the Bs value increased slightly,and soft magnetic properties improved greatly,due to the reduction of stress release and free volume defects.The H_c decreased from 34 A/m of as-quenched state to 0.9 A/m annealed,and?_e increased from 1300 of as-quenched stated to 15000 annealed.The domain structure of the amorphous strip surface was transformed from the original small random stripe domain into the wide regular stripe domain after annealing treatment.The bar alloy still has a yield strength of 4.2 GPa and a certain plasticity and toughness,and the hardness reaches 1000 Hv.With the increase of annealing temperature,the strength of bar alloy did not decreased,and the ductility and toughness of the bar only slightly decreased,and the hardness increased.When the annealing temperature of the alloy was above the glass transition temperature,the soft magnetic performance of the strip deteriorated due to the destruction of the original stable structure,but its saturation magnetic induction further improved,and the yield strength and the plasticity and toughness of the alloy greatly reduced.