Development and Soft-magnetic Properties Modulation of High B_s Fe(Co)SiBPC Amorphous Alloys

Author:Zhao Cheng Liang

Supervisor:wang xin min


Degree Year:2018





Fe-based amorphous alloys with structures ordered in short range and disordered in long range,exhibit outstanding soft magnetic properties(SMPs),containing high saturated magnetization flux density(Bs),low coerecivity,low core loss,etc.Which have been widely used in electric and electronic devices.Owing to the trend of devices with lower volume and higher efficient,novel Fe-based amorphous alloys are needed to possess higher Bs than presently used ones.Hence,how to overcome the limitation of the glass-forming ability and the manufacturability and make a higher Bs alloy is a hot point in developing new Fe-based amorphous alloys.Here we focus on developing novel amorphous alloys with high Bs and excellent SMPs.On the one hand,we study the alloy composition dependence on SMPs and manufacturability mechanism,developed high Bs amorphous alloy with low cost,which might replace presently used Metglas 2605SA1 and HB1M.On the other hand,amorphous alloys with high Bs close to Si-steel was also needed.For amorphous alloys with Bs close to Si-steel,we adopt field annealing which is essential to achieve excellent SMPs.The main results and unveiled mechanism were concluded as follows:1.Developed Novel FeSiBPC amorphous alloys Bs up to 1.69 T.We perform the composition design with consideration of low cost,high glass forming ability and high Bs.To achieve low cost,only Fe as metal and Si,B,P,C metalloids elements were chosen.After composition adjustment,FeSiBPC amorphous alloys with high Bs of 1.611.69 T were developed.The FeSiBPC amorphous alloys combine with high glass forming ability up to 81μm in ribbon thickness,low coerecivity of 25 A/m,good manufacturability that good SMP could be obtained for annealing in a wide temperature range of about 80°C.2.Pilot-scale study was conducted and surface crystallization mechanism were studied.Pilot-scale study the best FeSiBPC amorphous alloy and explore the technical skill of manufacturing ribbons and discuss the common surface crystallization problem in industry.The surface crystallization could be fully prohibited under 10 kPa air sub-pressure.After elementary analysis,Ti was found to be condensed in the surface and the Ti oxides was deemed as the impurity to arouse surface crystallization.High pressure of oxygen results in thick oxide layer on the surface.The oxide layer reduced the diffusion of Ti to surface and the surface crystallization was prohibited.There were two ways to restrain surface crystallization:manufacture under air sub-pressure and purification of the melt such as fluxing the alloy liquids with B2O3-CaO.3.FeCoSiBPC system amorphous alloys with high Bs of 1.74 and 1.86 T were developed and low coerecivity after field annealing were achieved.Based on our previously developed FeSiBPC system,through Co-doping and increase the FeCo content,we get access to Fe68Co15Si2B11P3C1 and Fe71Co15Si2B9.5P2C0.5 amorphous alloys.Fe71Co15Si2B9.5P2C0.5 amorphous alloy with 1.86 T could form ribbons with thickness over 33μm.Field annealing was applied to improve the SMPs.Amorphous alloys with extremely low coerecivity of about 1 A/m and the high permeability of 11k were prepared.4.The mechanism of field effects on soft-magnetic properties was discussed.By comparing the field and normal annealing process,different performances of magnetic properties,macro-scale/micro-scale magnetic structures and microstructure were studied.Magnetic field could repress the high random anisotropy Fe(Co)cluster with2Co near neighbor,lead to a highly magnetically ordered structure,which lower the hysteresis.The magnetic field also suppress the growing up of crystal clusters,eliminate the free volume by structure relaxation.Which will reduce the pinning effect and lower the coerecivity.