Effect Of Heat Treatment And Element Substitution On Microstructure And Soft Magnetic Properties For Fe/FeCo-based Nanocrystalline Alloys

Nanocrystalline soft magnetic alloy has been applied widely in the field of engineering and technology due to their excellent soft magnetic properties.This investigation aims to explore the effective ways to improve the soft magnetic properties for nanocrystalline alloys,which focus on the following concerns.The first one is the heat treatment that could tailor the magnetic softness for amorphous and nanocrystalline alloys.The second one is the substitution of element that could optimize some aspects of magnetic performance.And the last one is the high-temperature magnetic softness and the effect of magnetic field annealing for amorphous and nanocrystalline alloys.The detail results are abstracted as following.(1)The effect of magnetic field annealing and cycle annealing on the crystallization process and microstructure together with soft magnetic properties are investigation for Fe-and FeCo-based alloys.The crystalline volume fraction is increased by magnetic field annealing which is due to the fact that the applied field accelerates the precipitation of nanograins,and thus enhanced the saturation induction density of FeCo-based alloy.Meanwhile,the coercivity and hysteresis loss decrease due to the reduction of saturation magnetostriction by magnetic field annealing.The cycle annealing is conducted to the Fe-based alloy without Nb content.The coarsening of nanograins is effectively restrained by cycle annealing,which reduced the coercivity of the Fe-based nanocrystalline alloy.A high saturation induction density of 1.83 T is achieved by cycle annealing which is due to the increased crystalline volume fraction.(2)The effects of partially substituting Fe and Si by Ge and Ga respectively on the microstructure and soft magnetic properties are investigated for Fe-based alloy with high Si content.The Curie temperature increases from 365°C to 410°C for the asquenched alloy due to the addition of Ge.A high initial permeability of more than 5000 could maintain up to 600°C for the Fe-based alloy with 2at.% Fe substituted by Ge,which should be attributed to the strengthened magnetic exchange coupling between the adjacent nanocrystals.The first crystallization onset temperature corresponding to the precipitation of soft magnetic crystalline phase reduces for the Fe-based alloy with Si substituted by Ga,and the temperature interval is extended for forming single crystalline phase.The initial permeability is enhanced to 40000 at ambient temperature and 26000 at high temperature of 400°C for the Fe-based alloy with 3at.% Si substituted by Ga.(3)The effect of magnetic field annealing on the soft magnetic properties at high temperature is investigated for Finemet-type alloys.The magnetic moments align along the applied field,the movement of domain wall dominate the subsequent magnetization process and the alloy would be magnetized more easily along the direction of field annealing.Thus,the amorphous alloy annealed in magnetic field exhibited the increased initial permeability at ambient temperature.The high-temperature initial permeability of Co-and Ni-containing Finemet is improved by field annealing,which arises from the strengthen exchange coupling between the unlike atom-pairs(i.e.Fe-Co and/or Fe-Ni).