Research Of Preparation Process And Properties For Iron Based Nanocrystalline Powder Cores

ABSTRACT:Nanocrystalline soft magnetic material receives much concern for its unique structure and excellent magnetic properties and low cost. Nanocrystalline based soft magnetic powder core can replace traditional Fe-Ni, MPP and Sendust powder core because of its excellent soft magnetic properties. According to technical parameters of application and production conditions, the composition for producing has been determined. Meanwhile, the influence of preparation procedure of powder and powder cores on the relative density, compressive strength, frequency characteristics, spectral characteristics, DC superposition characteristic, coercivity and core loss have been investigated. The main contents are as following:(1) Compared with Fe73Si3B24alloy, the distance between primary crystallization peak and second crystalline peak, the difference between the primary and second stage’s apparent crystallization activation energy of Fe784Cu0.6Nb2.5Si9.5B9alloy both are larger. This means that Fe78.4Cu0.6Nb2.5Si9.5B9alloy was much easier to obtain the microstructure of amorphous mixed with nanocrystalline. The suitable crystallization technique for Fe78.4Cuo.6Nb2.5Si9.5B9and Fe73Si3B24amorphous alloy is540℃and520℃for40minutes, respectively.(2) Soft magnetic nanocrystalline powders can be obtained by subsequent annealed ribbon ball milling, atomization and ball milling the atomization powders. During the process of ball milling atomization powders, with the elongation of ball milling time, the interplanar space, amount of amorphous and crytal strain of the powders increase and the grain size declines. After being ball milled for202hours, the amount of amorphous cotent of Fe78.4Cu0.6Nb2.5Si9.5B9and Fe73Si3B24powders close to98%and78%, respectively. With the elongation of ball milling time, the saturation magnetic induction of the powders is almost unchanged and the coercivity of these powders slightly increases.(3) The soft magnetic properties and compressive strength are influenced by powder preparation procedure, such as powder size, kind of coating agent as well as its amount, compacting pressure, the annealing temperature and powder size proportioning.Power cores with high permeability and high compressive strength can be obtained by using large size (>150μm) ball milled ribbon powders and power cores with excellent DC superposition characteristic, low coercivity and low core loss can be obtained by using small size (<40μm) ball atomization powders.Organic coating agent is more helpful than inorganic coating agent in increasing the soft magnetic properties of powder cores. The decrease of permeability and rise of coercivity accompanied with the increase of coating agent. With the increase of coating agent, the DC superposition characteristic gets better and the core loss decrease.Increasing the compact pressure can improve the relative density, strength and effective permeability and decrease the coercivity and loss of the powder cores. But it is little impact on the DC superposition characteristic.With annealing temperature increasing under400℃, the relative density and strength of powder cores keep stable, the effective permeability rise, coercivity and loss decline. While the annealing temperature rise to450℃, the eddy current loss rised according to the destroy of surface of coating layer. Then the total loss rise.The significantly improvement for effective permeability, spectral characteristics and DC superposition characteristic can be got by suitable powder size proportioning, such as (a)80%100-150μm+20%<40μm ball milled ribbon powders and (b)55%100-150μm ball milled ribbon powders+45%<40μm atomization powders. This can also reduce coercivity and control core loss. The industrial productions of these two kinds of matching methods have been achieved. There are105figures,14tables and169references in this thesis.