Dependence Of Structural Anisotropy On Magnetic Properties Of Fe Based Soft Magnetic Composites

The soft magnetic composite is composed of soft magnetic alloy particles coated with an insulating layer on the surface,and therefore has the advantages of high magnetic flux density of the metal soft magnetic material and high resistance of the soft ferrite,and can simultaneously satisfy the requirements of miniaturization and high frequency use of the device.Due to the existence of a non-magnetic insulating dielectric layer,the conventional soft magnetic composite material generates a large amount of non-magnetic air gap in the magnetic circuit,resulting in a low effective magnetic permeability.In order to solve the common problem of low magnetic permeability,the thesis redesigns the structure of soft magnetic composites.Through the ball milling and magnetic field orientation process,the parallel ordered structure of the sheet alloy along the magnetic ring plane is formed,and the different soft magnetic composition and the effect of anisotropic structure on the AC-DC characteristics of soft magnetic composites are studied.The main findings of the thesis are as follows:Flaky Fe₄N particles were prepared by ball-milling and nitriding.The parameters of ball-milling is 500 rpm?4h and 15:1 mass ratio of Fe and ball.The parameters of nitriding is 3 h?550°C and ammonia to hydrogen ratio of 2:1.The anisotropy structures were obtained by magnetic field orientation,and the structures are as following:?1?all particles are parallel with the horizontal plane of magnet ring??2?part of particles are parallel with the horizontal plane of magnet ring??3?all particles are vertical to the horizontal plane of magnet ring and?4?part of particles are vertical to the horizontal plane of magnet ring.The AC-DC magnetic properties and structural anisotropy of polymer-based Fe₄N soft magnetic composites were investigated The DC magnetic properties show that?1?sample is most likely to be magnetized,and?3?is the hardest.The AC magnetic properties show that?1?sample has the highest magnetic permeability and lower magnetic losses,and?3?sample has the lowest magnetic permeability and the highest magnetic loss.These are all due to the different magnetic resistance and demagnetizing field along the magnetic circuit.The AC-DC magnetic properties and structural anisotropy of Fe soft magnetic composites were investigated after improving the ratio of magnetic phase.The annealing temperature of the magnetic ring was determined to be 650°C by comparing the AC performance and the internal stress.Structural anisotropy could also be obtained through forming process by oil compressor The DC magnetic properties show that the?1?sample is still the most easily magnetized,and?3?sample is the hardest.The AC magnetic properties show that?1?sample has the highest magnetic permeability and the lowest magnetic loss,and the?3?sample has the lowest magnetic permeability and the highest magnetic loss.The AC and DC magnetic properties and structural anisotropy of Fe,Fe/Fe₄N and Fe₄N soft magnetic composites were investigated after improving particles'insulation properties.Pure Fe/Fe₄N phase is obtained by nitriding for 1 h at 350°C and ammonia to hydrogen ratio of 2:1.All the samples obtained ideal anisotropic structures and showed the similar AC-DC magnetic properties.The Fe/Fe₄N samples exhibit a stable effective permeability and the lowest magnetic loss,which may have something to do with Fe/Fe₄N compound interface.