| FeSiB amorphous ribbons as a type of soft magnetic materials,exhibit excellent magnetic properties including high saturation induction density, low coercivity, high electrical resistivity and three-dimensional (3D) isotropic ferromagnetic behavior. Such properties makes them promising applications in the electrical and electronical areas.Through grinding the ribbons into powders to fabricate soft magnetic composites(SMCs), FeSiB products with various shapes can be obtained for wider applications. In this study, powder metallurgy was used to fabricate FeSiB SMCs. The influence of powders production as well as insulation coating on the magnetic performance of the FeSiB SMCs was studied. X-ray diffraction (XRD), scanning electron microscopy(SEM),four-point probe resistivity meter and auto testing system for magnetic materials were used to investigate the effects of milling parameters, solvent of insulating coating, compaction pressure and annealing on the morphology and properties of the SMCs. The key factors affecting the properties of the SMCs were also determined and optimized. Following conclusions can be drawn:1) It is difficult to grind the ribbons annealed below 350 ? due to high tenacity.On the other hand, the magnetic performance deteriorates after annealing at temperatures above 350 0C,which is resulted from the precipitation of FeSi crystalline structure. Annealing at 350 ? for 1 h is beneficial to obtain FeSiB SMCs with high permeability, low core loss, high quality factor and excellent DC-bias.2) Milling plays a crucial role in determining the properties of the FeSiB SMCs.The hysteresis loss occupies more than 60% of the total core loss of the FeSiB SMCs(measured below 150 KHz). The internal stress could not be completely released due to limited annealing temperature,which leads to high hysteresis loss. Milder milling with less stress generated is beneficial for reduced coercivity and hysteresis loss.Meanwhile,reduced milling parameters give rise to smooth surfaces of the magnetic powders in the preparation of continuous insulation coating. This results in high electrical resistivity and low eddy current loss of the SMCs. The core loss drops approx.50% after the milling parameter is changed from 400 r/min for 8 h to 300 r/min for 6 h.3) While orthorphosphoric acid is used to fabricate the FeSiB SMCs, uniform insulation coating can be achieved using alcohol as the passivator solvent for decreased core loss. The surfaces of the magnetic powders tend to be oxidized with water as the passivator solvent,while acetone hinders the complete surface passivation as a result of limited reaction time caused by low boiling point and strong volatility of the acetone.With the content of orthophosphoric acid varied between 0.2?0.8 wt% in alcohol, the permeability drops and lowest core loss can be obtained with 0.6 wt% of orthophosphoric acid.4) The optimized compaction pressure is 2000 MPa and the most suitable annealing conditions are determined as 400 ? for 1 h. Increased compaction pressure is beneficial to improved density and effective permeability, but it also leads to damage in the insulation coating and high internal stress. Annealing temperatures below 400 ?are insufficient for complete stress relaxation for the SMCs, while precipitation of the?-Fe phase occurs with annealing temperatures higher than 425 ?.5) The FeSiB SMCs, with effective permeability of 43 and core loss of 125 mW/cm3 (50 KHz, 50 mT), was obtained by powder metallurgy with optimized processing parameters including embrittling annealing (350 ? /1 h), milling (300 r/min for 6h), passivation (0.6 wt% orthophosphoric acid diluted with alcohol), compaction(2000 MPa) and annealing (400 ?/1 h). |
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