Compositional And Technological Optimization Of Fe-B-Cu Based Amorphous-nanocrystalline Soft Magnetic Materials

FeB-based soft magnetic materials have a wide range of applications in electronic andelectric industries. Decades of years have passed since the first nanocrystalline soft magnet wasinvented. A great improvement has been made on the key soft magnetic properties about thesaturation flux density, the coercivity and the core loss by a large amount of researches ofFeB-based alloys on different compositions and annealing conditions. In this dissertation, thepreparation and the as-spun properties of traditional FeSiBCuP alloys were invesgated firstly.On the basis of these researches and the analysis of the recent papers, the new-type FeBCusoft aollys were investigated in detail.The amorphours-nanocrystalline soft magnetic materials were fabricated by meltspinning and appropriate heat treatment. X-ray diffractometer (XRD), differential ScanningCalorimeter (DSC), scanning electronic microscopy (SEM), vibrating sample magnetometer(VSM), DC soft magnetometers and other devices were employed to characterize themicro-structure and properties of the samples. The effects of the different elements addingand different heat treatment on the final properties of these materials were investigated. Themain research scope and the conclusions are as follows:(1) The results of traditional FeSiBCuP show the complete amorphous alloys could notbeen fabricated with high Fe content (over84at.%). The core loss value increased as the Sicontent increased. The adding of Cu was favor to improve the crystallization degree. Theadding of P perhaps could enhance the glass-forming ability. Tiny adjustment of Fe/B rationexhibits small effect on the properties of the materials. So, the composition and Fe contentshould be chosen reasonably. According to the XRD results, the as-spun ribbons exhibit (200)preferred as the different cooling rate between contact side and free side.(2) The Fe83.5B15Cu1.5alloys including a large amount of (200) preferred α-Fe exhibitoptimal magnetic properties after annealing. When these as-spun ribbons were annealed at390℃for10min, the optimal properties of a maximμm Bsof1.83T and a low Hcof8.7A/mwere obtained. These oriented grains were favor to increase the nucleation and suppress thegrowth of α-Fe. When the amorphous ribbons of Fe83.5B15Cu1.5were annealed at420℃for10min, a maximμm Bsof1.75T and a low Hcof9.2A/m were obtained. The lower crystallinity, the larger growing tendency and the lower soft magnetic properties perhapsbecause the rare nucleation sites of amorphous ribbons. The precipitation of α-Fe throughpre-treating the amorphous ribbons improves the final crystallization degree and suppressesthe growth of grain size, then a maximμm Bsabout1.8T was gained. However, the Hcvalueincreased rapidly when increasing the annealing time, perhaps because the growth of grainsize and the generation of second phase.(3) The pre-treatment Fe83.5B15Cu1.5(2) ribbons that were heated to300℃for10min andthen annealled at300℃for5min, exhibit a low Hcof12.5A/m, the higher Bsof1.78Tcompare with the Fe83.5B15Cu1.5(2) ribbons after annealled at420℃for10min directly.Because the DSC result shows there is almost no nucleation of α-Fe at300℃, the improvingof crystallinity and the maintaining small grain size may be attributed to more Cu clusters.(4) The Hcvalue decreased, the thermostability of α-Fe was improved and the generationof second phase was suppressed by increasing P content of Fe83.5B15-xCu1.5Pxalloys. When anannealling temperature increased, the Hcvalue tends to be larger due to the growth of α-Fegrain size. The Hcvalue of the annealed alloys without the second phase stably rose up maybe because the α-Fe grains including in as-spun ribbons could suppress and control the growthof α-Fe. When4at.%P were added and these Fe83.5B11Cu1.5P4as-spun ribbons were annealedat470℃for10min, the optimal properties of a high Bsof1.78T and a low Hcof36A/m wereobtained.