The Preparation Of Bulk Amorphous/Nanocrystalline Soft Magnetic Materials

Bulk amorphous and nanocrystalline magnetic material has become very much apioneering research issue because of its excellent magnetism properties. In this paper, thehistory of bulk amorphous and nanocrystalline magnetic material and the researchprogress is reviewed. The chemical composition of the Fe-based bulkamorphous/nanocrystalline alloy, its manufacture technique, microstructure, propertiesand the relationship between them are investigated. It's difficult to obtain the high purity FeP alloy that used as the raw material for thepreparation of Fe-based bulk amorphous. To solve the problem, a new technique: diffusionin low temperature + rapidly heating, is presented to synthesis the high purity FeP alloywith pure iron powder and pure phosphor powder. With the similar technique, a series ofeutectic alloys such as Fe89.87P10.13wt%,Ni81P19at%,,Fe68.4S31.6wt%,Ni77S23wt%,Co88.5P11.5wt% have been synthesized successfully. In this thesis a new compound technique: flux-melting + copper casting, is presentedto prepare bulk amorphous alloy from industrial raw materials. A series of copper mouldshave been designed. With the different copper mould, bulk amorphous alloys can beprepared easily with different shapes such as rod, plate, cylinder and ring. Bulk amorphous alloys (Fe40Ni40P14B6) 100-xGax(x=4⁶)have been prepared in theform of 3-mm-diam rods or 1-mm-thick plates by utilizing industrial raw materials. Theglass synthesis consists of flux-melting and copper casting. Differential scanningcalorimetry and X-ray diffraction show that amorphous alloys can formed for x=4-6. Theproperties measurements indicate that the amorphous alloys possess strong corrosionresistance and excellent soft magnetic properties. The microhardnessvalue of theamorphous alloy is lower than that of the crystalline alloy with the same composition. Ithas been demonstrated that Ga addition can be greatly helpful to increase theglass-forming ability of Fe40Ni40P14B. The main reason of increasing the glass-formingability should be that the Ga addition restrains the crystallization of the Fe3Ni3B,(Fe,Ni)23B6. It has been demonstrated that In addition can replace part of Ga addition, which haslittle influence on the glass-forming ability of (Fe40Ni40P14B6) 100-xGax(x=4⁶). However,The price of pure indium is far lower than that of pure gallium. Therefore, It is veryimportant that gallium can replace by indium. IIIBulk amorphous alloy (Fe40Co40P14B6)95Ga5 has been prepared in the form of Φ2×20mm rods and 0.8×6×20 plates by industrial raw material.. The glass synthesis consistsof flux-melting and copper casting. The glass-forming ability of six kinds of Fe-based alloys has been compared.According the glass-forming ability, the order may beFe65.5Cr4Mo4Ga4P12C5B5.5>Fe72Al5Ga2P11B4C5Si1^{Fe40Ni40P14B6}96Ga4^{Fe40Ni40P14B6}94(Ga4In2)>(Fe40Co40P14B6)95Ga5>>(Fe40Ni40Mo4B16) 95Ga5. The high undercooling solidification microstructure of Fe40Ni40P14B6 alloy has beenresearched. It has been found that the samples have different microstructures if thesolidificotion conditoin is different. After fluxing, if the cooling rate is low, the specimenwith high undercooling is occupied by subnetwork microstructure. If the cooling rate ishigh, the eutectic microstructure varies from dendrite containing tertiary dendrite arms,dendrite containing secondary dendrite arms to nanofiber with the alloy's undercoolingincreasing. Bulk nanocrystalline alloy (Fe40Ni40P14B6)96Ga4 has been prepared by suitablycontrolled annealing treatment of the bulk amorphous alloy. When the samples anneal inthe temperature between Tg and Tx for 60min, the crystallization occures. Under thedifferent annealing condition, the microstructure presents two kinds of morphologys:crystal reunion composed of nanocrystal and equiaxed grain. When the annealingtemperature is 710K, the annealing time is 60min,...