Due to the characteristics of excellent soft magnetic properties, good mechanical properties, high reactivity and catalytic properties, amorphous powders have been widely used in the field of aerospace, shipbuilding, automobile, metallurgy and chemical industry. High quality amorphous magnetic powders should have the features of fine size, high purity, spherical and concentrated of particle size distribution. However, due to the poor glass forming ability of traditional amorphous alloys, the amorphous powders can only be prepared by crushing the amorphous ribbons through ball milling method, which exhibit irregular morphology, wide range particle size distribution and high oxygen content. Restricted by domestic technical level the development of devices for preparing amorphous powder is slow. Therefore, it is urgent to develop a new equipment for manufacturing fine size amorphous powder. 

Now, the soft magnetic materials team in Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences (NIMTE, CAS) has developed new multistage pulverization technique. This new technology has drawn lessons from foreign advanced technology, which can produce spherical amorphous powders with fine size and low oxygen content. In this technology, gas atomization was used at the first stage to produce alloy powders with molten metal. Subsequently, the atomized alloy droplets were flown down, and then crushed into a rapidly notating disk with a high speed of 150~470 m/s. In this process, smaller droplets shrink into spherical and solidified to fine powder, while the half solidified and non-solidified droplets were broken to the smaller ones. The average particle size of fine powders can decrease to about 10 μm. This new technology has advantages of high cooling rate, fine particle size and narrow distribution range, low production cost, low energy consumption, safety and reliability, etc. Based on this technology, we have applied for national invention patent (No.201410421086.5) and are working with a local company to develop a pilot-plant device. In the development process, the team members have participated in the design and optimization of equipment drawings. They have checked the quality and specification of the various components of the equipment, to ensure that the multistage crushing atomization equipment was successfully developed. Subsequently, by adjusting the parameters such as the temperature and flux of molten metal, holding time, flux and direction of gas, flux and direction of the cooling water, tangential velocity of rotating disk, the distance between disk and nozzle for molten metal, we have solved the technical issues of nozzle clogging, powder particles packing and determined the best conditions of preparation process, the average particle size of powders was 17 μm，which was decreased for 72% compared with gas atomization. In the future, we will strengthen cooperation with the company and achieve large-scale preparation of amorphous magnetic powders to promote the industrialization of related technologies.

Dr.Yaqiang Dong dongyq@nimte.ac.cn

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