Magnetic Alloy Powders fabricated by a New Counterrotating Rapidly Quenching Method and Related Powder Properties

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Rapidly solidified Fe based magnetic ally powders were fabricated by a new counterrotating method and the powder properties were investigated. This new atomizing method was develpod by the authors in this work. The atomizing apparatus consisits of a inverse T shaped quartz nozzle for ejecting molten alloys and a wine-cup shaped cooling disk with a diameter of 240mm. Both the nozzle and the cooling disk were rotated in opposite direction about a vertical coaxial. The maximum revolving speed of the nozzle and the disk was 10000 rpm.The molten alloy ejected by centrifugal force was atomized and solidified rapidly on the surface of the cooling disk. The alloys were melted and quenched in Ar gas atomospere in order to avoid oxidation. The compositions of alloys were Fe_<82>B_<18> and Nd_2Fe_<14>B.The powders obtained had good sphericity and smoothness. Less than 80% of the cumulative size distribution by weight, the particle size was about 10 m to 200 m and the average diameter of powders was about 100 m. The cooling rate was about 10^4゜C/s to 10^7゜C/s. Microscopic examination made on the cross section of powders. The grain size decreased with decrease of the particle diameter. Small particles of FeD less than about 44 m was almost non-crystalline in structure. In the case of NdFeD powders, the grain size was about microns to submicrons.