Phase formation in undercooled NdFeB alloy droplets

Small droplets of NdxFe100-1.5xB0.5x alloys (x = 11.8-15) were undercooled and solidified using the drop tube technique for the purpose of studying me tastable phase formation in this technically important alloy system. It was found that primary gamma -Fe phase has been suppressed in most of the drop lets due to significant undercooling levels achieved prior to solidificatio n. Consequently, the primary crystallization either of metastable Nd2Fe17By (y approximate to1) phase or of Nd2Fe14B phase has been favored. The forme r occurs predominantly to low Nd alloys (x = 11.8-13), while the latter pre vails in Nd-rich alloys (x = 14-15). By means of thermomagnetic analysis an d powder X-ray diffraction analysis, it was determined that the metastable Nd2Fe17By,. phase has a Curie temperature of about 100 degreesC and a hexag onal structure with lattice parameters as a = 0.496 and c = 0.416 run. (C) 2001 Elsevier Science B.V. All rights reserved.