Undercooling-dependent solidification behavior of levitated Nd14Fe79B7 alloy droplets

Bulk Nd14Fe79B7 alloy droplets were processed using electromagnetic levitation technique for the purpose of studying their metastable solidification behavior at significant melt undercoolings. The results show that gamma-Fe solid solution, Nd2Fe14B compound and the metastable Nd2Fe17Bx compound were solidified as primary phase in sequence of increasing bulk undercooling level. The critical undercoolings were determined to be 45 K and 60 K, respectively. Following primary gamma-Fe formation, the Nd2Fe17Bx compound was solidified peritectically prior to the Nd2Fe14B compound. However, primary Nd2Fe14B formation was quite predominant over the whole sample volume. In case of primary Nd2Fe17Bx formation, the Nd2Fe14B compound was solidified also in a peritectic manner. The metastable Nd2Fe17B, compound was found to decompose into alpha-Fe plus Nd2Fe14B during the post-solidification process. The phase selection mechanisms were discussed in terms of in-situ observations on the solidification process. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.