Undercooling-dependent solidification behavior of levitated Nd14Fe79B7 alloy droplets

Abstract Bulk Nd 14 Fe 79 B 7 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 γ-Fe solid solution, Nd 2 Fe 14 B compound and the metastable Nd 2 Fe 17 B x 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 γ-Fe formation, the Nd 2 Fe 17 B x compound was solidified peritectically prior to the Nd 2 Fe 14 B compound. However, primary Nd 2 Fe 14 B formation was quite predominant over the whole sample volume. In case of primary Nd 2 Fe 17 B x formation, the Nd 2 Fe 14 B compound was solidified also in a peritectic manner. The metastable Nd 2 Fe 17 B x compound was found to decompose into α-Fe plus Nd 2 Fe 14 B during the post-solidification process. The phase selection mechanisms were discussed in terms of in-situ observations on the solidification process.