CRYSTALLIZATION OF AMORPHOUS MELT-SPUN ND15FE77BX (X=6-14) ALLOYS

In the process of crystallization of amorphous melt-spun Nd15Fe77Bx (x = 6-14) alloys, it was found that the crystallization behavior strongly depended upon the boron content even in the same equilibrium three-phase coexistence range. The Nd2Fe14B phase was crystallized directly from the amorphous state in the amorphous Nd-Fe-B materials with relatively lower boron content (Nd15Fe77B6 and Nd15Fe77B8 alloys). In contrast, the metastable body-centered-cubic (bcc) a-iron phase crystallized from the amorphous state prior to the crystallization of the Nd2Fe14B phase in the amorphous Nd-Fe-B materials with relatively higher boron content (Nd15Fe77B10, Nd15Fe77B12, and Nd15Fe77B14 alloys). The existence of the metastable bcc a-iron phase in the amorphous matrix was confirmed by TEM studies, magnetic measurements, and in situ observation by x-ray diffraction. The formation of the metastable phase stabilized the amorphous state, increasing the crystallization temperature of the Nd2Fe14B phase.