Crystallization of amorphous melt-spun Nd₁₅Fe₇₇B_x (x = 6–14) alloys

In the process of crystallization of amorphous melt-spun Nd₁₅Fe₇₇B_x (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) α-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 α-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.