Influence of Roller Speed on Magnetic Properties and Structures of α-Fe/Nd 2 Fe 14 B Nanocomposite Magnets Prepared by Melt-spinning

The crystallization behaviours of nanocomposite made by a function of quenching rate (roller speed) were studied. The results showed that there was one step crystallization process for the alloy quenched at roller speed of 32 ㎧, which could be shown as, Am (amorphouse) + α-Fe+Nd₂Fe₁₄B → α-Fe+Nd₂Fe₁₄B. For the alloy quenched at roller speed of 40 ㎧, there was two steps crystallization process taking place at different temperatures, which could be shown as, Am → α-Fe+Nd₂Fe₂₃B₃+Nd₂Fe₁₄B+Am' → α-Fe+Nd₂Fe₁₄B. The presence of transition phase (Nd₂Fe₂₃B₃) was harmful to get fine and uniform grain size during crystallization process. Uniform microstructures and high magnetic properties could be attained for the as-quenched alloy containing less amorphous phase and no presence of transition phase during annealing treatment. For the alloy prepared at roller speed of 32 m/s, the following properties were obtained, Br = 0.904 T, iHc = 801 ㎄/m, (BH)max = 122 kJ/㎥ and Mr/Ms = 0.6.