Investigation on bulk Nd-Fe-Al amorphous/nano-crystalline alloy

Cylindrical ingots of bulk amorphous Nd₇₀Fe₂₀Al₁₀ with a diameter of 8 mm were prepared by a copper mold casting method. It was proved experimentally with X-ray diffraction, scanning electron microscopy and differential scanning calorimetry that the as-prepared alloy samples consisted mainly of the amorphous phase with a minute amount of nano-crystalline phase. The onset crystallization temperature (T_x) and the melting temperature (T_m) of the samples were 743 and 823 K, respectively, from DSC results. The temperature interval between T_x and T_m, ΔT = T_m - T_x, is 80 K and the resulting ratio of T_x/T_m is 0.90. Both a high T_x/T_m ratio and a small ΔT are considered the reasons for the good glass-forming ability. The Curie temperature (T_c) of these samples was 525 K from magneto-thermal gravimetric analysis. This measured value is higher than the highest T_c among binary Nd-Fe amorphous alloys. Annealing treatments were carried out for the as-cast samples to obtain dual-phase samples with different volume fractions of nano-crystalline phase. Magnetic measurement results indicated that the hard magnetic behavior is weakest for samples with 40% of nano-crystalline phase. The curve of the measured hysteresis loop area versus the volume fraction of nano-crystalline phase concaves upward, which agrees with what we predicated in our previous simulation results. © 2002 Elsevier Science B.V. All rights reserved.