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

Abstract 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 (Tx) and the melting temperature (Tm) of the samples were 743 and 823 K, respectively, from DSC results. The temperature interval between Tx and Tm, ΔT=Tm−Tx, is 80 K and the resulting ratio of Tx/Tm is 0.90. Both a high Tx/Tm ratio and a small ΔT are considered the reasons for the good glass-forming ability. The Curie temperature (Tc) of these samples was 525 K from magneto-thermal gravimetric analysis. This measured value is higher than the highest Tc 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.