Abstract: Cylindrical ingots of bulk amorphous Nd70Fe20Al10 with a diameter of 8 mm were prepared by a copper mold casting method. It was proved that as-prepared samples are mainly consisted of amorphous phase by measurement of X-ray diffraction, observation of scanning electronic microscopy and analysis of differential scanning calorie. The onset crystallization temperature (Tx) and the melting temperature (Tm) of the samples were measured to be 743 K and 823 K, respectively. The temperature interval between Txand Tm(ΔTm) is as small as 80 K and the resulting reduced ratio of Tx/Tm is as high as 0.90. The extremely high Tx/Tm and the small ΔTm values are assumed to be the reason for the achievement of the large glass-forming ability. The Curie temperature (Tc) of these samples was determined to be 525 K by magnto-thermal gravity analysis, which is higher than the highest Tc of binary Nd-Fe amorphous alloys. Dual phase alloys of different nano-crystalline volume fraction were obtained by means of various annealing treatments to the as-prepared samples. The magnetic measurement indicated that the hard magnetic behaviour of the dual phase samples deteriorates most at the volume fraction about 40%, which has predicted in our previous theoretical computation.
Investigation on bulk rare-earth Nd-Fe-Al amorphous/nano-crystalline alloy
Abstract:
Cylindrical ingots of bulk amorphous Nd 70 Fe 20 Al 10 with a diameter of 8? mm were prepared by a copper mold casting method. It was proved that as prepared samples are mainly consisted of amorphous phase by measurement of X ray diffraction, observation of scanning electronic microscopy and analysis of differential scanning calorie. The onset crystallization temperature ( T x) and the melting temperature ( T m) of the samples were measured to be 743?K and 823?K, respectively. The temperature interval between T x and T m (Δ T m) is as small as 80?K and the resulting reduced ratio of T x/ T m is as high as 0.90. The extremely high T x/ T m and the small Δ T m values are assumed to be the reason for the achievement of the large glass forming ability. The Curie temperature ( T c) of these samples was determined to be 525?K by magnto thermal gravity analysis, which is higher than the highest T c of binary Nd Fe amorphous alloys. Dual phase alloys of different nano crystalline volume fraction were obtained by means of various annealing treatments to the as prepared samples. The magnetic measurement indicated that the hard magnetic behaviour of the dual phase samples deteriorates most at the volume fraction about 40%, which has predicted in our previous theoretical computation.[
Fig.1 Morphology and outer surface appearance of cylindrical NbFeAl samples with diameter of 8 mm prepared by copper mold casting
图2 热处理前后NbFeAl样品的X射线衍射图
Fig.2 XRD patterns of NbFeAl samples (a) —Sample A without heat treatment; (b) —Sample B annealed for 4 min at 590 K; (c) —Sample C annealed for 10 min at 590 K