Hard magnetic bulk amorphous Nd-Fe-Al alloys of 12 mm in diameter made by suction casting

Bulk amorphous Nd70Fe20Al10, Nd65Fe25Al10 and Nd60Fe30Al10 alloys with hard magnetic properties were produced in a cylindrical form with a diameter of 12 mm and a length of 70 mm by sucking their molten alloys into a copper mold. The sucking force was generated from the rapid movement (5.0 m/s) of piston with a diameter of 12 mm which was set at the center of the copper mold. The casting velocity was evaluated to be as high as 3.5 kg/s. Neither cavity nor hole is seen on the outer surface of the bulk amorphous alloy and the crystallization temperature (T-x) and melting temperature (T-m) are 761 and 866 K, respectively, for the bulk amorphous Nd70Fe20Al10 alloy. Consequently, the temperature interval of supercooled liquid defined by the difference between T-m and T-x, Delta T-m(= T-m-T-x) is as small as 105 K and the reduced crystallization temperature (T-x/T-m) is as high as 0.88. The small Delta T-m and high T-x/T-m values are presumed to be the origin for the achievement of the large glass-forming ability for the Nd-Fe-Al alloys. The bulk amorphous Nd70Fe20Al10, Nd65Fe25Al10 and Nd60Fe30Al10 cylinders exhibit hard magnetic properties of 0.076 to 0.086 T for remanence, 291 to 321 kA/m for intrinsic coercive held and 13 to 16 kJ/m(3) for maximum energy product at 298 K which are nearly the same as those for the corresponding bulk amorphous cylinders with diameters of 1 to 5 mm prepared by conventional casting. The hard magnetic properties for the Nd-Fe-Al amorphous alloys with large glass-forming ability are promising for future progress as a new type of hard magnetic materials.