Hard Magnetic Bulk Amorphous Nd-Fe-Al Alloys of 12 mm in Diameter Made by Suction Casting

摘要

Bulk amorphous Nd_(70)Fe_(20)Al_(10), Nd_(65)Fe_(25)Al_(10) and Nd_(60)Fe_(30)Al_(10) 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 Nd_(70)Fe_(20)Al_(10) alloy. Consequently, the temperature interval of supercooled liquid defined by the difference between T_m and T_x, ΔT_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 ΔT_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 Nd_(70)Fe_(20)Al_(10), Nd_(65)Fe_(25)Al_(10) and Nd_(60)Fe_(30)Al_(10) cylinders exhibit hard magnetic properties of 0.076 to 0.086 T for remanence, 291 to 321 kA/m for intrinsic coercive field 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.