MAGNETIC-PROPERTIES OF ND-FE-B MAGNETS PREPARED BY METAL INJECTION-MOLDING

Nd-Fe-B alloy powder was kneaded at 283K with a binder of methylcellul ose dissolved in water. The mixture was injected at 293K into a die at 353K, which is slightly above the sol-gel transformation temperature of methylcellulose. A magnetic field of 1.35MA/m was applied to produc e alignment in the direction of easy magnetization in the molded body. The molded body was dehydrated by vacuum drying to suppress oxidation of the alloy powders. By heating the molded body in hydrogen at 573K for 0.5h, about 80w/o of the carbon in the binder was removed, but the oxygen in the binder remained. With a binder of 2w/o aqueous methylce llulose solution, these treatments suppress the residual oxygen and ca rbon levels in the sintered Nd-Fe-B alloy to 9000ppm and 1000ppm, resp ectively. The highest coercivity and maximum energy product for a sint ered anisotropic magnet prepared by the cited process are 1.10MA/m and 287.2kJ/m(3), respectively, which are about the same levels as those obtained by conventional dry compaction.