Enhancement of Coercivity of Nd-Fe-B Sintered Magnets by Grain Size Reduction

For the purpose of increasing the coercivity of the Nd-Fe-B sintered magnets without Dy substitution, we explored a possibility of enhancing the coercivity by grain size reduction of the sintered body by employing the starting powder with an ultimately small particle size. To produce Nd-Fe-B alloy powder with such a small particle size, and to handle it to produce sintered bodies without oxidation, we developed a special jet mill and a special process called pressless process (PLP). By utilizing these techniques, it has become feasible to produce Nd-Fe-B sintered magnets with a coercivity of 1.59 MA/m without Dy substitution which is compared with 0.87 MA/m for the commercially available Nd-Fe-B sintered magnets containing no Dy.