High performance Nd-Fe-B sintered magnets made by the wet process

The wet process for the fabrication of Nd-Fe-B sintered magnets has been developed on the mass production scale. In this process, mineral oil is used as a solvent to prevent the milled powder and green bodies from oxidation. It is removed before sintering. As a result, the oxygen uptake during storage is less than 0.01 wt %/day. By reducing the oxygen content and the total rare earth (TRE) content in sintered magnets to less than 0.2 and 29.3 wt %, respectively, magnets with (BN)(max)/H-i(c) greater than 50 MGOe/10 kOe, 45 MGOe/15 kOe, and 32 MGOe/32 kOe were obtained with high reliability. The magnets produced by this wet process also show better corrosion resistance and 20% higher mechanical strength than those made by conventional methods. These characteristics may be explained by a smaller grain size, smaller TRE content, and higher density produced by the wet process. (C) 1998 American Institute of Physics. [S0021-8979(98)15211-8].