Magnetic properties of sintered Nd‐Fe‐B magnets from hydrided materials

Hydrogen decrepitation is a very effective method of pulverizing Nd‐Fe‐B‐type alloys for sintered magnets. Jet‐mill response of hydrided materials is much better than that of unhydrided materials, i.e., shorter milling time is required and finer particle size is obtained for hydrided materials. The sinterability of hydrided powder is also improved from that of unhydrided powder. The minimum sintering temperature for obtaining full density (≳98% of theoretical density) magnets made from hydrided powders ranges between 900 and 950 °C, while that for magnets made from unhydrided powders ranges between 1050 and 1100 °C. Magnets made from hydrided powder sintered at low temperatures usually exhibit high coercivity comparable to or greater than that of the magnets made from unhydrided powder sintered at high temperatures followed by subsequent heat treatment. The enhancement of sinterability and the increase in coercivity of Nd‐Fe‐B magnets are discussed.