Nd-Fe-B-Cu HD-processed sintered magnets: properties and microstructure

Sintered permanent magnets were produced from an Nd/sub 17/-Fe/sub 76.5/-B/sub 5/-Cu/sub 1.5/ alloy by a two-step heat treatment at 1370 K and 870 K following hydrogen decrepitation (HD)-processing. Optimized heat-treatment yielded magnetic properties of H/sub cj/=950 kA/m, B/sub r/=1.1 T, and (BH)/sub max/=230 kJ/m/sup 3/. These properties were hardly affected by cooling rates, in contrast to Cu-free magnets. Microstructural observations showed that the homogeneous distribution of a newly found intergranular phase is important for the development of good coercivity. This phase, the composition of which was determined to be Nd/sub 30/Fe/sub 65/Cu/sub 5/ by TEM and EDX, was shown by differential thermal analysis investigations to form at approximately=870 K. Isolated regions of Nd/sub 2/Fe/sub 17/ in the as-sintered material were dissolved after heat treatment.<
>