Effect of small Zr additions on the microstructure of Sm2Fe17

Microstructure and phase composition of Sm10.5+delta Fe89.5-delta -x Zr-x s amples with delta = 0, 1.5 and x = 0, 1, 2 were investigated. The Zr additi on reduces the amount of Sm-rich phase and free alpha -Fe in as-cast materi als, whereas the Sm addition (only investigated for Zr-containing alloys) r educes the amount of free alpha -Fe on cost of a higher amount of Sm-rich p hase, The Zr is not uniformly distributed in the as-cast materials, forming Zr-rich (Sm, Zr)Fe-3 phase (10-20 at % Zr) besides 1:3 and 2:17 phases wit h lower Zr content (less than or equal to at % Zr). However, after homogeni zation, these Zr- rich regions disappeared and the Zr was then uniformly di stributed in the 1:3 phase regions. The hard magnetic properties of all sam ples were studied after milling and nitrogenation. The highest energy produ ct (BH)(max) of 146 kJm(-3) was obtained for the homogenized Zr-free sample . However, the properties of the as-cast materials are improved hy the Zr-a ddition, with the optimum composition of Sm12Fe87 Zr-1 N-y showing a (BH)(m ax) of 125 kJm(-3).