Effect of small Zr additions on the microstructure of Sm/sub 2/Fe/sub 17/

Microstructure and phase composition of Sm/sub 10.5+/spl delta//Fe/sub 89.5-/spl delta/-/spl infin//Zr/sub /spl infin// samples with /spl delta/=0, 1.5 and x=0, 1, 2 were investigated. The Zr addition reduces the amount of Sm-rich phase and free /spl alpha/-Fe in as-cast materials, whereas the Sm addition (only investigated for Zr-containing alloys) reduces the amount of free /spl alpha/-Fe on cost of a higher amount of Sm-rich phase. The Zr is not uniformly distributed in the as-cast materials, forming Zr-rich (Sm, Zr)Pes phase (10-20 at% Zr) besides 1:3 and 2:17 phases with lower Zr content (/spl les/1 at% Zr). However, after homogenization, these Zr- rich regions disappeared and the Zr was then uniformly distributed in the 1:3 phase regions. The hard magnetic properties of all samples were studied after milling and nitrogenation. The highest energy product (BH)/sub max/ of 146 kJm/sup -3/ was obtained for the homogenized Zr-free sample. However, the properties of the as-cast materials are improved by the Zr-addition, with the optimum composition of Sm/sub 12/Fe/sub s/spl tau//Zr/sub 1/N/sub y/ showing a (BH)/sub max/ of 125 kJm/sup -3/.