Effect of small Zr additions on the microstructure of Sm2Fe17

Microstructure and phase composition of Sm_10.5+δFe_89.5-δ-∞Zr_∞ samples with δ=0, 1.5 and x=0, 1, 2 were investigated. The Zr addition reduces the amount of Sm-rich phase and free α-Fe in as-cast materials, whereas the Sm addition (only investigated for Zr-containing alloys) reduces the amount of free α-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 (⩽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)_max of 146 kJm ^-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 Sm₁₂Fe_sτZr₁N_y showing a (BH)_max of 125 kJm^-3