AEM studies of Sm:Co 2:17 permanent magnet alloys

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Abstract
A cast 2:17 alloy with composition Sm 10.5, Co 60.0, Fe 20.6, Cu 7.1, Zr 1.8 at. % was quantitatively analyzed with an analytical electron microscope (AEM). After a 24-h solution heat treatment at 1160 °C and rapid cooling, the microstructure was highly twinned, mostly 2:17R. Isothermal aging at 800 °C produced the microstructure typical of 2:17 permanent magnets. After 72 h, the 2:17R matrix phase composition was Sm 10.5, Co 61.7, Fe 22.4, Cu 4.8, Zr 0.5 at. %. The coherent boundary and platelet phases were too small to analyze independently, so two phase regions, including the matrix phase, were measured. The procedure yielded excellent results for the boundary phase: Sm 17, Co 33.6, Fe 4.8, Cu 43, Zr 1–2 at. %. Semiquantitative results were obtained for platelet-matrix phase mixtures: Sm 6(5–8), Co 60, Fe 14(13–15), Cu 5, Zr 15(14–17). Selected area diffraction patterns of the platelet could be indexed as with a=0.5 nm and c=0.8 nm. These results for the platelet phase differ significantly from those of previous investigations.