High coercivity powders based on Sm-Fe-Ta-N prepared by a novel technique

Abstract

Nitrided Sm2Fe17-based materials possess excellent intrinsic magnetic properties. In this study, we investigate two compositions, Sm13.7Fe86.3 and Sm13.8Fe82.2Ta4.0. The stoichiometry of each phase was determined and the SmFeTa material was found to include Ta3Fe7, in addition to the Sm2Fe17, SmFe2, and SmFe3 phases observed in the SmFe alloy, but without the α-iron dendrites characteristic of the binary material. SEM and TEM studies revealed that in the cast structure, approximately 2.0% Ta is initially dissolved in the Sm2(FeTa)17 phase; however, HDDR processing causes the formation of Ta-based precipitates, leaving a 2: 17 phase with much less dissolved Ta. The HDDR process, with subsequent nitrogenation, was used to prepare coercive powders. The coercivities of these powders were found to be very dependent on the HDDR conditions and Ta addition. The highest coercivity achieved was 1280 kA/m for the composition with Ta.