Nanotwin-assisted nitridation of quenched FeNi alloy nanopowders for rare-earth-free magnets

L10-ordered FeNi alloy with a high uniaxial magnetic anisotropy and large magnetic moment is a promising candidate for rare-earth-free permanent magnets applications. However, the synthesis of this chemically ordered phase remains a longstanding challenge because of its low chemical order-disorder transition temperature (200-320 & DEG;C). Although a non-equilibrium synthetic route based on a nitrogen topotactic reaction has been proposed as a valid approach, the volume fraction and degree of chemi-cal ordering of the product phase are limited. Herein, we propose a promising approach that promotes the efficient formation of L10-ordered nitride phase in FeNi nanopowders by introducing a quench-ing treatment during a low-oxygen induction thermal plasma process. The quenched FeNi nanopow-ders possessed much smaller powder sizes (40.4 vs 74.0 nm), exhibited higher number densities of nanotwins (39.8% vs 24.1%) and formed much larger volume fraction (33.6 wt.% vs 0.6 wt.%) of or-dered phase than the unquenched nanopowders. Notably, quenching-induced high-density nanotwins led to the dominant coverage of serrated {001} crystal facets over the surfaces of the FeNi nanopow-ders. Such unique features substantially accelerated the formation of the L10-ordered nitride phase in the FeNi nanopowders because the (001) crystallographic orientation had the highest nitrogen diffu-sivity. This work provides not only a valid synthetic approach for mass production of the L10-ordered nitride phase in FeNi nanopowders but also novel insights into the crystal-defect-assisted nitridation of nanomaterials. & COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )