Grain refinement mechanism of soft-magnetic alloys with nanocrystals embedded in amorphous matrix

To obtain uniform and stable nanostructure with fine a-Fe grains is very important for the wide applications of Fe-based nanocrystalline soft-magnetic alloys. In this study, the nanos-tructure evolution of the Fe84.75Si2B9P3C0.5Cu0.75 (at.%) alloy after annealing under different conditions was characterized in detail. It is found that the alloy exhibits excellent struc-tural stability, which can maintain small a-Fe grains for a prolonged annealing time at low temperature. The increase of annealing temperature and/or annealing time will lead to the precipitation of compound phases in the intergranular amorphous interphase, which affects the a-Fe grains size greatly and determines the structural stability. The elemental mappings of the nanostructured alloys reveal that metalloid elements are enriched in the intergranular amorphous interphase, wrapping around a-Fe grains. The grain refinement and nanostruc-ture stability of these alloys are derived from the shielding and soft-impingement effects of the core-shell like structure. The nanostructure stability is lost with the precipitation of compound phases in the intergranular amorphous interphase, owing to the break-down of the shielding layer, which results in the rapid coarsening of alpha-Fe grains by coalescence. (c) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).