Grain refinement mechanism of soft-magnetic alloys with nanocrystals embedded in amorphous matrix
Tao Liu, Hua Zhang, Fengyu Kong, Anding Wang, Yaqiang Dong, Aina He, Xinmin Wang, Hongwei Ni, Yong Yang
Abstract
To obtain uniform and stable nanostructure with fine α-Fe grains is very important for the wide applications of Fe-based nanocrystalline soft-magnetic alloys. In this study, the nanostructure 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 structural stability, which can maintain small α-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 α-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 α-Fe grains. The grain refinement and nanostructure 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 α-Fe grains by coalescence.