Refining nanocrystalline-amorphous composite structure for superior soft magnetics in FeBSiPMoCu alloys via localized dynamic high-entropy effect enhanced by Mo micro-alloying

The amorphous formability (AFA), thermal stability, microstructure and soft-magnetism of Fe_83-xB₈Si₄P₄Mo_xCu₁ (x = 0–4) alloys were systematically investigated, and the mechanism of Mo micro-alloying induced grain refinement was discussed. It is found that the Mo alloying can effectively enhance the AFA and soft-magnetism, as well as enlarge the heat treatment parameter window. Superior soft magnetism containing high B_s of 1.48–1.76 T, low H_c of 6.7–11.4 A/m and high μ_e of 1.57–2.21 × 10⁴ was obtained by annealing for 10 min in a common vacuum furnace. The α-Fe(Si) grains in the nanocrystalline-amorphous composite structure were refined from 27 nm to 17 nm, due to the slow diffusion rate for grain growth and stabilized amorphous matrix composed with Fe, B, P and Mo. The enrichment of amorphous forming elements can introduce localized dynamic high-entropy effect during the structure evolution, which is beneficial for the fine structure in multi-component alloys. These Mo-containing alloys with attractive magnetism and processability should be promising candidates for scale production and electromagnetic applications.