Unusual alloying effects of Co and Ni on structure and magnetic properties of Fe-Si-B-Cu nanocrystalline alloys with pre-existing α-Fe nanocrystals

Alloying Co and Ni in traditional Fe-based nanocrystalline alloys always brings about crystals refinement and magnetic softness improvement, while we found opposite phenomena in Fe_81.3Si₄B₁₃Cu_1.7 nanocrystalline alloy with pre-existing α-Fe nanocrystals in present work and clarified the related mechanism by investigating the structure evolution of melt-spun (Fe, Co, Ni)_81.3Si₄B₁₃Cu_1.7 alloys. The Co and Ni alloying lowers the number density (N_d) of pre-existing α-Fe nanocrystals in the as-spun alloys by suppressing the formation of Cu-enriched clusters. The effect of Ni alloying is more distinct than that of Co and adding 10 at.% Ni completely eliminates the nanocrystals. The decreased N_d leads to the weakened competitive growth between the nanocrystals, combined with the absence of diffusion-suppression, resulting in the slightly crystals coarsening and corresponding magnetic softness deterioration in the annealed Co-containing alloys and much more distinct ones in the annealed Ni-containing alloys.