A study on the role of Ni content on structure and properties of Fe-Ni-Si-B-P-Cu nanocrystalline alloys

Amorphous-forming ability (AFA) and thermal stability of melt-spun Fe85-xNixSi2B8P4Cu1 (x = 0-20) alloys and their crystallized structure, magnetic and mechanical properties have been investigated. The increase of Ni content from 0 to 20 at.% gradually improves the AFA with enlarging the critical thickness for amorphous formation from 14 to 38 mu m. Adding 5 at.% Ni increases the number density (N-d) of nucleation sites by properly delaying the Cu atoms clustering process during annealing and refines the alpha-(Fe, Ni) grains, which leads to a magnetic softness improvement of the nanocrystalline alloys. The excessive Ni (>= 10 at.%) decreases the N-d due to the overinhibition of the Cu clustering, resulting in the grains coarsening and magnetic softness deterioration. The Fe80Ni5Si2B8P4Cu1 nanocrystalline alloy possesses finer alpha-(Fe, Ni) grains with an average size of 22 nm, a lower coercivity of 14.3 A/m and saturation magnetic flux density of 1.77 T as compared with those of 40 nm, 105.3 A/m and 1.84 T, respectively, for the Fe85Si2B8P4Cu1 alloy. In addition, the nanocrystalline alloys with 2.5-10 at.% Ni show reduced brittleness compared with the Ni-free alloy owing to the grain refinement, and the alloys with 15-20 at.% Ni possess further decreased brittleness as a consequence of the reduced alpha-(Fe, Ni) phase volume fraction. (C) 2019 Published by Elsevier B.V.