Grain refinement in Fe-rich FeSiB(P)NbCu nanocomposite alloys through P compositional modulation

The progressive addition of P in Fe-rich FeSiB(P)NbCu nanocomposite alloy leads to grain refinement of α-Fe nanocrystals i.e, dense nucleation and grain growth inhibition. The P addition leads to linear reduction of α-Fe nanocrystallite size (D) and increases nucleation density (Nd) from ~ 30 nm and 2.5 × 1022 (0 at% P) to ~ 15 nm and 0.9 × 1023 for (8 at% P). The refined microstructure leads to coercivity reduction from 74 A/m (0 at% P) to 9.4 A/m (8 at% P), in agreement with Random-Anisotropy Model. The P assisted synergistic grain refinement mechanism is explained in the context of crystallization activation energy, selective solute re-distribution and enhanced stabilization of intergranular amorphous matrix. The 4 at% P alloy shows optimal soft-magnetic properties of 10.2 A/m and 1.64 T.