Mechanism of active dissolution of nanocrystalline FeSiBPCu soft magnetic alloys

Nanocrystalline Fe83.3Si3B10P3Cu0.7 alloys have a heterogeneous microstructure consisting of α-Fe nanocrystals with an average size of few tenths of nanometers and an amorphous residual phase. Nanocrystalline alloy annealed at 698 K has a saturated magnetic flux density of 1.81 T and coercivity of 11.8 A m− 1. Its hetero-amorphous microstructure undergoes active dissolution in H2SO4, and α-Fe grains are preferentially dissolved in the form of micro-coupling cells between anodic α-Fe grains and cathodic amorphous residue and Cu clusters. Because the P enrichment in the residual phases inhibits the anodic dissolution of Fe and the α-Fe grains act as sacrificial anodes, the amorphous residual phases do not readily dissolve. The final residual phase is amorphous and has a nanoporous structure with a pore size similar to that of the precipitated α-Fe grains after annealing. The active dissolution behavior is determined by the microstructure of nanocrystalline Fe83.3Si3B10P3Cu0.7 alloys.