As-quenched and nanocrystallized structure for Nb-poor Fe–Nb–B–P–Cu soft magnetic alloys melt spun in air

The as-quenched and nanocrystallized structures for Nb-poor Fe–Nb–B(–P–Cu) alloys melt spun in air have been investigated. The Nb-poor Fe85Nb6B9 alloy has the as-quenched structure composed of an amorphous phase and large α-Fe grains with 20–45 nm in size. The large α–Fe grains should remain after crystallization and result in a nonuniform nanocrystalline structure with the low permeability (μe) of 14 000 at 1 kHz. The simultaneous replacement of B by 1 at % P and Fe by 0.1 at % Cu for the alloy decreases the α-Fe grain size to nanoscale in an as-quenched state, and realizes a uniform crystallized nanostructure and good magnetic properties (μe=41 000 at 1 kHz and Bs=1.61 T) comparable to those of the typical Fe–M–B nanocrystalline alloys with a fully amorphous phase in an as-quenched state produced in a vacuum or Ar atmosphere. This result indicates that the precursor to the uniform nanostructure with high μe is not always a fully amorphous phase, and there is a possibility to realize the higher Bs materials with higher Fe contents.