Nanocrystalline structure and initial permeability of annealed Fe_73.5Cu₁M0₃Si_13.5B₉ alloy

Abstract

The nanocrystalline structure of annealed Fe_73.5Cu₁M0₃Si_13.5B₉ alloy was investigated using X-ray diffraction and transmission electron microscopy. The relationship between the initial permeability and the microstructural parameters of the annealed alloy is discussed in this paper. The crystalline phase in annealed Fe_73.5Cu₁M0₃Si_13.5B₉ alloy is the α-Fe(Si) phase with a D0₃ superstructure. The volume fraction, silicon content, and degree of order of the α-Fe(Si) phase increased with an increase in the annealing temperature. In the temperature range of 460–560°C, the α-Fe(Si) phase had a grain size of 14 nm, and its grain number increased as the annealing temperature was increased. The D0₃ ordered region in the α-Fe(Si) grain was approximately spherical and its size increased as the annealing temperature increased. The size of the D0₃ ordered region was 14.0 nm at a temperature of 560°C, which is close to that of the α-Fe(Si) grain. There was an obvious change in the microstructure of the residual amorphous phase during annealing, the nearest atomic distance and the short range order of residual amorphous phase reaching a maximum and minimum respectively at 520°C. The initial permeability of annealed Fe_73.5Cu₁M0₃Si_13.5B₉ alloy was not only dependent on the microstructure of the α-Fe(Si) phase but was also related to the microstructural state of the residual amorphous phase.