Influence of annealing temperature on the microstructure of Cu-rich phase in nanocrystalline Fe73 5Cu1Mo3Sh3.5B9 alloy

摘要

In recent years, there have been numerous studies on the nanocrystalline Fe73.5Cii1Nb3Si13.5B9 alloy developed by Yoshizawa el al. [1], since it exhibits excellent permeability while maintaining a high saturation magnetization. Recently, a number of studies involving analyses with atom probe field ion microscopy (APFIM) and high resolution electron microscopy (HREM) by Hono et al. [2, 3], and analyses of extended X-ray absorption fine structure (EXAFS) by Kim et al. [4], Sakurai el al. [5] and Ayers et al. [6] have focused on the behaviour of Cu in the alloy during the annealing process. The purpose of these studies is to better understand how Cu acts to refine the scale of the crystallized microstructures in the alloy. The results of the studies have shown that Cu will cluster into nanometre scale regions at the beginning of the annealing stage and will then form a Cu-rich fee phase. With optimal heat treatment conditions, the microstructure of the alloy consists primarily of an a-Fe(Si) phase and a residual amorphous phase as well as the Cu-rich phase. Hono et al. [2], Kim et al. [4] and Ayers et al. [6] suggest that the formation of Cu clusters and a Cu-rich phase act to catalyse nucleation of Fe-rich nanocrystals, which is very significant for the formation of ultrafine nanocrystalline structure in the alloy. However, the influence of the annealing temperature on the microstructure of the Cu-rich phase in the alloy has not been investigated in detail. In addition, in the similar alloy Fe73.5Cu1M03Si13.5B9, direct evidence for the existence of Cu clusters or a Cu-rich phase has not been reported so far.