The precipitation sequence obtained during crystallization of an amorphous Co65Si15B14Fe4Ni2 magnetic alloy

The microstructures developed during crystallization of an initially amorphous Co65Si15B14Fe4Ni2 magnetic alloy were investigated using transmission electron microscopy, X-ray diffraction (XRD) and energy dispersive X-ray (EDX). The microstructural evolution involved at least three steps: (a) primary precipitation from an amorphous matrix; (b) nanoprecipitation at primary precipitateʹs boundaries as well as inside the primary precipitates; (c) heterogeneous microstructures. At 600 °C grains about 100 nm in size and a secondary phase at the center of the grains were observed. XRD results showed that the intermetallic compounds Co2Si and Co3B2 had formed during the crystallization of the Co65Si15B14Fe4Ni2 alloy. The difference in compositions between the large grains and the amorphous matrix was attributed to boron diffusion from EDX composition analysis. The irregular heterogeneous microstructure was deduced to be a morphological transformation from the large grains rather than a crystal structural transformation. Inside the large grains, a highly modulated nanolamellar structure with a wavelength of about 10 nm was observed.