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

The microstructures developed during crystallization of an initially amorphous Co₆₅Si₁₅B₁₄Fe₄Ni ₂ 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 precipitate's 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 Co₃B ₂ had formed during the crystallization of the Co₆₅Si ₁₅B₁₄Fe₄Ni₂ 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.