EXAFS analysis of grain boundaries in nanocrystalline Fe 85Zr 7B 6Cu 2 alloys

Abstract

Nanocrystalline Fe 85Zr 7B 6Cu 2 alloys were obtained from the formerly amorphous Fe 85Zr 7B 6Cu 2 alloy by a heat treatment at several temperatures ranging from 480°C to 600°C. The ultrafine nanocrystalline structure of bcc-Fe grains with a grain size of 3–15 nm diameter embedded in an amorphous matrix was established using transmission electron microscopy. X-ray absorption spectra at the Fe K-edge for Fe 85Zr 7B 6Cu 2 amorphous and nanocrystalline alloys and metallic Fe foil were measured using synchrotron radiation. Fourier analysis of extended X-ray absorption fine structure (EXAFS) for alloys was performed and two models of grain boundaries in nanocrystalline Fe 85Zr 7B 6Cu 2 alloys were proposed. The heat treatment of alloys at temperatures of 480°C and 500°C creates simple boundaries between crystalline grains and amorphous matrix, while the heat treatment at higher temperatures from 540°C to 600°C can produce boundaries in the form of Fe-free interfaces with thickness of about 0.3 nm. A model of an Fe-free interface being a barrier for grain growth can explain the nanocrystallization phenomenon of Fe 85Zr 7B 6Cu 2 alloys.