EXAFS analysis of grain boundaries in nanocrystalline Fe85Zr7B6Cu2 alloys

Nanocrystalline Fe85Zr7B6Cu2 alloys were obtained from the formerly amorphous Fe85Zr7B6Cu2 alloy by a heat treatment at several temperatures ranging from 480 degrees C to 600 degrees 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 Fe85Zr7B6Cu2 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 Fe85Zr7B6Cu2 alloys were proposed. The heat treatment of alloys at temperatures of 480 degrees C and 500 degrees C creates simple boundaries between crystalline grains and amorphous matrix, while the heat treatment at higher temperatures from 540 degrees C to 600 degrees 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 Fe85Zr7B6Cu2 alloys. (C) 1999 Elsevier Science S.A. All rights reserved.