EXAFS analysis of grain boundaries in nanocrystalline Fe85Zr7B6Cu2 alloys

Nanocrystalline Fe85Zr7B6Cu2 alloys were obtained from the formerly amorpho us Fe85Zr7B6Cu2 alloy by a heat treatment at several temperatures ranging f rom 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 amor phous matrix was established using transmission electron microscopy. X-ray absorption spectra at the Fe K-edge for Fe85Zr7B6Cu2 amorphous and nanocrys talline alloys and metallic Fe foil were measured using synchrotron radiati on. Fourier analysis of extended X-ray absorption fine structure (EXAFS) fo r alloys was performed and two models of grain boundaries in nanocrystallin e Fe85Zr7B6Cu2 alloys were proposed. The heat treatment of alloys at temper atures of 480 degrees C and 500 degrees C creates simple boundaries between crystalline grains and amorphous matrix, while the heat treatment at highe r temperatures from 540 degrees C to 600 degrees C can produce boundaries i n 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 nano crystallization phenomenon of Fe85Zr7B6Cu2 alloys. (C) 1999 Elsevier Scienc e S.A. All rights reserved.