Subnanometer scale study of segregation at grain boundaries in an Fe(Si) alloy

The Gibbsian interfacial excess of silicon (Gamma(Si)) was determined, on an atomic scale, for 14 grain boundaries (GBs) in a single-phase Fe-3 at.% Si alloy, using a unique combined atom-probe field-ion microscopy/transmission electron microscopy (APFIM/TEM) approach. The specimens were equilibrated at 823 K for 14.5 or 72.5 h before the analyses. TEM was first employed to determine the five geometric degrees of freedom (DOFs) of each GB: unit rotation axis, c, rotation angle, theta, and unit GB plane normal, n. APFIM analyses were then utilized to obtain integral profiles perpendicular to the GB planes and from these profiles Gamma(Si) was determined for each GB. The values of Gamma(Si) are displayed in three dimensions as a function of sin(theta(dis)/2) and cos(angle c,n); theta(dis) is the disorientation angle. This three-dimensional plot represents Gamma(Si) as a function of the five macroscopic DOFs and is a direct representation of GB phase space segregation data. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.