Identification of a bilayer grain boundary complexion in Bi-doped Cu

Using aberration-corrected scanning transmission electron microscopy, we have directly observed a bilayer grain boundary complexion in Bi-doped Cu, akin to that observed in Ni-Bi [Science, 333: 1730 (2011)]. In comparison with the Ni-Bi bilayer, the Cu-Bi bilayer appears to exist in a much narrower chemical potential window attributable to the fact that Cu-Bi and Ni-Bi have different pair-interaction potentials. Furthermore, these bilayers often form in conjunction with nanoscale faceting. This study demonstrates that direct imaging of the atom columns provides a more accurate understanding of the structure, chemistry and distribution of the adsorbates in a grain boundary and their role in embrittlement. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.