Misorientation dependence grain boundary complexions in <111> symmetric tilt Al grain boundaries

Since polycrystalline alloys consist of a complex network of various types of grain boundaries (GBs), detailed atomic-scale analysis of how some impurities are distributed at every type of GBs is necessary to fully understand the implications of GB segregation on material's performance. In this study, we present the atomic-scale structural combined with a chemical analysis of segregation induced GB complexions across the various types of Al alloy 7075 GBs using aberration-corrected microscopy and crystal orientation mapping assisted with precession electron diffraction. The result shows multilayer Cu GB segregation containing non-uniformly segregated mixed atomic columns across the interfaces. Two distinct types of Cu GB segregation behavior were observed, point and parallel array, analyzed by means of a displacement field obtained from the dichromatic pattern. Atomistic simulations were performed to test the energetic feasibility of the observed segregation behavior. As per the knowledge of the authors, this is the first report on experimental analysis of segregation induced periodic ordered structured GB complexions on Al alloy system. Furthermore, every GBs of the films were segregated uniquely forming ordered structures along the interface. The distance between two consecutive high segregated units was periodic for the point segregated GBs and followed a trend of a theoretical model of dislocation spacing. Based on the distance between two high segregated units, it is inferred that highly misorientated GBs are more segregated than low misoriented GBs. This study demonstrates that the misorientation between the neighboring grains significantly influences the segregation behavior across the interface and consequently, the structure of segregation-induced GB complexions. (C) 2019 Acta Materialia Inc. Published