Crystallography of Fe2Al5 phase at the interface between solid Fe and liquid Al

In this study, the microstructures and crystallographic features of a eta-Fe2Al5 phase formed on pure Fe hot-dipped in a pure Al melt at 750 degrees C were examined in order to understand the eta phase layer formation having a saw-tooth morphology. A number of the columnar eta grains (forming the eta phase layer) grow towards the solid Fe (alpha-Fe) side along the [001] direction, resulting in a significant saw-tooth morphology at the interface between the eta and alpha-Fe phases. The neighboring eta grains have high-angle boundaries with a common [001] axis. In the eta phase layer, the low-angle boundaries develop close to the liquid Al side, and their density becomes higher with longer dipping times, resulting in the development of a fine dislocation substructure in the eta phase. In the alpha-Fe phase, fine substructure consisting of a high density of low-angle boundaries develops around the growth tips of the columnar grains. These substructure developments are likely responsible for the alpha -> eta transformation strain. A possible mechanism for the formation of this eta phase layer having a saw-tooth morphology will be discussed in terms of the stress field caused by the alpha -> eta transformation. (C) 2015 Elsevier Ltd. All rights reserved.