Abstract
An automated method has been developed to characterize the type and spatial distribution of twinning in crystal orientation maps from synchrotron X-ray Laue microdiffraction results. The method relies on a look-up table approach. Taking into account the twin axis and twin plane for plausible rotation and reflection twins, respectively, and the point group symmetry operations for a specific crystal, a look-up table listing crystal-specific rotation angle-axis pairs, which reveal the orientation relationship between the twin and the parent lattice, is generated. By comparing these theoretical twin-parent orientation relationships in the look-up table with the measured misorientations, twin boundaries are mapped automatically from Laue microdiffraction raster scans with thousands of data points. Taking advantage of the high orientation resolution of the Laue microdiffraction method, this automated approach is also applicable to differentiating twinning elements among multiple twinning modes in any crystal system.
Highlights
Crystal twinning, referring to two or more homogeneous individuals oriented by a defined symmetry element outside the crystal’s point group, is commonly observed during crystal growth, recrystallization annealing, phase transformation (Li et al, 2014) and plastic deformation (Cahn, 1954)
Twinned crystals usually exhibit unique effects distinct from their untwined counterparts in the aspects of mechanical behavior (Christian & Mahajan, 1995; Salem et al, 2005; Kaschner et al, 2006), texture evolution (Brown et al, 2005; Proust et al, 2007), and other physical properties. Because they have a lower interfacial energy than ordinary grain boundaries (OGBs), twin boundaries (TBs) have a major impact on yield stress (Konopka & Wyrzykowski, 1997), work hardening (Bouaziz et al, 2008) and fatigue cracking initiation (Heinz & Neumann, 1990), and cause migration of twin walls in some shape memory alloys induced by external magnetic fields (Likhachev & Ullakko, 2000)
A ‘look-up’ approach is developed to determine and map the crystal twinning by comparing the orientation outputs of a mXRD raster scan with a calculated look-up table, which is established taking into account geometric relationships between twin pairs and the rotational symmetry of the point group
Summary
Crystal twinning, referring to two or more homogeneous individuals oriented by a defined symmetry element outside the crystal’s point group, is commonly observed during crystal growth, recrystallization annealing, phase transformation (Li et al, 2014) and plastic deformation (Cahn, 1954). Twinned crystals usually exhibit unique effects distinct from their untwined counterparts in the aspects of mechanical behavior (Christian & Mahajan, 1995; Salem et al, 2005; Kaschner et al, 2006), texture evolution (Brown et al, 2005; Proust et al, 2007), and other physical properties. Often, because they have a lower interfacial energy than ordinary grain boundaries (OGBs), twin boundaries (TBs) have a major impact on yield stress (Konopka & Wyrzykowski, 1997), work hardening (Bouaziz et al, 2008) and fatigue cracking initiation (Heinz & Neumann, 1990), and cause migration of twin walls in some shape memory alloys induced by external magnetic fields (Likhachev & Ullakko, 2000). A ‘look-up’ approach is developed to determine and map the crystal twinning by comparing the orientation outputs of a mXRD raster scan with a calculated look-up table, which is established taking into account geometric relationships between twin pairs and the rotational symmetry of the point group
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