Laboratory for Multiscale INterfaces Design in Solids (MINDS)
Research
Twinning in HCP Metals
(1) Three-dimensional nature of twin domains
Y. Liu, N. Li, S. Shao, M. Gong, J. Wang, R.J. McCabe, Y. Jiang and C.N. Tomé. “Characterizing the boundary lateral to the shear direction of deformation twins in magnesium.” Nature Communications 7 (2016): 11577.
In this work, we for the first time identify and characterize the “dark side” of {10-12} twins using high-resolution transmission electron microscopy and atomistic simulations, and find that the “dark side” of twins is formed by coherent twin boundaries and semi-coherent twist prismatic-prismatic boundaries.
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(2) {11-22} twinning accomplished by multiple types of twinning dislocations (TDs)
M. Gong, S. Xu, D. Xie, S. Wang, J. Wang, C. Schuman and J.S. Lecomte. “Steps and {11-21} secondary twinning associated with {11-22} twin in titanium.” Acta Materialia 164 (2019): 776-787.
In HCP metals, most twinning modes is accomplished by nucleation and migration of one type of TD. In this work, high-resolution transmission electron microscopies explored various steps along {11-22} coherent twin boundaries. Using atomistic simulation and topological analysis, we conclude that 3-layer TD is the elementary TD and 1-layer TD is the reassembly TD. TDs with the other heights can be treated as reassembly of 1-layer and 3-layer TDs.
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(3) Interaction between dislocations and three-dimensional twins
M. Gong, G. Liu, J. Wang, L. Capolungo and C.N. Tomé. “Atomistic simulations of interaction between basal <a> dislocations and three-dimensional twins in magnesium.” Acta Materialia 155 (2018).
In this study, we for the first time conduct atomistic simulations of the interaction processes of basal <a> dislocations approaching a three-dimensional {-1012} twins. We find that mixed <a> dislocations dissociate on normal-TBs while transmit on lateral-TBs. Screw dislocation can transmit into twin but may cross-slip near lateral-TBs.
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(4) Criterion to predict secondary twin variant selection
S. Xu, M. Gong, Y. Jiang, C. Schuman, J.S. Lecomte and J. Wang. “Secondary twin variant selection in four types of double twins in titanium.” Acta Materialia 152 (2018): 58-76.
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Two new methods, modified displacement gradient accommodation (m-DGA) and nucleation via dislocation dissociation (NDD), have been developed to predict secondary twin variant selection. These two methods correctly predict four types of secondary twinning in titanium, implying that the preferred secondary twin variant would, to the greatest extent, relax plastic deformation associated with the primary twining and the nucleation of the secondary twin variant is facilitated by the accumulation of available gliding dislocation at the primary twin boundary.
