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Twins in hexagonal close-packed polycrystals, most often nucleate at grain-boundaries (GBs), propagate into the grain and terminate at opposing GBs. Regularly, multiple parallel twins of the same variant form inside the same grain. When twins terminate inside the grains, rather than the grain boundary, they tend to form a staggered structure. Whether a staggered twin structure or the more common grain spanning twin structure forms can greatly affect mechanical behavior. In this work, the underlying mechanism for the formation of staggered twins is studied using an elasto-visco-plastic fast Fourier transform model, which quantifies the local stresses associated with 1012-type staggered twins in magnesium for different configurations. The model results suggest that when a twin tip is close to the lateral side of another twin, the driving force for twin propagation is significantly reduced. As a result, the staggered twin structure forms.
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Micromechanical Fields Associated with Irregular Deformation Twins in Magnesium
Abstract Understanding and controlling the development of deformation twins is paramount for engineering strong and stable hexagonal close-packed (HCP) Mg alloys. Actual twins are often irregular in boundary morphology and twin crystallography, deviating from the classical picture commonly used in theory and simulation. In this work, the elastic strains and stresses around irregular twins are examined both experimentally and computationally to gain insight into how twins develop and the microstructural features that influence their development. A nanoprecession electron diffraction (N-PED) technique is used to measure the elastic strains within and around a $$\left\{ {10\overline{1}2} \right\}$$ 10 1 ¯ 2 tensile twin in AZ31B Mg alloy with nm scale resolution. A full-field elasto-viscoplastic fast Fourier transform (EVP-FFT) crystal plasticity model of the same sub-grain and irregular twin structure is employed to understand and interpret the measured elastic strain fields. The calculations predict spatially resolved elastic strain fields in good agreement with the measurement, as well as all the stress components and the dislocation density fields generated by the twin, which are not easily obtainable from the experiment. The model calculations find that neighboring twins, several twin thicknesses apart, have little influence on the twin-tip micromechanical fields. Furthermore, this work reveals that irregularity in the twin-tip shape has a negligible effect on the development of the elastic strains around and inside the twin. Importantly, the major contributor to these micromechanical fields is the alignment of the twinning shear direction with the twin boundary.
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- Award ID(s):
- 2051390
- PAR ID:
- 10411840
- Date Published:
- Journal Name:
- Journal of Materials Engineering and Performance
- Volume:
- 32
- Issue:
- 6
- ISSN:
- 1059-9495
- Page Range / eLocation ID:
- 2688 to 2699
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s11665-022-07196-3
