Papers by Keyword: Twin Boundaries

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Authors: Kuniaki Yagi, Hiroyuki Nagasawa
Authors: Seiichiro Ii, N. Matsuzaki, Yasuhiro Morizono, Minoru Nishida
Authors: Hisaomi Iwata, Ulf Lindefelt, Sven Öberg, Patrick R. Briddon
Authors: Yoshito Nishimura, Nagato Ono, Sei Miura
Abstract: In order to make clear the micro-yielding mechanisms of polycrystalline metals including twins, the movement of dislocations in the surface grains of Cu-6.8at%Al alloy and pure Mg polycrystals during the early stages of deformation was directly observed by using etch pit technique. The fresh dislocations multiply from the Frank-Read sources within the grains, and pile up against the twin and grain boundaries of two kinds of specimens. The pile-up dislocations on the primary and/or secondary slip planes are also confirmed in Cu-6.8at%Al alloys. Especially during the compressive loading for pure Mg, the occurrence of deformation twins is remarkable with an increase of strain rate, whereas the distribution of fresh dislocations tends to decrease in the surface grains. The present results suggest that the effect of twin boundaries on micro-yielding is almost equivalent for that of grain boundaries, which act as barriers to moving dislocations even in the pre-yield deformation.
Authors: Alexander Kahrimanidis, Uta Klement
Abstract: Electrodeposition is an advanced synthesis technique which involves the creation of a coating or free-standing material through an electrolytic process. Organic additives such as saccharin have been frequently used in electroplating operations to moderate deposit growth rates and to control film quality. In the present study, plating of Nickel without additives has resulted in a sub-microcrystalline microstructure and a <110>-fibre texture in growth direction. Structural units in form of groups of grains possessing a common <110>-zone axis in growth direction and low-Σ relationships between them have been found in the microstructure by use of EBSD. Upon annealing, grain growth sets in. However, the structural units and the texture are preserved up to 550°C. This means that the structural units stabilize the microstructure; there is no orientation change when grain growth occurs (e.g. by twinning). The low-Σ boundaries of the structural units are described in detail and texture development upon annealing is discussed in connection with results from previous studies on Ni and Ni-alloys of different initial texture.
Authors: Hiroyuki Nagasawa, Takamitsu Kawahara, Kuniaki Yagi
Authors: Y. Wang, Wen Zhu Shao, Liang Zhen, L. Lin, Y.X. Cui
Abstract: The nucleation and development of dynamic recrystallization (DRX) in hot deformed superalloy Inconel 718 during uniaxial compression were investigated by optical microscopy and electron back-scattered diffraction (EBSD) technique. The results showed that the discontinuous dynamic recrystallization was the predominant DRX mechanism in this alloy. The variations of partial crystallographic orientations led to the individual nucleation inside the deformed grains, which implied the occurrence of local continuous dynamic recrystallization. The progressive subgrain rotation can be confirmed neither near the prior high angle grain boundaries nor within the original grains. It was found that, as the strain increased, the initial twin boundaries were gradually transformed to ordinary mobile high angle boundaries. Meanwhile, the new twin boundaries were formed inside the recrystallized grain necklaces. It was suggested that the characteristics of the twin boundaries evolution with increasing strain were associated with the transformation of initial twin boundaries as well as the generation of new ones, which resulted in the development of DRX.
Authors: Andriy Ostapovets, Václav Paidar
Abstract: The structures of {121} twin boundary in orthorhombic 2H martensite are modeled using Finnis-Sinclair type many-body interatomic potentials. The boundary corresponds to type-I twinning in 2H martensite of Cu-Al-Ni, Cu-Zn-Al and Au-Cd alloys. Three possible configurations of the {121} boundary are found. The structure with the lowest energy possesses a non-corrugated central {121} plane.
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