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[en] Deformation twins in Mg–Gd alloys are investigated. It is found that the dominant twinning mode switches from {10$\overline{1}$2} twinning to {11$\overline{2}$1} twinning, with an increase in the Gd concentration in Mg. Our first-principles calculations suggest that the formation of the {11$\overline{2}$1} twin in the Gd-rich alloy is triggered by the reduced {11$\overline{2}$1} twin boundary energy, which results from strain relaxation along the twin boundary. Furthermore, this twinning mode is suggestive to be activated in other Mg alloys with a high concentration of solute atoms having larger size than Mg.

[en] The results of a study on the occurrence of serrated [101^-2] twin interfaces in zirconium and titanium indicate that these serrations form on planes containing the twinning shear direction. During twin growth these serrations occur preferentially at the interface corresponding to the prominent corner produced at the free surface by the twinning shear. The occurrence of serrations is favoured, however, when the twinning shear results in a relatively small amount of surface tilt. When the surface tilt is relatively large, well-formed serrations in [101^-2] twin interfaces occur less frequently since they cannot be easily accommodated. It is proposed that the ease with which the deformation modes of these h.c.p. metals accomodate the serrations is an important factor in determining the conditions that favour the occurrence of serrations. This proposal would also explain why the occurrence of serrated twin interfaces is principally a surface phenomenon. (Auth.)

[en] Twinning processes during dynamic recrystallization were examined. The spatial frequency distribution of the twin grain boundaries in the recrystallized areas was determined and correlated with the various deformation degrees in the recrystallized areas by way of a deformation simulation according to Taylor. The measured twinning frequency in the last developed DRX areas is comparable with the frequency observed in the non-dynamically recrystallized initial material. So it is assumed that the twinning process is of similar significance to DRX and recrystallization in the autenitic steel. It could be revealed that twinning occurs during growth of the recrystallization nuclei, and therefore has an influence on the kinetics of the dynamic recrystallization. (orig./MM)

[en] Due to easy activation of tensile twinning in Mg, multiple $\left\{10\overline{1}2\right\}$ twin variants can interact with each other and form twin-twin boundaries over the course of plastic deformation. Previous studies using 2-D settings provide only a partial understanding of these interactions, especially the non-cozone ones. Here, atomistic simulations are used to study the 3-D structural characteristic and evolution of the non-cozone $\left\{10\overline{1}2\right\}$ twin-twin junctions. The study reveals the existence of new twin-twin boundaries (TTBs) such as TTB_BP and TTB_K2, formed after the interaction between the basal prismatic and conjugate twin interfaces with the coherent twin boundary. For both non-cozone twin-twin interactions, the $\left\{\overline{1}2\overline{1}2\right\}$ TTB and its associated twin-twin junctions are found to play a major role in the $\left\{10\overline{1}2\right\}$ twin's stability and mobility. Specifically, they promote the growth of the 3-D twin in both the normal and forward directions during the interaction and hinder the detwinning process upon unloading.

[en] Highlights: • The individual effect of DRXed grain, subgrain and deformed grain on the texture modification was studied. • The role of subgrain in the DDRX and CDRX was elucidated, respectively. • The variant selection of tension twins and the corresponding effect on the basal texture were investigated. The individual effect of DRXed grains, subgrains and deformed grains on the basal texture of Mg–Zn–Zr alloy during hot tensile deformation was systematically studied by extracting corresponding grains. The results show that the final texture was the result of compromise between the randomized texture of DRXed grains and preferred texture of subgrains and deformed grains. The texture attribute of subgrain did not change fundamentally compared with that of deformed grain, both of which dominated the final texture profile. Prismatic dislocations exerted a profound effect on the compatible deformation of unDRXed grains, giving rise to a sharp $\left[01\bar{1}0\right]$ fiber. Few basal dislocations could be detected in the unDRXed grains due to the premature exhaustion of such slip operation and subsequent substitution by non-basal slips. Subgrains, in terms of DDRX, were caused by the interaction between basal and non-basal dislocations, resulting in the protrusions segmented by the subgrain boundaries (sub-GBs) whose misorientation increased gradually as trapping dislocation proceeded. As a result, these protrusions were segregated from the parent grains and transformed into DRXed grains. CDRX proceeded by high activity of profuse dislocations. In this case, sub-GBs came from the realignment and incorporation of the accumulated dislocations in the vicinity of dislocation forest, which subdivided one grain into several subgrains that could be converted into DRXed grains in situ via the transformation from LAGBs to HAGBs by consecutively absorbing dislocations. Besides, twinning deformation was an auxiliary way of compatible deformation, which could reorientate parent grains so as to reactivate the slip systems. The contribution of resulting $\left\{10\bar{1}2\right\}$ twins to the final texture was not significant yet. Ultimately, the selection of $\left\{10\bar{1}2\right\}$ twin variants was also discussed.

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[en] In this work we present a new method to produce gold nanorods based on the bio-reduction process. The nanorods produced tend to show twins appearing either as bands or concentric forms, generating a new type of nanorods based on a decahedral structure. Examples of these two types of twins are presented here. The main conclusion is that the bio-reduction method to produce nanorods is a good alternative to the electrochemical methods

[en] This work presents a mechanism of deformation-twin-induced grain boundary failure, and demonstrates the mechanism using molecular dynamics simulations. Deformation twinning is observed as the dominant mechanism during tensile deformation of columnar nanocrystalline body-centered cubic Mo. As a twin approaches a grain boundary, local stress concentration develops due to the incompatible plastic deformations in the two neighboring grains. The magnitude of the stress concentration increases as the twin widens, leading to grain boundary cracking by nucleation and coalescence of microcracks/voids.