Twin Interactions Research Articles

On the formation of [formula omitted] boundary via [formula omitted]-[formula omitted] twin–twin interaction in magnesium

{101̄2} twinning occurs extensively in Mg to accommodate plastic deformation. With multiple active twin variants, twin–twin interaction occurs and this often forms twin–twin boundaries. In this work, the {112̄2} twin–twin boundary is studied using electron backscatter diffraction (EBSD) analysis and atomistic simulations. EBSD data show that many of the twin–twin boundaries align well with {112̄2} or {112̄6} planes. Further, atomistic simulations reveal dynamically the formation of {112̄2} boundary via the interaction of two non-co-zone {101̄2} twin variants. Moreover, the twinning mode of the {112̄2} boundary is found to be an extension twin with second undistorted plane of {112̄6}. In addition, the {112̄2} boundaries contribute significantly to the 60°〈011̄0〉 peak in the misorientation histogram; they also play an essential role in the unique strong strain hardening under c-axis tension. Our findings are crucial for completing the twinning theories for Mg.

Deformation twin interactions with grain boundary particles in multi-phase magnesium alloys

Deformation twinning is necessary for achieving strain in plastically hard directions in magnesium alloys under ambient conditions, but can also contribute to void formation and crack propagation that lead to early failure. This is especially true for instances of twin transmission between grains, which result in longer continuous twin boundaries and higher twin volume fractions. Coarse grain boundary particles have the potential to modify twinning behavior, but this effect has not been studied. This work uses a Crystal Plasticity – Fast Fourier Transform model to predict twinning behavior and transmission likelihood, parameterized to simulate different morphologies of the β-phase intermetallic common to Mg-Al alloys. Of these microstructures, those with particles directly in the path of impingement were found to decrease the stresses generated in the neighboring grain, similarly decreasing the likelihood of twin transmission across the boundary. Size and aspect ratio were found to play key roles in determining the resultant stress, but are dependent upon the orientation of the neighboring grain. Particles located near the impingement site were found to exacerbate the stress state and make transmission more likely. Instances where transmission was likely to be prevented were also predicted to undergo reduced twin thickening.

Three-dimensional atomic scale characterization of [formula omitted] twin boundaries in titanium

The {112¯2}<1123¯> compression twin can accommodate a considerable amount of strain under c-axis compression in Ti. However, unlike the tensile {101¯2}〈1¯011〉 twin, the structure of {112¯2}<1123¯> compression twins has not been completely characterized. Here, we apply a combined technique of HR-TEM characterization, topological analysis, and atomistic simulations to explore the facets that bound the {112¯2}<1123¯> twin in Ti. In addition to the currently known facets (CTB and B-Py), six new facets are observed and categorized for the first time from atomic-scale TEM observations along five crystallographic directions. The six new facets are (112¯0)//(112¯6), PrPr1, PyPy1, (211¯1)//(1¯21¯1), (11¯04)//(011¯1¯), and (011¯0)//(211¯4). Results from the topological and computational analysis are in reasonable agreement with and support the HRTEM observations. Specifically, (1) the observed facets align with low-index interfaces in both twin and matrix domains, (2) the facets with lower surface energies are found to form extended interfaces, and (3) high-surface-energy facets are found at the twin tip region and explained by the fact that the energy of the combined facet and facet junction configuration is energetically preferred in the twin tip region. These results not only provide a comprehensive understanding of the 3D structure of {112¯2}<1123¯> compression twins in Ti, but also validate the MD procedure and the Ti interatomic potential employed. This is extremely important for future study of {112¯2} twin mobility and interactions with other defects, both features that remain extremely challenging to capture in experiments.

Отдельные подходы к цифровой трансформации государственного управления

The article describes the features of digital transformation for public administration and civil service. Public administration should become the basis of changed public relations; ensure the solution of the most significant issues affecting citizens through the use of data in a single information (digital) space. Coordinated work and ensuring horizontal and vertical cooperation between public authorities and local self-governments are an integral part of this process. Digital transformation is understood as the process of creating a single national digital space. The provision of public services and the execution of powers take place through the interaction of digital twins of government bodies and government civil servants. At the same time, other business entities, non-profit organizations, residents of the country, and their associations will be able to connect to this information space. The implementation of this concept will contribute to improving the efficiency and quality of public administration.

Intra-pair interaction and peculiarities of self-identity of twins in preschool age

The subject of this research is the self-identity of twins in preschool age. The goal is to determine correlations between the behavioral indicators of intra-pair interaction and the parameters of functionality of self-identity of twins of preschool age. Detailed analysis is conducted on the role of twin situation and intra-pair interaction of twins in the development of self-identity in preschool age. The twin situation is interpreted as a special social situation of development that defines the formation of personality of twins; it is associated with the occurrence of specific intra-pair interactions that determine the development of self-identity of a preschooler. The research methodology is based on the cultural-historical approach that reveals the role of social situation in child&amp;rsquo;s development (L. S. Vygotsky), concept of self-identity (S. L. Rubinstein, L. I. Bozhovich), studies on twins (T. B. Morozov, M. T. Miliora). The empirical base is represented by 100 twins of preschool age. This article is first to give theoretical substantiation and empirical proof to the existence of correlation between the behavioral indicators of intra-pair interaction of twins and characteristics of self-identity of dizygotic and monozygotic twins in preschool age. The following conclusions were made: dizygotic and monozygotic twins may have a different nature of intra-pair interaction, which relates to the peculiarities of self-identity preschoolers; dizygotic twins have high possibility of rivalry with their twin; monozygotic twins are rather oriented towards cooperation. The proclivity for cooperation in the process of joint activity creates the foundation for positive self-esteem, self-acceptance, and assessment of own performance. The proclivity for rivalry allows the twins to be more independent, take responsibility for the results of their work, creates foundation for the development of self-identity, self-cognition, and self-understanding.

Microstructural and hardness evolutions of a cold-rolled cobalt

Abstract The microstructural and hardness evolutions of cold-rolled cobalt (Co) were investigated by electron backscatter diffraction, electron channeling contrast imaging, transmission electron microscope and Vickers hardness tests. The original Co has a dual phase structure with a mixture of hexagonal closed-packed and face-centered cubic structures. More than half fraction of the boundaries in the original Co present a particular orientation of ~ 71 ° / 11 2 ‾ 0 > . During cold rolling, different deformation mechanisms including dislocation slip, twinning, martensite phase transformation and stacking faults were activated, and their mutual interactions eventually refined the grains to nano scale. Multiple twinning systems including { 10 1 ‾ 2 } , { 11 2 ‾ 2 } and { 10 1 ‾ 1 } were activated, which play a dominant role at the early deformation stage, while these twins were eventually refined through dislocation – twin interactions. Basal a, pyramidal c+a and partial dislocations were all triggered to accommodate the local strain. Partial dislocation gliding is responsible for the reversible martensite phase transformation. The Vickers hardness results indicate a stable strain hardening process during the whole cold rolling process.

Deformation behavior of Ti-6Al-4V microstructures under uniaxial loading: Equiaxed Vs. transformed-β microstructures

The dual-phase titanium alloy Ti-6Al-4V can be thermomechanically treated to produce a variety of microstructures to obtain desired mechanical properties. The extreme microstructure morphologies were developed by heat treatment of mill annealed microstructure to equiaxed, and transformed-β microstructures (lamellar) of coarser α-lath and α′-laths (martensite). The uniaxial tensile test shows the highest elongation in the equiaxed microstructure followed by coarse α-lath lamellar, while the α′-lath morphology has the least elongation. The higher ductility in the equiaxed microstructure is due to smaller slip length compared to coarse α-lath lamellar. On the other hand, the poor ductility of the α′-lath is due to premature crack initiation. Both equiaxed and coarse α-lath lamellar microstructures mostly show prismatic and pyramidal slip <a>/ <c + a>. In addition to this, though less prevalent, these microstructures exhibit twinning as the other deformation mechanism, which is uncommon in Ti-6Al-4V. The twin boundary interaction with the grain boundary led to the damage nucleation, causing the intra-grain crack. In the coarse lath lamellar (furnace cooled) morphology, the crack was mostly observed at the junction of α-colonies as well at the α-layer grain boundary/α-colony interface due to strain localization. However, in the lamellar (water quenched), the primary α′-lath shows the void nucleation at the junction of the primary and secondary-α′ interface, which coalesce to form microcrack and further grow instantly to fracture. The void nucleation is generally observed in a basal orientation along the primary α′-lath, oriented 45° to the loading axis, and having dominant pyramidal slip (<a>/<c + a>). Thus, the deformation mechanisms slip, twin, and fracture depend on the microstructure morphology in Ti-6Al-4V.

In Situ Characterization of the Effect of Twin-Microstructure Interactions on {1 0 1 2} Tension and {1 0 1 1} Contraction Twin Nucleation, Growth and Damage in Magnesium

Through in situ electron backscatter diffraction (EBSD) experiments, this paper uncovers dominant damage mechanisms in traditional magnesium alloys exhibiting deformation twinning. The findings emphasize the level of deleterious strain incompatibility induced by twin interaction with other deformation modes and microstructural defects. A double fiber obtained by plane-strain extrusion as a starting texture of AM30 magnesium alloy offered the opportunity to track deformation by EBSD in neighboring grains where some undergo profuse {1 0 1 2} twinning and others do not. For a tensile loading applied along extrusion transverse (ET) direction, those experiencing profuse twinning reveal a major effect of grain boundaries on non-Schmid behavior affecting twin variant selection and growth. Similarly, a neighboring grain, with its ⟨c⟩-axis oriented nearly perpendicular to tensile loading, showed an abnormally early nucleation of {1 0 1 1} contraction twins (2% strain) while the same {1 0 1 1} twin mode triggering under ⟨c⟩-axis uniaxial compression have higher value of critical resolved shear stress exceeding the values for pyramidal ⟨c + a⟩ dislocations. The difference in nucleation behavior of contraction vs. compression {1 0 1 1} twins is attributed to the hydrostatic stresses that promote the required atomic shuffles at the core of twinning disconnections.

Twinning in rolled AZ31B magnesium alloy under free-end torsion

The mechanical response and microstructure evolution in a rolled AZ31B magnesium alloy were experimentally characterized using companion thin-walled tubular specimens under free-end monotonic torsion. The tubular specimens were made with their axes along the normal direction of the rolled magnesium plate. The shear stress-shear strain response shows a subtle sigmodal shape that is composed of four distinctive stages of strain hardening. Basal slips and tension twinning are operated throughout the shear deformation. Both tension twinning and compressing twinning are favored. Growth and interaction of tension twins with multiple variants lead to formation of twin-twin boundaries (TTBs). The collective hardening effects by twin boundary (TB) and TTB result in a unique rise of the strain hardening rate in Stage II and III. In addition to primary twins, tension-compression double twins and tension-compression-tension tertiary twins with detectable sizes are observed in the tension-twin favorable grains whereas compression-tension double twins are detected in the tension-twin unfavorable grains; all of which become more observable with the increasing shear strain. During Stage IV deformation where TTB formation exhausts, non-basal prismatic slips become more significant and are responsible for the progressive decrease in strain hardening rate in this stage. Swift effect, which is commonly observed in textured materials, is evidenced under free-end torsion. The origin of Swift effect is confirmed to be dislocation slips at a shear strain less than 5% but is predominantly due to tension twinning at a larger plastic strain.

Mechanisms of crack generation in high-pure tungsten exposed to high power density plasma

The mechanisms of crack formation in the tungsten divertor plates irradiated by hydrogen plasma under ITER-type steady-state and transient events are investigated. The stresses and defects of samples‘ initial structure are annealed as a result of steady-state irradiation with Falcon ion source, which generates 2 keV hydrogen ion flux of ~ 1022 m-2s−1 and power density ~ 1.7 MW × m−2. Quasi-stationary plasma accelerator QSPA Kh-50 provides pulsed hydrogen plasma loads which operating mode simulates transient events (type I ELMs) in ITER: ion impact energy is about 400 eV, maximum plasma pressure is 0.32 MPa, pulse duration is 0.25 ms. The diffraction maxima profiles, positions, intensities, half-widths, and intensity distributions are analyzed. The origin of crack formation is found to be in the plastic deformation of surface layers by the twinning mechanism. The latter is reinforced by the interaction of twins with the hydrogen-filled micro-pores. The micro-pores appear as a result of hydrogen saturation of subtraction loops formed due to the coalescence of vacancy complexes.

Atomistic mechanisms of twin–twin interactions in Cu nanopillars

Twinning is an important mode of plastic deformation in metallic nanopillars. When twinning occurs on multiple systems, it is possible that twins belonging to different twin systems interact and forms a complex twin–twin junctions. Revealing the atomistic mechanisms of how twin–twin interactions lead to different twin junctions is crucial for our understanding of mechanical behaviour of materials. In this paper, we report the atomistic mechanisms responsible for the formation of two different twin–twin interactions/junctions in Cu nanopillars using atomistic simulations. One junction contains two twin boundaries along with one Σ9 boundary, while the other contains five twin boundaries (fivefold twin). These junctions were observed during the tensile deformation of [100] and [11¯0] Cu nanopillars, respectively.

Effects of Zr addition on the deformation behavior, microstructure and mechanical properties of dental Ti alloys

Aiming to obtain a martensite-free microstructure of Ti–Zr alloys with a combination of enhanced deformability and improved mechanical properties for dental application, two high Zr-containing Ti-based alloys were prepared with commercially pure titanium as a control. The effects of Zr addition on the deformation mechanism, microstructure and mechanical properties were investigated. After thermo-mechanical processing and cold deformation, samples were characterized using Vickers microhardness, tensile tests, X-ray diffraction (XRD) scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD and TEM examinations revealed that the increasing Zr addition suppressed the deformation twining and favored the deformation-induced face-centered cubic (FCC) phase, the corresponding reason was discussed. There is a competition between the deformation twin and FCC phase. The two types of FCC phase were simultaneously found with orientation relationships (ORs) of Basal-type: <11–20>HCP//<110>FCC and {0001}HCP//{111}FCC and Prismatic-type: <0001>HCP//<001>FCC and {10-10}HCP//{110}FCC. This phase transformation enhanced the deformability during processing. As the Zr addition increased, the microhardness, mechanical strength and plasticity are increased concurrently. The interactions of twins were found to cause brittle fracture of Ti20Zr alloy. Based on the texture analysis, the activated slip systems of FCC phase were determined via calculating the Schmid factor. The FCC phase not only provided additional slip systems but also impeded dislocation slip effectively, improving the strength-plasticity of Ti30Zr alloy. The findings will provide a novel approach associated with the strengthening-toughening mechanism of metallic materials.

Phase field modelling of annealing twin formation, evolution and interactions during grain growth

Grain boundary engineering involves manipulation of grain boundary character and network to improve the properties of materials. Twin boundaries which form during annealing of low and medium stacking fault energy face centered cubic materials play an important role in grain boundary engineering. In this work, we study the formation, growth, interactions and annihilation of annealing twins using a phase field model. The model incorporates twin formation through growth accidents on grain boundaries and triple junctions. The results indicate that higher stored energy gradients in the microstructure enhance the twin formation and their rate of growth. Also, recovery with a slower rate of stored energy decay increases twin formation events and delays the annihilation of the twins. The influence of the variant selection (based on the axes of misorientation of the twin boundaries with the parent grains) on the nature of their interactions with other twins and coincident site lattice boundaries is examined. The variant selection is found to affect the interactions of twins with other coincident site lattice boundaries thereby influencing the grain boundary character distribution.

Microstructure and mechanical properties of CoCrFeMnNi high entropy alloy with ultrasonic nanocrystal surface modification process

In this study, mechanical properties improvement of equiatomic CoCrFeMnNi treated with an ultrasonic nanocrystal surface modification (UNSM) was studied. The applied UNSM treatment with static loads of 10 N, 20 N, and 60 N provided a severe plastic deformation, which produced a gradient structure. The near-surface area exhibited a high number of dislocation densities and deformation twin interaction, leading to a surface strengthening and hardness improvement of up to 112% than the deformation-free interior region. Increment of dislocation densities and deformation twin formation on the surface also enhanced the yield and ultimate tensile strength of the UNSM-treated specimens. Furthermore, the combination of hard nanocrystallites layer on the surface and ductile coarse grain in the specimen interior as a result of the UNSM treatment successfully maintained the strength–ductility balance of the CoCrFeMnNi.

Dislocation dissociation induces secondary twinning in titanium

The twin–twin interaction phenomenon in Ti is studied by incorporating experimental observation and theoretical analysis. Secondary $$ \{ {10\bar{1}2} \} $$ twins are stimulated in primary $$ \{ {11\bar{2}2} \} $$ and $$ \{ {11\bar{2}4} \} $$ via twinning dislocation dissociation. Primary twin variants are found either share the same $$ \langle {10\bar{1}0} \rangle $$ zone axis or with different zone axes. Schmid law, dislocation theory and crystallographic analysis are used to investigate the formation processes and physical mechanisms of the twin–twin interaction phenomenon. Results show that non-Schmid secondary twins are stimulated under the effect of primary twinning interactions. Besides to secondary twinning dislocations, glissile and sessile dislocations generate as a result of primary dislocation dissociation. Glissile dislocation glide on the easy slip prismatic plane, while sessile dislocation accumulates and leads to the increase of local strain.

Structural characteristics of {10[formula omitted]1} contraction twin-twin interaction in magnesium

Twin interface characteristics play a crucial role in elucidating twin propagation, twin-twin and twin-dislocation interactions, and then affect their mechanical properties. Herein, focusing on magnesium as a model of a hexagonal close-packed structure, we investigate the structural characteristics of \\{101¯1} contraction twin, depending on crystallographic analysis, molecular dynamics simulations and transmission electron microscopy observations. The geometrical features reveal that it is preferential to form acute twin boundaries during the processes of twin-twin interactions. Subsequently, the dynamics simulations results demonstrate that the propagation process of {101¯1} contraction twin is mainly related to the migration of {101¯3} twin boundaries in twin tip, and its thickening process is dominantly associated with the movement of multiple-layered steps. Additionally, two twin-twin interaction modes- tip-twin boundaries crossing transmission and tip-tip collision-have been successfully constructed, dependent on the preferential acute growth mode of contraction twins. Finally, typically structural characteristics on both free-growth of single contraction twin and twin-twin interactions have been confirmed in the ultrahigh pressure pure magnesium by transmission electron microscopy observations. This work clarifies fundamental physics of {101¯1} contraction twins in hexagonal close-packed metals, which can also be applied to other systems to explain twin strengthening mechanisms.

Atomic-level study of twin–twin interactions in hexagonal metals

Abstract

The interaction of deformation twins with long-period stacking ordered precipitates in a magnesium alloy subjected to shock loading

We report atomic-scale observations on the interaction of {101ˉ2} deformation twins with 14H long-period stacking ordered (LPSO) phase in a magnesium alloy. It was found that the interaction strongly depends on the thicknesses of LPSO plates as well as the thickness ratios between LPSO plates and twins. We observed three size-dependent structure responses of LPSO to incoming twins: (1) pure shearing of thin LPSO plates in line with the incursive {101ˉ2} twins; (2) twin-to-dislocation ‘switch’ from the alpha-Mg matrix to LPSO when LPSO/twin thickness ratios are below a critical value of 0.17 ± 0.01; and (3) elastic deformation of LPSO to accommodate the propagation of incoming twin when LPSO/twin thickness ratios are larger than 0.17 ± 0.01. Moreover, the inter-plate spacing of LPSO also influences the propagation modes of twins by controlling nucleation sites of new twins. These size-dependent interactions are accomplished by local structural transition of face-centered cubic units of LPSO during thin plate shearing and formation of gliding dislocations during LPSO deformation and twin blocked. The atomic-scale observations provide fundamental insights into these interaction modes and, hence, the precipitation strengthening mechanisms in Mg alloys under both quasi-static and dynamic loadings.

The adaptive resilience of living cultural heritage in a tourism destination

This article analyzed a living cultural heritage destination’s adaptive resilience from the perspective of social-ecological systems (SES). The aim was to test the SES framework at Hoi An Ancient Town, a cultural World Heritage Site in central Viet Nam by (1) delineating the adaptive renewal cycle in the historical context of destination development; (2) examining community resilience to spatio-cultural changes induced by mass tourism; and (3) identifying characteristics of tourism systems via the control mechanisms of the panarchy’s cross-scale interactions. Findings from Hoi An extend the conventional SES approach by revealing the complex context of social relationships that typify human-related adaptation in cultural living heritage destinations. Contrary to conventional SES theory that depicts cross-scale interactions as one-way mechanisms, we propose a multidimensional model of twin interactions concurrently characterized by contrasting forces of bottom-up “revolt” and top-down “remember” functions. Findings from historical, contemporary and systematic dimensions shed light on incorporating Indigenous knowledge and practices into heritage conservation as a form of community resilience. Our analysis also extends the continuity notion of a living heritage site in developing countries, applying an SES framework to complex political, social, cultural and economic concerns in order to contextualize tourism development in Hoi An.

Effect of twin boundary spacing on the deformation behaviour of Au nanowire

The deformation behaviour of Au twinned nanowire is investigated by molecular dynamic simulation. It is found that the relationship of yield strength with twin boundary spacing (TBS) can be divided into three ranges. The deformation mechanism of Au twinned nanowire is revealed according to the dislocation–twin interactions. For those with large and medium softening TBS ranges, some Shockley partial dislocations and stair-rod dislocations are formed, and a small step is left on the TBs during the dislocation–twin interactions. But the amount of dislocations in the nanowire with medium TBS is remarkably larger than that with large TBS, and more different {111} slip planes are activated. For that with small strengthening TBS range, lots of Shockley partial dislocations are formed, and they form highly-localized shear zone at the middle of nanowire. TBs undergo a destruction and following recovery process during the dislocation–twin interactions, and the TBS is enlarged during this process.