Twin Structure Research Articles

Nucleation centers for martensite with habitus {110} in the shape memory alloys

The dynamic theory of martensitic transformations (MT) considers the formation of habit planes of martensite crystals as a consequence of the propagation of a controlling wave process (CWP). The general ideology makes it possible, by comparing the observed habits with calculations of the elastic fields of defects (as a rule, dislocations), to identify nucleation centers. In a number of cases (In-Tl alloys, Ni50Mn50 alloys, Heusler alloys …) under MT in the shape memory alloys, {110} habits are observed (in the basis of the initial cubic phase), which often have a fine twin structure with twin boundaries of the same type. This highly symmetric structure is described by the CWP containing longitudinal waves (both relatively long-wavelength ℓ and short-wavelength s) propagating along the 4-order symmetry axes. In this paper, it is shown that such habits are associated with rectilinear segments of dislocation loops with directions Λ along <001> and Burgers vectors along <010> (or <110>) orthogonal to Λ, both for sliding and for prismatic loops. The tetragonality, the relative volume change during the MT, and the dependence of the start temperature M s on changes in the concentration of alloy components are also briefly discussed.

Analysis of grain size and five-fold twins during rapid solidification processes inTi3Al alloy.

The wide application of titanium aluminum (Ti–Al) intermetallic compounds for aerospace and automotive fields has accelerated the research and development of Ti3Al alloy. In this study, simulation is adopted to investigate the crystallization behavior during rapid solidification of Ti3Al alloys using molecular dynamics at different cooling rates of 1010 K s−1, 1011 K s−1, 1012 K s−1, and 1013 K s−1. The evolution of microstructures is characterized by taking advantage of the average potential energy, the pair distribution function and visualization. The results show that the system has formed a microstructural configuration with the face-centered cubic structure as the main structure and the hexagonal close-packed structure as the supplement. An increase in the cooling rate will reduce the grain size of the alloy, which in turn will increase the number of grains. At the cooling rate at which the alloy can crystallize, the system forms five-fold twin structures. Meanwhile, we obtain a deeper insight into the properties of five-fold twins in terms of atoms on different sites, and establish a standard model of the same specification for comparison to get the commonality and differences of the five-fold twins between the standard and the solidified. In addition, the evolution of dislocation densities and distribution of dislocation lines in the system under different conditions are analyzed. This study further explores crystallization behavior on the atomic scale and it is hoped that this research will contribute to expanding the understanding of Ti3Al alloy during the growth process.

The mechanism of plasticity and phase transition in iron single crystals under cylindrically divergent shock loading

Cylindrically divergent shock loading significantly influences the plasticity and phase transition of iron. In this study, the mechanisms of plasticity and α→ε phase transition are investigated using large-scale nonequilibrium molecular dynamics simulation. We find that iron undergoes a local bcc–hcp–bcc–hcp (bcc: body-centered cubic; hcp: hexagonal close-packed) phase transition under cylindrically divergent shock loading with cylinder axis lying in [001] and [110] directions. A bcc lattice reorientation driven by resolved shear stress occurs during the hcp–bcc reverse transition and results in bcc twins, which transform into hcp twin structures with an unexpected c-axis, as compared with planar shock. Moreover, we analyze the coupling behavior between plasticity and phase transition and find that collective movement and rearrangement of atoms induced by plastic slip on the shuffle plane play a key role in the activation of phase transition, which significantly differs from that of planar shock.

On the inhomogeneous deformation behavior of magnesium alloy beam subjected to bending

Magnesium (Mg) alloys have attracted worldwide attention as potential lightweight structural materials. However, it is still a big challenge to manufacture or process Mg alloys that have good formability and endure high strength. This mainly stems from the lack of understanding the anisotropic mechanical behavior of Mg alloys subjected to inhomogeneous deformation which exists inevitably in various material processing routes. In this respect, the current work seeks to explore and understand the bending behavior of Mg alloy. Mechanical response and microstructure development were experimentally characterized by performing four-point bending tests, with the use of the in-situ digital-image-correlation (DIC) and ex-situ electro backscattered diffraction (EBSD) measurements. Meanwhile, a crystal plasticity-based approach was proposed and used to illustrate the characteristic deformation behavior under four-point bending. The inhomogeneous and anisotropic nature of the mechanical response of Mg alloys under bending is successfully captured by the proposed approach in terms of the moment-curvature relation, the deformed cross-sectional shape of the beam, the developed textures at different regions of the beam, the spatial distribution of the stress and strain components, and the twin volume fraction. The insight of the slip/twinning mechanisms underlying the bending behavior of Mg alloy beam offers a novel way for designing/tuning gradient twinning structures that might lead to the optimized properties of Mg alloys.

Enhancement of phonon skew scattering in epitaxial Pt/Co/Pt trilayers by crystal engineering

Three types of (111)-oriented Pt/Co/Pt trilayers with single-crystalline structures on MgO substrates were fabricated to investigate the mechanisms of the anomalous Hall effect. By introducing 2-monolayer (ML) Cr insertion between a MgO (001) substrate and a Pt underlayer in Pt/Co/Pt epitaxial structures, the Hall resistivity is significantly enhanced compared with that of single-crystalline Pt/Co/Pt deposited on a MgO (111) surface. Furthermore, the detailed crystalline structures were characterized by in situ reflection high-energy electron diffraction, low-energy electron microscopy, and low-energy electron diffraction. It suggests that a twinning structure of the 7-ML ferromagnetic Co layer, which is composed of two twinned traces differing by 90\ifmmode^\circ\else\textdegree\fi{}, can be achieved by crystal engineering with Cr insertion. By fitting with proper scaling of anomalous Hall effect, the dominant contribution to the Hall resistivity can be confirmed as skew scattering, and the remarkable enhancement of ${\ensuremath{\rho}}_{xy}$ is attributed to the high phonon skew scattering parameter originating from the specific twinning structure.

Microbiota composition is moderately associated with greenspace composition in a UK cohort of twins

Exposure to natural environments, known as greenspace, appears to positively influence health, yet the mechanisms are unclear. Given that gut microbiota are associated with inflammatory disorders more prevalent in urban areas and individuals with lower greenspace exposure, microbiota may act as a mediator between greenspace and health. Using 2443 participants of the TwinsUK cohort, microbiota differences were compared in relation to rural/urban living and with quantiles of area-level greenspace at three different neighbourhood distances: 800 m, 3000 m and 5000 m. Using microbiota data captured from faecal samples using 16S rRNA marker gene sequencing, small compositional differences in association with 3000 m greenspace (p = 0.003) in models adjusted for confounders of microbiota variance (sequencing depth, antibiotics use, body mass index, frailty, age, diet, region and socioeconomic variables) were observed. Differences in abundances of genus were observed for all measures of greenspace in adjusted models; a key pathogenic genus was increased in abundance in association with urbanicity (Escherichia/Shigella, logFC = 0.73742, padj <0.001). Further, utilising the twin structure, within-pair differences in microbiota composition were compared and associations with 800 m greenspace observed (factor level significance in association with greatest difference, β = 0.08, p = 0.0162) as were differences in Escherichia/Shigella. The microbiota signature of those with a greater exposure to greenspace, but not necessarily explicitly rural individuals, was distinct from other individuals, suggesting microbiota as a potential mediator for greenspace and health.

Digital Twins for Wind Energy Conversion Systems: A Literature Review of Potential Modelling Techniques Focused on Model Fidelity and Computational Load

The Industry 4.0 concept of a Digital Twin will bring many advantages for wind energy conversion systems, e.g., in condition monitoring, predictive maintenance and the optimisation of control or design parameters. A virtual replica is at the heart of a digital twin. To construct a virtual replica, appropriate modelling techniques must be selected for the turbine components. These models must be chosen with the intended use case of the digital twin in mind, finding a proper balance between the model fidelity and computational load. This review article presents an overview of the recent literature on modelling techniques for turbine aerodynamics, structure and drivetrain mechanics, the permanent magnet synchronous generator, the power electronic converter and the pitch and yaw systems. For each component, a balanced overview is given of models with varying model fidelity and computational load, ranging from simplified lumped parameter models to advanced numerical Finite Element Method (FEM)-based models. The results of the literature review are presented graphically to aid the reader in the model selection process. Based on this review, a high-level structure of a digital twin is proposed together with a virtual replica with a minimum computational load. The concept of a multi-level hierarchical virtual replica is presented.

Feature-based modeling for industrial processes in the context of digital twins: A case study of HVOF process

Industrial process modeling is currently undergoing a fundamental transformation, leading towards interconnected close-loop twins of models, i.e., the parametrically-controlled real-world physics model, and its corresponding digitalized virtual system model. Between these models, a highly time-sensitive mutual validation mechanism and a coherent and consistent control strategy are applied, which demand complex virtual-and-real world model-based information mapping and synchronization. Thus, this research proposes a semantic conceptual framework for industrial process modeling in the context of digital twins. Based on a hierarchical structure of digital twins, this framework modularizes the modeling process in terms of the semantic information modules of physics in the real-world phenomena, and clarifies inter-module associations and near-real-time data transmission coupled with virtual analysis in CAE environment so that the time-sensitive phenomenon information objects distributed on virtually-separated sub-level physics models can be supported for representing the real-world process comprehensively. Advanced feature concept is adopted to construct the digital models as the basic compositions of any virtual industrial process. The related feature definitions are extended in this work so that the common characteristics in the concept of digital twins could be generically and concisely represented. To validate the modeling method, the digital model of a prototyped High-velocity Oxygen-fuel (HVOF) coating process system was constructed as the case study. The data from the nozzle trajectory, the flame, and the in-flight particle behavior, and the transient thermal performance of the coating layer and substrate were synchronously incorporated for simulating the transient phenomena of the substrate component temperature and coating thickness distribution on the substrate surface. The final simulation result validates that the feature-based digital model is able to comprehensively reflect the real-world scenario on the virtual side. To illustrate how the developed model provides meaningful feedback to the real-world control, a general digital twin setup of the model is given at the end of the case study.

Shop Floor Digital Twin in Smart Manufacturing: A Systematic Literature Review

The digital twin is currently recognized as a key technology allowing the digital representation of a real-world system. In smart manufacturing, the digital twin enables the management and analysis of physical and digital processes, products, and people in order to foster the sustainability of their lifecycles. Although past research addressed this topic, fragmented studies, a lack of a holistic view, and a lack of in-depth knowledge about digital twin concepts and structures are still evident in the domain of the shop floor digital twin. Manufacturing companies need an integrated reference framework that fits the main components of both physical and digital space. On the basis of a systematic literature review, this research aims to investigate the characteristics of the digital twin for shop floor purposes in the context of smart manufacturing. The “hexadimensional shop floor digital twin” (HexaSFDT) is proposed as a comprehensive framework that integrates all the main components and describes their relationships. In this way, manufacturing organizations can rely on an inclusive framework for supporting their journey in understanding the shop floor digital twin from a methodological and technological viewpoint. Furthermore, the research strengthens the reference literature by collecting and integrating relevant contributions in a unique framework.

Interface structure of (130) twin in the U-14.0 at.% Nb alloy: an experimental and theoretical study

In this work, we report an experimental and theoretical study of the (130) twin system in the U-14.0 at.% Nb alloy using aberration-corrected TEM in combination with first-principles calculations. We clearly give the atomic structure of (130) twin and its twin boundary energy for the first time. We evidence that the widely used (130) twin system in pseudo-orthorhombic system is in fact the (101) twin system in the monoclinic crystal system. Through first-principles calculations, we also find that the local atomic structure of Nb significantly affects the twin boundary energy due to the depleted charge zone at Nb atom and charge-rich zone around Nb atom. These results may help us better understand the deformation mechanism in low-symmetry U metal and U-Nb alloys.

Effects of SiC on the microstructures and mechanical properties of B4C–SiC–rGO composites prepared using spark plasma sintering

In this study, B4C–SiC–rGO composites with different SiC contents were prepared by spark plasma sintering at 1800 °C for 5 min under a uniaxial pressure of 50 MPa. The effects of SiC on the microstructures and mechanical properties of the B4C–SiC–rGO composites were investigated. The optimal values for flexural strength (545.25 ± 23 MPa) and fracture toughness (5.72 ± 0.13 MPa·m1/2) were obtained simultaneously when 15 wt.% SiC was added to 5 wt.%–GO reinforced B4C composites (BS15G5). It was found that SiC and rGO inhibited the grain growth of B4C and improved the mechanical properties of the B4C–SiC–rGO composites. The clear and narrow grain boundaries of rGO–B4C and rGO–SiC, as well as the semi-coherent B4C–SiC interface, indicated strong interface compatibility. The twin structures of SiC and B4C observed in the composites improved their fracture toughness. Crack deflection and crack bridging caused by the SiC grains as well as rGO bridging and rGO pull-out were observed on the crack propagation path.

Effect of extrusion plus rolling on damping capacity and mechanical properties of Mg–Y–Er–Zn-Zr alloy

Many common strengthening means are not favorable for damping capacity of alloys. While twin and long-period stacking ordered phase (LPSO) in magnesium alloys are beneficial to improve both damping and mechanical properties. To obtain a kind of Mg alloy with both high mechanical properties and damping capacity, it is proposed to introduce twin and LPSO structure into Mg–4Y–2Er–2Zn-0.6Zr (wt.%) alloy through extrusion and rolling. The influence of LPSO structure and twin on the mechanical properties and damping capacity was studied. The results show that, under the combined actions of extrusion and rolling, the twin form in both the matrix and LPSO phase, which is beneficial to synergistically enhance the damping and mechanical properties of the alloy.

Simulation study on the diversity and characteristics of twin structures in GaN

Gallium nitride (GaN) is a promising material for high-frequency and high-power electronics owing to its high thermal stability, wide bandgap, and high breakdown voltage. Monocrystalline GaN films are usually produced by metal organic chemical vapor phase deposition using Si, SiC, or Al 2 O 3 as the substrate. However, the difference in lattice constants and thermal expansion coefficients causes many defects in GaN epilayers . In particular, the formation of twins will strongly influence the electronic properties of GaN-based devices. In this study, the solidification process of GaN was simulated by molecular dynamics at a cooling rate of 10 12 K/s, and the twin structures in GaN were discussed. The results of this simulation showed two types of twins, including coherent twin and rotating twin, which were analyzed by visualization technology. The formation of twins was related to the coexistence of zinc blende and wurtzite phases. Furthermore, the types of twins were closely associated to the stacking ways of zinc blende and wurtzite structures. In general, it is essential to study the microstructure and the structural evolution of twin GaN, in order to give references to experiments about the growth and characteristics of twins. • Zinc blende and wurtzite nucleated randomly and formed lots of complex structures at the beginning of crystallization. • Coherent and rotating twins were formed according to different stacking methods of zinc blende and wurtzite structures. • The rules for the combination of twin structures in GaN crystals have been summarized and it can be generalized. • An error in the stacking sequence can cause the metastable phase c-GaN to start seeding the h-GaN phase.

Digital twin of the management process of field service teams of an electric grid company

Modern electric grid companies are focused on minimum economically feasible costs and are aimed at improving the efficiency of financial and economic activities through the rational use of resources. The digital twin structure is proposed for the management of field service teams in the event of accidents and technological failures in an electric grid company. The digital twin includes an agent model, a system dynamics model, a geographic information system component, and modules with experiments. The description of the simulation model of management of field service teams in the event of accidents and technological failures is formalized, the input and output information on the model components is highlighted, the information is structured, and the scheme of the system dynamics model is created. Experiment designs for the digital twin of the management of field service teams in the event of accidents and technological failures in order to determine the best reliability and cost indicators are developed. The developed approach can be used to create digital twins of the management process of field service teams in the event of accidents and technological failures for various electric grid companies by selecting the parameters of simulation models according to the statistical reports by electric grid companies and connecting the appropriate GIS modules.

Microstructure and tribological behaviors of diffusion bonded powder sintered Cu–Sn based alloys

Owing to good self-lubricating performance, tin bronze is widely used in industrial fields. As tin bronze parts manufactured by powder metallurgy, their tribological performances are influenced by raw powder. In this work, four types of self-lubricating copper alloy composites (CuSn10 (D), CuSn10, CuSn10Pb10 (D) and CuSn10Pb10) were prepared by sintering completely alloyed powder and diffusion alloyed copper tin powder. The morphology, element distribution and microstructure of raw powder and their sintered Cu alloy composites were observed. The tribological properties of Cu alloys were investigated by block-ring friction test under different working conditions and their worn surface and wear debris were analyzed. The results show that the diffusion alloyed powder has an irregular dendritic morphology and its sintered Cu alloy is more likely to produce twin structure which enhances the hardness and the bearing capacity of the material. Compared with completely alloyed powder sintered CuSn10 sample, the wear rate of CuSn10 (D) sintered from diffusion alloyed powder was reduced by 83.96%, 74.39%, and 67.63% under three typical working conditions. Under dry friction conditions, the wear rate of CuSn10 (D) is reduced by 63.64% than CuSn10, and CuSn10Pb10 (D) is 25% lower than CuSn10Pb10. The investigation on the wear tracks and wear debris of Cu alloy composites showed that the diffusion alloyed powder sintered samples are inclined to form a more consecutive and integral third-body layer on wear tracks and which contributes to the better wear resistance.

Seismic Analysis of Twin Tower Structures

Abstract: In today's world, new concepts for skyscraper construction are required to mitigate the negative effects of seismic and wind forces. Since the world's most populous cities are experiencing land shortage, in this area tall buildings act as very important roles in modern cities. Due to the speedy increase in population and reduction in accessibility of land, vertical accommodation is obtaining a lot of preference which is resulting in vertical town development. Nowadays tall buildings rise higher and higher, with more and more complex and individual plan and elevation, such as multi-tower buildings. The multi-tower buildings refer to two or more towers connected with one large podium or conjunction parts at different levels. It is well known that the podium and conjunction parts shall be designed very carefully to meet the internal force and thedeformation between towers. Nowadays, when building multistory building, height is not the only pursuit. More unique forms are in trend to show the rich connotation and vitality of buildings. Connected twin tower structures conform to these requirements, and many connected structures in different forms have been or are being built in recent years. In present research work considering effects of influencing parameters like the height of the tower, connection with podium and depth of podium with two parallel towers (Twin-Tower). The main objective of this study is to analyze twin tower structure G+4 podium+25 floor building using linear dynamic earthquake analysis. We have considered four models with different combinations of twin tower with podium to achieve desirable results in terms of story drift, displacement and base shear under seismic forces for seismic zone IV and medium type of soil using Response Spectrum Analysis with the help of ETABS v19 software. Keyword: Twin Tower Structure, Podium, Etabs Software Packages.

Characterization of primary, secondary and tertiary {20[formula omitted]1} successive internal twins in the D019 ordered hexagonal α2-Ti3Al phase

Due to the lack of independent slip systems and the difficulty in mechanical twinning, D019 ordered α2-Ti3Al phase is known to be of substantial mechanical anisotropy, which partly accounts for the low ductility of two-phase (α2+γ) TiAl alloys. However, recent studies have shown that in Al-rich α2 phase compression deformation twins can be activated, which could be beneficial for the ductility of the alloys. In the present study, for the first time, we have revealed a novel internal twinning mechanism of α2 phase in a TiAl alloy deformed at high temperature. Three twin generations of a common type {202¯1}<1¯014> were revealed: Secondary twins formed within the primary twin, and tertiary twins formed in the secondary twin. It is important to note that this internal twin structure can only be observed in the <21¯1¯6> direction but not the commonly used <112¯0> direction. The shear plane P of all twin variants is of type {12¯10}. Due to the variation of the twinning elements between the twin variants, the twinning shear is blunted. The interfaces between the twin variants are characterized by high-resolution electron microscopy. Special attention was paid to the structure of the coherent and incoherent twin boundaries. The effect of chemical ordering is discussed. Our results also shed light on the complex twinning mechanisms in hexagonal structures.

Hierarchical twinning and light impurity doping enable high-performance GeTe thermoelectrics

Microstructure engineering fulfilled by phase transformation elicits the reduced thermal conductivity κ in thermoelectric materials. We demonstrate that the multiscale hierarchical twinning structure could exist in the GeTe alloys as the phase transformation from cubic β-GeTe to rhombohedral α-GeTe is manipulated by two-step cooling. The coexistence of nanoscale and microscale herringbone structures yields the low-lying κ, attributing to the reorientation of martensitic variants and pile-up of martensitic twinning. Dilute dopants of Cu and Bi/Sb further suppresses hole carrier concentration nH to the order of 1020 cm−3, leading to the enhanced power factor PF = S2ρ−1 of α-GeTe. Meanwhile, the phase diagram engineering probes the solubility limit of Cu in the single-phase GeTe, diminishing the formation of undesired impurity phases. These strategies boost the peak zT value to 1.5 at 698 K in the light-doped Bi0.01Cu0.01Ge0.98Te alloy. The multiscale twin hierarchy and carrier optimization synergistically enhance the thermoelectric performance of GeTe-based alloys that provide a new chapter in search of green energy resources out from phase change materials.

Experimental studies and DFT calculations to predict atomic arrangements at twin boundaries and distribution behaviors of different solutes in complex intermetallics

HAADF-STEM observations illustrate that the probabilities of appearance of (111) microtwins with different twinning structures in μ phase were different. Based on this, 8 possible (111) twinning models with different twin boundary structures are established and discussed via DFT. Experimental characterization and DFT calculations reveal a close relation between the probabilities of appearance of these (111) microtwins and the interface energy at the twin boundaries: the smaller the energy is, the easier the twinning structure is to form and exist stably. TB5, with the smallest interface energy, is exactly the abundantly-existing twinning structure observed in HAADF. Moreover, via DFT simulation, distribution behaviors of the solute elements Cr, Mo, Re, Ni at the twin boundary of TB3 and the atomic arrangement at (111) twin boundary of C15–Cr2Nb crystal have been predicted and analyzed. The methods of DFT simulation and analysis on the twin boundaries provide a new strategy to study the twinning structures of complex-structured crystals and preferred distribution of different solutes at the twin boundary, etc.

Molecular engineering by σ-linkers enables delayed fluorescence emitters for high-efficiency sky-blue solution-processed OLEDs

Two novel thermally activated delayed fluorescence (TADF) emitters, namely Me2AcBO and F2AcBO, based on the 9,9-dimethrylacridine donor and a rigid oxygen-bridged cyclized boron acceptor, were designed and synthesized for highly efficient blue solution-processed organic light-emitting diodes (OLEDs). Me2AcBO and F2AcBO feature a twin structure derived by coupling two individual TADF monomers through non-conjugated linkers. The two new emitters exhibit 3D molecular structures, excellent thermal/morphological properties, high photoluminescence quantum yields over 97%, and high reverse intersystem crossing rates on the order of 106 s−1, which greatly benefit the high device efficiency. Solution-processed sky-blue TADF OLEDs based on Me2AcBO and F2AcBO achieved the maximum external quantum efficiency of 11.0% and 10.9%, respectively, with Commission Internationale de L’Eclairage (CIE) coordinates of (0.14, 0.25). Interestingly, relatively low efficiency roll-offs of 33% and 34% at the luminance of 1000 cd/m2 were demonstrated for Me2AcBO and F2AcBO based devices, respectively. This study presents a novel strategy to realize highly efficient sky-blue TADF emitters for solution-processed OLEDs.