Twin Structure Research Articles

Phase constitution and texture distribution in the vortex zone of Co/Cu explosive welded plates

Cobalt has a reputation for its excellent electrical and magnetic properties, and exceptional wear and corrosion resistance, which has many applications in the batteries, electronic industry and semiconductor industry. In this work, the explosive welding technique was successfully performed to join Co/Cu dissimilar metals. To reveal the phase constitution and texture distribution of the vortex zone at Co/Cu joining interface, the electron backscatter diffraction (EBSD) test was carried out. It was concluded that the typical vortex structure composed of fine crystal band, sub-grains and twin structures was formed at the Co/Cu joining interface. In addition, the dynamic recrystallized structure and local internal stress at the vortex was attributed to severe plastic deformation and rapid solidification of liquid metals resulted from high strain state collision. Furthermore, the S, copper, brass and fiber deformation textures and the cube and gross recrystallization textures were confirmed at the vortex zone due to plastic deformation and dynamic recrystallization.

Deformation mechanisms of a novel multiphase Zr–30Ti–7Nb–4Sn alloy consisting of β, α′ and α″ phases

A novel multiphase Zr–30Ti–7Nb–4Sn alloy consisting of β, α′ and α″ phases was designed and fabricated, with an aim to elucidate the mechanical mechanisms responsible for the deformation behavior in the multiphase Zr-based alloys involving two different martensites. Based on the synchrotron X-ray diffraction (SXRD) and electron backscatter diffraction (EBSD) analyses, these two different martensites can be unambiguously discriminated: one type is hexagonal closed-packed (hcp) α′ martensite exhibiting an orthorhombicity value of 1.00 and a typical acicular morphology, the other is orthorhombic α″ martensite possessing an orthorhombicity value of 0.97 and a lath-like morphology with (110)α″-type internal twinning structures. In situ SXRD reveals that during loading, no stress-induced martensitic (SIM) transformation occurs between β phase and α′ martensite, and the notable “stress-plateau” is attributable to the extensive β→α″ SIM transformation and the reorientation of pre-existing α″ martensitic variants. During unloading, the reverse α″→β SIM transformation occurs in an incomplete manner, eventually leading to the residual macroscopic strain (∼4.3%) that persists in the Zr–30Ti–7Nb–4Sn specimen after unloading.

Understanding the Role of Copper Vacancies in Photoelectrochemical CO2 Reduction on Cuprous Oxide.

Controlling the electronic and photoexcited properties of cuprous oxide (Cu2O) through slight modifications of the synthesis method can impact a wide range of emerging technologies. Herein, we consider copper vacancies in Cu2O as a prototype of a p-type oxide semiconductor for studying the impact of crystal and electronic structure on carbon dioxide photoreduction. Oriented films of copper vacancy modulated Cu2O consisting of nano twin structures are electrodeposited by changing the potential in an aqueous alkaline copper(II)-lactate solution. The copper vacancies introduce tail states inside the band gap, improving the hole concentration and facilitating the charge separation and transfer in the Cu2O photocathode. This study gives an in-depth view of how a cation-deficient structure regulates and promotes photoelectrochemical activity toward CO2 reduction.

Unravelling the nucleation and growth of [formula omitted] twins

A recently proposed mechanism of {112¯2} twin nucleation in Ti by reverse phase transformation is analysed. It is demonstrated that, not only nucleation, but also growth mechanism of an already formed twin is connected to the possibility of the phase transformation in the system, which leads to the existence of several competing structures of twin boundary. The twin growth is mediated by subsequent glide of step-like defects (disconnections) along the {112¯2} boundary. The twin shear is completed by gliding of pair of disconnections, which also converts twin boundary structure between two alternative variants.

Grain refinement leading to the ultra-high coercivity in L1-Mn1.33Ga bulk magnet via hot deformation

We achieved ultra-high coercivity of 5.65 kOe in L10-Mn1.33Ga alloy via the hot deformation (HD) method and revealed the hardening mechanism. Hot deformation led to recrystallization and grain refinement, where the average grain size was reduced to about 1.5 μm for HD-88% magnet. The coercivity mechanism indicated a weak pinning model by magnetic mini-loop analysis. It was found that small grains were formed, accompanied by a certain number of {111} ⟨11-2⟩ twins for HD magnets. The magnetic domain observation showed that both the sub-micro grain boundary and the twin boundary were acted as the pinning center of the domain wall, but the latter had weaker pinning effect. The ultra-high coercivity of the HD-88% Mn1.33Ga magnet originated mainly from the pinning of the grain boundary enhanced by grain refinement. Further grain refinement and twin structure inhibition will be promising approaches in order to obtain higher magnetic properties for L10-MnxGa bulk magnets.

Общий подход к созданию цифровых двойников мобильных канатных дорог на основе мобильных транспортно-перегрузочных канатных комплексов

The article considers the conceptual approach and practical aspects of creating digital twins of mobile ropeways formed by two end mobile transport and reloading rope units based on self-propelled multi-axle wheeled chassis of high load capacity and cross-country ability. The approach is based on a systematic representation and analysis of the design and operating modes of a mobile ropeway. As a consequence, the digital twin is formed as a multilevel hierarchical structure. It combines information mathematical models of various functional purposes and varying degrees of mutual connectivity, which are distributed by levels depending on the degree of complexity and the possibility of their further aggregation into information mathematical models of a higher level. In relation to a typical mobile ropeway, a structural and functional analysis was carried out, on the basis of which its basic components were established, and calculated structural elements (technical devices and systems) were determined, requiring the development of the necessary individual information mathematical models. Approaches to aggregation of several individual models of computational elements connected by common characteristic quantitative parameters of modeling into group information mathematical models, and then into mode and complete information mathematical models of structural and functional components of a mobile ropeway are considered. The system approach considered in the article and the multilevel hierarchical structure of the digital twin developed on its basis are useful and effective from the point of view of ensuring the modularity of creating a digital twin, its modification for mobile ropeways of a different design, the possibility of using previously developed information mathematical models for similar computational structural elements.

Type III and IV deformation twins in minerals and metals

SignificanceHistorically, two types of twins (I and II) have been categorized for twinning in minerals and metals. When analyzed by the topological model, a crystallographic construction used to define the defect structure of interfaces, triclinic and some other low-symmetry crystals do not fall into either category and instead form two new twinning types, namely, III and IV. Aside from accurately describing twin structures, these concepts are important for understanding the deformation of minerals such as plagioclase and for deriving constitutive models for the deformation.

Microstructure and mechanical properties of twinning induced plasticity steel prepared by optical floating zone method

The three twinning induced plasticity (TWIP) steels were directionally solidified (DS) using the optical floating zone (OFZ) method at the withdrawal rates of 7 (DS7), 15 (DS15), and 30 μm s-1 (DS30) for the first time. The results showed that the relatively low withdrawal rate of 7 μm s-1 was unfavorable to the growth of DS, and the hybrid morphology was observed, which included equiaxed grains, columnar grains, amorphous coarse grains, and a few stray grains. With the increase of withdrawal rate, the volume fraction of columnar grain and dendrite grain increases, and the spacing decreased correspondingly, increasing microhardness and tensile strength. The samples exhibited outstanding plasticity, especially the DS15 had the highest elongation of 96%. This is attributed to the strong TWIP effect with a higher work hardening rate and the strongest ability of uniform plastic deformation at medium to large strains. Compared with the other two samples, the twin structure formed in the DS15 is more homogeneous and prevalent. The interaction between high-density dislocations and increased grain boundaries from the refined columnar grains and dendrites coupled with activated deformation twins, which contributes to the highest work hardening rate in the whole plastic deformation process of DS30.

Structure of digital metrological twins as software for uncertainty estimation

Abstract. Ongoing digitalization in metrology and the ever-growing complexity of measurement systems have increased the effort required to create complex software for uncertainty estimation. To address this issue, a general structure for uncertainty estimation software will be presented in this work. The structure was derived from the Virtual Coordinate Measuring Machine (VCMM), which is a well-established tool for uncertainty estimation in the field of coordinate metrology. To make it easy to apply the software structure to specific projects, a supporting software library was created. The library is written in a portable and extensible way using the C++ programming language. The software structure and library proposed can be used in different domains of metrology. The library provides all the components necessary for uncertainty estimation (i.e., random number generators and GUM S1-compliant routines). Only the project-specific parts of the software must be developed by potential users. To verify the usability of the software structure and the library, a Virtual Planck-Balance, which is the digital metrological twin of a Kibble balance, is currently being developed.

Synergetic deformation mechanism in hierarchical twinned high-entropy alloys

The mechanical properties of crystalline materials can be efficiently optimized using a hierarchical twinned structure. Conventional deformation mechanisms for coherent Σ3 boundaries generally involve three basic models: cross-slip, partial dislocation step, and full dislocation step. In this study, we report a novel deformation mechanism that allows the co-existence of twin-separation, phase transformations, grain rotation, and cracking, around a triple junction of twin boundaries in a hierarchical twinned high-entropy alloy. The deformation mechanisms in the reference high-entropy alloy (Fe-30Mn-10Co-10Cr at.%) were investigated using LAADF-STEM. The triple junction of the hierarchical twinned structure gradually deformed during in-situ strain and showed mechanisms significantly different from that observed in the purely twinned structures. These new mechanisms are referred to as “novel synergetic deformation mechanisms of hierarchical twin boundaries”. Understanding the fundamental mechanisms of the hierarchical twin boundaries under deformation could assist the design of strong and ductile bulk materials with hierarchical twinned structure.

К вопросу о структуре цифровых двойников опасных производственных объектов

The structure of the digital twin of a hazardous production facility is considered, the construction of which is based on the concept approved by the Coordinating Committee for Integrated Automation of Production and Technological Processes, Metrological Support and Communications of PJSC Gazprom. Overview is given concerning the innovative developments in the field of fire and industrial safety reflecting the process of digital transformation of safety technologies. Among them: remote monitoring systems at hazardous production facilities designed to carry out permanent state supervision; robotic complexes for fire extinguishing; software systems for scenario modeling of accidents, fires and evacuation of people, risk assessment, calculation of parameters of the affecting factors; virtual training complexes for interactive training of the personnel; digital twins of oil fields, gas turbines, nuclear power plants. Based on the reviewed scientific papers and federal legislation in the field of industrial safety, the concept of a digital twin of a hazardous production facility is formulated, and the principal structure of its technical equipment is considered. The function of each element of the digital twin structure of a hazardous production facility is established. Typical tasks solved by means of digital twins of hazardous production facilities and the effects of their implementation are identified. SWOT-analysis was conducted related to the advantages, disadvantages, opportunities, and negative factors in the digital transformation of hazardous production facilities. The image of future industrial systems with the use of digital twins in the field of industrial safety was formed.

Thin films of the alpha-quartz Si_xGe_{1-x}O_2 solid solution

SiO_2 with the alpha-quartz structure is one of the most popular piezoelectrics. It is widely used in crystal oscillators, bulk acoustic wave (BAW) devices, surface acoustic wave (SAW) devices, and so on. GeO_2 can also be crystallized into the alpha-quartz structure and it has better piezoelectric properties, with higher piezoelectric coefficient and electromechanical coupling coefficients, than SiO_2. Experiments on bulk crystals and theoretical studies have shown that these properties can be tuned by varying the Si/Ge ratio in the Si_xGe_{1-x}O_2 solid solution. However, to the best of our knowledge, thin films of Si_xGe_{1-x}O_2 quartz have never been reported. Here we present the successful crystallization of Si_xGe_{1-x}O_2 thin films in the alpha-quartz phase on quartz substrates (SiO_2) with x up to 0.75. Generally, the films grow semi-epitaxially, with the same orientation as the substrates. Interestingly, the Si_{0.75}Ge_{0.25}O_2 composition grows fully strained by the quartz substrates and this leads to the formation of circular quartz domains with an ordered Dauphiné twin structure. These studies represent a first step towards the optimization of piezoelectric quartz thin films for high frequency (> 5 GHz) applications.

An in-situ TEM characterization of electron beam induced dislocation motion in a single-crystalline gold thin film

Dislocation motions driven by electron-beam illumination were in-situ observed in a single-crystalline gold thin-foil specimen, under a medium-voltage transmission electron microscope operated at 200 kV. The dislocation motion characteristics were in-situ observed under the bright-field and weak-beam dark-field conditions. The structures formed through the dislocation motion were also characterized using bright−/dark-field imaging and high-resolution techniques. Two types of dislocation motions are concluded, where one type of motion left no apparent traces, and the other type left a clear trace of passage. The dislocation motions have jerky behaviors, and the motions are accelerated when the beam intensity is increased. The immobile trace structures left by the dislocation motions are identified to be twin structures oriented along the 〈111〉 crystal directions. The dislocation motion mechanism is discussed and the motion might be caused by the electron beam heating effect or the electron beam induced phonon effects. The dislocation disassociation, planar defect formation in the Au crystal, and the beam heating impacts are also discussed.

Surface modification and twinning behavior in gradient graphene-based TiC/Ti6Al4V composite

Gradient materials have significant potential to break strong plastic tradeoffs. Graphene with a strong affinity for titanium alloys has an influential application value for material modification. In this study, microstructure evolution and deformation behavior of graphene-based TiC/Ti6Al4V composites processed by friction stir processing (FSP) have been investigated. Electron backscattered diffraction (EBSD) reveals uniform microstructure in the stir zone (SZ). Transmission electron microscopy (TEM) observations reveal distinct microstructures at different depths from the processed surface. The SZ includes nano/micro grains and TiC nanoplates. Twin structure exists in both α matrix and TiC. Stress-induced martensitic transformation is suppressed. As depth increases, TiC gradually disappears and the FSP-induced texture {-2116} < 2–1–11 > becomes slightly stronger. Moreover, there exists special crystallographic orientation relation: (111)TiC//(0001)Ti. In the base metal (BM), larger grains are observed, and dislocation structure becomes the dominant defect feature. Nanoindentation results show that hardness decreases first and then increases from the processed surface to the bulk metal. The distribution of hardness is the result of combined action of strengthening effect of TiC twins and deformation adaptation effect of α twins.

Glassy or Amorphous? A Demonstration Using G-Phase Copper Containing a Fivefold Twinning Structure.

The G-phase, a new metastable phase with its potential energy sitting right in the middle of the glass and crystal, was recently discovered in some simulations when the molten metallic liquid was quenched down to room temperature. In comparison with ordinary glass, the G-phase has a more ordered short-range structure but a similarly disordered long-range structure. The question is whether the G-phase can be termed a new type of glass. In this work, G-phase Cu is made in a molecular dynamics simulation using rapid quenching or isothermal annealing. Weak oscillations are found in the long-range atomic structure. The pseudo-fictive temperature is significantly lower than the Kauzmann temperature; fivefold twinning structures are distinguished in the G-phase whose constituent atoms are face-center-cubic or hexagonal-cubic-packed. This evidence suggests that G-phase Cu is not a glass. However, the G-phase is also metastable against crystallization. Therefore, G-phase Cu is neither a glass nor a crystal but belongs to a new mesophase.

DEVELOPMENT OF PLASTIC DEFORMATION IN TWO-DIMENSIONAL COPPER POLYCRYSTALS WITH DIFFERENT TWIN STRUCTURE

Experimental studies of regularities of occurrence and development of substructural and orientational heterogeneity of polycrystalline copper foils with different twin structure in the process of their deformation in conditions of active tension have been carried out. It is shown that by selecting the regime of thermal treatment of fine-grained copper foil three types of samples with different twin structure can be obtained. The first type is characterized by the presence of twins, which differ in size, shape and type of boundaries. Samples of the second type contain twins with faceted boundaries. Samples of the third type contain parallel twins with rectilinear boundaries. Such a variety of twin structures not only predetermines the difference of mechanical characteristics for samples of different types but also regularities of substructure and orientation changes accompanying the plastic deformation of samples. The use of a highly sensitive imaging method that allows in situ characterization of substructural and orientational heterogeneity during deformation and other methods (optical and raster microscopy, interferometry) allowed us to detect specific features of the course of relaxation processes in samples of different types.

On the torsional and coupled torsion-tension/compression behavior of magnesium alloy solid rod: A crystal plasticity evaluation

Extensive attention has been paid to magnesium (Mg) alloys considering their potential as lightweight structural materials. However, it is still challenging to process and manufacture Mg materials that carry high strength and good ductility. This issue mainly arises from a lack of understanding toward the anisotropic mechanical behavior of Mg alloys in response to large deformation in a multiaxial stress state, which is unavoidably in existence under various material processing routes. In this regard, we seek to understand the torsional and coupled torsion-tension/compression behaviors of a magnesium alloy subject to large-strain deformation. The elastic viscoplastic self-consistent (EVPSC) model, which incorporates the twinning-detwinning (TDT) scheme and takes a torsion-specific finite element (TFE) approach, was employed to illuminate the inhomogeneous and multiaxial features of the torsional deformation in the AZ31 Mg alloy subjected to free/fixed-end torsion and coupled torsion-tension/compression. Experimental validation was conducted by characterizing the mechanical responses of the torsional specimens under the loading paths of free-end torsion and coupled torsion-tension. Our model successfully captures the Swift effect along with the shear texture, which is hardly predicted by conventional constitutive models. In addition, our model reveals that twinning is nearly equally active under free-/fixed-end torsion, while twinning under coupled torsion-tension and torsion-compression is promoted and suppressed, respectively. The comparison between the simple shear and pure torsion by simulation demonstrates that the significant bulk stress existing within the torsional rod is ascribed to the strong interaction between the cylindrical elements in the EVPSC model. As a final thought, we believe that the TFE-EVPSC-TDT model not only highlights the inhomogeneous and multiaxial features underlying the torsional and coupled torsion-tension/compression behaviors of the Mg alloy solid rod, but more significantly, can be used as a numerical tool for designing/tuning gradient twinning structures that may lead to optimized properties of Mg alloys.

СТРУКТУРНО-ФУНКЦИОНАЛЬНАЯ СХЕМА ЦИФРОВОГО ДВОЙНИКА ИСПЫТАТЕЛЬНОГО КОМПЛЕКСА СИСТЕМЫ ЭЛЕКТРОСНАБЖЕНИЯ КОСМИЧЕСКИХ АППАРАТОВ НА ОСНОВЕ МНОГОУРОВНЕВОЙ КОМПЬЮТЕРНОЙ МОДЕЛИ

Relevance Space exploration with the help of automatic spacecraft — satellites for various purposes, deep space exploration devices, has been going on for decades. Despite this, even with the current level of reliability, spacecraft fail without having exhausted the entire period of active existence. The basic part, the so-called platform of the spacecraft, as a rule, consists of its life-supporting systems: a temperature control system, an orientation system, a propulsion system, an on-board computer control system. A failure in the operation of each of them leads to an emergency situation on board, but it is enough for any part of the power supply system to fail so that the device eventually turns out to be completely inoperable. In this regard, the power supply system of the spacecraft must be subjected to high-quality ground testing, undergo several stages of testing, from autonomous to complex as part of the spacecraft. In order to confirm the predicted reliability and operability of the spacecraft power supply system, the nominal and limit modes of its operation should be simulated in ground conditions. But, for obvious reasons, the use of on-board solar and battery batteries in ground conditions, as well as the entire complex of service and useful electrical loads, is difficult and ineffective. Therefore, in order to carry out a full-fledged ground experimental testing, a special class of control and verification equipment is used – hardware and software complexes that simulate the operating modes of the power supply system, consisting of simulators of solar, rechargeable batteries and onboard electrical load, automated connection control systems. Aim of research To bring the structure of the digital twin of the spacecraft power supply system and implement a computer model of the digital twin to automate the tasks of designing, developing and ground testing of the power supply system. Research methods The method of component circuits, methods of system analysis. Results The structure of the digital twin of the spacecraft power supply system is given. A computer model of a digital double has been implemented in the domestic environment of multilevel computer modeling of MARS. The digital twin was integrated into the test bench of the power supply system by interacting with real databases and a control computer Keywords: spacecraft power supply system, ground tests, control and verification equipment, battery simulator, solar battery simulator, electric load simulator, automation of the test process, digital twin

КОНЦЕПЦІЯ СТВОРЕННЯ МОДЕЛІ ЦИФРОВОГО ДВІЙНИКА ІНТЕЛЕКТУАЛЬНОГО ШПИНДЕЛЬНОГО ВУЗЛА

The digital twin technology isthe basis for the implementation of a cyber-physical technological system and is the core technol-ogy of Industry 4.0. A digital twin of a spindle unit is a dynamic virtual model that connects the spindle unit as a real physical object with its digital model in real time via two-way information links and reflects all the features of its design and functioning during its life cycle in real time. The key component of the digital twin of the spindle unit is its model, which is a set of digital models that describe its design, technological, operational, parameters and physical and mechanical processes that occur during the operation of the spin-dle unit and reflect the impact of these parameters on the quality and efficiency of its functioning during the life cycle in real time. Therefore, the paper considers the concept of creating a model of a digital twin of a spindle unit.The introductory part of the article formulates the issues and relevance and analyzes the works that propose approaches to the creation ofdigital twins, in particular, their models. In the main part of the paper, we first propose definitions of the terms digital twin of a spindle unit and its model. The conceptual structure of the digital twin of the spindle unit is presented. A list of characteristics of the model of the digital twin of the spindle unit is defined. The structure of the model of the digital twin of the intelligent spindle unit is determined and the stages of its model creation are given, the tasks to be solved at these stages are specified.It is shown that building a model of a digital twin of a spindle unit has a two-directional character and cannot be con-sidered a fully completed process, since the model of a digital twin of a spindle unit will be constantly refined and updated until the spindle unit is out of service. It is noted that when creating a model of a digital twin of a spindle unit, it is necessary to consider in detail the following key issues: high-precision modeling, model integration, model verification, model con-sistency, mechanisms of functioning and evolution of models.In the conclusions, attention is paid to the unresolved problematic issues that currently exist in the implementation of the model of a digital twin of a spindle unit. The generalized concept of creating a model of a digital twin of an intelligent spindle unit presented in this paper will allow further specifying the content of the stages of creating a digital twin of a spindle unit and forming a methodology for its creation.

Towards the additive manufacturing of Ni-Mn-Ga complex devices with magnetic field induced strain

Laser powder bed fusion ( L -PBF) is used to produce foam-like Ni-Mn-Ga with tailored microscale and mesoscale features. Ni50-Mn28.2-Ga21.8 (at%) powder was gas atomised and processed in an L -PBF system with a range of energy density from 26.24 and 44.90 J/mm 3 . We characterised microscale and mesoscale properties, such as the chemical composition, crystal structure, magnetisation measurements, density, and porosity measurements as a function of process parameters, in a systematic design of experiment. Preliminary research on macroscale properties included tensile testing and magnetic field induced strain (MFIS) measurements. Results show how controlling process parameters allows tailoring the Ni-Mn-Ga polycrystalline microstructure. Hence, obtaining twinned martensitic structures with a predominant orientation going across the visible grain boundaries. All the processed samples showed a 56 Am 2 /kg magnetisation level, close to Ni-Mn-Ga 10 M single crystals. Mesoscale results show a distinctive porosity pattern that is tailored by the process parameters and the laser scanning strategy. In contrast, macroscale mechanical tensile test results show a brittle fracture of Ni-Mn-Ga due to the high porosity with yield stress 2–3 times higher than shown in single crystals. In sum, we built geometrically complex demonstrators with (i) microscale twinned martensitic structures with a predominant orientation going across the visible grain boundaries and (ii) mesoscale tailored periodic porosity patterns created by modifying power, scanning speed, and scanning strategy systematically. L -PBF demonstrates great potential to produce foam-like polycrystalline Ni-Mn-Ga, reducing grain boundary constraints and thus the magnetic force needed for MFIS.