Twin Structure Research Articles

In-plane and out-of-plane orientations of YBCO and their correlation with a/b-axis twin structures

In-plane and out-of-plane orientations of YBCO and their correlation with a/b-axis twin structures

Self-activated epitaxial growth of ScN films from molecular nitrogen at low temperatures

Unlike naturally occurring oxide crystals such as ruby and gemstones, there are no naturally occurring nitride crystals because the triple bond of the nitrogen molecule is one of the strongest bonds in nature. Here, we report that when the transition metal scandium is subjected to molecular nitrogen, it self-catalyzes to break the nitrogen triple bond to form highly crystalline layers of ScN, a semiconductor. This reaction proceeds even at room temperature. Self-activated ScN films have a twin cubic crystal structure, atomic layering, and electronic and optical properties comparable to plasma-based methods. We extend our research to showcase Sc’s scavenging effect and demonstrate self-activated ScN growth under various growth conditions and on technologically significant substrates, such as 6H–SiC, AlN, and GaN. Ab initio calculations elucidate an energetically efficient pathway for the self-activated growth of crystalline ScN films from molecular N2. The findings open a new pathway to ultralow-energy synthesis of crystalline nitride semiconductor layers and beyond.

In situ atomic observations of aggregation growth and evolution of penta-twinned gold nanocrystals

The twin boundaries and inherent lattice strain of five-fold twin (5-FT) structures offer a promising and innovative approach to tune nanocrystal configurations and properties, enriching nanomaterial performance. However, a comprehensive understanding of the nonclassical growth models governing 5-FT nanocrystals remains elusive, largely due to the constraints of their small thermodynamically stable size and complex twin configurations. Here, we conducted in situ investigations to elucidate the atomic-scale mechanisms driving size-dependent and twin configuration-related aggregation phenomena between 5-FT and other nanoparticles at the atomic scale. Our results reveal that surface diffusion significantly shapes the morphology of aggregated nanoparticles, promoting the symmetrical formation of 5-FT, especially in smaller nanoparticles. Moreover, the inherent structural characteristics of 5-FT mitigate the dominance of surface diffusion in its morphological evolution, retarding the aggregation evolution process and fostering intricate twin structures. These findings contribute to advancing our capacity to manipulate the configuration of twinned particles, enabling more predictable synthesis of functional nanomaterials for advanced engineering applications.

Open-Source Solutions for Real-Time 3D Geospatial Web Integration

Abstract. The recent development of Urban Digital Twin (UDT) structures and the spread of Internet of Things (IoT) technology have extended the concept of Digital Twin (DT) to urban environment representation, enabling real-time connections between geospatial representations and their real-world counterparts. Concurrently, advancements in surveying technologies and web geospatial services have facilitated the acquisition of extensive 2D and 3D geospatial data, making their spatial integration essential. While some proprietary software solutions have recently enabled initial examples of UDT by integrating various 3D geospatial data and real-time sensor acquisition, the development of open-source solutions for real-time web-based geospatial management remains a challenge. This work demonstrates a possible open-source solution for developing a UDT accessible via the web. The case study involves the web visualization platform of the new Faculty of ITC building at the University of Twente in Enschede (The Netherlands), which is connected in real-time with weather data services provided by Visual Crossing (1). The platform is based on an HTML5 framework and employs WebGL JavaScript graphic libraries to visualize different modules of 3D web visualization that integrate various local and remote 3D datasets. The framework adopted in this experiment can be used in the future for developing low-cost UDT web platforms beneficial for researchers, municipalities, and private companies interested in the real-time geospatial management of urban environments.

Microstructural Evolution and Mechanical Properties of Extruded AZ80 Magnesium Alloy during Room Temperature Multidirectional Forging Based on Twin Deformation Mode.

This study investigates the preparation of ultrahigh-strength AZ80 magnesium alloy bulks using room temperature multidirectional forging (MDF) at different strain rates. The focus is on elucidating the effects of multidirectional loading and strain rates on grain refinement and the subsequent impact on the mechanical properties of the AZ80 alloy. Unlike hot deformation, the alloy subjected to room temperature MDF exhibits a lamellar twinned structure with multi-scale interactions. The key to achieving effective room temperature MDF of the alloy lies in combining multidirectional loading with small forging strains per pass (6%). This approach not only maximizes the activation of twinning to accommodate deformation but ensures sufficient grain refinement. Microstructural analysis reveals that the evolution of the grain structure in the alloy during deformation results from the competition between {101¯2} twinning or twinning variant interactions and detwinning. Increasing the forging rate effectively activates more twin variants, and additional deformation passes significantly enhance twin interaction levels and dislocation density. Furthermore, at a higher strain rate, more pronounced dislocation accumulation facilitates the transformation of twin structures into high-angle grain boundaries, promoting texture dispersion and suppressing detwinning. The primary strengthening mechanisms in room temperature MDF samples are grain refinement and dislocation strengthening. While increased dislocation density raises yield strength, it reduces post-yield work hardening capacity. After two passes of MDF at a higher strain rate, the alloy achieves an optimal balance of strength and ductility, with a tensile strength of 462 MPa and an elongation of 5.1%, significantly outperforming hot-deformed magnesium alloys.

Austenite-martensite interfacial patterns and energy dissipation of phase transformation in Ni-Mn-Ga single crystal

The martensitic phase transformation occurs in Shape Memory Alloys (SMA) via the nucleation/propagation of the Austenite-Martensite interface (A-M interface), which is a transition region (domain) between the two coexisting phases. For providing compatibility, the transition region consists of various martensitic twin structures (laminates), forming different interfacial patterns, such as parallel laminates and branching laminates. Due to the energy accumulation in the interfacial structures (e.g., elastic mismatch and twin-boundary surface energy), the interfacial patterns should be relevant to the driving force (energy dissipation) and the associated kinetics of the phase transformation. In this paper, we adopt a special thermal loading, small-temperature-gradient “heating-cooling-reheating”, to control the A-M interface's forward and reverse propagation to generate different interfacial patterns in a Ni-Mn-Ga single crystal SMA with the observation on the twin structures (by optical microscope and SEM) and the InfraRed measurement on the temperature hysteresis of the interface propagation (for characterizing the thermal driving force). Simple energetic analysis indicates that the thermal driving force (energy dissipation) is directly related to the stored energy in the interfacial structure, particularly the large mismatch elastic energy near the habit plane. This study not only provides the details of the various interfacial patterns and their dependence on the loading path, but also indicates the driving force and the associated mechanism about the pattern evolution to understand the phase transformation process.

Coupling defect-inherent built-in electric fields to promote directional charge migration for rapid photocatalytic degradation of levofloxacin

By enhancing the intrinsic built-in electric field (IEF) of the catalyst through defect engineering, and coupling the IEF of the catalyst via an S-type heterojunction structure, a 3-in-1 IEF is formed, which drives the directional migration of electrons and holes, and can effectively improve photocatalytic performance. In this paper, an oxygen vacancy-type Bi2WO6 (Ov-BWO) composite with twin-type Zn0.5Cd0.5S (ZCS) was synthesized to construct an S-scheme heterojunction. The twin structure results in an IEF in ZCS that points from the twin plane Zn to the twin boundary S. The oxygen vacancies, on the other hand, create an internal electric field from Bi and W to O by altering the local charge density. By coupling the IEF of the catalyst through the S-type heterojunction, an enhanced IEF is formed, pointing from the twin plane Zn to the O in Ov-BWO, enabling rapid directional migration of photogenerated charge carriers. Furthermore, potential Levofloxacin (LVFX) intermediates and degradation pathways were found by combining Liquid chromatography-mass spectrometry (LC-MS) data with Density Functional Theory (DFT) simulations. This study systematically elucidates the photocatalytic degradation system, from catalyst design to the degradation process of pollutants, through the analysis of theoretical calculations and experimental results.

Adapting Segment Anything Model for 3D Brain Tumor Segmentation With Missing Modalities

ABSTRACTThe problem of missing or unavailable magnetic resonance imaging modalities challenges clinical diagnosis and medical image analysis technology. Although the development of deep learning and the proposal of large models have improved medical analytics, this problem still needs to be better resolved.The purpose of this study was to efficiently adapt the Segment Anything Model, a two‐dimensional visual foundation model trained on natural images, to address the challenge of brain tumor segmentation with missing modalities. We designed a twin network structure that processes missing and intact magnetic resonance imaging (MRI) modalities separately using shared parameters. It involved comparing the features of two network branches to minimize differences between the feature maps derived from them. We added a multimodal adapter before the image encoder and a spatial–depth adapter before the mask decoder to fine‐tune the Segment Anything Model for brain tumor segmentation. The proposed method was evaluated using datasets provided by the MICCAI BraTS2021 Challenge. In terms of accuracy and robustness, the proposed method is better than existing solutions. The proposed method can segment brain tumors well under the missing modality condition.

Effects of laser non-uniform shock peening on the microstructure and fatigue performance of SUS 304 stainless steel welded joints

Residual tensile stresses and microstructural heterogeneity in welded joints are primary factors that degrade fatigue performance. As an effective post-weld strengthening method, Laser Shock Peening (LSP) can address these issues. Given the personalized demands of different regions, this paper proposes a Laser Non-Uniform Shock Peening (LNUSP) technique. This approach involves applying high pulse energy to the weld zone (WZ) and heat-affected zone (HAZ), and low pulse energy to the base material (BM) to achieve a more uniform residual compressive stress distribution and refined microstructure, thereby improving overall performance and service life. Results indicate that LSP transforms residual tensile stresses on the weld surface into compressive stresses. Compared to original samples, uniformly LSP-treated samples, and locally LSP-treated samples, LNUSP-treated samples exhibit more uniform residual stress and hardness distribution. LSP significantly increases surface hardness, with LNUSP-treated samples achieving a maximum hardness of 308.3 HV. Additionally, LSP induces martensitic transformation in the BM and WZ areas, alters grain orientation, and promotes dislocation movement, resulting in dislocation tangling, dislocation networks, and twin structures, which refine grain size. Consequently, LSP markedly improves joint fatigue performance, delaying fatigue crack propagation. The fatigue life of LNUSP-treated samples is increased by 25.41 % compared to original samples, reaching levels comparable to high-energy large-area impacts. This enhancement is attributed to the uniform residual stress and refined grain structure.

Micromechanical response of graphene coating on nt-TiAl under nanoindentation

The nanoindentation response of graphene (Gr) coating on nanotwin titanium-aluminum (nt-TiAl) matrix composites was studied using molecular dynamics (MD) simulation. The indentation velocity, twin boundary spacing, and parallel and vertical Z-axes are studied. The results show that the bearing capacity and hardness of Gr coating is significantly higher than that after coating failure, and the load-displacement curve shows the same phenomenon. Damage to the substrate material at varying speeds is indicated by atomic aggregation near the Gr coating, with the center of aggregation showing a negative correlation with indentation velocity. The matrix's damaged area is larger when the twin layer is perpendicular to the Z-axis and deeper when parallel, showing that the twin structure limits material damage by hindering dislocation expansion. Moreover, the presence of Gr coating delayed the matrix's plastic deformation process. This delay effect significantly improves the mechanical properties of composites, which have potential applications in aerospace.

TSKPD: twin structure key point detection in point cloud

The point cloud keypoint detection algorithm like USIP that uses downsampling first and then fine-tuning the sampling points cannot effectively detect the defect part of the single view defect point cloud, resulting in the inability to output the keypoints of the defect part. Therefore, this paper proposes the twin structure key point detection algorithm named TSKPD based on the idea of contrastive learning, which uses two single-view defect point clouds to synthesize relatively more complete key points for learning, so as to promote the network model to learn the features of the complete point cloud. The robustness of key point detection of point cloud is effectively improved, and the detection of single view defect point cloud is realized. The test results on ModelNet40 and ShapeNet datasets show that the coverage rate of TSKPD on the missing part of the single view defect point cloud is 12.62 higher than the existing optimal algorithm.

Novel multitarget directed ligands inspired by riluzole: A serendipitous synthesis of substituted benzo[b][1,4]thiazepines potentially useful as neuroprotective agents

Riluzole, the first clinically approved treatment for amyotrophic lateral sclerosis (ALS), represents a successful example of a drug endowed with a multimodal mechanism of action. In recent years, different series of riluzole-based compounds have been reported, including several agents acting as Multi-Target-Directed Ligands (MTLDs) endowed with neuroprotective effects. Aiming at identical twin structures inspired by riluzole (2a-c), a synthetic procedure was planned, but the reactivity of the system took a different path, leading to the serendipitous isolation of benzo[b][1,4]thiazepines 3a-c and expanded intermediates N-cyano-benzo[b][1,4]thiazepines 4a-c, which were fully characterized. The newly obtained structures 3a-c, bearing riluzole key elements, were initially tested in an in vitro ischemia/reperfusion injury protocol, simulating the cerebral stroke. Results identified compound 3b as the most effective in reverting the injury caused by an ischemia-like condition, and its activity was comparable, or even higher than that of riluzole, exhibiting a concentration-dependent neuroprotective effect. Moreover, derivative 3b completely reverted the release of Lactate Dehydrogenase (LDH), lowering the values to those of the control slices. Based on its very promising pharmacological properties, compound 3b was then selected to assess its effects on voltage-dependent Na+ and K+ currents. The results indicated that derivative 3b induced a multifaceted inhibitory effect on voltage-gated currents in SH-SY5Y differentiated neurons, suggesting its possible applications in epilepsy and stroke management, other than ALS. Accordingly, brain penetration was also measured for 3b, as it represents an elegant example of a MTDL and opens the way to further ex-vivo and/or in-vivo characterization.

Nacre-like surface nanolaminates enhance fatigue resistance of pure titanium

Fatigue failure is invariably the most crucial failure mode for metallic structural components. Most microstructural strategies for enhancing fatigue resistance are effective in suppressing either crack initiation or propagation, but often do not work for both synergistically. Here, we demonstrate that this challenge can be overcome by architecting a gradient structure featuring a surface layer of nacre-like nanolaminates followed by multi-variant twinned structure in pure titanium. The polarized accommodation of highly regulated grain boundaries in the nanolaminated layer to cyclic loading enhances the structural stability against lamellar thickening and microstructure softening, thereby delaying surface roughening and thus crack nucleation. The decohesion of the nanolaminated grains along horizonal high-angle grain boundaries gives rise to an extraordinarily high frequency (≈1.7 × 103 times per mm) of fatigue crack deflection, effectively reducing fatigue crack propagation rate (by 2 orders of magnitude lower than the homogeneous coarse-grained counterpart). These intriguing features of the surface nanolaminates, along with the various toughening mechanisms activated in the subsurface twinned structure, result in a fatigue resistance that significantly exceeds those of the homogeneous and gradient structures with equiaxed grains. Our work on architecting the surface nanolaminates in gradient structure provides a scalable and sustainable strategy for designing more fatigue-resistant alloys.

Atomistic simulations of structure and motion of twin interfaces reveal the origin of twinning in NiTi shape memory alloys

Shape memory alloys (SMAs) are functional materials featuring unique shape recovery properties that make them suitable for key industrial applications. The essential process controlling this fascinating performance is microstructural twinning. Some twin systems are much more frequently observed than others, yet a fundamental mechanistic understanding of this evidence is missing, which hampers SMA design. Here, we consider the prototypical NiTi SMA to show that the emergence of twinning can be strongly affected by twin interface mobility. In this work, we adopt an integrated approach combining crystallographic theory, state-of-the-art atomistic modelling, topological model, and validation with high-resolution transmission-electron micrographs. Atomistic simulations confirm that the occurrence of twins is dictated by the driving force for twin boundary motion rather than interfacial energy. Moreover, our findings settle long-standing questions by elucidating the propagation mechanisms of twin interfaces, which the established martensite crystallography and kinetic theories could not address conclusively. The newly discovered understanding of the role of interface mobility in twin formation can be used to predict variant selection and guide the design of SMAs with improved functional performance.

Enhanced mechanical properties of TZM alloy via doping Y2O3 along with creating heterogeneous grain structures

The further application exploration of TZM alloys have been hindered by the limited strength especially at high temperatures. Herein, we propose a strategy to enhance the mechanical properties of TZM alloys by introducing heterostructures through Y2O3 doping combined with rotary forging (RF). The particle stimulated nucleation (PSN) mechanism promotes fine grains (FGs) nucleate close to the micron-sized second phase particles. The mechanical properties of Y2O3-TZM (YTZM) alloy are improved through the synergistic strengthening influence of back stress strengthening and second phase strengthening. The ultimate tensile strength (UTS) of YTZM at room temperature and 1000 °C is 820 MPa and 433 MPa, respectively, which are about 15% and 51% higher than that of TZM. In addition, the FCC-oxides generated by adding Y2O3 can trigger twinning, stacking faults, and 9R structures during high-temperature deformation, and the long-period stacked ordered phase (LPSO) nucleates at the stacking faults and twin boundaries through the 9R structures, which is more conducive to alleviate the stress concentration at the oxide/matrix interface and improve the dislocation blocking ability. The present strategy provides a paradigm for the development of high-performance TZM alloys through creating heterostructures.

Microstructure evolution and twinning-induced plasticity (TWIP) in hcp rare-earth high- and medium-entropy alloys (HEAs and MEAs) due to tensile deformation

The microstructure evolution due to the tensile deformation of the equiatomic quinary high-entropy alloy Ho-Dy-Y-Gd-Tb (HEA-Fb) is assessed. HEA-Fb has extraordinarily similar alloying elements. It is one of the few hexagonal-close-packed single-phase representatives of HEA. HEA-Fb is compared to the equiatomic quaternary medium-entropy alloy (MEA) Ho-Dy-Gd-Tb with no Y (4-Y). For a hexagonal HEA, in contrast to the cubic HEA, little information on plastic deformation and underlying mechanisms is available. A detailed study using electron microscopy-based multi-scale characterization (SEM, S/TEM, and STEM-EDS) explains significant differences between the ductile behavior of the quaternary MEA 4-Y and the brittle behavior of the quinary HEA-Fb at room temperature. Twinning during plastic deformation is decisive for ductility, which challenges the widely discussed high-entropy effect on the mechanical behavior of the HEA. For the quaternary MEA 4-Y, a twinning-induced plasticity effect is found. In the latter, oxidized twins are present in the undeformed state. In both alloys, the twin orientations are indexed as [2¯201], while the matrices have the perpendicular [112¯0] orientation. Additionally, the analysis of twin structures confirms the importance of twin boundaries as obstacles for dislocations and stacking fault mobilities. The results are discussed in the context of the existing knowledge gaps in the field of hexagonal MEAs and HEAs.

Effect of surface high-density twinned structure on the fatigue crack initiation of Ti–6Al–4V

Fatigue crack initiation sites would transfer from surface to subsurface of metal specimens through shot peening (SP) or laser shock surface strengthening. This phenomenon is typically attributed to the introduction of compressive residual stress on the surface of the specimen during the surface strengthening process. In this study, Ti–6Al–4V specimens featuring a high-density twinned structure on their surfaces, which eliminated compressive residual stress, were fabricated. Fatigue test result revealed that fatigue crack initiation sites in specimens with twinned structures were predominantly located in the subsurface, near the junction area between the twinned structure and the matrix. This phenomenon was accompanied by an increase in fatigue life. The microstructural features in the fatigue crack source were analyzed using focused ion beam (FIB) coupled with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). It was observed that primary crack formed in badly oriented grains that are difficult to initiate dislocation slip according to the Schmid factor (SF). Nonetheless, TEM observations revealed the activation of basal <a> dislocations in these grains, potentially leading to crack nucleation along basal slip bands and subsequent propagation along the basal plane. Our results suggest that a high-density twin structure on the surface can enhance the fatigue strength of Ti–6Al–4V by transferring the fatigue crack source to the subsurface.

Influences of Al particles on structure and properties of Ni–Al composite coatings with nanoscale twin structure

Nickel-aluminum (Ni–Al) composite coatings containing nickel nanoscale twins have been prepared by co-electrodeposition on copper substrate. Effects of Al particles on microstructure, chemical composition, friction properties, and corrosion resistance of Ni–Al coatings were investigated. It presents an even and compact structure with granular surface that Al are evenly dispersed in pyramidal-like nickel lattice. Adding Al could alter crystal orientation, refine grains and promote strengthening effects induced by nanoscale twinning. It can enhance anti-corrosion properties and decrease the coefficient of friction (COF). The minimum COF was obtained at 10 g L−1 Al. The larger amounts and even dispersion of Al, the better corrosion resistance and the smaller COF. Increasing Al from 20 to 40 g L−1, incorporated Al in top surface rose from 20.86 to 30.13 wt%, which was larger than in cross section from 13.93 to 18.86 wt%. As the incorporated depth increased, the particle color changed from grey to dark. Nano-twins were generated around enveloped Al particles. The roughness increased as Al rose from 10 to 40 g L−1. The average roughness (Ra) was of 191–231 nm. Ni–Al-5g and Ni–Al-80g have excellent anti-corrosion features, owning the maximum Rct of 1437.2 and 1565.1 kΩ cm2, respectively, associated with the amount and distribution of Al particles, preferred orientation, grain sizes, and twinned structure. The enhanced corrosion resistance might be due to the generation of uniform, compact aluminum oxide layer by doping Al in nickel.

Exact solutions for clamped spherical and cylindrical panels via a unified formulation and boundary discontinuous method

Numerous works in both recent and historical literature have concentrated on formulating theories to perform static analysis on simply-supported shell structures. However, it is worth noting that obtaining analytical solutions for clamped boundary conditions presents a strong challenge. In this paper, closed-form solutions for clamped cross-ply laminated and sandwich shells are achieved by employing a robust and hybrid methodology not previously reported in the literature. The high versatility of the Carrera Unified Formulation (CUF), based on the Equivalent-Single-Layer (ESL) description, is utilized to implement several refined shell theories. The Principle of Virtual Displacements (PVD) is utilized to derive the strong form of the governing equations in terms of displacement variables. As the main novelty, these equations are solved by the Boundary Discontinuous Fourier-based method (BDM) which provides highly accurate analytical solutions. The validity and robustness of the proposed methodology are assessed through a detailed comparison with references available in the open literature, as well as with FEM 3D results obtained with commercial software. Furthermore, the stress recovery technique is exploited to fulfill zero-stress and interlaminar continuity (IC) conditions. The findings might be useful in training artificial intelligence (AI) models, which, for instance, could facilitate the development of digital twin structures.

Mechanical properties and microstructure evolution of Sn–Bi-based solder joints by microalloying regulation mechanism

Sn–Bi based solders are used in electronic packaging for interconnection processes. However, the rate of research on the comprehensive performance of solders is difficult to match the rapid development of advanced manufacturing of integrated circuits, resulting in the inability to obtain interconnect structures with excellent reliability for electronic devices. To demand a more effective modification method, we chose to dope 1.0 wt % In element in Sn58Bi–1Sb alloy. The strength, micromechanical properties and creep resistance of the solder were improved due to the combined effect of solid solution strengthening and diffusely distributed second phase strengthening. Furthermore, the addition of In element dramatically improved the thermal properties and wettability due to the generation of Bi3In5 intermetallic compounds (88.9 °C) and the activation energy of the solder wettability reaction was reduced to 247.36 J/mol. Notably, the addition of In element increased the amount of β-Sn phase deviation and decreased the Schmid factor value of β-Sn phase, resulting in a significant increase in the strength and micro-zone creep resistance. Under the action of current, a large amount of uniform Bi particle deviations and sub-crystalline structures persist in the β-Sn phase of the Sn58Bi–1Sb1In solder matrix. In the Cu/Sn58Bi–1Sb1In/Cu joints, many Bi particles are staggered in the β-Sn phase. Since the resistivity of the β-Sn phase is smaller than that of the Bi phase, the energization process leads to a possible further increase of the local currents at certain locations in the β-Sn phase, which reduces the electromigration resistance of the β-Sn phase. After energization, the biphasic twin structure with excellent electromigration resistance starts to degrade. The results show that the doping of In element comprehensively improves the performance of Sn58Bi–1Sb solder. It opens up a new idea for the design of alloying modification of tin-bismuth based solder.