Twin Spacing Research Articles

Atomistic investigation on the anisotropic elastic and plastic responses of nanotwinned metals

Introducing nanotwins into materials is one of the important strengthening methods to achieve the synergistic improvement of strength and ductility. The anisotropic mechanical behaviors of nanotwinned materials have been widely studied by experimental and computational methods. The dominant deformation mechanisms about dislocation slippages can be effectively switched among three modes, and controlled by twin spacing and the angle between twin boundaries (TBs) orientation and loading direction. Particularly, most of previous researches mainly focused on the deformation mechanisms during the plastic flow stage and researchers paid little attention on the anisotropic characteristics of TBs at the elastic stage which are also essential to manufacture the high-performance materials. Therefore, this study is aiming to systematically investigate the anisotropic effect of TBs both at the elastic and plastic stages within the single crystalline or polycrystalline systems by molecular dynamics (MD) simulations. It is revealed that, when the loading direction is parallel to twin planes, the introduction of TBs in single crystalline models will significantly affect the characteristics of atomic bond rotation and elongation dominated elastic deformation, which can alter the Poisson’s ratio of materials, generate elastic-softening behavior and inhomogeneous elastic deformation. At the plastic flow stage, the deformation mechanism transforms from trans-twin dislocation slippage into the coexistence of Hard Mode I and threading dislocation slippage (Hard Mode II) when the loading direction changes from parallel to perpendicular direction with respect to TBs. Moreover, the dislocation segments at the conjunction of trans-twin dislocation play a momentous role in enhancing material strength. The results for polycrystalline models are consistent with that of single crystalline ones. These findings are expected to be beneficial for the development of high-performance nanostructured materials for structural and functional applications by strain engineering and defect regulation.

Effect of heterogeneous microstructures on mechanical properties of thin gradient nanotwinned copper foils

Strengthening of metals generally weakens ductility, but gradient strengthening is an exception. Heterogeneous microstructures, characterized by variations in grain size and twin spacing (structural gradients), were incorporated into 20-μm thin nanotwinned copper (NT-Cu) foils to enhance their mechanical properties. Four distinct heterogeneous NT-Cu samples, including two-layer (2L) structures and three-layer (3L) structures, were produced through rotary electroplating. The mechanical properties, work hardening rates, and microstructural features of these samples were systematically analyzed and compared. The results showed that an increase of 9.5 %, 6.4 %, and 20.1 % in ultimate tensile strength, yield strength, and work hardening rate, respectively, could be achieved in 3L structures, and the elongation was maintained at 5.5 %. The significant structural gradients and two interfaces of 3L structures were confirmed to stimulate the production of geometrically necessary dislocations (GNDs), which increased strength and work hardening rate. Two interfaces of 3L structures also contributed to the efficient moderation of plastic strains and thus improved the ductility. This study significantly enhances the strength and ductility of thin electroplated NT-Cu foils by introducing heterogeneous microstructures, promoting the application of thin NT-Cu films in electric vehicles, batteries, and the semiconductor industry.

Substrate orientation influence on nanotwinning in magnetron sputtered CoCrFeMnNi and Ni coatings

This study reveals the influence of crystal orientation on formation of growth twins in magnetron-sputtered coatings. A comparison between materials with low and high stacking fault energy (SFE) was made: CoCrFeMnNi (25 mJ/m2) and Ni (125 mJ/m2). The coatings were grown on a polycrystalline 316L stainless-steel substrate with near-random crystal texture, providing a comprehensive selection of samples on a single substrate. Electron backscatter diffraction was used to identify the film orientation, followed by transmission electron microscopy of selected regions.The presence and density of twins depended on both the material and the growth orientation. For Ni, nanotwins were observed on < 5 % of the substrate grains, on growth directions closest to 〈111〉 . All other film orientations grew epitaxially with a cube-on-cube relationship. For CoCrFeMnNi, nanotwinning was observed on 50 % of the substrate grains, deviating < 35° from 〈111〉 . In the nanotwinned regions, the twin spacing was 10–100 nm for Ni and 2–20 nm for CoCrFeMnNi. The presence of nanotwins increased hardness in both materials. The mechanism behind these differences is discussed, together with other parameters for controlling twin density. Our results show that control of the growth process can be used for nanotwin-engineering in magnetron-sputtered materials with low SFE.

Molecular Dynamics Study on the Mechanical Behaviors of Nanotwinned Titanium

Titanium and titanium alloys have been widely applied in the manufacture of aircraft engines and aircraft skins, the mechanical properties of which have a crucial influence on the safety and lifespan of aircrafts. Based on nanotwinned titanium models with different twin boundary spacings, the impacts of different loadings and twin boundary spacings on the plastic deformation of titanium were studied in this paper. It was found that due to the different contained twin boundaries, the different types of nanotwinned titanium possessed different dislocation nucleation abilities on the twin boundaries, different types of dislocation–twin interactions occurred, and significant differences were observed in the mechanical properties and plastic deformation mechanisms. For the {101-2} twin, basal plane dislocations were likely to nucleate on the twin boundary. The plastic deformation mechanism of the material under tensile loading was dominated by partial dislocation slip on the basal plane and face-centered cubic phase transitions, and the yield strength of the titanium increased with decreasing twin boundary spacing. However, under compression loading, the plastic deformation mechanism of the material was dominated by a combination of partial dislocation slip on the basal plane and twin boundary migration. For the {101-1} twin under tensile loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane and crack nucleation and propagation, while under compression loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane and twin boundary migration. For the {1124} twin, the interaction of its twin boundary and dislocation could produce secondary twins. Under tensile loading, the plastic deformation mechanism of the material was dominated by dislocation–twin and twin–twin interactions, while under compression loading, the plastic deformation mechanism of the material was dominated by partial dislocation slip on the basal plane, and the product of the dislocation–twin interactions was basal dislocation. All these results are of guiding value for the optimal design of microstructures in titanium, which should be helpful for achieving strong and tough metallic materials for aircraft manufacturing.

Application of Digital Twin Technology in Synthetic Aperture Radar Ground Moving Target Intelligent Detection System

In recent years, the detection performance of SAR-GMTI (synthetic aperture radar-ground moving target indication) algorithm based on deep learning has always been limited by insufficient measured data due to the heavy operation complexity and high cost of real SAR systems. To solve this problem, this paper proposes an overall DT-based implementation framework for SAR ground moving target intelligent detection tasks. In particular, by virtue of a SAR imaging algorithm, a high-fidelity twin replica of SAR moving targets is established in digital space through parameter traversal based on the prior target characteristics of the obtained measured datasets. Then, the constructed SAR twin datasets is fed into the neural network model to train an intelligent detector by fully learning features of the moving targets and preset the SAR scene in the twin space, which can realize the robust detection of ground moving targets in related practical scenarios with no need for multiple and complex field experiments. Moreover, the effectiveness of the proposed framework is verified on the MiniSAR measured system, and a comparison with traditional CFAR detection method is given simultaneously.

Enhancement of anti-oxidation and tensile strength of nanotwinned Cu foils by preferential Ni electrodeposition

In this study, Ni was employed to enhance the mechanical properties of nanotwinned copper (NT-Cu) foils due to its excellent oxidation resistance and compatibility with Cu. The tensile strength of the NT-Cu foils was enhanced 12.6 % (752.8 to 847.3 MPa) by Ni co-electrodeposition. During the electroplating, it was found that Ni ions inhibited the Cu growth, causing the reduction potential (overpotential) to shift in the negative direction. It resulted in a reduced deposition rate and decreased the twin spacing of the foils. Additionally, Ni ions acted as impurities for the grain refinement. Time of flight secondary ion mass spectrometry (TOF-SIMS) results indicated that Ni atoms were deposited on the top and bottom of the foils due to the limiting current density of Ni. The NT-Cu-Ni exhibited low roughness and performed superior resistance to oxidation compared to the NT-Cu. X-ray photoelectron spectroscopy (XPS) was also utilized to characterize the oxidation of the Cu (Ni) alloys. These mechanisms contributed to high strength, low resistivity, and excellent oxidation resistance of the NT-Cu-Ni foils for future battery materials.

Insights into the mechanisms of optical cavity-modified ground-state chemical reactions

In this work, we systematically investigate the mechanisms underlying the rate modification of ground-state chemical reactions in an optical cavity under vibrational strong-coupling conditions. We employ a symmetric double-well description of the molecular potential energy surface and a numerically exact open quantum system approach—the hierarchical equations of motion in twin space with a matrix product state solver. Our results predict the existence of multiple peaks in the photon frequency-dependent rate profile for a strongly anharmonic molecular system with multiple vibrational transition energies. The emergence of a new peak in the rate profile is attributed to the opening of an intramolecular reaction pathway, energetically fueled by the cavity photon bath through a resonant cavity mode. The peak intensity is determined jointly by kinetic factors. Going beyond the single-molecule limit, we examine the effects of the collective coupling of two molecules to the cavity. We find that when two identical molecules are simultaneously coupled to the same resonant cavity mode, the reaction rate is further increased. This additional increase is associated with the activation of a cavity-induced intermolecular reaction channel. Furthermore, the rate modification due to these cavity-promoted reaction pathways remains unaffected, regardless of whether the molecular dipole moments are aligned in the same or opposite direction as the light polarization.

Molecular dynamics simulation of CoCrFeMnNi with twin boundaries under high-speed impact

Based on the hybrid modeling framework of atomic scale and continuum, molecular dynamics (MD) was the method to study the shock wave, elastic-plastic dual-wave, and microstructure of CoCrFeMnNi high entropy alloy (HEA) with twin boundary under high-speed impact. The interaction between dislocation and twin interfaces is significant to the plastic deformation of HEA, but research on them as initial defects is still limited. Therefore, this article simulates and analyzes the impact velocity and twin spacing and proves that HEA with twin boundaries can synergistically improve strength and flexibility by comparing the wave simulation process and variation of spalling strength between HEA with TB and crystal Ni. The simulation results show that TB affects the propagation of shock waves in HEA and provides deformation sites for the generation of dislocations. Unlike single-crystal HEA, there is a smoother impact response process, and the maximum tensile stress during the fracture stage can reach 41 GPa, which is about 34.12% higher than that of single-crystal HEA. The research results may contribute to a better understanding of HEA with TB and help apply complex load scenarios such as explosive loads.

Quantitative assessment of microstructural damage for interior crack initiation and high cycle fatigue life modeling

Axially loaded cyclic tests of a nickel-based alloy were conducted at 550 °C, 630 °C and 650 °C and stress ratios of −1, −0.3 and 0.5 up to high cycle fatigue regime. Multiscale characterizations and quantitative analyses of microstructural damage were carried out to illustrate the physics and mechanics of interior microstructure induced fatigue strength degradation and cracking. Results showed that the fatigue strength increased with the decreases of twin spacing, the size and aspect ratio of carbide, and γ′ phase size. Twin collapse due to slip band-twin interaction was found for the first time and confirmed as a form of crack initiation process, followed by short crack growth forming facets with significant contribution from shear stress. A new mechanistic fatigue life model of interior microstructure induced cracking was established with sound agreement with experimental data. All these combined into a design-manufacturing integrated approach which are capable of ensuring the safe operation and maintenance of service structures in long-life regime.

Indentation-induced plastic behavior of nanotwinned CuNi alloy: an atomic simulation

This study uses molecular dynamics simulations to explore the mechanical properties of a nano-twinned copper–nickel alloy during indentation. We investigate the impact of twin boundary (TB) angles and spacing on the alloy’s behavior. The plastic deformation process is primarily driven by dislocation generations, slips, and TB interactions, directly affecting the alloy’s hardness. Significant findings include: (1) hardness initially decreases, then increases with increasing TB angle θ, and for TB spacing d greater than 1.25 nm, hardness can be predicted using a simple proposed model; (2) dislocation density ρ experiences significant variations, leveling off at an indentation depth around 1.0 nm; (3) when TB spacing d exceeds 1.25 nm, plastic deformation is dominated by dislocation nucleation, slips, and boundary interactions, while smaller spacings lead to TB migration and the presence of independent dislocation loops, giving rise to force fluctuations along indentation.

Federated Learning for Digital Twin-Based Vehicular Networks: Architecture and Challenges

A digital twin uses a virtual model of the physical system to fulfill the diverse requirements (e.g., latency, reliability, quality of physical experience) for emerging vehicular network applications. Although a twin-based implementation of vehicular networks can offer performance optimization, modeling a digital twin is a significantly challenging task. Federated learning (FL) is a better privacy-preserving, distributed learning scheme that can be used to model twin models. Although FL can offer performance enhancement, it requires careful design. Therefore, in this article, we present an overview of FL for a twinbased vehicular network. A general architecture for FL-enabled digital twins for a vehicular network is presented. Our proposed architecture consists of two spaces, such as twin space and the physical space. A physical space consists of all the physical entities (e.g., cars and edge servers) required for vehicular networks, whereas, the twin space refers to the logical space that is used for the deployment of twins. A twin space can be implemented either using edge servers and cloud servers. We also outline a few use cases of FL for the twin-based vehicular network. Finally, the paper is concluded and an outlook on open challenges is presented.

Research on the "shape-performance-control" integrated digital twin system for boom-type roadheaders

The boom-type roadheader plays a crucial role in coal mining. However, conducting the real-time monitoring of the mechanical performance and comprehensive adaptive cutting in the dynamic cutting process are challenging. To address these issues, a digital twin system that integrates the elements of “shape, performance, and control” for roadheaders is presented in this paper. The system comprises three components: physical space, service space, and twin space. The service space forms the core of the entire system. Within this space, twin models and control models are created using numerical simulation, artificial intelligence and multi-source data fusion technology. These models serve the purpose of predicting the roadheader’s mechanical performance and controlling the swing speed of the cutting arm. The physical space is built using technologies such as robot kinematics, electrical systems, hydraulic transmission, and other relevant techniques. This approach facilitates the transmission of multi-sensor data to twin models. The control model then manages the roadheader’s function based on the output signals from the control model. The twin space is constructed utilizing physical rendering engines, databases, and 3D modelling tools. This space visualizes and stores the movement, performance, and control parameters of the roadheader. The results demonstrate that the average absolute error between the measured data from the test’s three position strain gauges and the predicted data from the twin system is 10.38 MPa. Furthermore, the twin system achieves an average update interval of 0.34 s, allowing real-time stress monitoring of the structural components of the roadheader and preventing damage caused by overload. The proposed control model enables adaptive adjustment of the swing speed of the cutting arm in approximately 0.3 s. This improvement significantly enhances the adaptive cutting capabilities of roadheaders when dealing with complex coal and rock formations.

Effect of N on microstructure evolution and strain hardening of high-Mn austenitic steel during tensile deformation

The present study investigated the microstructure evolution and strain hardening of two types of high-Mn austenitic steels, i.e., Fe−18.5Mn–7Cr−0.6C (00 N) and Fe−18.5Mn–7Cr−0.6C−0.21 N (21 N), during tensile deformation. The results revealed that the addition of N increased the yield and tensile strength of high-Mn austenitic steel with almost no loss of elongation. The strain hardening of the 00 N and 21 N steels was closely related to the microstructure evolution. At the initial tensile deformation stage, dislocation slip was the dominant deformation mechanism of the two test steels. Due to the addition of N, the dislocation cross-slip in the 21 N steel was suppressed, leading to a higher strain hardening rate. With the increase of true strain, the mechanical twins became active. At a true strain of 0.18, a unique network structure of mechanical twins and dislocation cells was formed in the 00 N steel, and the thickness and spacing of mechanical twins were lower, which increased the resistance of dislocation motion and made its strain hardening rate slightly higher than that of the 21 N steel. However, at a true strain of 0.37, the thickness and spacing of mechanical twins in the 21 N steel decreased rapidly, which increased the difficulty of dislocation movement, resulting in a higher strain hardening rate than that of the 00 N steel. In short, the increased resistance of dislocation motion was the fundamental reason for the enhanced strain hardening rate, rather than mechanical twins.

Twin spacing and grain size dependent tensile deformation mechanism of a nano-ploycrystalline Ni-based alloy

It is easy to form twins in Ni-based wrought superalloys with low stacking fault energy, but the effect of grain size and twin spacing on mechanical properties in nano-ploycrystalline Ni-based alloys is rarely studied. Based on the composition of a novel Ni-based wrought superalloy, molecular dynamics simulations were used to study the effect of grain size and twin spacing on the deformation behavior of the Ni57Cr19Co19Al5 alloy. The results show that the elastic modulus and tensile strength of the nano-polycrystalline Ni57Cr19Co19Al5 alloy exhibit clear grain size dependence. As the grain size exceeded 16 nm, the elastic modulus remained unchanged. The tensile strength and grain size satisfy the Hall–Petch relationship, and the dislocation motion dominates the plastic deformation. For the grain size below 16 nm, the elastic modulus decreases as the grain size decreases. The tensile strength and the grain size exhibit an inverse Hall–Petch relationship. The grain boundary sliding and grain torsion mechanisms dominated plastic deformation in the nano-polycrystalline Ni57Cr19Co19Al5 alloy without twin. In the nano-polycrystalline Ni57Cr19Co19Al5 alloy containing twins, the twin boundaries inhibited the torsion of grains, and grain boundary sliding dominated plastic deformation.

Tailoring the nanotwin spacing of Ni-Mo-W alloys via composition and substrate temperature control

Alloy chemistry and deposition conditions can strongly influence the structure and properties of nanostructured materials. However, in Ni-Mo-W alloys, the limited influence of deposition rate on the twin spacing compels the exploration of other routes to tailor the structure and properties. This study was undertaken to investigate the effect of composition and substrate temperature on the nanotwin spacing of sputter-deposited Ni-Mo-W alloys. Increasing the Ni content from 84 at.% to 93 at.% doubled the average twin spacing from 1.8 nm to 3.8 nm, while raising the substrate temperature from room temperature to 200°C for a fixed Ni content of 91 at.% resulted in an increase from 2.9 nm to 5.0 nm. Concurrent weakening of the {111} texture occurred with both increased Ni and temperature. The combined effectiveness of composition and temperature demonstrated here provides a potential process window for tuning the twin spacing while maintaining the strongly textured columnar structure.

Effect of initial twins on mechanical properties of additive manufacturing CoCrNi alloy and molecular dynamic simulation

The influence of twins on laser additive CoCrNi MEA was analyzed by experiments and molecular dynamic simulation. Results showed that the traditional laser additive CoCrNi MEA was prone to slip in the (111) direction. EBSD analysis showed an obvious 60°(111} axial angle pair relationship, which is related to the slower cooling rate. The results of molecular dynamic simulation showed that the yield strength of CoCrNi MEA increases first and then decreases, and the material has a critical twin density. When the twin density is less than the critical twin density, the strength of the material increases due to the thinning effect of the twin boundary on the grain. When the twin density is greater than the boundary twin density, the nucleation and proliferation of the twin boundary and the junction of the two become the dominant factors of the material deformation. When the twin density is far from the critical value, the twin spacing becomes smaller, the dislocation sources increase, the dislocation nucleation and proliferation increase, and the strength of the material decreases.

Dynamic compression responses of heterogeneous-structured CrMnFeCoNi high-entropy alloy at cryogenic temperatures

Dynamic compression experiments are conducted on a heterogeneous-structured CrMnFeCoNi high-entropy alloy (HEA) at different strain rates (1000–5000 s−1) and temperatures (123–293 K) with a split Hopkinson pressure bar system. Yield strength and strain hardening rate increase considerably with decreasing temperature at 5000 s−1 (low-temperature strengthening), but are insensitive to strain rate at 173 K, which can be well described by the Zerilli–Armstrong model. Compared to typical aluminum alloys and homogeneous-structured CrMnFeCoNi HEA, the heterogeneous-structured HEA exhibits higher thermal sensitivity and strain hardening rate. Microstructural characterizations show that dislocation density in the fine-grained domains increases more drastically than in the coarse-grained domains, inducing high deformation gradient between the coarse- and fine-grained domains. At 123 K, nano-scale primary and secondary deformation twins form in grain interior, along with a great number of stacking faults on twin boundaries; the twin width and spacing in coarse grains are considerably higher than in fine grains. In addition, the twin density at 123 K is significantly higher than that at 293 K. Overall, the increased deformation twinning and deformation gradient contribute to pronounced strengthening and strain hardening with decreasing temperatures in the heterogeneous-structured HEA under dynamic compression.

Path planning method for Camellia oleifera forest trenching operation based on human-robot collaboration

In order to realize the independent and safe operation of trenching robot in Camellia oleifera forest, operation path planning is the key link. Aiming at the problem of trenching operation path planning in complex dynamic Camellia oleifera forest environment, a trenching operation path planning method of Camellia oleifera forest based on human-robot collaboration was proposed. In order to meet the requirements of trenching operation in Camellia oleifera forest, the ring trenching operation path was planned around Camellia oleifera tree; Aiming at the unknown obstacles in the dynamic Camellia oleifera forest environment, the digital twin technology was used to map the dynamic Camellia oleifera forest environment into the twin space in real time, assist the operator to recognize the dynamic Camellia oleifera forest environment information and issue decision instructions. According to the man-machine collaborative decision-making instructions and dynamic environmental information, the twin environment model of Camellia oleifera forest was updated in real-time, and the collision detection method combining virtual and real was adopted to avoid collision and re-plan the trenching operation path. The experimental results show that the repetition rate of the trenching operation path of the Camellia oleifera forest planned by this method is reduced by 1.64 percentage points, the slope standard deviation is reduced by 40.365 %, and the operation path is more stable; In addition, the re-planning of the operation path of the trenching robot based on digital twin under human-robot cooperation prevents collision with the dynamic obstacles of the Camellia oleifera forest, which provides a new idea for the intelligentization of the trenching operation of the Camellia oleifera forest.

Nano-precipitation strengthening regulated by nanotwins in CoCrNi alloy with super-high strength

The number and size of precipitates directly influence the strengthening of the high-temperature alloys. As special coherent interfaces, nano-twinned (NT) boundaries are pre-set in CoCrNi-based superalloy to regulate the distribution of nano-precipitates for further strengthening the mechanical property. High density of NTs with twin spacings of 2–200 nm is produced in CoCrNi alloy by surface mechanical rolling treatment (SMRT), and L12 (Ni3Ti)-type precipitates are induced by the low-energy NT boundaries, as well as grain boundaries, after aging at 700 °C for 4 h. The CoCrNi alloy with L12 nano-precipitates exhibits a super-high mechanical property, characterized by 2019 MPa of a yield strength (σy) and 2300 MPa of an ultimate tensile strength (σu), much higher than the CoCrNi alloy counterpart of 840 (σy) and 1100 (σu) MPa, respectively. Meanwhile, the treated CoCrNi alloy also delivers a reasonable elongation of 7.0%. The super-high strength is mainly ascribed to the high density L12 nanoprecipitates grown on the NT boundaries, while the elongation is sustained by the NTs boundaries.

Effect of cold rolling on microstructure and mechanical property of a novel (Fe50Mn30Co10Cr10)97C2Mo1 high entropy alloy

Effect of cold rolling on microstructural evolution and mechanical properties of a novel (Fe50Mn30Co10Cr10)97C2Mo1 high entropy alloy has been investigated via electron microscopy and tensile testing. The results show that the alloy is mainly deformed via dislocation and twinning due to its low stacking fault energy. With increasing thickness reduction, the dislocation density first increases, up to a maximum of ∼29.3 × 1014 m−2 at CR 60 %, then reduces, to 21.1 × 1014 m−2 at CR 90 %. The width and spacing of the deformation twins gradually decrease with an increase of thickness reduction. TEM examination also reveals that shear bands produce in CR 40 % sample, and that its volume fraction gradually increases with increasing thickness reduction. Such microstructural evolution with cold rolling, gives rise to a quick enhancement of yield strength of the alloy (1926 MPa for CR 90 % vs. 239 MPa for the as-homogenized sample) whereas a clear loss in ductility. However, the cold-rolled samples at low to medium strains show a good combination of strength and ductility, e.g., CR 20 % sample has a yield strength of 800 MPa (, which is 3.3 times higher than that of as-homogenized HEA) and an elongation of 30 %, while 1300 MPa yield strength and 15 % elongation for CR 40 % sample.