Metal Boundary Research Articles

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy.

Positron annihilation lifetime spectroscopy (PALS) is a valuable technique to investigate defects in solids, such as vacancy clusters and grain boundaries in metals and alloys, as well as lattice imperfections in semiconductors. Positron spectroscopy is able to reveal the size, structure and concentration of vacancies with a sensitivity of 10-7. In the field of porous and amorphous systems, PALS can probe cavities in the range from a few tenths up to several tens of nm. In the case of polymers, PALS is one of the few techniques able to give information on the holes forming the free volume. This quantity, which cannot be measured with macroscopic techniques, is correlated to important mechanical, thermal, and transport properties of polymers. It can be deduced theoretically by applying suitable equations of state derived by cell models, and PALS supplies a quantitative measure of the free volume by probing the corresponding sub-nanometric holes. The system used is positronium (Ps), an unstable atom formed by a positron and an electron, whose lifetime can be related to the typical size of the holes. When analyzed in terms of continuous lifetimes, the positron annihilation spectrum allows one to gain insight into the distribution of the free volume holes, an almost unique feature of this technique. The present paper is an overview of PALS, addressed in particular to readers not familiar with this technique, with emphasis on the experimental aspects. After a general introduction on free volume, positronium, and the experimental apparatus needed to acquire the corresponding lifetime, some of the recent results obtained by various groups will be shown, highlighting the connections between the free volume as probed by PALS and structural properties of the investigated materials.

Atomistic modeling of metal–nonmetal interphase boundary diffusion

Atomistic computer simulations are applied to investigate the atomic structure, thermal stability, and diffusion processes in Al–Si interphase boundaries as a prototype of metal–ceramic interfaces in composite materials. Some of the most stable orientation relationships between the phases found in this work were previously observed in epitaxy experiments. A non-equilibrium interface can transform to a more stable state by a mechanism that we call interface-induced recrystallization. Diffusion of both Al and Si atoms in stable Al–Si interfaces is surprisingly slow compared with diffusion of both elements in Al grain boundaries but can be accelerated in the presence of interface disconnections. A qualitative explanation of the sluggish interphase boundary diffusion is proposed. Atomic mechanisms of interphase boundary diffusion are similar to those in metallic grain boundaries and are dominated by correlated atomic rearrangements in the form of strings and rings of collectively moving atoms.

Mapping of Sensing Performance of Concentric and Non-Concentric Silver Nanoring

Sensors play a critical role in improving overall human quality of life. They have been employed in most aspects of our lives. A recently emerging sensing platform is based on plasmonic resonance at the boundary of metals and dielectrics. Localized surface plasmon resonances–based sensors offer miniaturization, a simple setup, and relatively high sensitivity for real-time measurements. The reported figure of merit (FOM) of the LSPR-based sensor is generally limited, primarily due to its broad resonance peak. Nanorings composed of metal nanoparticles are known for their broad-range resonance tunability, high field localization, and large sensing area. Asymmetry of the nanoring with the introduction of core offset relaxes the selection rule for mode mixing, thus resulting in a narrower resonance peak. This may overcome broad resonance peak restriction. Concentric and non-concentric nanorings were simulated using the boundary element method implemented with the MNPBEM toolbox. We map the performance of nanoring sensors over a wide range of geometrical variations, namely, diameter, ring shell thickness, and the offset of the inner ring to the center of the outer ring wall (core offset). Sensitivity and FOM were found to rely substantially on the nanoring size parameters. The sensing performance map helps to obtain optimized nanoring parameters for the intended spectral range region. The obtained high sensitivity and FOM are much higher than the data available in the literature over visible and NIR ranges. The findings demonstrate the potential of nanorings for biosensing applications. Doi: 10.28991/ESJ-2023-07-04-04 Full Text: PDF

Mdapy: A flexible and efficient analysis software for molecular dynamics simulations

The mdapy is a library for pre- and postprocessing molecular dynamics simulation data. Benefitting from the just-in-time compile technology of TaiChi mdapy can be written in pure Python while possessing similar speed to those written in C++. mdapy is designed with highly paralleled and makes full advantages of modern computer resources on both multicore CPU and GPU architecture. The package implements a fast module to find the neighbors of particles in both free and periodic boundaries, based on which it offers a wide variety of methods to analyze atomic environments, such as standard centrosymmetry parameters, radial distribution function and newer methods, such as atomic entropy fingerprint. In addition, mdapy can be used to create the geometric structure of polycrystals with metallic or graphene grain boundaries by Voronoi diagram. mdapy can directly read the DUMP and DATA format defined in LAMMPS code, and, in practice, it accepts any other format by converting it into NumPy ndarray format. This design philosophy enables seamless integration with abundant scientific ecosystems in the Python community and easy cooperation with other analysis codes like OVITO or freud. Program summaryProgram Title: mdapyCPC Library link to program files:https://doi.org/10.17632/dtdkxvcsc9.1Developer's repository link:https://github.com/mushroomfire/mdapyCode Ocean capsule:https://codeocean.com/capsule/5271472Licensing provisions: BSD 3-clauseProgramming language: Python, C++Nature of problem: Atomic environment analysis and generation of the initial structure are important in molecular dynamics simulations. Many analysis methods relying on particle neighbors, such as radial distribution functions and atomic entropy, are computationally intensive and need to be carefully implemented to scale to large systems. Traditional code is often written in C++ or Fortran to guarantee performance while causing difficulty in installation and secondary development due to the complexity of the programming language.Solution method: mdapy is written in parallel to quickly perform neighbor finding, provides a set of analysis methods and creates an atomic geometry structure on multicore CPU and GPU. Over 95 percent of mdapy is written in Python with a uniform API to call. All data are stored in NumPy ndarray, making users easy to install, use and secondary develop.Additional comments including restrictions and unusual features:1. mdapy provides fast parallel implementations of neighbor finding in periodic and free boundary system.2. mdapy can generate a polycrystalline model with graphene grain boundaries.3. mdapy is helpful for analyzing the melting process by the mean squared displacement and Lindemann index at the atomic level.4. mdapy is very easy to install via pip install mdapy without any compile steps and can be run on Windows, Linux and Mac OS with Python 3.7-3.10.5. mdapy has detailed documentation to make it easier to use.

Phase transformation induced transitional twin boundary in body-centered cubic metals

Phase transformation induced transitional twin boundary in body-centered cubic metals

Corrosion Resistance of 309L Stainless Steel Claddings on Carbon Steel Produced with Wire-Fed Directed Energy Deposition

Additive manufacturing (AM) tools are capable of applying overlay austenitic stainless steel (SS) claddings to carbon steel components. The benefits of this approach over arc welding include a smaller heat-affected zone, residual stress reduction, and material savings. In particular, wire-directed energy deposition is a suitable technique because of its low material cost and high rate of production compared to other AM methods. However, metallurgical variations in composition, phase fraction, and microsegregation can potentially influence the corrosion behavior of such claddings. In this work, 309L SS is clad on carbon steel substrates and electrochemical methods are used to measure their general and pitting corrosion resistance in simulated marine environments (3.5 wt% NaCl solutions). Two-layer claddings are fabricated with four laser powers to understand the effects of bulk chemical composition, austenite/δ-ferrite phase fractions, and individual phase compositions on corrosion behavior. The two-layer claddings are compared to a single-layer cladding, wrought 304 SS, and the carbon steel substrate for a comprehensive assessment of corrosion performance. The two-layer claddings are remarkably resistant to general corrosion in the 3.5 wt% NaCl environment because of their high Cr content (21.6 wt% to 23.3 wt% Cr). The single-layer cladding exhibits localized corrosion at unmixed Fe-rich peninsulas that originate at the dissimilar metal boundary and protrude into the first cladding layer. All two-layer claddings possess higher pitting corrosion resistance than wrought 304 SS, demonstrating their effectiveness as a corrosion-resistant barrier. The pitting corrosion resistance is superior for claddings made with lower laser powers, due to low dilution and greater δ-ferrite contents.

Surface modification of alloys by high-energy pulsed particle beams

The effect of particle beams on the surface of alloys is often used to obtain a material with desired characteristics. Mathematical modeling of such surface modification leads to the study of diffusion in the presence of an intense external source of diffusant. In this case peculiarities in material structure may be of great importance. A special role belongs to inter-grain boundaries in metals, the vicinities of which are regions of accelerated diffusion. Moreover, if the surface treatment by particle beam is carried out with short impulses comparable with relaxation times of diffusion and chemical processes to their equilibrium course, it may be necessary to explicitly consider the particle transfer rate in the material, for example, using the non-classical laws.In this paper we discuss the model of the treatment process by particle beam, which takes into account both the feature of grain boundary diffusion and finiteness of relaxation times of diffusion fluxes in the boundaries and in the volumes of grains. The problem is considered in two-dimensional formulation. The grains and their boundaries are treated as separate phases with different diffusion properties. The grains are represented in the form of rectangles, located at equal distances from each other. The relative size of the boundary phase may vary. Using generalized equations for diffusion fluxes with finite time of relaxation, we come to diffusion equations of hyperbolic type for the volume and the grain-boundary phases. It is assumed that between the diffusant and the treated material a summary chemical reaction occurs with formation of a summary product. A numerical study allowed us for the first time to establish the features of grain-boundary diffusion and to study the dynamics of reaction product formation for treatment times comparable to relaxation times. The effect of pulse duration and grain size on the diffusant concentration distribution for these conditions was investigated.

Thermally activated increase of the average grain size as the origin of resistivity enhancement in NbO2 films grown by pulsed-laser deposition

We investigated $\mathrm{Nb}{\mathrm{O}}_{2}$ thin films grown by pulsed-laser deposition on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$(0001) substrates. Increasing the growth temperature from 700 to $900{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, a clear improvement of the structural quality and the interface abruptness has been observed for the epitaxial films, together with an increase in the average grain size from tens of nanometers to above 100 nm. For achieving high film resistivities, increasing the average grain size is found to be crucial. For a more detailed investigation of the carrier transport characteristics, Raman spectroscopy is demonstrated as a powerful tool. In the case of relatively large grain sizes, we reveal that the film resistivities directly correlate with the carrier concentration in the $\mathrm{Nb}{\mathrm{O}}_{2}$ grains. The results obtained for comparatively small grain sizes can be explained by carrier transport via a percolation mechanism along metallic grain boundaries in accordance with a previously reported model.

Catalytic Activity of Defect-Engineered Transition Me tal Dichalcogenides Mapped with Atomic-Scale Precision by Electrochemical Scanning Tunneling Microscopy.

Unraveling structure-activity relationships is a key objective of catalysis. Unfortunately, the intrinsic complexity and structural heterogeneity of materials stand in the way of this goal, mainly because the activity measurements are area-averaged and therefore contain information coming from different surface sites. This limitation can be surpassed by the analysis of the noise in the current of electrochemical scanning tunneling microscopy (EC-STM). Herein, we apply this strategy to investigate the catalytic activity toward the hydrogen evolution reaction of monolayer films of MoSe2. Thanks to atomically resolved potentiodynamic experiments, we can evaluate individually the catalytic activity of the MoSe2 basal plane, selenium vacancies, and different point defects produced by the intersections of metallic twin boundaries. The activity trend deduced by EC-STM is independently confirmed by density functional theory calculations, which also indicate that, on the metallic twin boundary crossings, the hydrogen adsorption energy is almost thermoneutral. The micro- and macroscopic measurements are combined to extract the turnover frequency of different sites, obtaining for the most active ones a value of 30 s-1 at -136 mV vs RHE.

Charge instability of topological Fermi arcs in chiral crystal CoSi

Topological boundary states emerged at the spatial boundary between topological non-trivial and trivial phases, are usually gapless, or commonly referred as metallic states. For example, the surface state of a topological insulator is a gapless Dirac state. These metallic topological boundary states are typically well described by non-interacting fermions. However, the behavior of topological boundary states with significant electron–electron interactions, which could turn the gapless boundary states into gapped ordered states, e.g., density wave states or superconducting states, is of great interest theoretically, but is still lacking evidence experimentally. Here, we report the observation of incommensurable charge density wave (CDW) formed on the topological boundary states driven by the electron–electron interactions on the (001) surface of CoSi. The wavevector of CDW varies as the temperature changes, which coincides with the evolution of topological surface Fermi arcs with temperature. The orientation of the CDW phase is determined by the chirality of the Fermi arcs, which indicates a direct association between CDW and Fermi arcs. Our finding will stimulate the search of more interactions-driven ordered states, such as superconductivity and magnetism, on the boundaries of topological materials.

Неравномерность микротвердости и микроструктуры малоуглеродистой стали, прокатанной на двухклетьевом прокатно-дрессировочном стане

The relevance of the study is proved by two factors. One of them is the necessity to study the nature of the change in the microstructure of the cross-section of extra-thin tinplate made of TS 435 steel (analogue of 08ps steel) skin-passed in a new DSR-1250 mill of the Miory Metal Rolling Plant. The second factor is the need to develop an effective method for obtaining accurate geometry characteristics of an oblique cut of tinplate 0.19 mm or less thick. The purpose of the work is to determine the changes in microhardness and microstructure over the thickness of tinplate samples and identify the existence of a layer microstructure necessary for this type of flat-rolled products. The study was carried out on the selected samples of tinplate of TS 435 steel 0.19 mm thick. This tinplate was rolled from an annealed strip, 0.224 mm thick. The total magnitude of reduction in the mill was 15 %, and the reduction in the skin-pass stand was at least 3 %. The authors carried out measurements of microhardness at different points over the thickness of the selected tinplate samples. The microhardness values over the strip thickness were averaged using 6th degree polynomial interpolation. To study the grain dimension, a number of microstructure images were taken in various areas over the sheet thickness with ×500 magnification. The microstructure studies showed a pronounced strain microstructure with grains elongated in the direction of rolling. At the very boundary of metal contacting the rolls, the grains received the greatest deformation. The highest values of microhardness were identified in two zones adjacent to both strip surfaces and in the central layers along the strip thickness. The change in the microhardness values along the sheet thickness has a wave-like character with three pronounced zones of increase in hardness and two zones of a decrease in its values. The zones with the lowest microhardness values are located between the zones with the maximum values.

Review on the Solid-State Welding of Steels: Diffusion Bonding and Friction Stir Welding Processes

Solid-state welding (SSW) is a relatively new technique, and ongoing research is being performed to fulfill new design demands, deal with contemporary material advancements, and overcome welding defects associated with traditional welding techniques. This work provides an in-depth examination of the advancements in the solid-state welding of steels through diffusion bonding (DB) and friction stir welding (FSW). Considerable attention was given to DB of steel, which overcame the difficulties of segregation, cracking, and distortion stresses that are usually formed in liquid-phase welding techniques. The defects that affected DB included two types: two-dimensional defects of a metallic lattice, i.e., phases and grain boundaries, and three-dimensional defects, i.e., precipitation. FSW, on the other hand, was distinguishable by the use of relatively low heat input when compared to fusion welding processes such as tungsten inert gas (TIG), resulting in the formation of a limited heat-affected zone. Moreover, fine grain structures were formed in the FSW interface because of the stirring tool’s severe plastic deformation, which positively affected the strength, ductility, and toughness of the FSW joints. For instance, higher strength and ductility were reported in joints produced by FSW than in those produced by TIG. Nevertheless, the HAZ width of the specimens welded by FSW was approximately half the value of the HAZ width of the specimens welded by TIG. Some defects associated with FSW related to the diffusion of elements, such as C/Cr atoms, through the weld zone, which affected the local chemical composition due to the formation of rich/depleted regions of the diffused atoms. Moreover, the lack-of-fill defect may exist when inappropriate welding conditions are implemented. On the other hand, the stirring tool was subjected to extensive wear because of the high hardness values, which negatively affected the economical usage of the FSW process. A summary of the results is presented, along with recommendations for future studies aimed at addressing existing difficulties and advancing the solid-state technology for steel.

STEM/EDS and APT study on the microstructure and microchemistry of neutron irradiated ZIRLOTM

A nanoscale characterization study was carried out on SRA ZIRLO™ at various cycles, aiming to highlight the effect of irradiation-induced alloying element (Sn, Nb, Fe) redistribution on the in-reactor corrosion kinetics. Using a combination of scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), and atom probe tomography (APT) in both oxide and metal, the results confirmed the existence of i) Nb-rich native precipitates and irradiation-induced platelets (IIPs)/nanoclusters in both metal and oxide, and ii) solute segregation to the metal and oxide grain boundaries. One of the most important findings is that the Nb/Zr ratio in the metal solid solution at high burnup is only about 0.2 at.%. All three alloying elements (Sn, Fe, Nb) have segregated to oxide grain boundaries at high burnup. The effects of these microstructural and microchemistry changes in SRA ZIRLO™ on its in-reactor corrosion mechanism are discussed.

Two-dimensional obstructed atomic insulators with fractional corner charge in the MA2Z4 family

According to topological quantum chemistry (TQC), a class of electronic materials has been called obstructed atomic insulators (OAIs), in which a portion of valence electrons necessarily have their centers located on some empty Wyckoff positions (WPs) without atom occupation in the lattice. The obstruction of centering these electrons coinciding with their host atoms is nontrivial and results in metallic boundary states when the boundary is properly cut. Here, on the basis of first-principles calculations in combination with TQC analysis, we propose two-dimensional ${MA}_{2}{Z}_{4}$ $(M=\mathrm{Cr}, \mathrm{Mo}, and \mathrm{W}; A=\mathrm{Si} \mathrm{and} \mathrm{Ge}; Z=\mathrm{N}, \mathrm{P}, \mathrm{and} \mathrm{As})$ monolayers are all OAIs. A typical case is the recently synthesized ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ (${\ensuremath{\alpha}}_{1}\text{\ensuremath{-}}{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$). Although both ${\ensuremath{\alpha}}_{1}$- and ${\ensuremath{\alpha}}_{2}\text{\ensuremath{-}}{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ monolayers are topological trivial insulators, it has valence electrons centering empty WPs and the in-gap corner states at the three vertices of triangle-shaped nanodisk samples respecting ${C}_{3}$ rotation symmetry, which can be explained by the filling anomaly of electrons. In addition, the ${\ensuremath{\alpha}}_{2}\text{\ensuremath{-}}{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ monolayer exhibits unique OAI-induced metallic edge states along the $(1\overline{1})$ edge. The readily synthesized ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ is quite stable and has a large bulk bandgap of 1.94 eV, which makes the identification of these edge and corner states most possible for experimental clarification.

How Sn addition influences texture development in single-phase Fe alloys: Correlation between local chemical information, microstructure and recrystallisation

Sn addition is known to affect the recrystallisation texture development of α -Fe. To date, even though the texture effect of Sn has been experimentally verified, although indirectly, the underlying mechanism has not been studied. In the present study, we focus on the static recrystallisation behaviour of Fe-Si-Sn alloys to elucidate the texture preferences assessing for the effect of Sn solute addition. The experimental approach is based on sequential electron back-scatter diffraction (EBSD) texture analysis complemented with a site-specific chemical analysis of grain boundaries by atom probe tomography (APT). It is directly observed through our experiments that boundary segregation phenomena, which occur at the onset and later stages of recrystallisation, provide crucial understanding of texture development. Especially in the presence of solute, the orientation dependence of the energy stored by deformation largely determines the course of the subsequent recrystallisation. In the Fe-Si-Sn alloy, recrystallisation at the highest stored energy grains is hindered. As a consequence of segregation, {001}〈110〉 orientations recrystallise at later stages of the process, forming predominantly grains with orientations of the { h 11}〈1/ h 12〉 fibre. These grains are suggested to form following an oriented nucleation mechanism, while their growth could be interpreted with Ibe and Lücke's theory of selective growth of 26.5 〈110〉 boundaries in bcc metals. • Sn affecting recrystallization texture evolution; during short annealing times. • Local correlative study with in-situ EBSD and site-specific atom probe tomography. • Key mechanisms discussed; segregation effect on recrystallization nucleation-growth. • Gamma-fibre ({111} <uvw>) recrystallization greatly reduced due to Sn segregation. • Segregation promoting the intensity of {411}<148> recrystallization texture.

Effective Model for Fractional Topological Corner Modes in Quasicrystals.

High-order topological insulators (HOTIs), as generalized from topological crystalline insulators, are characterized with lower-dimensional metallic boundary states protected by spatial symmetries of a crystal, whose theoretical framework based on band inversion at special k points cannot be readily extended to quasicrystals because quasicrystals contain rotational symmetries that are not compatible with crystals, and momentum is no longer a good quantum number. Here, we develop a low-energy effective model underlying HOTI states in 2D quasicrystals for all possible rotational symmetries. By implementing a novel Fourier transform developed recently for quasicrystals and approximating the long-wavelength behavior by their large-scale average, we construct an effective k·p Hamiltonian to capture the band inversion at the center of a pseudo-Brillouin zone. We show that an in-plane Zeeman field can induce mass kinks at the intersection of adjacent edges of a 2D quasicrystal topological insulators and generate corner modes (CMs) with fractional charge, protected by rotational symmetries. Our model predictions are confirmed by numerical tight-binding calculations. Furthermore, when the quasicrystal is proximitized by an s-wave superconductor, Majorana CMs can also be created by tuning the field strength and chemical potential. Our work affords a generic approach to studying the low-energy physics of quasicrystals, in association with topological excitations and fractional statistics.

STUDY OF THE REASONS FOR CORROSION OF METALLIC OIL

Pipeline transport is considered to be the most efficient and economically feasible type, unlike rail, land or other types of transportation. Transported products are usually petroleum products with various physical and mechanical properties that can have various negative effects on the pipeline material, thereby causing corrosion, wear, leakage and emissions. The relevance of research in this direction is due to the fact that due to the relatively complex composition of Kazakhstan's oils during oil pumping, triboelectric effects at the phase interface cause the occurrence of electric charges, which lead to an increase in the efficiency of chemical reactions that cause corrosion of the pipeline material. Therefore, it is necessary to develop specific ways to protect oil pipelines from damage caused by metal corrosion. IR spectroscopic analysis of oil shows the presence of various types of hydrocarbons. Based on the oil dispersal of JSC Ozenmunaigas, the complexity in the molecular composition of oil causes electrical effects that lead to an increase in the corrosion rate. All this should be taken into account when developing corrosion protection. In the process of transportation in the volume of oil and petroleum products, due to the complex microstructure and certain heterogeneity of the macrostructure, electrostatic charges can be formed. Since electrification and heat generation occur during tribolytic effects, these processes require refinement of heat transfer processes at the micro-macro level. In this case, the potential difference between individual sections of the liquid volume can be quite large. Chemical and physico-chemical methods of instrumental analysis were used in the work. In this work, experimental values of the specific electrical conductivity of oil and petroleum products were obtained under laboratory conditions, which allow us to judge their dielectric nature. In this work, the triboelectric effect was studied at the site of the boundary of metals and organic liquids (oil, fuel oil, etc.) to determine their effect on the corrosion of pipeline metals. and the values of electrical conductivity of oils and petroleum products are established.

Casimir boundaries, monopoles, and deconfinement transition in ( 3+1 )- dimensional compact electrodynamics

Compact U(1) gauge theory in ($3+1$)-dimensions possesses the confining phase, characterized by a linear raise of the potential between particles with opposite electric charges at sufficiently large interparticle separation. The confinement phenomenon is generated by condensation of Abelian monopoles at strong gauge coupling. We study the properties of monopoles and the deconfining order parameter in zero-temperature theory in the presence of ideally conducting parallel metallic boundaries (plates) usually associated with the Casimir effect. Using first-principle numerical simulations in compact U(1) lattice gauge theory, we show that as the distance between the plates diminishes, the vacuum in between the plates experiences a deconfining transition. The phase diagram in the space of the gauge coupling and the interplane distance is obtained.

Disconnection-mediated motion of 〈110〉 tilt grain boundaries in α -Fe

It is possible for $\ensuremath{\langle}110\ensuremath{\rangle}$ tilt grain boundaries (GBs) in bcc metals to perform a conservative displacement by the glide of intrinsic GB line defects, namely, disconnections. The paper presents the characteristic of these defects in ${112}$ and ${332}$ twin boundaries, their vicinal GBs, and the ${116}$ GB studied by molecular dynamics simulation. The sources of disconnections and their interaction with the other GB dislocations are described together with their role in the shear-coupled GB migration. The absence of gliding disconnections in the ${111}$ GB impedes the shear-coupled GB migration, but two pure shuffles inside the coincident site lattice unit facilitate the transformation of the ${111}$ GB into ${110}/{001}$ or ${110}/{112}$ facets in regions of concentration of stresses.

The physical origin of observed repulsive forces between general dislocations and twin boundaries in FCC metals: An atom-continuum coupling study

• The intrinsic interaction between a dislocation and a twin boundary (TB) is investigated with an accurate atom-continuum coupling model. • The dependence of dislocation-TB interaction on Burgers vectors of dislocations is investigated. • The long-range interaction between a TB and a general dislocation is proven to be negligibly weak compared to the interaction between dislocations. • It is shown that experimentally observed repulsion to dislocations from TBs is actually from dislocation-type defects on TBs. • Previously proposed or adopted interaction laws between dislocations and TBs are conceptually unified in a framework. The combination of ultrahigh strength and excellent ductility of nanotwinned materials is rooted in the interaction between dislocations and twin boundaries (TBs). Quantifying the interaction between TBs and dislocations not only offers fresh perspectives of designing materials with high strength and ductility, but also becomes the cornerstone of multiscale modeling of materials with TBs. In this work, an atom-continuum coupling model was adopted to quantitatively investigate the interaction between dislocations and TBs. The simulation shows that the dislocation–TB interaction is much weaker than the interaction between dislocations at the same distance. Simulation of the early stage of dislocation pileups further verifies that the experimentally observed repulsive forces are essentially from the dislocations or kink-like steps on TBs. The interaction between TBs and dislocations with different Burgers vectors was demonstrated referring to the elastic theory of dislocations. With the intrinsic interaction between dislocations and TBs being clarified, this work will promote further development of the multiscale simulation methods, such as discrete dislocation dynamics or phase-field method, of materials with TBs by providing a quantitative description of the interactions between TBs and dislocations.