Twin Spacing Research Articles

Effect of rolling temperature on microstructure evolution and mechanical properties of high carbon high manganese steel

The effects of rolling temperature ranging from −55 to 300 °C on dislocation density, twinning behavior and correlative tensile properties of a high carbon high manganese steel were investigated. Results showed that the twinning behavior was enhanced at −55 °C but suppressed at 300 °C. The twin thickness and spacing increase with the rolling temperature. At low rolling reduction of 10%, the dislocation multiplication rate decreased with the increase in rolling temperature. However, the dislocation multiplication rate maintained high level when rolled at high rolling reduction and high temperature. At a given rolling reduction, the samples rolled at −55 °C possessed higher work hardening rate. Especially, the strength of −55°C-rolled-20% sample was higher than that of 300°C-rolled-30% sample and was equivalent to room temperature (RT)-rolled-30% sample. Concurrently, the elongation of the −55°C-rolled-20% sample was higher than the other two. The contributions of dislocation strengthening and twin strengthening to the yield strength of high carbon high manganese steel after rolling at different conditions were calculated by the parameter model. The dislocation strengthening effect played a dominant role under various deformation conditions. Twin strengthening effect showed a temperature sensitivity in the temperature range selected in the present study. Lower rolling temperature showed greater contribution of twin strengthening, whereas the dislocation strengthening effect was insensitive to temperature.

Effects of substrate bias on the sputtering of high density (111)-nanotwinned Cu films on SiC chips

This article presents a study of the influence of the substrate bias on the microstructure, preferred orientation, and mechanical and electrical properties of nanotwinned Cu film. The formation of a nanotwinned structure and (111) surface orientation can be properly controlled by applied substrate bias. High density nanotwinned structures were introduced into Cu films sputtered on SiC substrates with over 90% of (111)-orientation at − 150 V. Densely packed Cu nanotwins were observed within the columnar grains stacked up on each other along the film growth direction, with an average twin spacing of 19.4 nm. The Cu films deposited on SiC substrate via bias sputtering had surface roughness of 8.6 to 15.8 nm. The resistivity of the copper nanotwinned films sputtered with various substrate biases varied. The optimal indentation, 2.3 GPa, was found in the nanotwinned Cu film sputtered with a bias voltage of − 150 V. The effects of Ar ion bombardment on microstructure, surface morphology and properties are further discussed.

In situ study on radiation response of a nanotwinned steel

Recent radiation studies on nanotwinned pure metals suggest that twin boundaries are appealing defect sinks, as they can transport and eliminate radiation-generated defects. However, radiation response of twin boundaries in nanotwinned steels is less well understood. Here, we investigate the microstructural evolution of a nanotwinned steel using in situ Kr++ irradiation to 4 dpa at ambient temperature. The in situ results show that nanoscale deformation twins in steels can effectively suppress the formation of ordered dislocation loop rafts. Furthermore, the formation of dislocation loop rafts and Frank loops depends prominently on twin spacing. The underlying mechanisms of the enhanced radiation resistance are discussed. The present study makes a positive step forward for the potential application of nanotwinned structural steels to nuclear reactors.

In situ thermal-microstructure characterization of a phase-transforming alloy satisfying cofactor conditions

We establish an experimental platform to combine the differential scanning calorimetry (DSC) with an in situ observation of microstructure by differential interference contrast microscope (DInM). We carry out the experiment on a phase-transforming alloy Au31Cu24Zn45 that closely satisfies the cofactor conditions - the strongest crystallographic compatibility constraints between phases. We confirm that the phase formation events observed by DInM agree well with the heat exchange profile characterized by DSC. We also observe different morphology of twins evolves differently, depending on the twin spacing. Through the quantitative analysis of various morphological domains in the temporal space, we discover that the scaling law between the twin evolution time and the fineness is linear, by which the characteristic transformation time for single variant martensite can be determined for this compatible martensite alloy as 0.636s.

Hierarchical equations of motion approach to hybrid fermionic and bosonic environments: Matrix product state formulation in twin space.

We extend the twin-space formulation of the hierarchical equations of motion approach in combination with the matrix product state representation [R. Borrelli, J. Chem. Phys. 150, 234102 (2019)] to nonequilibrium scenarios where the open quantum system is coupled to a hybrid fermionic and bosonic environment. The key ideas used in the extension are a reformulation of the hierarchical equations of motion for the auxiliary density matrices into a time-dependent Schrödinger-like equation for an augmented multi-dimensional wave function as well as a tensor decomposition into a product of low-rank matrices. The new approach facilitates accurate simulations of non-equilibrium quantum dynamics in larger and more complex open quantum systems. The performance of the method is demonstrated for a model of a molecular junction exhibiting current-induced mode-selective vibrational excitation.

Strain hardening behavior and microstructure evolution of gradient-structured Cu-Al alloys with low stack fault energy

Nanocrystallization can significantly improve the strength and hardness of metallic materials, but usually sacrifice ductility due to low work hardening capability. Heterostructured materials are an emerging class of materials with superior performances, because of their outstanding work hardening capability. In this work, a type of heterostructured material, a gradient structured Cu-Al alloy, was produced by surface mechanical attrition treatment (SMAT) at liquid nitrogen temperature. After SMAT processing, the yield strength was increased to more than 1.5 times, and the ductility remained almost unchanged. In conjunction with hetero-deformation induced (HDI) hardening, stacking fault energy is another important factor to increase the strain hardening in the system. Low stacking fault energy increased the density of stacking fault, and led to a finer spacing of nano twins (∼5.4 nm) and higher dislocation storage (8 × 1013 m−2) in the SMATed Cu-Al alloy at the intermediate strain stage. A significant up-turn of strain-hardening rate was also induced by low stacking fault energy.

Effect of Electroplating Current Density on Tensile Properties of Nanotwinned Copper Foils

In this study, nanotwinned copper (nt-Cu) foils were fabricated using a rotary electroplating system. Their microstructures (orientation, grain size, and twin spacing) and correlated tensile properties were substantially tuned by manipulating the electroplating current density. The nt-Cu foils were further heat-treated at 150 °C for 1 h and tensile-tested to characterize their thermal stability. We found that the mechanical properties of the nt-Cu foils are directly associated with the electroplating current density. The ultimate tensile strength (UTS) increases with increasing in the current density, reaching the maximum values at 25 ASD. The great enhancement can be attributed to the decrease in twin spacing and grain size. We also discovered that the UTS and ductility remain approximately intact under a high temperature, indicating the excellent thermal stability of such nt-Cu foils.

Effect of Twin Boundary Density on Mechanical Behavior of Al0.1CoCrFeNi High-Entropy Alloy by Molecular Dynamics Simulation

Molecular dynamics simulation method was used to study the influence of co-lattice twin boundary (TB) spacing on the deformation behavior of Al0.1CoCrFeNi high-entropy alloy single crystal under uniaxial tension. Studies have shown that there is a “critical distance” between the twin boundaries, and the sensitivity of the two sides to the change of the twin spacing is different, and the influence of the evolution of the deformation mechanism of the different twin spacing is analyzed from the number of defects and the evolution of the dislocation density. The results show that as the distance between twins decreases, the deformation mechanism gradually transforms from dislocation slip accompanied by defects, such as stacking faults and secondary twins, to a deformation mode of amorphous phase transition. The research aims to provide guidance and reference for the design of high-performance high-entropy alloys.

Dislocation re-emission induced staged work hardening in graphene-nanotwin reinforced Cu: A molecular dynamics simulation study

Graphene and nanotwins are two effective reinforced microstructural features to achieve improved mechanical properties of metallic composites, while the two features are generally applied separately. In this study, graphene/nano-twinned Cu nanocomposites models with different arrangement of the graphene and twin boundaries were designed by using molecular dynamics (MD) simulations, and the dislocation processes and the interactions between dislocation and graphene/twin were simulated and investigated. The simulation results indicated the arrangement of graphene and nanotwin affects the work hardening behaviors in the graphene/nano-twinned Cu composites, i.e., two staged work hardening behavior corresponded to cyclic process of dislocation hindrance-absorption-reemission in the model with relatively small twin spacing and twin-graphene spacing, while the work hardening dominated by dislocation intersection and multiplication occurred in the model with large twin-spacing. The simulation provided herein demonstrated that the special arrangement of graphene and nanotwins led a way to tailoring the mechanical properties of metallic composites with various work hardening behaviors. Graphical abstract Highlights 1. Dislocation reactions between twins and graphene were simulated and analyzed. 2. Twin-graphene distance and the twin distance play key roles in the reaction. 3. The mechanism corresponding to work hardening changes in the limited two distances.

Effect of Twin Spacing on the Mechanical Behavior and Deformation Mechanism of Nanotwinned Al

Effect of Twin Spacing on the Mechanical Behavior and Deformation Mechanism of Nanotwinned Al

Formation of High Density ⟨111⟩ Textured Nanotwins in Evaporated Ag Thin Films Through Post-Deposition Ion Bombardment

For the production of Ag thin films containing a high density of nanotwins, evaporated Ag films were bombarded with an Ar+ ion beam with voltage of about 0.1 KeV. After the post-evaporation ion bombardment for 15 min, the equiaxial coarse grains in the surface region of the originally as-evaporated Ag films transformed into slender nanotwinned columns containing a highly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\langle 111\rangle $ </tex-math></inline-formula> textured nanotwinned structure with very thin twin spacing of about 8.6 nm. The nanotwinned columns increased with extension of the ion bombardment time to 30 min. The appearance of (111)-oriented fine grains in top-view electron backscatter diffraction (EBSD) images confirmed the high density of Ag nanotwins. Meanwhile, the roughness of the thin films increased after ion bombardment of the evaporated Ag films. Finally, a mechanism of nanotwin formation based on stress relaxation in evaporated Ag films through post-deposition ion bombardment is proposed.

A gradient Eshelby force on twinning partial dislocations and associated detwinning mechanism in gradient nanotwinned metals

It is well known that the driving force on dislocation glide is the Peach-Koehler force which is proportional to the resolved shear stress on the slip plane. Here, we report a type of configurational force, referred to as the gradient Eshelby force, that can drive the motion of twinning partial dislocations on twin boundaries (TBs) in the absence of any resolved shear stress and cause detwinning in gradient nanotwinned (GNT) metals, an emerging class of multiscale metallic materials with exceptional mechanical properties and novel deformation mechanisms. Specifically, we consider the Eshelby-force-driven motion of twinning partial dislocations and associated detwinning mechanism in GNT metals made of preferentially oriented TBs and columnar grain boundaries (GBs) with spatially varying twin spacing and grain size. Large-scale molecular dynamics simulations validate the proposed Eshelby-driven detwinning mechanism, where twinning partial dislocations are nucleated from GBs and glide on TBs near the region with the steepest local gradient, leading to extensive TB migration and twin annihilation. This study demonstrates the important role of Eshelby force in controlling twinning partial glide and TB migration in GNT metals, which may have broad implications on plastic deformation in gradient nanostructured metals.

Tuning the strength-ductility synergy of nanograined Cu through nanotwin volume fraction

Nanograined (NG) metals with nanotwinned (NT) regions can overcome the inferior ductility of NG metals and achieve high strength and modest ductility. Based on the strain gradient plasticity and Johnson–Cook failure criterion, we simulate the dependences of their strength and ductility on volume fraction, twin spacing, as well as shape and distribution of NT regions in NG Cu. It is found that these factors have significant impact on the overall ductility. In particular, the overall ductility abnormally decreases with the increase in the volume fraction of NT regions, which is directly related to the failure modes of this material system. Interface debonding can explain the above abnormal decrease in overall ductility. In addition, with the increase in twin spacing, fracture of NT regions can cause different reversals of overall ductility. We also found that, when the NT regions are of the oblique square type, the overall ductility is significantly lower than when they are of the circular and square types. In most cases, the array arrangement of NT regions is superior to the staggered arrangement for the improvement of the overall ductility. It is believed that these reported results can contribute to a deeper understanding of this novel material system.

Evaporation of Ag Nanotwinned Films on Si Substrates With Ion Beam Assistance

High-density Ag nanotwinned films with a very thin twin spacing of about 6.05 nm have been deposited by electron beam evaporation for the first time. With ion beam assistance, Ag thin films with a highly <111> textured structure can be deposited on Si substrates pre-coated with Ti/Ag (111) seed layers. In contrast, the Ag films deposited without ion beam assistance exhibit mostly fine grains with about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.8~\mu \text{m}$ </tex-math></inline-formula> grain size and random annealing twins. The nanotwinned Ag films have a nanoindentation hardness of 1.23 GPa, about five times higher than that of Ag films deposited without ion beam assistance. For the mechanism of enhancing nanotwin formation in Ag films deposited with ion beam assistance, the energy and stress perspectives are both discussed. The formation of Ag nanotwins is ascribed to sufficient stress induced by ion bombardment under suitable parameters, which leads to the generation of twinning partial dislocations, formation of twin boundaries, and release of strain energy.

Automated Container Terminal Production Operation and Optimization via an AdaBoost-Based Digital Twin Framework

Digital twin (DT), machine learning, and industrial Internet of things (IIoT) provide great potential for the transformation of the container terminal from automation to intelligence. The production control in the loading and unloading process of automated container terminals (ACTs) involves complex situations, which puts forward high requirements for efficiency and safety. To realize the real-time optimization and security of the ACT, a framework integrating DT with the AdaBoost algorithm is proposed in this study. The framework is mainly composed of physical space, a data service platform, and virtual space, in which the twin space and service system constitute virtual space. In the proposed framework, a multidimensional and multiscale DT model in twin space is first built through a 3D MAX and U3D technology. Second, we introduce a random forest and XGBoost to compare with AdaBoost to select the best algorithm to train and optimize the DT mechanism model. Third, the experimental results show that the AdaBoost algorithm is better than others by comparing the performance indexes of model accuracy, root mean square error, interpretable variance, and fitting error. In addition, we implement empirical experiments by different scales to further evaluate the proposed framework. The experimental results show that the mode of the DT-based terminal operation has higher loading and unloading efficiency than that of the conventional terminal operation, increasing by 23.34% and 31.46% in small-scale and large-scale problems, respectively. Moreover, the visualization service provided by the DT system can monitor the status of automation equipment in real time to ensure the safety of operation.

A crystal plasticity model for metal matrix composites considering thermal mismatch stress induced dislocations and twins

Originated at heterogeneous interfaces with distinct coefficient of thermal expansion (CTE), thermal mismatch stress is one of the critical influential factors to mechanical properties of metal matrix composites (MMCs). This stress is normally accommodated plastically by various defects, for example, high-density dislocations and twins in Al near heterogeneous interfaces in SiC/Al composites. Basic knowledge on the influence of defect characteristics is important but difficult to extrapolate from experimental results. However, existed theoretical models more focus on the influence of dislocation density, but less focus on defects variety, volume and distribution. In this paper, we propose a physics-based crystal plasticity model that has the capability of dealing with thermal mismatch stress induced dislocations and twins (denoted as TMDT model). The proposed TMDT model that is implemented in the Visco-Plastic Self-Consistent (VPSC) method considers defect heterogeneous distribution (gradient range), defect type (dislocations vs. twins) and defect volume fraction (twin spacing vs. twin volume). We demonstrate the validity and the capability of the VPSC-TMDT model in SiC/Al composites with thermal mismatch induced dislocations or twins. Furthermore, this model predicts the ultra-high strength of Graphene/Copper composites with high-density nanoscale twins, which is in turn the future aim for such nanocomposites.

Reinforced Cu precipitation strengthening by matrix transformation from martensite to austenite in high-strength low-alloy steel

We demonstrate here that a new type of Cu precipitation was observed in metastable austenite (γ′). The Cu precipitates had twin boundaries, array of atoms, dislocations with a large lattice misfit (~3.4 %) and close packed plane misfit (~5.4°) with matrix γ'. This was accomplished by partitioning and tempering heat treatment in a 0.117C-2.88Mn-1.13Ni-0.89Cu steel. Cu precipitation and austenitization occurred together during tempering, and Cu precipitates were nucleated in martensite, which subsequently migrated to austenite during austenitization. In view of the closed crystal relationship of martensite/Cu precipitate and martensite/austenite, crystal relationships between Cu, austenite and martensite were: {111}Cu//{111}γ'//{011}α, <011>Cu//<011>γ'//<111>α. Misfit between one pair close-packed plane (1–11)Cu and (1–11)γ' was inherent from the misfit between martensite and austenite. Twin boundaries (twin spacing ~2.5 nm) were inherent from twin boundary of 9R–Cu in martensite. The matrix transformation from martensite to austenite compressed the Cu precipitates, and contributed to lattice misfit and defects in Cu precipitate. The misfit and defects in Cu precipitates provided significant strengthening effect for γ′ and contributed to the excellent mechanical properties of the experimental steel. The mechanism of Cu precipitation was studied using 3DAP, HRTEM and thermodynamic simulation.

Microstructures and mechanical properties of (CoCrFeMnNi)100-xMox high entropy alloy films

The effects of Mo addition on the microstructures and mechanical properties of CoCrFeMnNi high entropy alloy films (HEAFs) were studied in this work. To achieve this, a series of (CoCrFeMnNi)100-xMox HEAFs was prepared by magnetron co-sputtering. The films were FCC without Mo addition and composed of FCC and HCP structures with minor Mo addition. With the further increase in Mo content, the films transformed to an amorphous structure. Nanoindentation revealed an initial decrease in hardness and then increase with the increasing Mo content. While the initial decrease in hardness could be attributed to the detwinning-induced softening for films with small twin spacing as observed by TEM after micropillar compression, the subsequent increase could be attributed to solid solution strengthening and formation of nanotwins with larger twin spacing and no detwinning observed after compression. Using scratch tests, the Mo-doped HEAFs exhibited a high hardness, good wear resistance and low coefficient of friction. The results of micropillar compression tests showed the increasing compressive yield strength and the decreasing fracture strain with the increasing Mo content. When x = 4.9, the film revealed the optimum mechanical properties with fracture strength of 6.51 GPa and little reduction in ductility.

Molecular dynamics study on the fracture mechanism in bimodal nanotwinned Cu with a composite structure

Utilizing molecular dynamics simulations, the authors investigate the notion of bimodal nanotwinned (NT) microstructure in strength-ductility trade-off. Using a coarse circular grain with twins embedded in a sea of nano-grains (without twins) as a surrogate, the paper explores three scenarios pertaining to the strength and failure strain mapping: (i) the effect of twin boundary (TB) inclination; (ii) the effect of coarse-grain size; (ii) the effect of twin boundaries spacings (TBSs). The central result is that there exists an optimum grain size at which the strength and failure strain are simultaneously improved. Meanwhile, the fracture mechanisms of bimodal NT microstructure are demonstrated by analyzing dislocation-TB interactions, which involve TB migration, deformation twinning, void generation, etc.

Effect of twin boundary on mechanical behavior of Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy by molecular dynamics simulation

The high-entropy alloys break through the traditional alloy structure and present unique and superior mechanical properties. However, the potential deformation mechanism of high-entropy alloy, which is regarded as a new member of alloy families in recent years, needs to be further investigated. In this paper, the mechanical properties of the nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy under tensile loading are studied by molecular dynamics simulation, and the effect of twin boundary on the deformation behavior of nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy is studied on an atomic level. The results show that the yield strength of the nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy increases with twin boundary spacing decreasing, presenting a Hell-Petch relationship. However, there is a critical value of the twin boundary spacing, which makes the sensitivity of the yield strength of the high-entropy alloy to the twin boundary spacing change significantly before and after this value. The results also indicate that the deformation mechanism of nano-twin Cr&lt;sub&gt;26&lt;/sub&gt;Mn&lt;sub&gt;20&lt;/sub&gt;Fe&lt;sub&gt;20&lt;/sub&gt;Co&lt;sub&gt;20&lt;/sub&gt;Ni&lt;sub&gt;14&lt;/sub&gt; high-entropy alloy changes from dislocation slip to amorphous phase transition with the decrease of twin boundary spacing. The research results of this paper have a certain reference value and guidance significance for designing and preparing high-performance high-entropy alloys.