Twin Modes Research Articles

Rotational deformation twins in a HfNbTaTiZr refractory high entropy alloy

Results of the analysis of deformation twins formed in a HfNbTaTiZr refractory high entropy alloy during compression deformation at 20 °C – 600 °C are reported. All studied twins were formed by rotation of the matrix crystal lattice around a 〈110〉 pole and have the common reciprocal twinning plane K2 = {001} and reciprocal twinning direction η2 = <11¯0>. At the same time, the twinning plane K1 and direction η1 depend on the degree of rotation of K2 and η2 around the common 〈110〉 pole. The following rotational twinning modes have been identified in HfNbTaTiZr: {11¯4}<22¯1¯> (38.94° rotation), {11¯5}<55¯2¯> (31.58°), {11¯6}<33¯1¯> (26.54°), {11¯7}<77¯2¯> (22.84°), and {11¯8}<44¯1¯> (20.04°). A rotational mechanism of twinning, with the rotation axis 〈011〉 or 〈001〉, is proposed as an alternative to the commonly accepted shear mechanism.

Influence of grain size on twinning behavior of WE43 magnesium alloy during room-temperature compression deformation

In the present study, room-temperature compression experiments and characterization experiments via optical microstructure (OM), X-ray diffractometer (XRD) and electron backscattered diffraction (EBSD) techniques were conducted on WE43 magnesium (Mg) alloy samples to investigate the grain size effect on twinning behavior. Three couples of solution treatments (823 K for 0.5 h, 798 K for 8 h, 823 K for 16 h, followed by water-quenching at ⁓333 K) were adopted and these solutionized samples are with different grain sizes of 48.5, 72.0 and 120.2 μm, respectively. Results show that {10-12} extension twin (ET) and {11-21} ET serve as major twinning modes during plastic deformation. For all 7.7%-deformed samples, although the volume fractions of {10-12} ETs and {11-21} ETs increase with the increasing grain size. {10-12} ETs are in growth stage, while {11-21} ETs are mainly in nucleation stage and they still maintain narrow and parallel to each other. Besides, {10-12} ETs mainly contribute to the rotation of c-axes of grains towards compression direction, while {11-21} ETs mainly contribute to the formation of a nearly ring-shaped texture component in (0002) pole figure. Twin variants analysis with the assistance of Schmid factor (SF) demonstrates that the activation of twin variants mainly obeys Schmid law. When only {10-12} ETs occur in individual grains, the maximum number of twin variants shows some positive relationship with the increasing grain size. By comparison, when both {10-12} ETs and {11-21} ETs occur in individual grains, the maximum numbers of twin variants are rarely influenced by the increasing grain size.

Insight into double twinning behavior of Mg–Gd rolled alloy at the nano scale: Role of micro-texture entropy

101¯1}− {101¯2} double twinning is a classical twinning mode with diverse variants in magnesium and its alloys. However, its variant selection criterion and its influence on the mechanical behaviors are still in debate. In this study, we proposed a view of micro-texture entropy to elucidate the double twinning behavior during large strain rolling of Mg–1.5Gd (wt%) alloy. Combined with the high spatial resolution scanning electron microscopy-transmission Kikuchi diffraction (SEM-TKD) technique, the detailed microstructure and micro-texture of the double twins in early stage of evolution were detected, and new insight into the variant selection and evolution of double twins was obtained. The observations suggest that the nucleation events of different double twin variants are influenced by their micro-texture entropy, the variants with lower micro-texture entropy are preferred. While the growth stage of double twins is affected both by their micro-texture entropy and the geometric factors between the primary and secondary twin systems; the former will influence their growth potential and the later can affect their growth space. A novel {101¯1}− {101¯3} double twin was also triggered to release the high local stress concentration during large strain rolling process.

Evolution of Microstructure and Crystallographic Texture in Deformed and Annealed BCC Metals and Alloys: A Review

Dislocation slips, twinning, shear banding (SBs), strain localization, and martensite formation are a few deformation modes that are activated in BCC metals and alloys. Strain, strain rate, and deformation temperature are other parameters that determine the activation of deformation modes in BCC alloys. This review focuses on several BCC alloys, such as beta-titanium (β-Ti), tantalum (Ta), and ferritic stainless steels (FSSs), all of which exhibit differences in deformation behavior. These alloys often undergo thermo-mechanical processing (TMP) to enhance their mechanical properties. TMP leads to the evolution of deformation-induced products, such as SBs, strain-induced martensite (SIM), strain localizations, and mechanical/deformation twins (DTs) during plastic deformation, while also influencing crystallographic texture. The deformation modes in β-Ti depend upon the stability of the β-phase (i.e., β-stabilizers); low-stability alloys show the formation of SIM along with slips and twins, whereas in highly stable β-Ti alloys, only slip+twin modes are observed as the primary deformation mechanisms. In the case of Ta, slip activity predominantly occurs on {110} planes, but it can also occur on planes with the highest resolved shear stress. The breakdown of Schmid’s law or non-Schmid behavior for Ta and Ta-W alloys has been discussed in detail. The cold rolling (CR) of FSSs results in the formation of ridges, which is an undesirable phenomenon leading to very low formability. The microstructures of the rolled sheets consist of elongated ferrite grains with in-grain SBs, which are preferentially formed in the γ-fiber-oriented grains. The formation of finer grains after recrystallization improves both the mechanical properties and ridging resistance in FSS. Therefore, this review comprehensively reports on the impact of TMP on the microstructural and crystallographic texture evolution during the plastic deformation and annealing treatment of β-Ti, Ta alloys, and FSSs in BCC materials, using results obtained from electron microscopy and X-ray diffraction.

The anisotropy of deformation twinning in bcc materials: Mechanical loading, temperature effect, and twin–twin interaction

By integrating atomistic simulations with theoretical calculations, we investigate the prevalence of {112} deformation twins in bcc materials and their sensitivity to the loading direction as well as temperature. Our atomistic simulations reveal the copious occurrence of {112} twins involving either hcp or fcc intermediate phases. The hcp and fcc cases occur in bcc titanium alloy during [100] compression and tension, respectively. Similarly, they can also manifest in bcc iron under different temperature conditions. Furthermore, by calculating the correspondence matrix, we identify the fcc and hcp cases as the normal deformation twin mode and the 1/2 atoms-shuffle mode, respectively. The twinning modes have a significant influence on twin–twin interactions and the final microstructure. Our theoretical calculation confirms that the selection of specific twin modes and twin variants is governed by the correlation between their deformation path and mechanical loading. The results underscore the crucial role of mechanical loading and temperature in activating the specific twin modes, thereby providing a novel avenue for engineering twin microstructures through carefully designed thermomechanical processing techniques.

180 Personalized approach to predict twin mode of delivery

180 Personalized approach to predict twin mode of delivery

Orientation effect on twin formation mechanisms of tungsten under uniaxial tension/compression

The orientation effect on the twin formation mechanism of body-centered cubic tungsten nanopillars was systematically investigated by molecular dynamics simulation. The simulation results reveal that anti-twins grow by the two-layer-by-two-layer staggered-shuffle mechanism. Tungsten nanopillars with their orientations close to [001] in the standard stereoscopic triangle are dominated by the twinning (anti-twinning) mode under tension (compression). On the contrary, tungsten nanopillars with their orientations close to the edge of [101]-[111] are dominated by the anti-twinning (twinning) mode under tension (compression). Tungsten nanopillars with their orientations in the center region of the standard stereoscopic triangle are dominated by twinning mode under both tension and compression. The above simulation results were discussed and well explained in terms of the Schmid factor and energy. The present work will extend our knowledge about the twin formation mechanism of body-centered cubic metals.

Efficient numerical strategies for an implicit volume fraction transfer scheme for single crystal plasticity including twinning and secondary plasticity on the example of magnesium

AbstractIn this work an efficient algorithm for a fully implicit single crystal plasticity routine including twinning and secondary plasticity is presented and implemented for the example of magnesium. The material model uses the volume fraction transfer scheme for the evolution of twinning, that is, plastic slip in newly formed twins (“secondary plasticity”) is resolved. This is considered particularly important, if the volume fractions of some twins reach the order of magnitude of the parent phase. However the resolution of secondary plasticity also implies a large number of unknowns, which is significantly reduced by a newly proposed algorithm. For magnesium a hardening model based on basal, prismatic, pyramidal a and pyramidal c+a slip modes as well as a tension and a compression twinning mode and yields a total of 18 slip systems and 12 twinning systems. As a special feature of the proposed algorithm, the total amount of 246 unknowns, due to simultaneous slip in the parent phase and the twinned phases, is reduced to only 31 unknowns. Additionally, thermodynamic consistency is ensured by including the second law with the Clausius–Duhem equation, which considers the change of free energy upon twinning as an additional driving force for twinning. Further, the setup of the time discrete nonlinear equation system using midpoint rule, as well as the analytical solution of the algorithmic tangent are given in detail. Finally, the implemented model is tested in finite element simulations and compared to single‐ and polycrystal compression and tension experiments.

Twinning induced spatial stress gradients: Local versus global stress states in hexagonal close-packed materials

Length scale dependent microstructural heterogeneities serve as effective pathways in engineering materials for providing simultaneous strength-ductility enhancement. In this regard, hexagonal close-packed (hcp) materials that exhibit a combination of slip and multiple twinning modes potentially act as ideal candidates that generate heterogeneous microstructures. However, such an inhomogeneous distribution of crystallographic defects also results in build-up of spatially heterogeneous local stress gradients that can be distinct from globally applied stress state. In particular, stress fields arising at the vicinity of deformation twins and due to their interaction with grain interfaces often act as precursors to damage nucleation in most hcp metals and alloys. Hence, assessment of such local stresses and their overall impact on plasticity becomes necessary in order to understand the relationship between twinning and fracture in hcp materials. The current work utilizes commercially pure titanium (cp-Ti) as a model material to investigate the impact of twinning induced stress gradients on the local mechanical response. By means of correlative multiscale structural characterization and local stress gradient measurements, we establish a definitive relationship between applied stress vis-à-vis local stress on the local plasticity behavior ahead of a {112¯2} compression twin-grain boundary intersection in cp-Ti. Additionally, the role of twin interfacial structure for tension and compression twinning modes are experimentally determined and their corresponding impact on the local stress fields and associated twin migration mechanisms is assessed.

Numerical investigation of buckling behavior of dented lined pipe under bending

The mechanically lined pipe, which consists of a carbon steel carrier and a thin-walled corrosion-resistant alloy liner, has proved to be a practical way to prevent the pipeline from internal corrosion. However, the local dent caused by third-party falling objects severely threatens the integrity of the lined pipe, especially the more fragile liner. This work investigates the influence of a local dent on the plastic responses and stability of a lined pipe system during bending. After validation of the numerical framework with the experimental results of a 12-inch lined pipe, the indentation and bending responses of two typical scenarios, namely, TDI and LDI, are examined. It is found that the liner could maintain a certain moment level after reaching the maximum instead of collapsing promptly. Furthermore, classic diamond buckling mode is observed in the TDI case, while the LDI case exhibits a twin triangular-shaped buckling mode. In addition, extensive parametric studies regarding important variables of the full-scale problem are performed. Amongst other findings, the buckling and collapse of the dented lined pipe are found to be affected by the orientation of the dent, which should be taken into account for practical dent evaluation.

The complexity of [formula omitted] twin interface structure and energetics in HCP materials

The quest for a deeper understanding of the mechanical properties of HCP alloys has been an ongoing effort. Due to the lack of a sufficient number of slip systems, twin nucleation and migration originate as a substantial plastic deformation mechanism in HCP metals. The paper uncovers the energetics and atomistic mechanism of the {112¯1}〈112¯6〉 which is one of the most prominent twin modes in HCP materials that has not been fully understood. In view of corrugated {112¯1}interfaces, the positioning of lattice/motif atoms needs to be clarified. First, we establish the initial twin boundary (TB) structure unambiguously via the lattice offsets resulting in volume invariancy and correct relative positioning of the twin variants. Secondly, the TB migration mechanism is determined from a crystallographic (zero net shuffle, Σs→=0) and energetic standpoints (minimum energy path). The Generalized Planar Fault Energy (GPFE) curves are calculated for Ti, Hf, Mg, and Zr. Such GPFE curves for this twin mode are calculated for the first time, and point to unusually high unstable energies (300-850 mJ/m2), and low migration barriers (<60 mJ/m2) for twinning accompanied with large shuffle magnitudes, |s→|, comparable to the Burger's vector (|s→|≅be>0.44Å).

UTILIZATION OF SPOT IMAGERY TO EVALUATE THE SUITABILITY OF RICE FIELD SPACE PATTERNS IN PADANG CITY

that are converted into built-up lands such as housing, shops and industry. According to Darmawan (2002), one of the factors that cause land change is the socioeconomic factors of the community related to the needs of human life. One of the provinces that experienced the largest paddy land conversion in Indonesia is the West Sumatra region. Many factors result in land use changes that have an impact on the land itself, such as social, and economic factors and also factors of increasing the number of inhabitants. Land use change is the transition of an old form and location of land use to a new one. Or the change in the function of agricultural land such as built-up land (Adhiatma et al., 2020).&#x0D; The selection of the Padang City Area as a research site was based on significant land use changes in Padang City, this was caused by several factors such as the rate of population growth in Padang City which increased every year based on BPS data in 2015-2020 period was 1.52% with a population of 909.04 thousand people in 2020.&#x0D; The spatial pattern that has been set by the government in general in the city of Padang is an area developed for the cultivation of rice fields covering an area of 4540.10 ha. Based on BPS data from Padang City, the area of paddy fields decreases by 0.7% every year which is converted into housing and shops and industries in Padang City. The development of built-up land that occurred in the city of Padang slowly changed the rice field area into a built-up area that was not by the provisions of the spatial pattern that had been set by the local government. The spatial pattern that has been set by the government so that the area of paddy fields can be maintained by utilizing remote sensing data. By using remote sensing data such as imagery. Spot imagery is one of the high-resolution remote sensing images that is a French-owned satellite that operates to provide remote sensing data. SPOT imagery provides an imaging instrument that is then carried out as an overlay method between the rice field map and the rice field space pattern that has been set by the government to see its suitability.&#x0D; High-resolution optics are synonymous with panchromatic (P) and Multispectral (Green, Red, and Near Infrared). SPOT imagery has a spatial resolution of 2.5meter 10meters with a wide viewing angle that covers 60 x 60 km or 60 x 120 km in twin mode instruments, and an orbital altitude of 822 km, SPOT provides an ideal combination of high resolution and also wide visibility that can meet the needs of data that is accurate enough for identification of rice fields.

Insights into plastic deformation mechanisms of austenitic steels by coupling generalized stacking fault energy and semi-discrete variational Peierls-Nabarro model

The generalized stacking fault energy (GSFE) is a key parameter to determine the plastic deformation mechanisms of austenitic steels. However, the underlying physics why the GSFE can affect the plastic deformation behaviors remains unclear. In this paper, the plastic deformation mechanisms of austenitic steels with different carbon (C) additions were investigated by coupling the GSFE with the semi-discrete variational Peierls-Nabarro (P–N) model. The internal mechanisms behind the P–N stress and plastic deformation were explained at atomic scale. It is found that the positions and contents of C atoms affect the GSFE of austenite, and thus regulate plastic deformation behaviors of austenitic steels by influencing dislocation core structure. As exemplified that with 4 ​at.%C in austenite, the intrinsic stacking fault energy increases from −433 to −264 mJ/m2, and the stacking fault width increases to 6.62b from 4.72b of FCC-Fe with b being the Burgers vector. This corresponds to the plastic deformation mechanism dominated by the ε martensitic transformation with the lattice changing from FCC to HCP. With increasing C contents to 8 ​at.%, the intrinsic stacking fault energy of austenite increases to −9.01 mJ/m2, while the stacking fault width decreases to 6.03b. The plastic deformation tends to proceed via the mechanical twinning mode. The present investigation establishes a solid foundation for clarifying the plastic deformation mechanisms of austenitic steels from the perspective of the dislocation core structure.

Intensity Correlations in Quantum Cascade Laser Harmonic Frequency Combs

A novel study on harmonic frequency combs emitted by quantum cascade lasers (QCLs) is presented here, demonstrating the presence of intensity correlations between twin modes characterizing the emission spectra. These originate from a four‐wave mixing process driven by the active medium's third‐order nonlinearity. The study of such correlations is essential for the engineering of a new generation of semiconductor devices with the potential of becoming integrated emitters of light with quantum properties, such as squeezing and entanglement. Starting from experimental results, the limits of state‐of‐the‐art technology are discussed as well as the possible methodologies that could lead to the detection of nonclassical phenomena, or alternatively improve the design of QCLs, in the compelling perspective of generating quantum correlations in mid‐infrared light.

Revealing the mode and strain of reversible twinning in B19′ martensite by in situ synchrotron X-ray diffraction

The challenges in the identification of reversible twinning modes and in the measurement of reversible twinning strain impede the thorough understanding of twinning induced elasticity (TIE). In this report, we exploited the mode and strain of reversible twinning in B19′ martensite in a Nb-nanowire/NiTiFe-matrix alloy. TIE strain up to 5.1% was achieved by pre-deforming the alloy up to an applied strain of 55.7%. In situ synchrotron X-ray diffraction (XRD) results show that B19′ (201¯) and (1¯11) twins were induced by pre-deformation. More importantly, a large portion of these twins were found reversible for the first time. It is suggested that the reversibility is probably facilitated by the internal stresses generated during large plastic deformation. Furthermore, the reversible twinning strain was measured using XRD based on a 'lattice strain matching' concept such that the contribution of reversible twinning to TIE was clarified. The measured twinning strain was compared with the calculated strain based on twinning crystallography.

Asymmetric [formula omitted] twin boundary and migration mechanism in hexagonal close-packed titanium

Classical twinning theory predicted that a simple shear was able to create a perfect, twinned structure without the need of atomic shuffles for (112¯1)[112¯6¯] twinning mode in hexagonal close-packed (HCP) metals, and the elementary twinning dislocation should be a two-layer zonal. However, it was revealed in the literature that this particular twinning mode could not have mirror symmetry between the parent and twin, and shuffles should be involved during twin boundary (TB) migration. These conflicting reports indicate that the (112¯1)[112¯6¯] twinning mechanism has not been completely resolved, and what configuration of twinning dislocation mediates twin growth is not well understood either. In this work, atomistic simulation is conducted to further understand the twinning mechanism in titanium. Novel structural analyses are performed to reveal how the parent lattice is transformed to the twin lattice. The results show that the mirror symmetry of a perfect, unrelaxed TB breaks down after relaxation, because of the very high repulsive force between the atom pairs on mirrored positions with a spacing less than half of the lattice constant. As a result, the stacking sequence of the twin differs from that of the parent after relaxation. During twin growth, each {11¯00} prismatic plane of the parent splits into two layers and reorganize into the prismatic planes of the twin, such that the twin prismatic are no longer aligned with the parent prismatic and the mirror symmetry breaks down. This process is accomplished by atoms shuffling in the opposite direction that is perpendicular to the twinning shear. The atomic shuffles spread over multiple consecutive twinning planes to minimize the shuffling magnitude on each twinning plane. Thus, the actual TB is no longer a single twinning plane, but a multi-layer interface zone. Careful examination shows that no well-defined twinning dislocation core can be identified, although single-layer steps can still be observed.

Deformation twins stimulated by {11[formula omitted]2} twinning in adjacent grain in titanium

Deformation twins are likely nucleated at and impeded by grain boundaries (GBs), developing shear transformation bands. Knowing the accommodated deformation in adjacent grains to the twinning shear is essential for understanding mechanical properties and the evolution of microstructure and texture of polycrystalline aggregates. Based on EBSD analysis, we characterize and statistically group accommodated deformation modes in the neighbor to {112¯2} compression twins (CTWs) in titanium with respect to the misorientation axis/angle. Two types of CTWs are preferably activated in adjacent grains with low misorientation angles, two types of extension twins (ETWs) are favorably activated in adjacent grains with high misorientation angles, and some of {112¯2} CTWs terminate at GBs with high misorientation angles. We discuss the preference of accommodated deformation modes and the selection of twin variants based on the SDGA criterion which couples the displacement gradient accommodation (DGA) and stress driven accommodation (SDA) criteria. Although misorientation angle of GBs is widely used to predict the preferred deformation modes, we demonstrate that misorientation axis that was often ignored, must be considered in determining the preferred deformation modes especially for large misorientation angles. Finally, we predict the misorientation angle/axis pairs with respect to the activity of four twinning modes and two slip systems as the best accommodation mechanism in adjacent grains. The results are useful for the implementation of intergranular deformation mechanisms in multiscale modeling and the design of HCP materials with specific GB characteristics.

Structural evolution during the cycling of NiTi shape memory alloys

Abstract The structural evolution in NiTi shape memory alloys subjected to pseudoelastic cycling is examined in the present study. Single crystals with [100] and [111] orientations were subjected to repeated compressive cycles and then studied by transmission electron microscopy (TEM). TEM observations were made at cycle numbers 1, 2, 5, 10, and 20 since the majority of degradation occurs during these initial cycle numbers. Under compression, single crystals with [111] orientations degraded much faster than crystals with [100] orientations. Under tension, single crystals with [100] orientations fractured in the elastic region, and crystals with [111] orientations showed considerable degradation as a function of cycling. Intermittent TEM observations on single crystals oriented along the [111] direction showed an increase in dislocation density on multiple active slip systems as a function of cycling. Single crystals oriented along the [100] orientation show a less dramatic increase in dislocation density as a function of cycling. TEM observations have revealed that dislocation structures formed near martensite plates have a similar periodicity as internal twin modes within the martensite. This observation implies that, although the interface between the martensite and parent phase is a low-energy boundary, the local disruptions due to internal twins create preferential nucleation sites for the formation of lattice defects.

In-situ synchrotron X-ray diffraction texture analysis of tensile deformation of nanocrystalline NiTi wire in martensite state

Tensile deformation of nanocrystalline superelastic NiTi wire in the martensite state at -90 °C until fracture was investigated by in-situ synchrotron X-ray diffraction texture analysis. The results were interpreted in terms of the activity of various transformation and deformation twinning modes. The strain components into the load axis as well as discontinuous rotations of the martensite crystal lattice due to activation of various twinning modes were calculated using an abstraction of “ideal <hkl> fibre textured polycrystal” and used to estimate the evolution of the martensite texture during the tensile test.It is found that the four fibre texture of selfaccommodated martensite transforms during the martensite reorientation stage in the tensile test into the sharp two fibre texture of the reoriented martensite reflecting its (001) compound twinned microstructure. Plastic deformation of martensite is claimed to proceed via peculiar deformation mechanism involving deformation twinning and kinking assisted by [100]/(011) dislocation slip. This deformation mechanism enables the nanocrystalline NiTi wire to deform at ∼1 GPa engineering stress up to very large plastic strains ∼50% with small strain hardening and brings about refinement of the austenitic microstructure of the NiTi wire down to nanoscale.

Four Directional Twinning Deformation of an Anisotropic Molecular Single Crystal Based on Three Different Modes of Mechanical Twinning

Introduction of mechanical twinnability is one of the most useful strategies to enhance deformability of crystalline materials by giving them an ability of reversible deformation over the elastic l...