Crystal Rotation Research Articles

A novel crystal rotation model of LDBs deformation in NiTi alloy

To investigate the deformation characteristics of Lüders-like bands (LDBs) in NiTi alloy, the uniaxial tensile testing was conducted under isothermal condition using the digital image correlation (DIC) technique. Based on the changes in the strain field near the LDBs during the initiation, propagation, and expansion of the LDBs, a novel crystal rotation model was proposed to explain the formation of the LDBs. The model focused on the microstructural evolution that occurred at the front of the phase transformation interface when the LDBs appeared, providing a fresh perspective on the mechanism of the formation of the LDBs.

Determination of the polarization plane specific rotation in gyrotropic crystals of the middle category by the spectrophotometric method

A large number of modern functional single crystals of the middle category belong to gyrotropic media. In these crystals, when light propagates along the optical axis, rotation of the plane of its polarization is observed. In this work a spectrophotometric method was used to obtain the dispersion dependences of the rotation angle of the polarization plane. This method is based on measuring the intensity of light passing through the polarizer–crystal–analyzer system, the crystal is a polished plane-parallel plate of a uniaxial gyrotropic crystal cut perpendicular to the optical axis. Measurements were carried out on a UV-Vis-NIR spectrophotometer Cary-5000 in the wavelength range of 200—1200 nm using polarizers — Glan–Taylor prisms. Polished plane-parallel plates of known SiO2 and α-LiIO3 crystals were used as samples. The obtained dispersion dependences of the spectral transmission coefficients are oscillating. Discrete values of the specific angles of rotation of the plane of polarization of light are calculated from the extremes on these dependencies. These discrete values can be approximated by the formulas Drude, Chandrasekhar and Vyshina, depending on what determines the nature of the rotational ability of the plane of polarization of light in each particular material. For the studied crystals, dependences of the modified Drude formula of the form 1/ρ = f(λ2) are plotted, these dependences should have a linear character in the case of an ideal crystal. The obtained experimental results correlate well with the available literature data. The advantages of this method are efficiency, the possibility of obtaining dispersion dependences of the specific rotation angle of the polarization plane, the need for a single sample, the possibility of assessing the nature of the rotational ability of specific crystals, the possibility of evaluating the structural perfection of the studied crystals.

Numerical simulation of thermal stress during the steady rotation in the growth of ADP crystals by solution circulating method

Transient numerical simulations were carried out to describe the temperature and thermal stress in ADP crystals during the steady rotation by solution circulating method (SCM). In a related paper (J. Crystal Growth 574 (2021) 126343), the effects of flow and heat transfer on the distribution of the supersaturation on the crystal face was discussed. This paper presents the corresponding results concerning the heat transfer occurring in the crystal. Emphasis is placed on studying the temperature and thermal stress distribution, since it is critically involved in the processes of crystal cracking. The evolution of the temperature and thermal stress in the crystal are studied as a function of crystal rotation rate, inlet velocity, and inlet temperature and crystal size. The numerical results seem to indicate that, as the rotation rate increases, the value of the σmax in crystal decreases and then increases, while the values of the σmax on crystal surface is increased. The increases of the inlet velocity and the inlet temperature lead to the increase of the σmax. Finally, As the crystal size gets large, the possibility of cracking arising in pyramidal zone is increased obviously.

In-situ TEM observations of nanovoid initiation and crack evolution in FCC phase of AlCoCrFeNi2.1 eutectic high-entropy alloy

The changes in microstructures after the exhaustion of dislocation-gliding ability but before cracking in the face-centered cubic (FCC) phase of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) were investigated by using in-situ transmission electron microscopy (TEM) tensile tests. It was found that crystal thinning area occurred ahead of the crack tip through dislocation gliding during loading. After that, crystal rotation and/or twinning took place in the crystal thinning area, which were the two main procedures after the exhaustion of dislocation glide ability but before cracking for this alloy. Nanovoids initiate in the dislocation-free zone ahead of the crack tips through crystal rotation induced by local high-stress concentration. Once the high-stress concentration at crack tip overcomes the critical twinning stress, new nanovoids are initiated near the deformation twin through Shockley partial dislocation (1/6 〈112〉 type) glide emitted from the deformation twin. The connection of these nanovoids would lead to the formation of nanocracks. Eventually, the “Y” and “zigzag” crack propagation paths were formed in the FCC phase for AlCoCrFeNi2.1 EHEA.

Evolution characteristics of orientation relationships during the co-evolution of α/β phase for Ti alloy

In the present work, the intrinsic characteristics of orientation changes during the co-evolution of α/β phase for Ti alloy are investigated. For this purpose, the typical hot compression samples are selected for related analysis. The α phase and β phase interact with each other and change together due to the coexistence of α and β phases in high temperature deformation of Ti alloy. It is found that the α and β phases still maintain BOR to a large extent even after deformation. The co-evolution between α and β phases is the key for the solid BOR. During deformation, the crystal rotation of α lamellae occurs, which is influenced by self-slip of α phase and interaction of α/β phase. The axis of crystal rotation are discovered to be [0001] and [11–20]. The rotation axis [0001] can be regarded as a result of the prismatic slip. The rotation axis [11–20] occupies a larger proportion, and it is affected by interaction of α/β phase. The [111] and [11–20] directions are the close-packed directions of BCC and HCP structures, respectively. A stable relationship of [111]β//[11–20]α can reduce the energy of the system and maintain the stability.

Study on Growth Interface of Large Nd:YAG Crystals

A study was performed on the growth interface of a large-diameter 1 at% neodymium-doped yttrium aluminum garnet (Nd:YAG) single crystal grown using the Czochralski method. Red parallel light and an orthogonal polarizing system were used to observe the distribution of the central and lateral cores of the crystal at different growth interfaces. The solid–liquid interface of large-diameter Nd:YAG crystal growth was mainly determined via the interaction between natural and forced convection. The shape of the solid–liquid interface was mainly controlled via maintaining the crystal rotation rate and the temperature field. Interface inversion generally occurred during the shoulder-expanding stage and late stages of the growth of the cylindrical portion of the crystal. The occurrence of interface inversion is directly related to the temperature field, process parameters, and diameter of the crystal. The growth shape of the crystal interface determined the size and distribution of the central and lateral cores of the crystal. The area of the central and lateral cores was reduced via adjusting the temperature gradient of the solid–liquid interface and crystal rotation speed.

In situ observation of crystal rotation in Ni-based superalloy during additive manufacturing process

Understanding the dynamic process of epitaxial microstructure forming in laser additive manufacturing is very important for achieving products with a single crystalline texture. Here, we perform in situ, real-time synchrotron Laue diffraction experiments to capture the microstructural evolution of nickel-based single-crystal superalloys during the rapid laser remelting process. In situ synchrotron radiation Laue diffraction characterises the crystal rotation behaviour and stray grain formation process. With a complementary thermomechanical coupled finite element simulation and molecular dynamics simulation, we identify that the crystal rotation is governed by the localised heating/cooling heterogeneity-induced deformation gradient and recognise that the sub-grain rotation caused by rapid dislocation movement could be the origin of granular stray grains at the bottom of the melt pool.

Tuning crystal orientation and chiral spin order in Mn3Ge by annealing process and ion implantation

The non-collinear antiferromagnetic Weyl semimetal Mn3X (X = Ga, Ge, Sn) system has attracted a lot of attentions owing to its robust anomalous Hall effect (AHE), large spin Hall angle and small net magnetization at room temperature. The high spin-charge interconversion efficiency makes it a super candidate in topological antiferromagnetic spintronic devices, which could facilitate ultra-fast operation of high-density devices with low energy consumption. In this work, we have realized to obtain different chiral spin structures in Heusler alloy Mn3Ge thin films, which originate from different crystalline orientations. The high-quality (0002)- and (200)-oriented single phase hexagonal Mn3Ge films are achieved by controllable growth, annealing process and ion implantation. The various magnetic properties and AHE behaviors are observed along a and c crystal axes, equivalent to magnetic field in and out of the inverse triangular spin plane. The observation demonstrates the manipulation of crystal structure accompanied with chiral spin order in a non-collinear antiferromagnetic Mn3Ge film, which is induced by energy conversion and defect introduction. The in situ thermal treatment induces crystal phase rotation up to 90° and robust AHE modulation, which is significantly important and highly desirable for flexible spin memory device applications.

Effects of Induced Current in Crystals on the Melt Flow and the Melt–Crystal Interface during Industrial 300 mm Czochralski Silicon Crystal Growth under a Transverse Magnetic Field

Due to the high magnetic field intensity during industrial 300 mm silicon crystal growth, typically up to 0.3 T, the crystal’s rotation under this transverse magnetic field (TMF) induces a current that is strong enough to impact both the melt flow and the melt/crystal interface (m/c interface) shape. This paper investigates the influence of TMF-induced current in crystals on the melt flow, temperature distribution, and interface shape through the conduction of three sets of 3D simulations that vary in the electrical conductivity of crystals, TMF intensities, and crystal rotation rates. Combined with experiments, the accuracy of the model has been validated, and a reasonable electrical conductivity of the crystal has been predicted. The study findings reveal a shift in the driving force of forced convection from centrifugal to Lorentz force when the induced current in crystal is augmented. This alteration affects the melt flow and the m/c interface shape. Notably, this study serves as a significant complement to the conventional model, which overlooks the induced current in crystals, enhancing the accuracy and comprehensiveness of the simulation outcomes to provide a robust theoretical underpinning for industrial production.

Investigation of quasi-cleavage in a hydrogen charged maraging stainless steel

Slow strain rate tests on hydrogen-containing specimens of PH13–8Mo maraging stainless steel showed H-assisted subcritical quasi-cleavage cracking, accelerating material failure. Fractographic analysis revealed that quasi-cleavage is composed of flat brittle areas and rougher areas. Electron backscatter diffraction (EBSD) was performed on a secondary subcritically grown crack. High resolution EBSD showed significant crystal lattice rotation, hence consequential plastic deformation, concentrated between the main crack tip and the cracks located ahead of it. Quasi-cleavage consisted of {100} cleavage cracks connected by ductile ridges, suggesting a discontinuous mechanism, involving re-initiation of new cleavage cracks ahead the main crack tip.

Relaxation Rotation during Martensitic Transformation in Alloys with Thermoelastic and Nonthermoelastic Martensite

It is shown that application of the crystallographic theory of martensitic transformation instead ofthe phenomenological one allows proper understanding of the mechanism of martensitic transformation incrystallographic analysis and computing, in addition to the previous characteristics, a new important characteristic,that is, the relaxation rotation of martensite crystallites to obtain the invariant plane. It is demonstratedthat the angle of relaxation rotation is most strongly dependent on the crystallographic systems of the original and final phases, as well as on the lattice parameters of these phases. It has been discovered that scatteringof the texture peaks of martensite, determined as the integral half-width of the texture maximum, is in linear proportion to the angle of relaxation rotation of martensite crystals.

Dislocation behavior in Cu single crystal joints under the ultrasonically excited high-strain-rate deformation

• The interfacial evolution for ultrasonically welded joints was used to clarify the coupling effects of ultrasonic excitation and high-strain-rate deformation. • Transmission Kikuchi diffraction and transmission electron microscopy were used to analyze grain orientation and deformed microstructures simultaneously. • Ultrasonic excitation dramatically weakened the constraint of high-strain-rate and characteristic orientations on dislocation motion. • The first-principle calculation and applied strain-rate analysis were conducted to discuss the preferred deformation mechanism to accommodate the imposed plastic strain. The coupling effects of ultrasonic excitation and high-strain-rate deformation are the core factors for weld formation during ultrasonic welding. However, interfacial deformation behavior still shrouds in uncertainty because of the contradictory features between mutual dislocation retardation caused by severely frictional deformation and ultrasonic-accelerated dislocation motion. [101] and [111]-oriented Cu single crystals which tended to form geometrically necessary boundaries (GNBs) were selected as the welding substrates to trace the uniquely acoustoplastic effects in the interfacial region under the ultrasonically excited high-strain-rate deformation. It was indicated that for a low energy input, micro-welds localized at the specific interface region, and equiaxed dislocation cells substituting for GNBs dominated in the initial single crystal rotation region. As the welding energy increased, continuous shear deformation drove the dynamic recrystallization region covered by equiaxed grains to spread progressively. Limited discrete dislocations inside the recrystallized grains and nascent dislocation cells at the grain boundaries were observed in [101] and [111] joints simultaneously, suggesting that the ultrasonic excitation promoted motion of intragranular dislocation and pile-up along the sub-grain boundaries. The interfacial morphology before and after expansion of recrystallization region all exhibited the weakening of orientation constraint on dislocation motion, which was also confirmed by the similar micro-hardness in joint interface. The first-principle calculation and applied strain-rate analysis further revealed that ultrasonic excitation enhanced dislocation slipping, and enabled dislocation motion to accommodate severe plastic deformation at a high-strain-rate.

Synthesizing pseudo-Kossel lines from neutron transmission data. II. Validation with neutron diffraction data

A new method to recover the orientation matrix of a single crystal with a known unit cell by analyzing synthesized pseudo-Kossel lines from time-of-flight neutron transmission data has been outlined in a companion article [Dessieux et al. (2023). J. Appl. Cryst. 56, https://dx.doi.org/10.1107/S1600576723001346; referred to here as Article I]. In this work, validation of this new technique is presented by employing experimental neutron transmission and diffraction measurements performed on two copper single-crystal specimens. Time-of-flight spectra were recorded during rotation (ω) of the single crystals about a vertical axis perpendicular to the incident neutron beam. The λ–ω maps recorded in transmission are utilized to determine the crystal orientation with respect to the neutron beam, following the procedure presented in Article I. To validate the indexing procedure, the crystal orientations are compared with those obtained via conventional methods using the diffraction data. The resulting pseudo-Kossel lines across the 2D detectors are also observed for the first time.

Confronting Solid‐State Shear Bias: Magmatic Fabric Contribution to Crustal Seismic Anisotropy

AbstractSeismic anisotropy is controlled by aligned rock‐forming minerals, which most studies attribute to solid‐state shear with less consideration for magmatic fabric in plutonic rocks (rigid‐body rotation of crystals in the presence of melt). Our study counters this traditional solid‐state bias by evaluating contributions from fossil magmatic fabric. We collected samples from various tectonic settings, identified mineral orientations with electron backscatter diffraction and neutron diffraction, and calculated their bulk rock elastic properties. Results indicate that magmatic fabric may lead to moderate to strong anisotropy (3%–9%), comparable to solid‐state deformation. Also, magmatically aligned feldspar may cause foliation‐perpendicular fast velocity, a unique orientation that contrasts with a fast foliation typical of solid‐state deformation. Therefore, magmatic fabric may be more relevant to seismic anisotropy than previously recognized. Accordingly, increased considerations of magmatic fabric in arcs, batholiths, and other tectonic settings can change and potentially improve the prediction, observation, and interpretation of crustal seismic anisotropy.

Thermoelectric effect of a skyrmion crystal confined in a magnetic disk

We theoretically propose that an electric voltage can be generated by a thermal gradient with a rotating skyrmion crystal confined in a magnetic disk. We find that the rotation of a skyrmion crystal induced by diffusive thermal magnon currents in the presence of the temperature gradient gives rise to spinmotive forces in the radial direction through coupling to conduction-electron spins. The amplitude of the generated spinmotive force is larger for a larger temperature gradient at a lower temperature. The proposed phenomenon can be exploited as spintronics-based thermoelectric devices to realize the conversion of heat to electricity.

Deformation-induced grain rotation and grain boundary formation achieved through dislocation-disclination reactions in polycrystalline hexagonal close-packed metals

Grain boundary mediated plasticity (e.g., grain rotation and grain boundary sliding) plays a critical role in determining the deformation behavior of polycrystals, which is especially important for nanocrystalline metals or plastic deformation at elevated temperatures. However, due to the lack of a theoretical framework, the mechanism of deformation-induced grain rotation has not been well understood. By introducing a disclination-based description, we show that crystal rotation can be captured conveniently through the characteristic rotational vector of a disclination (i.e., the Frank vector). Under the framework of topological defect theory, grain boundary mediated plasticity can be treated as topological reactions between dislocations and disclinations, leading to rigorous predictions of grain/subgrain rotation through a pseudo-inverse solution for the reformulated Frank-Bilby equation. Systematic classifications of grain/subgrain rotation and grain boundary formation are raised for hexagonal close-packed (HCP) metals, which has been validated by Electron-Backscattered Diffraction characterizations in Mg alloys. Our work not only suggests a theoretical approach to investigate grain/subgrain rotation based on the topological correlation between dislocations and disclinations, but also provides a new insight into the plastic behaviors of polycrystalline HCP metals.

Study of the Antiferromagnetic State Nematics in EuFe2As2 by Using Spin-Resonance and Magnetic Measurements

Using electron spin resonance spectroscopy and SQUID-magnetometry we obtained direct evidence of the occurrence of magnetic domains in the antiferromagnetically ordered state of a {text{EuF}}{{{text{e}}}_{{text{2}}}}{text{A}}{{{text{s}}}_{{text{2}}}} single crystal. The resonance spectra of europium ions were measured in the temperature range from 4 to 200 K. Using an equation for the resonance field in an antiferromagnet that takes into account the exchange and anisotropy fields, we have performed an analysis of the angular dependence of the spectrum at a temperature of 4.8 K, measured upon the crystal rotation around the c axis. Data analysis showed that {text{EuF}}{{{text{e}}}_{{text{2}}}}{text{A}}{{{text{s}}}_{{text{2}}}} is the antiferromagnet with easy anisotropy plane. Besides, we found in the ab-plane the second order axes of easy magnetization for each of the two types of magnetic domains, related to the structural transition and the formation of twins. Magnetic anisotropy caused by the exchange interaction of europium ions with iron ions indicates the occurrence of nematic magnetic ordering in the basal ab plane. An estimate of the magnitude of the exchange field and the anisotropy field is obtained from the angular dependence of the resonance fields.

Multidynamic Crystalline Molecular Rotors Comprising an N‐Heterocyclic Carbene Binuclear Au(I) Complex Bearing Multiple Rotators

AbstractWe report multidynamic molecular rotations in crystals using a concave‐shape N‐heterocyclic carbene (NHC) binuclear Au(I) complex rotor bearing pyrazine and tetrahydrofuran (THF) molecules as multicomponent rotators. Single‐crystal X‐ray diffraction (XRD) measurements revealed that two THF molecules are located near the central pyrazine encapsulated by two bulky NHC ligands. From 2H solid‐state NMR analysis, it was observed that the pyrazine rotated in a 2‐fold site exchange with a 180° rotational angle and a 31 kJ mol−1 energy barrier, while the THF molecules showed a 23°‐38° libration with a lower energy barrier (14 kJ mol−1). Interestingly, the pyrazine rotation was accelerated when the THF molecules rotated in fast site exchange with a large angle of libration, suggesting that the rotators exhibit multidynamics in a correlated manner.

Method and Experimental Study of Zeolite Crystal Manipulation Based in Hydrodynamic Forces for Single Crystal Assessment

In this work, we report an optofluidic system for manipulation of orientation of zeolite crystals near the bottom of a rectangular cross-sectional, straight, quartz microfluidic channel. Manipulation is accomplished by using two computer-controlled syringe pumps that generate adequate hydrodynamic forces for translation and rotation of crystals. Rotation of a crystal around its longitudinal axis allows us to inspect its four major faces for defects. Coffin-shaped zeolite crystals have been studied by several authors by fixing them to a substrate, using two different crystals to assess the roof and gable orientations. The proposed system permits complete assessment of a single crystal by shifting it between roof and gable orientations; moreover the medium can be controlled. Computational fluid dynamics simulations show that crystals in free motion near the bottom of the channel should move faster than the velocity estimated from video. An opposing force, which prevents the crystals from moving freely, has been calculated in order to match translation velocities from simulations and experiments for three given flow rates. The reported optofluidic system is proposed as a novel tool that we believe will open new possibilities for individual zeolite crystal assessment by manipulation of its orientation and medium control.

Stress-Induced Inversion of Linear Dichroism by 4,4'-Bipyridine Rotation in a Superelastic Organic Single Crystal.

The molecular crystals that manifest unusual mechanical properties have attracted growing attention. Herein, we prepared an organic single crystal that shows bidirectional superelastic transformation in response to shear stress. Single-crystal X-ray diffractions revealed this crystal-twinning related shape change is owed to a stress-controlled 90° rotation of 4,4'-bipyridine around the hydrogen bonds of a chiral organic trimer. As a consequence of the 90° shift in the aromatic plane, an interconversion of crystallographic a-, b-axes (a→b' and b→a') was detected. The molecular rotations changed the anisotropic absorption of linearly polarized light. Therefore, a stress-induced inversion of linear dichroism spectra was demonstrated for the first time. This study reveals the superior mechanical flexibilities of single crystals can be realized by harnessing the molecular rotations and this superelastic crystal may find applications in optical switching and communications.