Crystallographic Rotation Research Articles

On the influence of austenite content in orientation selectivity and shear texture evolution during hot rolling of Fe-3 wt% Si grain-oriented electrical steel

A systematic investigation of the development of shear textures during hot rolling of Fe – 3 wt% Si steel has been carried out in the present work with a special focus on the influence of austenite in preferential orientation selectivity. This orientation selectivity was anticipated owing to the fact that texture evolution during thermomechanical processing is entirely an effect of crystallographic rotations and such rotations may experience constraining effects because of surrounding austenite. The influence of austenite on shear texture evolution was studied over a range of finish rolling temperatures (FRTs). The evolution of microstructure and microtexture within the surface-subsurface zone was studied adopting EBSD. Sharp Goss orientation was observed at lower FRT, while texture intensities of Brass and Copper were observed to be high at higher FRT. Additionally, it was inferred that in the surface-subsurface zone, next to the austenite, the ease of rotation about ND contributed to the higher observed frequency of the Brass orientation despite of its overall lesser fraction as compared to Copper orientation. The less observed frequency of Copper orientation near the austenite has been attributed to the resistance offered by the austenite to its adjacent ferrite grains while rotating about TD. This constraining effect of austenite has been shown to be consistent over the entire range of studied FRTs. Moreover, it has been shown that at higher rolling temperatures, the lower constraining effect by austenite paves the way for Goss orientation formation, which acts as the precursor to the formation of Brass at the FRT.

Accurate determination of active slip systems using a novel lattice rotation analysis: Quasi-in-situ EBSD/ECCI study on the homogeneous/heterogeneous deformation of polycrystalline zirconium

The accurate determination of slip systems is crucial for understanding deformation mechanisms of metals in particular, how slip/twining transfer or blocking occurs. This paper proposes a novel crystallographic lattice rotation analysis, which combines quasi-in-situ Electron Back Scatter Diffraction (EBSD) and Electron channeling contrast imaging (ECCI) techniques to precisely predict the active slip system with specific slip directions in polycrystalline Zr. Large data sets for hundreds of grains were quantitatively analyzed by this method to statistically gain deep insight on the deformation mechanism of Zr. Our results show that prismatic 〈a〉 slip is the primary slip system in most grains, and pyramidal 〈a〉 slip plays a secondary role in coordinating the local stress state of plastic deformation. The predicted slip direction is the same as the direction in which dislocation density increases. This method can serve as a complementary tool to the intragranular misorientation axis (IGMA) method, bridging the gap between macro-mechanical response and microstructural deformation mechanisms.

The Correlation between the Microstructure and the Characteristic Luminescence in the High Crystalline α-Ga2O3 Grown on the Thin-Wall Single Crystal Al2O3

A high-quality alpha-Ga2O3 thin film was grown on an Al2O3 single-crystal thin-wall channel structure. Alpha-Ga2O3 crystals are grown with a 3-fold symmetry template provided by the Al2O3 surface, which forms domain boundaries from the small rotation of the mosaic structure. The anti-phase domain (APD) was confirmed by convergent-beam electron diffraction (CBED), and it is believed to be developed at the stage of nucleation based on the unstable, or uneven Al-O bonding on the Al2O3 surface. The in-phase domain and the APD boundaries exhibit bright contrast in ADF, which originates from a local strain of crystallographic rotation and not from the local elemental fluctuations of gallium. As confirmed by CL measurement in TEM, the bandgap energy of alpha-Ga2O3 is inferred to be 5.56 eV with a near band edge transition of ~ 223 nm. Even though the heights and positions of peaks vary slightly from area to area, 4 distinct luminescence peaks and a long tail of wavelength are commonly observed throughout the crystal. 2-dimensional mapping with the specific wavelength window reveals a clear difference between the inside domain, in-phase domain boundary, and APD boundary. A luminescence peak of distinct 350 nm was observed at the APD boundary. Misorientation between domains was found, which leads to an in-plane mismatch in crystallographic lattices at the boundary when the two misoriented domains grow and the growth front merges. The imperfect lattice structure at the boundary is believed to create strain and intermediate states.

Generational assessment of EBSD detectors for cross-correlation-based analysis: From scintillators to direct detection

Introduced over ten years ago, cross-correlation-based electron backscatter diffraction has enabled high precision measurements of crystallographic rotations and elastic strain gradients at high spatial resolution. Since that time, there have been remarkable improvements in electron detector technology, including the advent of ultra-high speed detectors and the commercialization of direct detectors. In this study, we assess the efficacy of multiple generations of electron detectors for cross-correlation-based analysis using a single crystal Si sample as a reference. We show that, while improvements in precision are modest, there have been significant gains in the rate at which high-quality diffraction patterns can be collected. This has important implications in the size of datasets that can be collected and reduces the impact of drift and sample contamination.

Crystallographic rotation effect on the particle and spin across a half metal/semiconductor junction with Dresselhaus spin-orbit interaction

Theoretical studies were conducted on probability, conductance and spin polarization through a junction between a half metal (HM)/semiconductor with Dresselhaus spin-orbit coupling (DSOC), using the scattering theory and the continuous model in a two-dimensional system. The focus was on how the bulk orientation of the DSOC affects the charge and spin polarization. Results showed that the crystal face (100) makes a negative perpendicular to the normal wave vector of the system, resulting in a maximum value of the conductance spectrum and the spin polarization. However, the maximum value of the spin polarization can occur with any crystallographic orientation when the applied voltage reaches the crossing point of the DSOC. Moreover, the electron incident angle injection can cause a gap between in the transmission probability with spin up and spin down, corresponding to higher charge and spin polarization across the junction.

Crystallographic rotation of Ti-6Al-4V alloy with a fiber texture component under isothermal forging through experimental and CPFEM analyses

This study examined the crystallographic rotation behavior of α phase in a Ti-6Al-4V alloy under isothermal uniaxial forging at 800 ℃ and 850 ℃ with changing strain rates. The base material of a Ti-6Al-4V alloy bar comprised a strong <101¯0> fiber texture component along the longitudinal direction (designated as the Z-direction in this study). Compression tests (until a height reduction of 50%) were conducted along the Z-direction and radius direction, which is perpendicular to the Z-direction (hereafter designated as the Y-direction). Microstructural conversions for the forging conditions with strain rates lower than 10−1 s−1 occurred under continuous dynamic recrystallization in which grain sizes became finer under deformation. However, only at the high strain rate condition of 1 s−1, grain refinement accompanied by significant crystallographic rotations of [0001] from the radius direction to the longitudinal direction occurred when compressed parallel to the Z-direction. This study investigates the origin of the significant rotation of [0001] observed during compression along the Z-direction at a high strain rate of 1 s−1 through experimental and crystal plasticity finite element analyses. The results show that the anisotropic dislocation glides among prismatic <a>, basal <a>, and pyramidal <c+a> led to the significant rotation of [0001] under isothermal forging at a high strain rate of 1 s−1. Furthermore, the possibility of the frequent occurrence of twinning is discussed, and it was determined to be lower than that of the anisotropic dislocation glide for the origin of the significant rotation of [0001] observed during forging at a high strain rate of 1 s−1. Alternatively, a sub-grain formation and its rotation occurred at strain rates below 1 s−1, corresponding to the process condition of the enhanced thermally activated process.

Orientation relationships between precipitates and matrix and their crystallographic transformation in a Cu–Cr–Zr alloy

The orientation relationships between Cr precipitates and matrix in a Cu–Cr–Zr alloy with various aged states were investigated by transmission electron microscopy and High-resolution transmission electron microscopy, and the crystallographic transformations of orientation relationships were also analyzed by stereographic projection and discussed. Four kinds of orientation relationships were detected in the precipitation process of Cu–Cr–Zr alloy, and coexistence of Cr precipitates with Nishiyama-Wassermann relationship and Pitsch relationship was found in the peak-aged Cu–Cr–Zr alloy. The occurrence for cube-on-cube and Pitsch relationship in Cu–Cr–Zr alloy was thought to be caused by the retardation of additions and heterogeneous nucleation of Cr precipitates on dislocations respectively. Transformations of orientation relationships were observed during precipitation and the crystallographic rotation pathways of the transformations were represented by stereographic projection. The interrelationships of various orientation relationships were established by Bain strain and crystal rotation in the Cu–Cr–Zr alloy of this study.

Crystallographic Rotation during Solid-Phase Epitaxy of SrTiO3 from Nanoscale Seed Crystals

The crystallization of amorphous complex oxide layers from isolated seed crystals presents an opportunity to remove geometric constraints posed by thin-film epitaxial growth methods employing single-crystal substrates. The crystallization processes initiated by a distribution of isolated nanoscale seeds occur in a state of mechanical stress that is different from planar thin-film epitaxy. The effects of this stress were probed in the crystallization of the model perovskite oxide SrTiO3 nucleated by isolated nanoscale SrTiO3 seeds. Synchrotron nanobeam scattering and diffraction were used to probe the spatial distribution of crystalline and amorphous SrTiO3. Contributions to the diffraction patterns from these components were identified using non-negative matrix factorization. Individual SrTiO3 crystallites exhibit a lattice rotation resulting from the density difference between amorphous and crystalline SrTiO3. Stress at the crystal–amorphous interface advancing from the seeds produces a rotation of the crystal lattice at a rate of tens of degrees per micron of crystallization in the plane of the film. The rate of the lattice rotation provides insight into the crystallization mechanism. The lattice rotation indicates that nanoscale morphological control during solid-phase epitaxial crystallization from nanocrystal seeds can be achieved by manipulating the interface stress between the amorphous and crystalline phases to control dislocation dynamics.

Quasi-in-situ study on the crystallographic lattice rotation of tantalum during compression deformation

By employing a quasi-in-situ method, we investigated the crystallographic texture evolution process of high purity tantalum during compression deformation. The influence of grain size, aspect ratio, and initial orientations on the crystallographic lattice rotation process was analyzed in-depth using the electron backscatter diffraction technique. It is found that the randomly distributed grain orientations mainly evolve toward {111} and {100} orientations during compression, forming the two typical deformation textures in body-centered cubic metals. Furthermore, the crystallographic rotation direction and degree have no apparent linear relationship with grain size or grain aspect ratio but are mainly related to the grain orientation. Especially, the slight crystallographic rotation angle for {100} grain is primarily associated with the activation of multiple slip systems. Multiple slip systems mean different slip planes and different slip directions, and it is difficult for {100} grains to be dominated by a certain slip system and rotate to a large extent like {111} grains. In comparison, the large crystallographic rotation angle for {110} grain is mainly related to the strain coordination in local regions. {110} grains are easier to active slip systems than grains with other crystal plane orientations inferred from the critical shear stress, thereby the rotation of grains and inhomogeneous deformation occurred during the compression process.

Investigation of deformation mechanisms in an advanced FeCrAl alloy using in-situ SEM-EBSD testing

The deformation mechanisms associated with uniaxial tensile testing are studied by conducting tensile experiments of an FeCrAl alloy using scanning electron microscopy (SEM) coupled with electron backscattered diffraction (EBSD). Prior to the deformation, investigated alloy was consisting grain and precipitate size of ∼63.0 μm and ∼6.7 μm, respectively. The recorded SEM micrographs and EBSD data at increasing levels of strains revealed the complex phenomena of slip bands’ formation in the presence of surface grain morphology evolution and their (001), (110) and (111) crystallographic planes distortions. The grains with orientation (110)||tensile direction (TD) shows higher shape change; however, (001)||TD and (111)||TD oriented grains show higher lattice gradient formation. Extracted information from the EBSD indicates that the crystallographic rotations drive towards specific, fiber-like texture in relation to the loading direction. Postmortem analysis of the recorded microstructure during the tensile deformation explains the phenomena of crack formation in the hard-intermetallic particles before the ultimate tensile strength (UTS). However, after the UTS, pores were identified in the neck that resulted from extensive plastic deformation. In-depth analysis was carried out to identify the cause of cracks and pores formation phenomena during the tensile test.

Growth of Coronal Garnet in Anhydrous High-Fe Ultrabasic Rocks: The Interplay Between Metamorphic Reaction Progress, Local Strain Heterogeneity and Grain Boundary Diffusion

AbstractCoronal garnets at pyroxene-plagioclase interfaces are traditionally used to estimate P-T conditions and reconstruct P-T paths. However, the mechanism by which the coronal garnet grows is poorly constrained. We address the issue based on the analyses of textures, mineral compositions, and crystallographic orientations of coronal garnets and associated minerals. In the Bolangir anorthosite massif (Eastern India), coronal garnets are common at the interfaces of plagioclase phenocrysts and Fe-rich pyroxenes within ferrodiorites, and at ferrodiorite-anorthosite interfaces. The plagioclase phenocrysts comprise weakly recrystallized and chemically homogenous An-rich cores (Pl1) that are partly and/or completely replaced by mantles of smaller, chemically zoned, dynamically recrystallized An-poorer plagioclase (Pl2) grains. Chemically similar beads and coalescent grains of garnet occur inward within the recrystallized Pl2 mosaic lacking ferromagnesian minerals/Fe-Ti oxides. Aggregates of elongate garnet grains oriented orthogonal to ferrodiorite-anorthosite interfaces also form continuous corona layers. The coronal garnets formed at peak P-T conditions (900°C, ≤7 kb) due to the NC(FM)AS continuous reaction Pl1 + Opx + Cpx → Pl2 + Grt, and progressed from rim inwards into the phenocrysts. Well-faceted garnet corona associated with Pl2 exhibits a random crystal preferred orientation (CPO). However, low-angle subgrain boundaries, cellular microstructure, internal lattice distortion, and orientation dispersion with rational crystallographic rotation axis in the coronal garnets indicate locally developed growth-induced stress fields affecting the garnets.The growth of coronal garnets hosted within Pl2 well inside the plagioclase necessitates the transport of Fe, Mg from the melanocratic matrix along distances comparable to the radii (∼350 µm) of the phenocrysts. We argue that grain boundary diffusion along networks of grain boundaries of Pl2 provided pathways for Fe, Mg transport to the zones where coronal garnets formed via reactions that consumed Pl1 and produced Pl2. The formation of garnet induced heterogeneous strain development within the plagioclase phenocrysts, intense at the plagioclase margin and neighboring coronal garnets. The lack of CPO in the garnets attests to the absence of far-field stress; but dislocations and lattice distortion indicate that local stresses developed to accommodate garnet growth within plagioclase. In other words, garnet grew by a feedback mechanism that linked chemical potential gradient with the elastic contribution induced by the time-space varying local stresses generated by the growing garnet grains within the confines of the plagioclase phenocrysts.

Room temperature crack-healing in an atomically layered ternary carbide.

Ceramic materials provide outstanding chemical and structural stability at high temperatures and in hostile environments but are susceptible to catastrophic fracture that severely limits their applicability. Traditional approaches to partially overcome this limitation rely on activating toughening mechanisms during crack growth to postpone fracture. Here, we demonstrate a more potent toughening mechanism that involves an intriguing possibility of healing the cracks as they form, even at room temperature, in an atomically layered ternary carbide. Crystals of this class of ceramic materials readily fracture along weakly bonded crystallographic planes. However, the onset of an abstruse mode of deformation, referred to as kinking in these materials, induces large crystallographic rotations and plastic deformation that physically heal the cracks. This implies that the toughness of numerous other layered ceramic materials, whose broader applications have been limited by their susceptibility to catastrophic fracture, can also be enhanced by microstructural engineering to promote kinking and crack-healing.

Microscopic origins of the crystallographically preferred growth in evaporation-induced colloidal crystals

Unlike crystalline atomic and ionic solids, texture development due to crystallographically preferred growth in colloidal crystals is less studied. Here we investigate the underlying mechanisms of the texture evolution in an evaporation-induced colloidal assembly process through experiments, modeling, and theoretical analysis. In this widely used approach to obtain large-area colloidal crystals, the colloidal particles are driven to the meniscus via the evaporation of a solvent or matrix precursor solution where they close-pack to form a face-centered cubic colloidal assembly. Via two-dimensional large-area crystallographic mapping, we show that the initial crystal orientation is dominated by the interaction of particles with the meniscus, resulting in the expected coalignment of the close-packed direction with the local meniscus geometry. By combining with crystal structure analysis at a single-particle level, we further reveal that, at the later stage of self-assembly, however, the colloidal crystal undergoes a gradual rotation facilitated by geometrically necessary dislocations (GNDs) and achieves a large-area uniform crystallographic orientation with the close-packed direction perpendicular to the meniscus and parallel to the growth direction. Classical slip analysis, finite element-based mechanical simulation, computational colloidal assembly modeling, and continuum theory unequivocally show that these GNDs result from the tensile stress field along the meniscus direction due to the constrained shrinkage of the colloidal crystal during drying. The generation of GNDs with specific slip systems within individual grains leads to crystallographic rotation to accommodate the mechanical stress. The mechanistic understanding reported here can be utilized to control crystallographic features of colloidal assemblies, and may provide further insights into crystallographically preferred growth in synthetic, biological, and geological crystals.

Local variations in grain formation, grain boundary sliding, and whisker growth along grain boundaries in large-grain Sn films

Two grain boundaries (GBs) in a Sn-alloy film exhibited different morphological changes during thermal cycling: whisker growth and GB sliding. Along GB-I, pervasive nucleation of high-angle and low-angle GBs occurred, with whisker growth of some shallow grains depending on sub-surface GB geometry. Most whiskers showed substantial changes of crystallographic orientation and surface normal relative to the parent grains. Along GB-II, GB sliding was characterized by mass accumulation, crystallographic rotation, and localized yielding. Results for two GBs suggest that grain crystallography and GB geometry, particularly GB inclination, are critical in determining the extent of new grain formation and subsequent whisker growth.

Scaling diffraction data in the DIALS software package: algorithms and new approaches for multi-crystal scaling.

In processing X-ray diffraction data, the intensities obtained from integration of the diffraction images must be corrected for experimental effects in order to place all intensities on a common scale both within and between data collections. Scaling corrects for effects such as changes in sample illumination, absorption and, to some extent, global radiation damage that cause the measured intensities of symmetry-equivalent observations to differ throughout a data set. This necessarily requires a prior evaluation of the point-group symmetry of the crystal. This paper describes and evaluates the scaling algorithms implemented within the DIALS data-processing package and demonstrates the effectiveness and key features of the implementation on example macromolecular crystallographic rotation data. In particular, the scaling algorithms enable new workflows for the scaling of multi-crystal or multi-sweep data sets, providing the analysis required to support current trends towards collecting data from ever-smaller samples. In addition, the implementation of a free-set validation method is discussed, which allows the quantification of the suitability of scaling-model and algorithm choices.

Size-induced room temperature softening of nanocrystalline yttria stabilized zirconia

Nanocrystalline oxides exhibit exceptional resistance to plastic deformation, manifesting increased strength and hardness with reduced grain size that qualitatively follows the so-called Hall-Petch relationships. However, below a critical grain size, softening has been observed to occur, in the so-called inverse Hall-Petch regime. The mechanisms underlying these phenomena are still not well understood in oxides. Here we observe, using nanopillar compression, that the yield strength initially increases with decreasing grain size for yttria-stabilized zirconia ceramics produced by high-pressure spark plasma sintering. A hardening-to-softening transition occurs at grain sizes below ≈21 nm. The experiments indicate that this transition depends on strain rate, and the onset of the decrease in yield strength occurs before any shear fracture begins. Nanopillar compression combined with in situ electron diffraction demonstrates the onset of softening coincides with an increase in the amount of crystallographic rotation per unit strain, suggesting a change in deformation mechanism.

Differences in texture evolution from low-entropy to high-entropy face-centered cubic alloys during tension test

Texture evolution during tension test was investigated on three face-centered cubic (FCC) metals, namely, Ni (unary), equiatomic CrFeNi (ternary), and equiatomic CoCrFeMnNi (quinary) with small and large grain sizes of ~20 and ~100 μm, respectively. The microtextures for 18%, 36% and 54% engineering strains of a tension-interrupted specimen were characterized on the same area. The three metals exhibited a similar texture evolution, which the fraction of {001}//ND remains constant. However, the fraction of {011}//ND decreases, whereas that of {111}//ND increases. On the other hand, the fraction of <001>//RD also remains constant, that of <011>//RD decreases, and that of <111>//RD increases. However, the several differences still were found during plastic deformation. Fine-grained Ni initiated a significantly crystallographic rotation (CRo) at the lower strain, increased with strain and then remained nearly unchanged as strain was higher than 18%. Coarse-grained Ni delayed this rotation and slowly developed the trend at large strains. As for CrFeNi, the comparison between fine-grained and coarse-grained structure does not have obvious difference. As for fine-grained CoCrFeMnNi, it can be seen that an obvious CRo develops under 36% strain, and maintains constant over 36% strain. But the coarse-grained CoCrFeMnNi reveals that the significant CRo develops continuously from 0% to 54% strain. The mechanisms for the effects of number of element and grain size in the present study are elucidated.

The hierarchical texture evolution of RE-component during friction stir processing of Mg-RE/SiCp composite

This study offers a new approach to investigate the RE-texture evolution in a friction stir processed (FSP) Mg-RE/SiCp composite. Detailed textural analyses suggest that the new orientation of <11-21>//PD, has been evolved through a sequential crystallographic rotation owing to the simultaneous activation of prismatic and pyramidal slips. The effect of this textural evolution on the stretch formability of FS-processed materials is also examined via normal and planar anisotropy analyses.

Effect of asymmetric rolling under high friction coefficient on recrystallization texture and plastic anisotropy of AA1050 alloy

Abstract In asymmetric rolling (ASR) the circumferential velocities of the working rolls are different. This yields a complex deformation mode with shear, compression and rigid body rotation components. The main microstructural modification is on crystallographic texture, and, for aluminium alloys, this may improve the deformability after recrystallization. This work correlated the process variables, thickness reduction per pass (TRP) and velocity ratio between the upper and bottom rolls, with the texture development and the plastic properties after annealing. Finite element (FE) simulations were performed to quantify the influence of the strain components. Experimental data on texture, and plastic anisotropy were analyzed. In the sheet centre a crystallographic rotation of the compression components about the TD (transverse direction) axis was obtained, which yielded the development of {111}//ND (normal direction) texture components. On the surfaces the local variation of the velocity gradients caused an extra rotation component about ND. This yielded the increment of rotated cube components. After annealing the main texture components at the sheet centre were maintained and the texture intensity decreased. The planar anisotropy (Δr) was reduced but the normal anisotropy and deep drawability obtained by the Erichsen test were similar for all conditions. The most favourable reduction of Δr was obtained at a velocity ratio of 1.5 and TRP of 10%.

Crystallographic Orientation and Surface Charge-Tailored Continuous Polarization Rotation State in Epitaxially Ferroelectric Nanostructures

The multiple polarization states driven by polarization rotation could trigger giant piezoelectric responses in electromechanical sensors. Theoretically and experimentally, polarization rotation in...