High-energy Boundaries Research Articles

The origin of ∼ 2.5 Ga arc-related magmatic charnockites of Karimnagar, SE India, and implications for tectonic assembly in the Dharwar craton

In the Indian peninsula, the Singhbhum, Bastar, and Dharwar cratons in the South India Block (SIB) constitute a contiguous mass of >2.5 Ga crystalline rocks. Did the cratons develop as a coherently evolved mass since their origin, or do these cratons constitute an assembly of disparately evolved cratons? Variably-deformed charnockites in the Karimnagar granulite belt and associated blastoporphyritic granitoids at the NE fringe of the Eastern Dharwar Craton (EDC) contain enclaves of mafic granulites, high-Al metapelites and anatectic quartzofeldspathic gneisses. The charnockites are demonstrably intrusive into the enclave suite. The enclave suite exhibits steeply-plunging reclined folds; the axial planes of the folds coincide with the N-striking tectonic fabrics in the Karimnagar charnockite/granitoids. The foliated charnockites display magmatic flow texture defined by trains of euhedral alkali feldspar, contain euhedral-subhedral pyroxene phenocrysts, and the quartz grains exhibit abundant chessboard microstructure. The weakly-strained euhedral laths of feldspars and pyroxenes phenocrysts share high-energy boundaries between themselves, and with quartz. Emplacement temperatures of the magmatic charnockites at ∼900 °C are obtained from Al-in-Opx thermometry. Whole rock chemistry is consistent with an arc-related origin for most charnockites. In zircons within charnockites, variably zoned cores yield ages of 2680 ± 15 Ma and 2504 ± 12 Ma in the UPb Concordia plot. Recrystallized domains in zircon grains yielded upper intercept ages constrained between 2510 ± 4 Ma and 2509 ± 3 Ma, identical with the U-Th-Pb chemical ages (2502–2508 Ma) retrieved from monazites. The zircon εHf(t) values (− 4.85 to 1.31) suggest the ∼2.5 Ga magmatic charnockites were derived from <3.0 Ga crustal sources. The late Neoarchean magmatic charnockites in the EDC margin were emplaced in a 2.7–2.5 Ga convergent tectonic setting, and the high-T magmatic charnockites formed due to delamination of a subducting (E-W shortening) oceanic crust. The subduction possibly relates to the late Neoarchean growth of the Dharwar craton involving the assembly of disparately-evolved crustal blocks, now parts of the Dharwar craton. The findings suggest that the emplacement of Karimnagar magmatic charnockites in a contractional setting is unrelated to an accretion between the Eastern Dharwar and the Bastar cratons, as suggested by earlier workers.

Electron Backscatter Diffraction Analysis of Low-Misorientation-Angle Boundary and High-Energy Boundary in the Hot-Rolled Plate of Grain-Orientated Silicon Steel

In order to study the texture evolution and the formation of an inhomogeneous microstructure in hot-rolled plate of grain-orientated silicon steel, Fe3C (hexagonal) and ferrite phases in the subsurface layer were studied using electron backscatter diffraction. The results indicate that fiber texture (ferrite) mainly composed of {441}&lt;104&gt; and (110)[001] Goss oriented grains was formed at a depth of 25% of the thickness of hot-rolled plate. Matrix grains in the subsurface layer were arbitrary separated into irregular large grains (≥40 μm) and fine grains (&lt;40 μm), and the grain boundary characteristics and texture evolution of matrix grains were studied. The results indicated that the formation of the colonies of fine grains was the result of dynamic recrystallization, and high-frequency low-misorientation-angle boundaries (0~20°) were formed between large grains (≥40 μm) and fine grains (&lt;40 μm), which can be considered as the irregularity of large grains caused by solid-state wetting. Due to the texture evolution of large grains (≥40 μm), a large number of high-energy boundaries (20~45°) were formed between irregular large grains (≥40 μm), resulting in rapid consumption between adjacent large grains and the elongation of large grains along the rolling direction. Therefore, it can be assumed that the migration of low-misorientation-angle boundaries (0~20°) under solid-state wetting and high-energy boundaries (20~45°) are important mechanisms for non-uniform grain growth in hot-rolled plate of grain-orientated silicon steel.

Reduction of couplings in the Type-II 2HDM

The idea of reduction of couplings consists in the search for relations between seemingly independent couplings of a renormalizable theory that are renormalization group invariant. In this article, we demonstrate the existence of such 1-loop relations among the top Yukawa, the Higgs quartic and the gauge colour couplings of the Type-II Two Higgs Doublet Model at a high-energy boundary. The phenomenological viability of the reduced theory suggests the value of tanβ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ an \\beta $$\\end{document} and the scale in which new physics may appear.

Grain boundary migration in polycrystalline α-Fe

High energy x-ray diffraction microscopy was used to image the microstructure of α-Fe before and after a 600 °C anneal. These data were used to determine the areas, curvatures, energies, and velocities of approximately 40,000 grain boundaries. The measured grain boundary properties depend on the five macroscopic grain boundary parameters. The velocities are not correlated with the product of the mean boundary curvature and grain boundary energy, usually assumed to be the driving force. The total migration of a boundary consists of both translations approximately normal to the boundary and lateral changes in area. Through the lateral changes in area, low energy boundaries tend to expand in area while high energy boundaries shrink, reducing the average energy through grain boundary replacement. The driving force for this process is not related to curvature and might disrupt the expected curvature – velocity relationship.

Study on the recrystallization microstructure and texture evolution of a rolled 0.075 mm ultra-thin grain-oriented silicon steel

This paper investigated the recrystallization behavior of a rolled 0.075 mm ultra-thin grain-oriented silicon steel, and microstructure and texture evolutions were studied. At the early stage, dominant {hk0}<001> recrystallized grains were ascribed to the preferential {hk0}<001> nucleation, then their growth was reduced by texture pinning effect. In contrast, a few ‘random’ grains grew excessively to consume surrounding {hk0}<001> fine-grained matrix, meanwhile nuclei originating from initial non-Goss grains also showed size advantage and further grew. Despite of quasi-two-dimensional microstructure of ultra-thin sheet, the anisotropic surface energy did not show marked effect on grain growth difference. Those coarse grains, which were 10 times larger than the matrix grains, were surrounded by high energy (HE) boundaries, indicating that their growth was driven by high grain boundary mobility. With the increasing annealing time, the formation of {hk0}<001> oriented assemblies and the growth of non-{hk0}<001> oriented grains contributed to the overall grain size increase. Regarding the relationship between microstructure, texture and magnetic properties, {hk0}<001> texture was weakened and reduced magnetic induction accordingly, and the combination of growing while heterogeneous grain size and changing texture made iron loss a first decrease and then increase tendency. It is essential to control annealing time to obtain suitable combination of microstructure and texture.

The role of parent austenite grain size on the variant selection and intervariant boundary network in a lath martensitic steel

This study investigated the influence of parent austenite grain refinement on the intervariant boundary network (population and connectivity) in a lath martensitic steel. Parent austenite grain refinement revealed a progressive reduction in the fraction of the 60° misorientation boundaries in martensite, which was linked to a decrease in the 60°/[110] intervariant boundary population. The phenomenological theory of martensite crystallography demonstrated that the variant selection mechanism altered from the 3-variant clustering (V1V3V5) in the coarse parent austenite towards the 4-variant clustering (V1V2V3V4) in the fine parent austenite grain, due to the change in the lattice parameter of the parent and daughter phase in which the martensite transformation occurs, as measured using in situ neutron diffraction. The change in the variant clustering arrangement with the parent austenite grain refinement led to a progressive promotion of 60°/[111] and 10.5°/[011] intervariant boundaries at the expense of 60°/[110] martensite intervariant boundaries. Subsequently, the connectivity of low energy {110} tilt intervariant boundaries gradually increased through the refinement of parent austenite grain size, eventually reducing the high energy {110} twist boundary connectivity. This change improved the impact toughness of martensite produced from the fine-grained austenite as the weak connectivity of high energy boundaries delays the coalescence of voids, promoting ductile fracture.

The evolution of grain boundary energy in textured and untextured Ca‐doped alumina during grain growth

AbstractThe role of anisotropic grain boundary energy in grain growth is investigated using textured microstructures that contain a high proportion of special grain boundaries. Textured and untextured Ca‐doped alumina was prepared by slip casting inside and outside a high magnetic field, respectively. At 1600°C, the textured microstructure exhibits faster growth than the untextured microstructure and its population of low‐angle boundaries increases. Atomic force microscopy (AFM) is employed to measure the geometry of thermal grooves to assess the relative grain boundary energy of these systems before and after growth. In the textured microstructure, the grain boundary energy distribution narrows and shifts to a lower average energy. Conversely, the energy distribution broadens for the untextured microstructure as it grows and exhibits abnormal grain growth. Further analysis of the boundary networks neighboring abnormal grains reveals an energy incentive that facilitates their growth. These results suggest that coarsening is not the only dominant grain growth mechanism and that the system can lower its energy effectively by replacing high energy boundaries with those of low energy. The faster growth of lower energy boundaries suggests that isotropic simulations do not adequately account for anisotropic grain growth mechanisms or anisotropic mobility.

Gradient Recrystallization Behavior of a Moderate Warm-Rolled Non-Oriented Fe-6.5wt%Si Alloy

In Fe-Si alloy systems, the Fe-6.5wt%Si alloy shows low iron core losses and near-zero magnetostriction, thus having great potential for high-frequency applications. In this study, an Fe-6.5wt%Si alloy hot band was subjected to a moderate warm rolling with a thickness reduction of 40%, and then annealed at different temperatures. The recrystallization behavior was investigated using the EBSD technique. After the moderate warm rolling, the initial gradient structure of the hot band is inherited, leading to gradient recrystallization behaviors during the further annealing process. The sheet surface first densely nucleates and forms strong &lt;110&gt;//ND and {221}&lt;114&gt; textures. However, the &lt;110&gt;//ND and {221}&lt;114&gt; grains have fewer high-mobility and high-energy (20–45°) boundaries than the other oriented matrix grains, leading to insufficient growth advantages. In the center region, the recrystallization is slow, but the nuclei usually have larger sizes. The inheritance of the &lt;001&gt;//ND (θ-fiber) texture from the initial hot band appears. Some θ-fiber grains, which have easy-magnetized &lt;001&gt; axes lying in the sheet plane, preferentially nucleate in the strong α-fiber textured matrices and form a strong θ-fiber recrystallization texture in the center region.

Internal nitridation during creep of IN617 superalloy

Internal nitridation of IN617 was investigated during creep rupture at 1000 °C. The results indicated that internal nitridation seriously deteriorated creep properties. Various nitrides including π phase, AlN, Cr2N and TiN were found. Stable AlN and TiN precipitated inside grains and distributed widely. Less stable π phase and Cr2N only precipitated at the high-energy boundaries with sufficient N and Cr concentrations. Nitridation occurred all over the cross-section (8.9 mm thick) near the fracture surface of the creep specimen ruptured under 16 MPa. It suggested that creep aggravated internal nitridation because of providing continuous crack paths for nitrogen penetration.

Evolution of precipitation particles with respect to grain boundary energy in Grade 91 steel during creep exposure

ABSTRACT Precipitation particles evolution in ASME Grade 91 steel after 233,823 h of creep exposure at 600 °C was characterised after grain boundary energyclassification in terms of misorientation angle (MOA): Low energy boundary(LEB) with MOA up to 15°, high energy boundary (HEB) with MOA from 15° to 45°, andmedium energy boundary (MEB) with MOA from 45° to 63°. The number density of the Laves phase stronglydepends on the boundary energy classification by MOA: the largest in the HEB,followed in order by the MEB and the LEB. The Z-phase particles is preferentiallylocated in grain boundaries where at least one of adjacent boundaries is theHEB or the MEB. Even though the block boundaries belong tothe MEB in terms of MOA, they are not the preferential site for the Z-phase due to their exceptionally smallboundary energy.

Microstructure evolution of 316L stainless steel during solid-state additive friction stir deposition

ABSTRACT Solid-state additive friction stir deposition was employed to three dimensionally print a 316L stainless steel. The microstructure, texture and grain boundary distribution were characterised using five-parameter boundary analysis. The bulk microstructure was exceptionally fine (∼0.7 µm) throughout the thickness of the deposited layers, consisting of equiaxed grains along with sub-grains delineated by high and low angle boundary segments. The misorientation angle distribution of the deposited layers was considerably different from the as-received microstructure, exhibiting a significant reduction in the relative areas of ∑3 annealing twin boundaries due to their distortion by severe plastic deformation. The overall texture also exhibited strong shear components associated with FCC metals, suggesting that the microstructure refinement largely took place through progressive subgrain rotation, known as continuous dynamic recrystallisation. The grain boundary plane distribution revealed significantly lower anisotropy compared with the as-received material, showing two moderate peaks at the (111) and (110) orientations. The migration of high-angle mobile boundaries, which may have been induced by thermal cycle upon subsequent deposition along with the dislocation gradients between adjacent grains, slightly enhanced the intensity of low energy (111) orientations at the expense of (110) high-energy boundaries.

Revealing grain structure development and texture evolution during elastic stress-assist aging of Mg–Zn alloys

The evolution of grain structure and corresponding texture development of Mg alloys under the assist of multiple physical fields are interesting and meaningful topics, and are investigated in this paper in detail. The results show that the texture development of stress free (SF) aged alloy exhibits a remarkable difference in type and intensity to those of 100 MPa tensile stress (100-TS) and 100 MPa compressive stress (100-CS) aged alloys at 160 °C. In the early stage of SF aging, preferential growth of<11-20>//ED grains give rise to the enhancement of<11-20>//ED fiber component. The increased pinning force caused by considerable precipitates at high energy boundaries reduce the boundary mobility, and therefore lead to a weak basal texture at the end of aging. Heavily activated prismatic<a> dislocations under the action of 100-TS aging facilitate the precipitation of secondary phases at grain boundaries and lattice rotation induced continuous static recrystallization (CSRX) in the early stage of aging, which contributes to a weak basal texture and the formation of non-fiber texture. Upon further aging, the preferential growth of pre-existing<10-10>//ED grains and recrystallized grains formed by CSRX contribute the enhancement of<10-10>//ED basal fiber component. In the case of 100-CS aging, the slight growth of<11-20> grains and lattice rotation caused by prismatic<a> dislocations lead to the enhancement of<11-20>//ED texture component in the early stage of aging. After long-time compressive stress aging, preferential growth of<10-10>//ED grains gives rise to the formation of<10-10>-<11-20> double fiber components.

A multivariate meltpool stability criterion for fabrication of complex geometries in electron beam powder bed fusion

Process parameters for manufacturing of complex parts in electron beam powder bed fusion are usually derived from material-specific process windows, which are established by fabrication and evaluation of standardized cuboid specimen. The mechanisms defining low- and high-energy boundaries of the process window are well understood. The boundary emerging at high scan speeds and beam power however, was observed but the underlying mechanism is not further discussed. In addition, appropriate methodologies to transfer process parameters from standardized process windows to complex geometries are not readily available, as the meltpool geometry is significantly affected by the scan length. This work introduces and verifies a characteristic scan length dependent process parameter limit for the fabrication of complex geometries. Electron-optical process monitoring enables the surface characterization for a wide range of process parameter and the subsequent identification of the process parameter limit as a linear function of scan length. A semi-analytical heat conduction model is used to examine the corresponding meltpool geometries. The underlying mechanism is determined as the meltpool stability limit, which occurs, when the aspect ratio of the meltpool reaches the threshold for a liquid film instability. Based on the meltpool geometries for different scan lengths, an analytical relationship for the process parameter limit as a function of scan length is proposed. This relationship may be used as a guideline for the selection of process parameters and the development of new scan strategies for the fabrication of complex geometries.

Revealing Grain-Boundary-Induced Degradation Mechanisms in Li-Rich Cathode Materials.

Despite their high energy densities, Li- and Mn-rich, layered-layered, xLi2MnO3·(1 - x)LiTMO2 (TM = Ni, Mn, Co) (LMR-NMC) cathodes require further development in order to overcome issues related to bulk and surface instabilities such as Mn dissolution, impedance rise, and voltage fade. One promising strategy to modify LMR-NMC properties has been the incorporation of spinel-type, local domains to create "layered-layered-spinel" cathodes. However, precise control of local structure and composition, as well as subsequent characterization of such materials, is challenging and elucidating structure-property relationships is not trivial. Therefore, detailed studies of atomic structures within these materials are still critical to their development. Herein, aberration corrected-scanning transmission electron microscopy (AC-STEM) is utilized to study atomic structures, prior to and subsequent to electrochemical cycling, of LMR-NMC materials having integrated spinel-type components. The results demonstrate that strained grain boundaries with various atomic configurations, including spinel-type structures, can exist. These high energy boundaries appear to induce cracking and promote dissolution of Mn by increasing the contact surface area to electrolyte as well as migration of Ni during cycling, thereby accelerating performance degradation. These results present insights into the important role that local structures can play in the macroscopic degradation of the cathode structures and reiterate the complexity of how synthesis and composition affect structure-electrochemical property relationships of advanced cathode designs.

Formation of island grains in high-permeability grain-oriented silicon steel manufactured by the acquired inhibitor method

In high-permeability grain-oriented silicon steel, island grains are often observed in the final sheets. In this work, the formation of island grains was studied in high-permeability grain-oriented silicon steel manufactured by the acquired inhibitor method. It was found that the {210}<001> and {110}<112> orientations dominated in the island grains. To understand the formation mechanisms of island grains, the grain boundary characteristics were investigated. Abnormal growth of island grains occurs because their orientations have a higher frequency of high-energy boundaries in the primary recrystallization texture. The {210}<001> grains could be left behind as island grains because they had a low misorientation angle with a Goss orientation (about 20°), whereas the {110}<112> island grains formed because of the size advantage of abnormally growing grains. The conclusions were also supported by the results of the interruption experiment. The {210}<001> grains were observed in the subsurface sheared area of the hot band and mainly nucleated at the subsurface layer during primary recrystallization. In addition, it was confirmed that the island grains (except for the exact {210}<001> orientation) had a negative influence on the magnetic properties because of the large deviation angle of the <001> axis from the rolling direction.

Microstructural aspects of intergranular and transgranular crack propagation in an API X65 steel pipeline related to fatigue failure

Abstract In this research, we investigated microstructural aspects of intergranular and transgranular fatigue crack propagation in an API X65 steel pipelines. For this purpose, the fatigue testing, based on ASTM E647 Standard, was carried out on CT specimens. The micro-texture measurement results showed that fatigue micro-cracks propagates dominantly in transgranular manner through differently oriented grains. It was also observed that most of the grains involved in crack propagation are broken during the crack growth. Coincidence site lattice (CSL) boundaries are considered as crack resistant paths; however, there was an accumulation of Σ3 boundaries around the fatigue micro-cracks showing that such boundaries acts as high energy boundaries during crack propagation. Elongated manganese sulphide inclusion was determined as the most detrimental inclusion for crack propagation due to the highly disordered boundaries between metal matrix and this inclusion. In other words, this type of inclusion may initiate the fatigue crack due to a high stress concentration factor that can provide in some sharp edges. Moreover, it can facilitate fatigue crack growth by reducing the local fracture toughness. Many manganese sulphide inclusions were found on fatigue fracture surfaces.

The apatite forming ability of micro- and nanocomposites of α-Tricalcium phosphate/poly (D,L-lactide-co-glycolide)

ABSTRACTBioresorbable composites consist of micro- and nano-sized α-tricalcium phosphate (α-TCP) particles in a poly(D,L-lactic-co-glycolic acid) (PLGA) matrix were compared for their ability to form bone-like apatite in simulated body fluid (SBF). Due to the uniform distribution of α-TCP nanoparticles over the nanocomposite surface, enhanced apatite formation was observed. This enhanced apatite formation was achieved through faster and more uniform apatite nucleation. The presence of abundant high energy boundaries between α-TCP nanoparticles and PLGA matrix in nanocomposite provided a large number of suitable sites for calcium phosphate (CaP) nucleation. A homogeneous distribution of CaP nuclei formed after 5 days. The resulting apatite crystals grew to form a flake-like apatite layer. In contrast, CaP nucleation was only observed on the micrometre-size α-TCP particles in the microcomposite. After 14 days, a dense flake-like apatite was visible covering the surface of nanocomposite, whilst this surface layer was formed only on α-TCP particles in microcomposite.

Abnormal Grain Growth of Hi–B Steel in the Secondary Recrystallization

The microstructural evolution, grain boundary character distributions, and the behavior of inhibitors during abnormal grain growth (AGG) of the Hi–B steel in the secondary recrystallization were studied in a wide range of annealing temperatures. It is found that the transition in grain growth mode from normal to abnormal can be clearly observed at the temperature of 1040 °C. The Goss grain is surrounded by the highest number of high-energy boundaries, and the probabilities of special coincident site lattice boundaries are relatively lower at different annealing temperatures. This indicates that the high-energy boundary is responsible for the AGG and that the coincident site lattice boundary does not play a significant role in AGG. Moreover, the size distribution of inhibitors and the Zener factor, volume percentage at different annealing temperatures imply that the behavior of inhibitors is suitable for the AGG.

Secondary recrystallization behavior in strip-cast grain-oriented silicon steel processed by isothermal secondary annealing

The primary annealed sheets of strip-cast grain-oriented silicon steel were isothermally secondary annealed for 15 min under 100% H2 atmosphere. The microstructure and crystallographic orientation at different annealing temperatures were characterized and the secondary recrystallization behavior was elucidated. It was observed that relatively complete abnormal grain growth occurred at 1025 °C. Incomplete abnormal grain growth developed when the temperature was lower than 1025 °C, and normal grain growth occurred when the temperature was higher than 1025 °C. During the abnormal grain growth, both of the Goss and {110}⟨227⟩ grains developed because of the rapid decrease of the inhibiting force and the limited annealing time. Considering the high energy boundary (HE), coincidence site lattice boundary (CSL) and solid-state wetting (SSW) models for abnormal grain growth, the first one explained the development of the Goss and {110}⟨227⟩ grains. Another result was that several matrix grain colonies were observed in the interior or at the boundaries of secondary grains after abnormal grain growth. The grains at the periphery of these colonies showed a large fraction of high energy boundaries (20–45° misorientation) with the surrounding secondary grain and similar grain size with the unconsumed matrix grains. Therefore, these colonies were expected to be consumed by prolonging the annealing time and thus the limited annealing time was responsible for their occurrence. A possible explanation for the dominated high energy boundaries instead of low energy boundaries at the periphery of these colonies was proposed. All of these behaviors promoted the understanding of abnormal grain growth.

The Recrystallization Behavior of Unalloyed Mg and a Mg-Al Alloy

The static recrystallization behavior of pure Mg and Mg-4Al was characterized over a range of annealing temperatures. The electron backscatter diffraction grain orientation spread technique was used to quantify the level of recrystallization at various annealing times. Recrystallization kinetics were characterized using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) relationship and it was found that two sequential annealing stages exist. Stage 1 involves heterogeneous nucleation of recrystallization in regions with a high stored energy, including twins and grain boundaries, and can be represented by an Avrami exponent of n1 ranging from 0.35 to 0.6. During Stage 2, recrystallization occurred predominately in the interior of deformed grains with incomplete recrystallization generally observed even at annealing times in excess of two weeks. The second recrystallization stage exhibited a much lower Avrami exponent, n2, ranging from 0.02 to 0.2. Increasing the starting grain size in the pure Mg condition led to a significant delay in recrystallization. The addition of Al had a minimal effect on the recrystallization kinetics of Mg.