High-energy Boundaries Research Articles

On Goss Orientation in Strip Cast Grain‐Oriented Silicon Steel

In this study, the origin of Goss texture during intermediate annealing and Goss texture development during secondary annealing of strip cast grain‐oriented silicon steel are studied by electron backscattered diffraction (EBSD). The study indicates that Goss grains originate inside the shear bands of deformed {111}<112> and {111}<110> grains. Compared to {111}<110> grains, {111}<112> grains provide more number of nucleation sites for Goss grains. During subsequent recrystallization process, Goss grains exhibit a smaller growth rate than the average value of all the recrystallized grains. The development mechanism of Goss texture is concluded as oriented nucleation. Prior to secondary annealing, high fraction of high‐energy boundaries (20°–45° misorientation angle) are observed in the vicinity of Goss grains, while significantly low fraction of Σ5 + Σ7 + Σ9 boundaries are observed. During secondary annealing, the domination of high energy boundaries around Goss grains is maintained, but the fraction of Σ5 + Σ7 + Σ9 boundaries decrease to be similar to the matrix grains. After the onset of the abnormal grain growth, the growing Goss grains continue to consist of high fraction of high‐energy boundaries. These results are consistent with the high energy (HE) boundary model, which is used to explain the abnormal grain growth in the current strip casting route.

Ultra-thin grain-oriented silicon steel sheet fabricated by a novel way: Twin-roll strip casting and two-stage cold rolling

0.05–0.15 mm-thick ultra-thin grain-oriented silicon steel sheets were successfully produced by a novel processing route including strip casting, hot rolling, normalizing, two-stage cold rolling with intermediate annealing, primary recrystallization annealing and secondary recrystallization annealing. The evolutions of microstructure, texture and inhibitor along the processing were briefly investigated. The results showed that the initial Goss orientation originated due to the heterogenous nucleation of δ-ferrite grains during solidification. Because of the lack of shear deformation, only a few Goss grains were observed in the hot rolled sheet. After the first cold rolling and intermediate annealing, Goss texture was enhanced and distributed in the whole thickness. A small number of Goss grains having a high fraction of high energy boundaries exhibited in the primary recrystallization annealed sheet. A large number of fine and dispersed MnS and AlN and a few co-precipitates MnS and AlN with the size range of 10–70 nm were also observed. Interestingly, a well-developed secondary recrystallization microstructure characterized by 10–60 mm grains and a sharp Goss texture were finally produced in the 0.05–0.15 mm-thick ultra-thin sheets. A magnetic induction B8 of 1.72–1.84 T was obtained. Another new finding was that a few {2 3 0}〈0 0 1〉 and {2 1 0}〈1 2 7〉 grains also can grow up abnormally because of the high fraction of high energy boundaries and the size and number advantage, respectively. These non-Goss grains finally deteriorated the magnetic properties of the ultra-thin sheets. In addition, low surface energies of {hk0} planes may also contribute to the abnormal growth of Goss, {2 3 0}〈0 0 1〉 and {2 1 0}〈1 2 7〉 grains.

Effect of steel substrate thickness on the structure of coating and powdering resistance of galvannealed coating: significance of texture

We describe here the effect of steel substrate thickness on the structure and powdering behavior of galvannealed (GA) coating. The study indicated that the formability of GA coating was decreased and the powdering resistance was increased with increased substrate thickness. This was attributed to differences in microstructure and Fe-content in the coating, especially the thickness of intermetallic Γ phase. The change in the thickness of steel substrate changes the microstructure of substrate, including texture, grain boundary character, and crystallographic orientation, which had a significant impact on the powdering resistance of GA coating. With increased thickness of the substrate, the intensity of γ-fiber was decreased, the crystallographic orientation of (111)–(113)–(313)//RP (rolling plane) planes on the surface of the substrate was increased and (001)–(101)//RP decreased. Furthermore, the ratio between {113} and {111} orientations was decreased and the fraction of high energy boundaries was increased. All these factors played a vital role in the formation and growth of Fe-Zn intermetallic phase and finally led to a different phase structure and change in the powdering properties of GA coating.

Secondary Recrystallization Behaviors of Grain-Oriented 6.5 wt% Silicon Steel Sheets Produced by Rolling and Nitriding Processes

By rolling and nitriding processes, 0.23- to 0.3-mm-thick grain-oriented 6.5 wt% silicon steel sheets were produced. The core losses of grain-oriented 6.5 wt% silicon steel at frequencies ranging from 400 Hz to 20 kHz were lower than that of the grain-oriented 3 wt% silicon steel with the same thickness by 16.6–35.8%. The secondary recrystallization behavior was investigated by scanning electron microscopy, energy-dispersive spectroscopy, and electron backscattered diffraction. The results show that the secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, secondary recrystallized grain sizes become larger, and the sharpness of Goss texture increases. Because more \(\left\{ {110} \right\}\left\langle {116} \right\rangle\) grains in the subsurface and the central layer of the sheets have a lot of 20°–45° high-energy boundaries in addition to Goss grains, \(\left\{ {110} \right\}\left\langle {116} \right\rangle\) can be the main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. The increases in nitrogen content can increase the inhibitor intensity and hinder abnormal growth of a mount of \(\left\{ {110} \right\}\left\langle {116} \right\rangle\) grains and therefore enhance the sharpness of Goss texture.

Texture evolution during static recrystallization of cold-rolled magnesium alloys

Texture evolution in cold-rolled Mg-0.3Zn-0.1Ca, Mg-0.4Zn and Mg-0.1Ca (at.%) alloys during static recrystallization is monitored using a quasi-in-situ electron backscatter diffraction (EBSD) method. The quasi-in-situ EBSD results show that most of recrystallized grains formed in the early stage of recrystallization have randomised orientations in the ternary alloy and they grow uniformly during the recrystallization process. The formation and uniform growth of these recrystallized grains with randomised orientations give rise to a weak texture in fully recrystallized samples of the ternary alloy. A weak recrystallization texture also forms in the early stage of recrystallization in the two binary alloys, but it is gradually replaced by a strong basal texture via the preferential growth of recrystallized grains with specific orientations. The grain size in the ternary alloy is smaller than those in the two binary alloys at each stage of recrystallization, and the grain size distribution in the ternary alloy is significantly narrower than those in the two binary alloys after full recrystallization. Solute segregation to grain boundaries is observed in all three alloys in the fully recrystallized state. It is hypothesised that Zn and Ca atoms in the ternary alloy segregate strongly to high-energy boundaries of the recrystallized grains that would otherwise grow preferentially in the counterpart binary alloys, and that this co-segregation would significantly reduce the boundary mobility, by reducing grain boundary energy and enhancing solute dragging effect, and therefore lead to a more uniform growth of recrystallized grains with randomised orientations.

高純度3.3%Si鋼での二次再結晶発現

Possibility of the occurrence of secondary recrystallization in high purity material without containing inhibitor elements was investigated experimentally. Only in the sample with primary recrystallization annealing performed at 900°C, onset of secondary recrystallization was observed. The orientation of secondary recrystallized grains proved to be {110} <001> (Goss) orientation. It was also shown that normal grain growth was suppressed in the sample in which secondary recrystallization occurred. Narrow grain size distribution and strong texture accumulation were considered to help the stabilization of the matrix grains. Texture development during secondary recrystallization in the absence of inhibitors was discussed based on proposed growth models. It was shown from Grain Boundary Character Distribution (GBCD) analysis that the High Energy (HE) boundary model was applicable to secondary recrystallization and the Solid State Wetting (SSW) model was applicable to normal grain growth. The HE boundary was related theoretically to high mobility through high grain boundary diffusion coefficient. It was considered that reducing impurity elements exerted inherent high mobility of the HE boundary and hence led to the onset of the secondary recrystallization.

Parallel three-dimensional Monte Carlo simulations for effects of precipitates and sub-boundaries on abnormal grain growth of Goss grains in Fe–3%Si steel

Using parallel three-dimensional Monte Carlo simulations, we investigated the effects of precipitates and sub-boundaries on abnormal grain growth (AGG) of Goss grains based on real orientation data of primary recrystallized Fe–3%Si steel. The simulations showed that AGG occurred in the presence of precipitates which inhibited the grain growth of matrix grains, whereas it did not in the absence of precipitates. The role of precipitates in enhancing AGG is to maintain a relatively high fraction of high energy boundaries between matrix grains, which increases the probability of sub-boundary-enhanced solid-state wetting of an abnormally growing grain. The microstructure evolved by the simulation could reproduce many realistic features of abnormally growing grains, such as the formation of island and peninsular grains and merging of abnormally growing grains which appeared to be separated initially on the cross-section.

Five parameter distribution of planes in AA 5182 aluminium alloys with relevance to intergranular corrosion resistance

Alloys of AA 5182 are commonly used in the automotive industry to provide weight reductions in vehicle chassis. The strength of such alloys is based on the Mg content, with Mg causing the precipitation of a β-Al8Mg5 phase along the length of the grain boundaries in the microstructure. These precipitates are vulnerable to intergranular corrosion (IGC) in acidic environments. For this reason, the proportions of Mg in the microstructure must be limited, with >3 wt-%Mg causing intergranular attack. The alloys used in this study had an Mg content of 4·43%, so were vulnerable to IGC. Standard nitric acid mass loss tests were applied to determine the level of corrosion resistance in two samples subjected to various treatments. Using ‘five parameter’ analysis, the importance of the grain boundary plane and thermomechanical history to IGC resistance was determined. ‘Special’ planes were identified in the microstructure and their impact on IGC resistance was assessed. From such analysis, it was found that a high deformation level of 50% together with a simulated batch annealing heat treatment yielded the highest proportions of ‘special’ boundaries within the microstructure. ‘Special’ boundaries in this study were identified to be low angle boundaries, <111> twist boundaries and <110> tilt boundaries, which are associated with a reduced energy compared to random high angle boundaries. As precipitation generally occurs along high energy boundaries, ‘special’ boundaries reduce precipitate formation, thus reducing IGC intensity. Future implications include the introduction of a higher proportion of ‘special’ boundaries into the microstructure, allowing for an increase in Mg content in these alloys.

Effect of Cold Rolling Reduction Rate on Secondary Recrystallized Texture in 3 Pct Si-Fe Steel

The phenomenon of secondary recrystallization in 3 pct Si-Fe electrical steel subjected to relatively high cold rolling reduction rates has been investigated. The texture of the secondary recrystallized sample that has a cold rolling reduction rate of 97.2 pct consists mainly of {110}〈112〉 component, which is quite different from the ideal Goss ({110}〈001〉) texture obtained after lower cold rolling reduction rates. The grain boundary character distribution (GBCD) analysis on the primary recrystallized sample with a cold rolling reduction rate of 97.2 pct indicates that the {110}〈112〉 component has the highest frequency of high energy (HE) boundary with a misorientation angle between 20 and 45 deg, whereas the Goss component in the sample subjected to lower cold rolling reduction rates has the highest frequency of HE boundary. These results indicate that the component with the highest frequency of HE boundary surrounding it after primary recrystallization has the privilege to outgrow other components during secondary recrystallization. However, the GBCD analysis for coincidence site lattice (CSL) boundary points out that the Goss component has the highest frequency of CSL boundaries in the primary recrystallized texture irrespective of the cold rolling reduction applied. These results suggest that the HE model can predict the orientation relationship between the primary and secondary recrystallized textures better than the CSL model.

Change in grain-boundary ensemble upon the A1 → L12 phase transition in Ni3Mn alloy

The grain structure of Ni3Mn alloy is investigated in the states with short-range and long-range atomic orders that arise at the A1 → L12 phase transition. It is found that in ordering annealing, new boundaries of a general type form, the fraction of special-type boundaries (including twin boundaries) is reduced, the share of high-energy special boundaries with Σ > 11 increases, and the alloy’s texture is transformed into a “gray” texture.

Effect of Cold Rolling Reduction Rate on Secondary Recrystallized Texture in 3%Si-Fe

The phenomenon of secondary recrystallization in 3%Si-Fe under relatively high cold rolling reduction rate condition has been investigated. The texture of the secondary recrystallized sample under 97.2% cold rolling reduction rate condition consists of {110} orientation, which is quite different from Goss ({110}) orientation obtained under lower cold rolling reduction rate conditions. As a result of Grain Boundary Character Distribution (GBCD) analysis on primary recrystallized texture, {110} orientation has the highest frequency of High Energy (HE) boundary with misorientation angle between 20° and 45°. This result demonstrates that the orientation, which has the highest frequency of HE boundary in primary recrystallized texture, is selected during secondary recrystallization. However, as a result of GBCD analysis based on Coincidence Site Lattice (CSL) boundary, Goss orientation has the highest frequency of S9 (CSL) boundary in the primary recrystallized texture throughout all cold rolling conditions.

Blueprints of the no-scale multiverse at the LHC

We present a contemporary perspective on the String Landscape and the Multiverse of plausible string, $M$- and $F$-theory vacua. In contrast to traditional statistical classifications and capitulation to the anthropic principle, we seek only to demonstrate the existence of a nonzero probability for a universe matching our own observed physics within the solution ensemble. We argue for the importance of No-Scale Supergravity as an essential common underpinning for the spontaneous emergence of a cosmologically flat universe from the quantum ``nothingness.'' Concretely, we continue to probe the phenomenology of a specific model which is testable at the LHC and Tevatron. Dubbed No-Scale $\mathcal{F}\mathrm{\text{\ensuremath{-}}}SU(5)$, it represents the intersection of the Flipped $SU(5)$ Grand Unified Theory (GUT) with extra TeV-Scale vectorlike multiplets derived out of $F$-theory, and the dynamics of No-Scale Supergravity, which in turn imply a very restricted set of high-energy boundary conditions. By secondarily minimizing the minimum of the scalar Higgs potential, we dynamically determine the ratio $\mathrm{tan}\ensuremath{\beta}\ensuremath{\simeq}15--20$ of up- to down-type Higgs vacuum expectation values (VEVs), the universal gaugino boundary mass ${M}_{1/2}\ensuremath{\simeq}450\text{ }\text{ }\mathrm{GeV}$, and, consequently, also the total magnitude of the GUT-scale Higgs VEVs, while constraining the low-energy standard model gauge couplings. In particular, this local minimum minimorum lies within the previously described ``golden strip,'' satisfying all current experimental constraints. We emphasize, however, that the overarching goal is not to establish why our own particular universe possesses any number of specific characteristics, but rather to tease out what generic principles might govern the superset of all possible universes.

The No-Scale Multiverse at the LHC

We present a contemporary perspective on the String Landscape and the Multiverse of plausible string, M- and F-theory vacua, seeking to demonstrate a non-zero probability for the existence of a universe matching our own observed physics within the solution ensemble. We argue for the importance of No-Scale Supergravity as an essential common underpinning for the spontaneous emergence of a cosmologically flat universe from the quantum "nothingness". Our context is a highly detailed phenomenological probe of No-Scale ℱ-SU(5), a model representing the intersection of the ℱ-lipped SU(5) × U(1)x Grand Unified Theory (GUT) with extra TeV-Scale vector-like multiplets derived out of ℱ-theory, and the dynamics of No-Scale Supergravity. The latter in turn imply a very restricted set of high energy boundary conditions.We present a highly constrained "golden point" located near M1/2 = 455 GeV and tan β = 15 in the tan β – M1/2 plane, and a highly non-trivial "golden strip" with tan β ≃ 15, mt = 173.0-174.4 GeV, M1/2 = 455-481 GeV, and Mv = 691-1020 GeV, which simultaneously satisfies all the known experimental constraints, featuring also an imminently observable proton decay rate. We supplement this bottom-up phenomenological perspective with a top-down theoretical analysis of the one-loop effective Higgs potential. A striking consonance is achieved via the dynamic determination of tan β and M1/2 for fixed Z-boson mass at the local minimum minimorum of the potential, that being the secondary minimization of the spontaneously broken electroweak Higgs vacuum Vmin. By also indirectly determining the electroweak scale, we suggest that this constitutes a complete resolution of the Standard Model gauge hierarchy problem.Finally, we present the distinctive collider level signatures of No-Scale ℱ-SU(5) for the √s = 7 TeV LHC, with 1 fb−1 of integrated luminosity. The characteristic feature is a light stop and gluino, both sparticles lighter than all other squarks, generating a surplus of ultra-high multiplicity (≥ 9) hadronic jet events. We propose modest alterations to the canonical background selection cut strategy which are expected to yield significantly enhanced resolution of the characteristic ultra-high jet multiplicity ℱ-SU(5) events, while readily suppressing the contribution of all Standard Model processes, and allowing moreover a clear differentiation from competing models of new physics, most notably minimal supergravity. Detection by the LHC of the ultra-high jet signal would constitute a suggestive evocation of the intimately linked stringy origins of ℱ-SU(5), and could possibly provide a glimpse into the underlying structure of the fundamental string moduli, possibly even opening a darkened glass upon the hidden workings of the No-Scale Multiverse.

Challenges of the study on precipitation behaviors of MnS in oriented electrical steels

The studies of the thermo-mechanic principles and the kinetic analysis of MnS precipitation behavior in oriented electrical steels conducted in the last dozen years have been summarized. The problems and insufficiency in the fields concerning nucleation theory of MnS precipitation, the relationship between the precipitation and dynamic recrystallization of the matrix as well as the influence of high-energy boundary precipitation on the pinning effect of the boundary migration were discussed. Suggestions were proposed to modify researches concerning the initial position density for MnS nucleation, the mutual interaction between the precipitation and the dynamic recrystallization as well as the kinetic principles of precipitation nucleation on grain boundaries with different boundary energy, which would complete the related theory of MnS precipitation behaviors.

Defect structures in B12As2 epitaxial layers grown on (0001) 6H-SiC

A detailed analysis of the microstructure in B12As2 epitaxial layers grown by chemical-vapor deposition on (0001) 6H-SiC substrates is presented. Synchrotron white beam x-ray topography enabled macroscopic characterization of the substrate/epilayer ensembles and revealed the presence of a quite homogeneous solid solution of twin and matrix epilayer domains forming a submicron mosaic structure. The basic epitaxial relationship was found to be (0001)B12As2⟨112¯0⟩B12As2∥(0001)6H-SiC⟨112¯0⟩6H-SiC and the twin relationship comprised a 180° (or equivalently 60°) rotation about [0001]B12As2 in agreement with previous reports. Cross-sectional high resolution transmission electron microscopy revealed the presence of a ∼200 nm thick disordered transition layer which was shown to be created by the coalescence of a mosaic of translationally and rotationally variant domains nucleated at various types of nucleation sites available on the (0001) 6H-SiC surface. In this transition layer, competition between the growth of the various domains is mediated in part by the energy of the boundaries created between them as they coalesce. Boundaries between translationally variant domains are shown to have unfavorable bonding configurations and hence high-energy. These high-energy boundaries can be eliminated during mutual overgrowth by the generation of a 1/3[0001]B12As2 Frank partial dislocation which effectively eliminates the translational variants. This leads to an overall improvement in film quality beyond thicknesses of ∼200 nm as the translational variants grow out leaving only the twin variants. (0003) twin boundaries in the regions beyond 200 nm are shown to possess fault vectors such as 1/6[11¯00]B12As2, which are shown to originate from the mutual shift between the nucleation sites of the respective domains.

Experimental and computer model investigations of microtexture evolution of non-oriented silicon steel

The authors have performed a systematic set of experiments and corresponding computer simulations to investigate the microtexture evolution of non-oriented silicon steels. The experiments show that similar behaviour is observed during annealing at 800 and 900°C, grain growth occurs and the 〈110〉 fibre microtexture volume fraction decreases rapidly. The authors have imported the microstructures and grain orientations directly from the electron backscattered diffraction (EBSD) system into a Monte Carlo Potts model and used these to simulate the grain growth of the system. These simulations show that neither the residual size distributions of different microtexture fibres nor the presence of highly mobile high energy boundaries are responsible for the grain growth and 〈110〉 fibre microtexture decrease.

Fracture behavior of ∑9 [1 1 0] asymmetric tilt boundaries in Cu doped with Bi

Considerable intergranular embrittlement of Cu takes place due to segregation of Bi on grain boundaries. However, the concentration of Bi for the grain boundary segregation varies depending on the character of the grain boundary. In order to examine the relationship between the embrittlement and the character of the grain boundary, the dependence of the behavior of fracture on the inclination angle was experimentally observed at temperatures of T = 298 and 77 K for the ∑9 [1 1 0] asymmetric tilt boundary in Cu doped with Bi. For the high-energy boundary, the brittle fracture occurs in an intergranular manner at both temperatures. On the other hand, for the low-energy boundary, the ductile fracture takes place in a transgranular manner at T = 298 K but in a transgranular or intergranular manner at T = 77 K. The concentration of Bi for the grain boundary segregation may be large in the high-energy boundary but small in the low-energy boundary. According to estimation, the thermodynamic interaction between Cu and Bi in the grain boundary is repulsive. Furthermore, the repulsive interaction is more notable for the high-energy boundary than for the low-energy boundary. Consequently, the fracture occurs brittlely for the high-energy boundary with a large Bi concentration but ductilely for the low-energy boundary with a small Bi concentration.

Dissociation and faceting of asymmetrical tilt grain boundaries: Molecular dynamics simulations of copper

Energies and atomic structures of asymmetrical $\ensuremath{\Sigma}11[110]$ tilt grain boundaries in copper have been computed using molecular dynamics with an embedded-atom potential. Two interesting effects have been found: (1) The boundaries dissociate into a low-angle and a high-angle boundary separated by a layer of a fcc-based long-period structure containing intrinsic stacking faults, and (2) the high-energy boundary breaks into nanometer-size facets, some of which are not $\ensuremath{\Sigma}11$ and do not even belong to any coincident-site lattice (CSL). Thus, asymmetrical tilt boundaries locally deviate from the CSL and the average plane imposed by the macroscopic geometry, demonstrating a limitation of the CSL model of grain boundaries. The results are consistent with high-resolution transmission electron microscopy observation available in the literature.

Evolution of the Texture on Primary Recrystallization and Grain Growth in Fe-3%Si Steels

Recrystallization texture in grain oriented silicon steel at different annealing temperature is investigated. Normalized x-ray intensities of various orientation components observed in Orientation Distribution Function are used for comparison. The computed CSL boundary distributions about Goss component with annealing condition were calculated. The misorientation angle distribution is also measured in order to find the importance of high-energy boundary with misorientation 20~45° range for the secondary recrystallization of Goss grain. From the analysis of CSL boundary distribution and misorienation angle distribution, the distribution of CSL boundaries does not evidently show any preferred difference between Goss and other texture components. Whereas, the misorientation angle analysis shows that the number of 20°~45° misoriented boundaries is higher around the Goss grains than around other texture components.

Spatial correlation of high-energy grain boundaries in two-dimensional simulated polycrystals

A polycrystal undergoes microstructural changes to reach a lower energy state. In particular, the system evolves so as to reduce the total grain boundary energy. A simple two-dimensional model of a polycrystal comprised of randomly oriented crystalline grains suggests that energy minimization reduces or eliminates any spatial correlation among high-energy grain boundaries. Thus grain boundary engineering not only reduces the density of high-energy boundaries, but also prevents their organization into a coarse, albeit discontinuous, network.