Ideal Texture Research Articles

Modelling of Texture Evolution in High Pressure Torsion by Crystal Plasticity Finite Element Method

In this study, texture evolution during high pressure torsion (HPT) of aluminum single crystal is predicted by the crystal plasticity finite element method (CPFEM) model integrating the crystal plasticity constitutive theory with Bassani & Wu hardening model. It has been found by the simulation that, during the HPT process, the lattice rotates mainly around the radial direction of the sample. With increasing HPT deformation, the initial cube orientation rotates progressively to the rotated cube orientation, and then to the C component of ideal torsion texture which could be remained over a wide strain range. Further HPT deformation leads to the orientation towards to the ideal texture component.

Texture and Lattice Distortion Study of an Al-6061-T6 Alloy Produced by ECAP

Equal channel angular pressing (ECAP) is a severe plastic deformation (SPD) technique that produces nanostructured materials. Based on a remarkable grain size reduction, this process has led to improve mechanical properties, such as yield strength, fatigue, UTS, etc. In this work the characterization of the microstructure of the aluminum 6061-T6 alloy; plastically deformed up to ¾ µ 6, by the ECAP process, following route Bc, is presented. For this purpose, the ECAP processed samples were characterized by means of X-ray diffraction (for texture and line pro fi le analysis) and transmission electron microscopy. The initial crystallographic texture vanished after one ECAP pass and a new, well de fi ned, shear texture C a was generated. For the subsequent ECAP passes, more shear components: A 1 a , B a and B a were also developed. From the orientation distribution function analysis, a shift (generally less than 15°) between some experimental maxima and the reported ideal shear texture positions was observed. From these results, it was found that the microstructure generated with this process was stabilized after the 5th ECAP pass. Finally, the micro-strain analyses, in addition to the texture and transmission electron microscopy, contributed to the understanding of the effec t of the physical and mechanical processes that were activated during the SPD-ECAP techniques

Residual Stress Analysis of Strongly Textured Materials by Means of the Incremental Hole-Drilling Method – Survey on the Application Limits

AbstractIn sheet metal forming, residual stress distributions are often accompanied by crystallographic texture. Incremental hole-drilling for stress analysis is only reliably applicable for isotropic materials. The objective of this study is to determine the influence of texture on residual stress analysis using conventional evaluation methods and to specify the application limits in case of textured material states. A systematic finite element simulation study for ideal texture orientations is conducted with respect to the strain gage rosette orientation. The results of the numerical investigations show that reliable stress analysis on strongly textured materials is not feasible using the existing evaluation method. The application limits are given for the application of commercially available evaluation software with respect to degree of anisotropy, stress state and strain gage orientation.

Microstructure and mechanical properties of friction stir processed AISI 316L stainless steel

Friction stir processing was used to refine the grain structure in 2mm thick AISI 316L stainless steel sheets, with a pinless tool, at a constant traverse speed of 63mm/min and relatively low rotational speeds of 200 and 315rpm. Depending on the processing conditions, the initial grain size of 14.8μm in the base metal was subsequently decreased to 0.8–2.2μm in the processed areas. The microstructural characterizations by orientation imaging and transmission electron microscopy revealed that the grain structure evolution in the stir zone is primarily dominated by discontinuous dynamic recrystallization. The material flow was found to be near simple shear deformation and the developed textures were composed of a mixture of A/A‾ and C components of ideal simple shear textures. The mechanical properties were also evaluated by the longitudinal tensile tests and microhardness measurements. The obtained results showed that, despite a 50% decrease in ductility, the highest yield and ultimate tensile strength of the friction stir processed samples are respectively about 1.6 and 1.2 times higher than those of the base metal. In good agreement with the tensile properties, the increased hardness of the stir zone was attributed to the grain structure refinement.

Research on the Abnormal Grain Growth of Goss Grains in Strip-Cast 4.5%Si Grain-Oriented Electrical Steels

In conventional production of grain-oriented electrical steel, the content of silicon is limited to 3.0%~3.4%, which could control the ‘γ→α’ transformation process to obtain fine grain sizes in hot-rolling and disperse AlN particles in normalizing. In this study, the precipitation behaviors of S ans N in 4.5% Si-Fe alloy are inhibited during twin-roll strip casting process. And then the ideal microstructure and texture was obtained after the two-stage cold rolling and primary annealing. The evolution of microstructure and texture during the subsequent high temperature annealing were investigated. The results revealed that a sharp and developed Goss texture has been achieved by secondary recrystallization in the final annealing step and the magnetic induction B8 /Bsis above 1.76/1.90T.

Twinning characteristic and variant selection in compression of a pre-side-rolled Mg alloy sheet

{10−12} Twinning is one of the most important strain accommodation mechanisms for Mg alloy especially at room temperature deformation. Accompanying with twining, the lattice of matrix is rotated by large angles, and hence pre-twinning can be utilized to tailor texture of wrought Mg alloy. To better utilize this method, the present study aims to understand the twinning characteristic and variant selection in compression of a pre-side-rolled Mg alloy sheet. It confirms that the pre-generated twin lamellae can significantly enhance the yield strength for subsequent in-plane compression. But the amount of pre-side-rolling has different effect on the strain hardening rate between the two subsequent compression directions (transverse direction and rolling direction, designated as TD and RD, respectively). Moreover, the {10−12} twins in the two samples exhibit different morphology although the area fraction is nearly the same. Crystallographic analysis indicates that the variant selection in most twinned grains is consistent with Schmid law i.e., the twins are activated from the variant pair with the highest Schmid factor. In the cases of twin–twin transfer at grain boundaries, local strain accommodation is also important for variant selection. It reveals that a modified Schmid factor for rolling is effective in prediction of twin variants in pre-side-rolling. Further analysis on ideal texture indicates that the preference order of the six possible variants in side-rolling is the same with that in the subsequent TD compression, but varies from that in RD compression. This is consistent with the experimental observation that twin growth and coalescence is dominant in the former, whereas new twin variant is formed in the latter.

Anisotropy and Asymmetry of Yield in Magnesium Alloys at Room Temperature

Mechanical anisotropy and asymmetry are often pronounced in wrought magnesium alloys and are detrimental to formability and service performance. Single crystals of magnesium are highly anisotropic due to the large difference in critical resolved shear stress between the softest and hardest deformation modes. Polycrystalline magnesium alloys exhibit lower anisotropy, influenced by texture, solute level, and precipitates. In this work, a fundamental study of the effects of alloying, precipitate formation, and texture on the change in anisotropy and asymmetry from the pure magnesium single crystal case to polycrystalline alloys has been performed. It is demonstrated that much of the reduction in anisotropy and asymmetry arises from overall strengthening as solute, precipitates, and grain boundary effects are accounted for. Precipitates are predicted to be more effective than solute in reducing anisotropy and asymmetry, but shape and habit are critical since precipitates produce highly anisotropic strengthening. A small deviation from an ideal basal texture (15 deg spread) has a very strong effect in reducing anisotropy and asymmetry, similar in magnitude to the maximum effect produced by precipitation. Elasto-plastic modeling suggests that this is due to a contribution from basal slip to initial plastic deformation, even when global yield is not controlled by this mode.

Thermodynamic limits of nanophotonic light trapping in thin film silicon solar cells

We have extended an earlier thermodynamic treatment of light-trapping in lattice-textured solar cells to higher absorptances. This treatment is used to calculate the quantum efficiency spectra and short-circuit current densities JSC for thin-film silicon solar cells with ideal lattice textures. An optimal triangular lattice period of 900 nm yields a calculated JSC that is 2 mA/cm2 larger than for ideal random textures in a 1000 nm thick cell. We compare the calculations to recent experiments with periodically textured cells. While the experimental cells give JSC values that are comparable to the best cells with conventional textures, they do not show the features associated with the prediction of higher JSC. We discuss the role of imperfections in the periodic texturing, and suggest that cells used with solar tracking may realize the predicted JSC improvement.

Analysis of shear deformation by slip and twinning in low and high/medium stacking fault energy fcc metals using the [formula omitted]-model

Experimental tests involving shear stresses allow material to be deformed to very high plastic strain by overcoming localization phenomena. The simple shear texture development, which is also common near the surface of rolled parts, is important to study since it is directly connected to the metal anisotropy. Crystal plasticity models are used to simulate large deformation plasticity and texture evolution. The main insufficiency of most existing models is that they are, in certain cases, unable to predict all type of experimentally observed textures as well as texture transitions. In this paper, we show that the polycrystalline ϕ-model can be used to compute simple shear crystallographic texture transition for face-centered cubic metals (fcc) at large strains. This model takes into account the grains interaction effects but without the Eshelby inclusion theory. Predicted results are compared to experimental shear textures for medium stacking fault energy (SFE) metals (i.e. copper) and low SFE metals (i.e. silver). We show that the ϕ-model is able to predict a clear shear texture transition characterizing a range of fcc metals having high/medium to low SFE. The twinning mechanism is included in the ϕ-model in order to improve the predicted shear textures for low SFE metals. The effect of twinning on the ideal shear texture components is shown and is consistent with experimental results from the literature.

Recrystallization, texture evolution, and magnetostriction behavior of rolled (Fe81Ga19)98B2 sheets during low-to-high temperature heat treatments

In order to study the texture evolution and magnetostriction behavior in the rolled Fe–Ga–B sheets during the heat treatments from low to high temperatures, (Fe81Ga19)98B2 sheets were prepared and investigated. The phase structure, recrystallization, grain size, texture evolution, and magnetostriction behavior during the annealing from 525 to 1200 °C for 1–5 h were investigated using X-ray diffraction, electron backscattering diffraction, and standard strain-gauge measurements. Results indicated that the primary recrystallization temperature for 1-h annealing was found as 525–575 °C in (Fe81Ga19)98B2 sheets. Annealing the sample below 575 °C for 1 h, the release of rolling stress and increase of 〈100〉 η-fiber texture during the primary recrystallization jointly resulted in a rapid improvement in magnetostriction. After annealed between 575 and 1100 °C for 1 h, the grains of the sheets underwent a normal growth, and the three (α-, γ- and η-fiber) types of textures kept an approximate balance, leading to a plateau of magnetostriction around 75 ppm. When the abnormal grain growth proceeded above 1100 °C for 1 h, the proportion of η-fiber texture markedly increased, and the magnetostriction was subsequently increased to 97 ppm. For longer annealing durations, the strong ideal cube texture (η-fiber) was firstly formed and then changed to undesired texture (γ-fiber), producing a corresponding magnetostriction peak of 136 ppm at 2 h for the annealing at 1200 °C. The clear correlation among heat treatments, recrystallization, texture, and magnetostriction provides an essential understanding for Fe–Ga–B alloy sheets.

Martensitic Phase Transformation and Deformation Behavior of Fe–Mn–C–Al Twinning‐Induced Plasticity Steel during High‐Pressure Torsion

The transformation between the face centered cubic austenitic and hexagonal close‐packed martensitic phases during high‐pressure torsion processing was observed in a Fe–Mn–C–Al twinning‐induced plasticity steel. This phase transformation was not found in the same material processed by unidirectional compressive and tensile deformation. Initiated by the high‐pressure loading, the martensite phase initially increased with torsional strain but diminished subsequently. Texture evolution of the austenitic phase was compared with the ideal texture distribution of face‐centered cubic materials after shear deformation.

Microstructure evolution and texture development in a friction stir-processed AISI D2 tool steel

Crystallographic texture developments during friction stir processing (FSP) of AISI D2 tool were studied with respect to grain sizes in different tool rotation rates. Comparison of the grain sizes in various rotation rates confirmed that grain refinement occurred progressively in higher rotation rates by severe plastic deformation. It was found that the predominant mechanism during FSP should be dynamic recovery (DRV) happened concurrently with continuous dynamic recrystallization (CDRX) caused by particle-stimulated nucleation (PSN). The developed shear texture relates to the ideal shear textures of D1 and D2 in bcc metals. The prevalence of highly dense arrangement of close-packed planes of bcc and the lowest Taylor factor showed the lowest compressive residual stress which is responsible for better mechanical properties compared with the grain-precipitate refinement.

Ageing texture of hot rolled and solution treated Ti–Nb alloys

Abstract Ageing textures of three alloys, namely, Ti-8Nb, Ti-12Nb and Ti-16Nb have been studied in β STWQ and α + β STWQ specimens at three different temperatures. Ageing treatments in the present study are associated with phase transformation as well as the growth of orientations of the transformation products. The development of an ideal c-type texture depends on alloy composition, solution treatment and ageing treatment temperatures. The 450°C aged specimens of the alloys Ti-8Nb (β STWQ and α + β STWQ) and Ti-12Nb (α + β STWQ) possessed c-type texture. The presence of β phase weakens the basal component and strengthens non-basal components in {0002} pole figure. The resultant texture of 550°C aged specimens appears to be independent of the texture of the starting material.

Instrumental Textural Analysis of Muscadine Grape Germplasm

Twenty-six muscadine grape (Vitis rotundifolia Michx.) cultivars and selections were evaluated for a range of skin and flesh texture attributes. Two Vitis vinifera L. and one Vitis labruscana Bailey table grape cultivars were included for comparison. Penetration tests using a flat cylindrical probe were used to assess whole berry texture. Ideal whole berry texture is firm and easily broken down during mastication, which was measured as small berry deformation at first peak and berry maximum force, respectively. Muscadine berry deformation at first peak ranged from 4.35 to 7.82 mm and berry maximum force ranged from 5.7 to 13.9 N. V. vinifera table grape berries were firmer (3.14 to 3.19 mm berry deformation at first peak) and more tender (4.0 to 4.9 N berry maximum force) than muscadine berries. Berry penetration work was strongly correlated with both berry deformation at first peak and berry maximum force and ranged from 13.0 to 54.1 mJ in the muscadine germplasm. Penetration tests of muscadine berry flesh revealed a range of flesh firmness from very soft (0.65 N) to firm (3.06 N) but none was as firm as the V. vinifera berry flesh (3.9 N). Penetration tests of muscadine berry skins revealed newer selections bred for table use had relatively tender skins with a skin break force of 12.1 N, which was not different from V. vinifera samples. Berry penetration work and flesh maximum force were determined to be the most useful characteristics for routine screening of breeding program material.

Use of Osseocartilaginous Paste Graft for Refinement of the Nasal Dorsum in Rhinoplasty

In both primary and secondary rhinoplasty, establishment or refinement of nasal dorsal aesthetic lines is of paramount importance. Many different techniques used to create a cosmetically acceptable nasal dorsum have been published. The material to be used in nasal dorsal contouring should create a harmonic contour and should be easily shaped, long-lasting, and resistant to infection. Resection of the hump yields an osseocartilaginous complex as a single unit when an osteotome is used. Use of a rasp gives a good amount of fragmented material comprising bone, cartilage, soft tissues, and blood. The authors used this material as a paste graft to refine the nasal dorsum in rhinoplasty and retrospectively evaluated the outcomes. A retrospective chart review of 77 patients who underwent this procedure between 2003 and 2009 was performed. The follow-up period ranged from 22 to 40 months (median, 28 months). The postoperative evaluations included clinical examination and digital photographic documentation. The satisfaction of each patient was assessed with a questionnaire completed at the 12th postoperative month. The described graft, which combines the advantages of cartilage and bone, was shown to be clinically durable. This combination also results in an ideal texture and consistency for molding due to its diced form. The texture of this graft enables the surgeon to give a final shape to the nasal dorsum bimanually. In this study, a paste graft was shown to be a versatile and reliable composite material for nasal dorsal contouring and refinement.

Space resolved microstructural characteristics in the chip formation zone of orthogonal cut C45E steel samples characterized by diffraction experiments

Diffraction experiments with high energy synchrotron X-radiation were performed during orthogonal cutting of the steel C45E. The development of the microstructure was analysed by means of the evolution of integral X-ray peak intensities and FWHMs (Full Width at Half Maxima) at different measuring positions in the chip formation zone. Measuring positions were chosen around the primary and secondary shear zones and behind the cutting edge, to represent positions with a different degree of deformation. The results were compared to observations made from optical microscopy on the chip root samples. A strong change of the microstructure was observed during chip formation in dependence on the measuring position, namely a strong reduction of domain sizes and a reorientation which results in a bcc shear texture, which is described with the ideal textures (1 1 0)[0 0 1] and (1 1 2¯)[1 1 1]. The shear direction determined by optical microscopy could be brought into agreement with the shear direction observed in the 110 X-ray pole figure.

Effect of equal channel angular pressing on grain refinement and texture evolution in a biomedical alloy Ti13Nb13Zr

Evolution of texture and concomitant grain refinement during Equal Channel Angular Pressing (ECAP) of Ti - 13Nb - 13Zr alloy has been presented. Sub-micron sized equiaxed grains with narrow grain size distribution could be achieved after eight pass at 873 K. A characteristic ECAP texture evolved in alpha phase till four passes while the evolution of characteristic ECAP texture in the beta phase could be observed only beyond the fourth pass. On increasing the deformation up to eight passes, the texture in alpha phase weakens while the beta phase shows an ideal ECAP texture. A weaker texture, low dislocation density and high crystallite size values in alpha phase suggest the occurrence of dynamic recrystallization. The absence of texture evolution in beta phase till four passes can be attributed to local lattice rotations. The characteristic ECAP texture in the eight pass deformed sample is attributed to delayed dynamic recrystallization in the beta phase. (C) 2013 Elsevier Inc. All rights reserved.

Aesthetic Considerations in Forehead Reconstruction in Skin Carcinoma

Reconstruction of the forehead has been a challenge for many surgeons. Some use skin grafts, other microvascular flaps, but local flaps for coverage of forehead skin are still the cornerstone principle in providing the ideal skin color and texture. In this article, the forehead is classified into surgical reconstructive subunits. These subunits are set according to the surrounding structures. Flaps are rectangular in shape in mobility in order to follow the natural lines of the forehead.

A rate independent polycrystal model and a specific application for asymmetrically rolled aluminium sheets

AbstractThe asymmetric rolling process differs from conventional rolling through the use of different roll circumferential velocities or diameters. Using proper parameters, asymmetric rolling imposes intense shear deformations across the sheet thickness, leading not only to the occurrence of shear texture, but also to grain refinement [1]. In fact, some shear texture components are known to improve plastic strain ratio values, and thus formability.In this work, the rate‐independent polycrystal model of Gambin [2] was efficiently implemented and applied to predict the mechanical response of distinct texture components that appear after asymmetrical rolling. For FCC materials, this polycrystal plasticity model avoids the uniqueness issue related to the choice of the set of active slip systems by applying a regularized Schmid Law. Consequently, it generates yield surfaces with smooth corners where the normal vector is always uniquely defined. Also, it doesn't require the arbitrarily defined reference strain rate commonly used in the viscous‐approximation of rate‐dependent models.For validation purposes, a 1050‐O sheet was subjected to tensile and shear tests. The model could accurately simulate the measured results. In the end, ideal textures components were simulated and their mechanical response was evaluated. Hence, it is stated a solid basis to justify the improvement of sheet's mechanical properties after asymmetrical rolling when compared to conventional rolling. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A novel advancement flap for reconstruction of massive forehead and temple soft‐tissue defects

To describe the authors' experience with an extended deep-plane cervicofacial (EDPCF) advancement flap, a modification of the deep-plane cervicofacial flap, for reconstruction of large forehead and temple soft-tissue defects. Case series at a tertiary referral medical center. The charts of 11 consecutive patients who underwent EDPCF flap surgery for reconstruction of forehead and temple skin cancer defects were reviewed for demographics, smoking status, defect size, length of surgery and hospitalization, American Society of Anesthesiologists Physical Status Classification (ASA) grade, and postoperative complications. All patients had reconstruction of large forehead and temple defects following either primary resection or Mohs micrographic surgery for skin cancer. No skin grafting was required for secondary defects. The average defect size was 52.2 cm(2) . Patient ages averaged 74 years with a median ASA grade of 3. Thirty-six percent of patients admitted to smoking. Average operative time was 100 minutes, with 82% of patients treated on an outpatient basis. There were no complications of ectropion or facial nerve injury encountered. Partial distal flap necrosis occurred in one patient who admitted to smoking and resolved with conservative management. The EDCPF flap is a robust flap with a dual arterial supply and both rotation and advancement components. It is ideal in frail patients with good soft-tissue laxity and provides an immediate one-stage reconstruction with ideal skin color, texture, and thickness matches for large forehead and temple defects.