Observation and modeling of the through-thickness texture gradient in commercial-purity aluminum sheets processed by accumulative roll-bonding

The texture evolution in commercial-purity aluminum (AA1070) processed by accumulative roll-bonding (ARB) is investigated with the aid of X-ray diffraction and crystal plasticity modeling. The experimental results indicate strong texture gradients through the sheet thickness, from rolling-type textures with orthorhombic symmetry at the center to shear-type textures with monoclinic symmetry near the surface. The experimental textures are reproduced well by polycrystal plasticity modeling carried out with deformation histories from finite element simulations. The observations of a relatively strong {4 4 11}〈11 11 8〉 component at the center and a {0 0 1}〈1 1 0〉 component at the surface are attributed to their higher orientation stability than the other rolling- and shear-type orientations. Examination of the average through-thickness textures suggests that the ARB technique may not be an effective means to develop apparent {1 1 1}〈u v w〉 components and thus to enhance the normal anisotropy of plasticity of the bulk sheet materials.     

Texture memory effect in heavily cold-rolled Ni3Al single crystals

In Ni₃Al the cold-rolled Goss texture changed to a complicated one after primary recrystallization and returned to the original Goss during the subsequent grain growth, which can be referred to as the texture memory effect. In this study, we examined the evolution of grain orientations during the grain growth using the electron backscatter diffraction (EBSD) method. It was found that just after the primary recrystallization most of the grains had a 40°〈1 1 1〉 rotation relationship to the Goss texture, the remaining grains being Goss and other textures. The formation of the 40°〈1 1 1〉 rotated grains can be explained by a multiple twinning mechanism. In the grain growth, the Goss grains, which were surrounded by the 40°〈1 1 1〉 rotated grains, grew preferentially due to the high mobility of the 40°〈1 1 1〉 grain boundaries, leading to the texture memory effect.     

Effect of deformation and annealing on the formation and reversion of ε-martensite in an Fe–Mn–C alloy

Microstructure and texture evolution during cold rolling and subsequent annealing were studied in an Fe–22 wt.% Mn–0.376 wt.% C alloy. During rolling the deformation mechanisms were found to be dislocation slip, mechanical twinning, deformation-induced ε-martensite transformation and shear banding. At higher strains, the brass-type texture with a spread towards the Goss-type texture dominated. A decrease in the Cu- and S- components was attributed to the preferential transformation to ε-martensite in Cu- and S-oriented grains. The texture of ε-martensite was sharp and could be described as {1 1 2 9}〈3 3 6 2〉. The orientation relationship {1 1 1}^γ//{0 0 0 1}^ε and 〈110〉^γ//〈1 1 –2 0〉^ε between ε-martensite and austenite was observed but only certain variants were selected. On subsequent annealing, the ε-martensite transformed reversely to austenite by a diffusionless mechanism. Changes in length along rolling, normal and transverse directions on heating were anisotropic due to a combination of volume expansion and shape memory effects. The S-texture component increased significantly due to transformation from the ε-martensite.     

Deformation of wrought uranium: Experiments and modeling

The room temperature deformation behavior of wrought polycrystalline uranium is studied using a combination of experimental techniques and polycrystal modeling. Electron backscatter diffraction is used to analyze the primary deformation twinning modes for wrought alpha-uranium. The {1 3 0}〈3 1 0〉 twinning mode is found to be the most prominent twinning mode, with minor contributions from the ‘{1 7 2}’〈3 1 2〉 and {1 1 2}‘〈3 7 2〉’ twin modes. Because of the large number of deformation modes, each with limited deformation systems, a polycrystalline model is employed to identify and quantify the activity of each mode. Model predictions of the deformation behavior and texture development agree reasonably well with experimental measures and provide reliable information about deformation systems.     

Microstructure,texture and magnetic properties of strip casting Fe–6.2 wt%Si steel sheet

An Fe–6.2 wt%Si strip with equiaxed grains and mild {0 0 1}〈0 v w〉 fiber texture was produced by twin-roll strip casting process. Then the as-cast strip was treated with or without the hot rolling prior to the warm rolling and annealing. When the hot rolling was not introduced, a fine and heterogeneous warm-rolled microstructure was produced and led to a fine recrystallization microstructure and very weak {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. When the hot rolling was introduced, a coarse and homogeneous warm-rolled microstructure was produced and led to a very coarse recrystallization microstructure and much stronger {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. The annealed sheets with hot rolling showed a higher magnetic induction and a higher core loss than those without hot rolling.     

Contribution of non-octahedral slip to texture evolution of fcc polycrystals in simple shear

The contribution of non-octahedral {1 0 0}〈1 1 0〉 slip to texture evolution under simple shear in face-centred cubic (fcc) polycrystals was studied. It was found that, by adding the {1 0 0}〈1 1 0〉 slip system family to the usual {1 1 1}〈1 1 0〉, the ideal orientations remain the same. However, the stability of the ideal orientations, the rotation field and the rate of change of the orientation density function were affected by the non-octahedral slip activity. The stress state, the slip distribution and the form of the equipotential functions were also examined along the ideal fibres. Finally, the texture evolution in pure aluminium during equal channel angular extrusion was simulated and analysed.     

Deformation mechanisms of a 20Mn TWIP steel investigated by in situ neutron diffraction and TEM

The deformation mechanisms and associated microstructure changes during tensile loading of an annealed twinning-induced plasticity steel with chemical composition Fe–20Mn–3Si–3Al–0.045C (wt.%) were systematically investigated using in situ time-of-flight neutron diffraction in combination with post mortem transmission electron microscopy (TEM). The initial microstructure of the investigated alloy consists of equiaxed γ grains with the initial α′-phase of ～7% in volume. In addition to dislocation slip, twinning and two types of martensitic transformations from the austenite to α′- and ε-martensites were observed as the main deformation modes during the tensile deformation. In situ neutron diffraction provides a powerful tool for establishing the deformation mode map for elucidating the role of different deformation modes in different strain regions. The critical stress is 520 MPa for the martensitic transformation from austenite to α′-martensite, whereas a higher stress (>600 MPa) is required for actuating the deformation twin and/or the martensitic transformation from austenite to ε-martensite. Both ε- and α′-martensites act as hard phases, whereas mechanical twinning contributes to both the strength and the ductility of the studied steel. TEM observations confirmed that the twinning process was facilitated by the parent grains oriented with 〈1 1 1〉 or 〈1 1 0〉 parallel to the loading direction. The nucleation and growth of twins are attributed to the pole and self-generation formation mechanisms, as well as the stair-rod cross-slip mechanism.     

Investigation of early stage deformation mechanisms in a metastable β titanium alloy showing combined twinning-induced plasticity and transformation-induced plasticity effects

As expected from the alloy design procedure, combined twinning-induced plasticity and transformation-induced plasticity effects are activated in a metastable β Ti–12 wt.% Mo alloy. In situ synchrotron X-ray diffraction, electron backscatter diffraction and transmission electron microscopy observations were carried out to investigate the deformation mechanisms and microstructure evolution sequence. In the early deformation stage, primary strain/stress-induced phase transformations (β → ω and β → α″) and primary mechanical twinning ({3 3 2}〈1 1 3〉 and {1 1 2}〈1 1 1〉) are activated simultaneously. Secondary martensitic phase transformation and secondary mechanical twinning are then triggered in the twinned β zones. The {3 3 2}〈1 1 3〉 twinning and the subsequent secondary mechanisms dominate the early-stage deformation process. The evolution of the deformation microstructure results in a high strain-hardening rate (～2 GPa), bringing about high tensile strength (～1 GPa) and large uniform elongation (>0.38).     

Microstructure and microtexture evolution during strain path changes of an initially stable Cu single crystal

The microstructure and microtexture evolution in a deformed Goss oriented crystal were characterized after a sample rotation and consequent change in strain path, over a range of scales by optical microscopy, high resolution scanning electron microscopy equipped with field emission gun and electron packscattered diffraction facilities and transmission electron microscopy orientation mapping. High purity copper single crystals with initial Goss{1 1 0}〈0 0 1〉 orientation were channel-die compressed 59% to develop a homogeneous structure composed of two sets of symmetrical primary microbands. New samples with ND rotated orientations of Goss{1 1 0}〈0 0 1〉, brass{1 1 0}〈1 1 2〉, M{1 1 0}〈1 1 1〉 and H{1 1 0}〈0 0 1〉, were then cut out and further compressed in channel-die by a few per cent. The change in flow stress could be correlated with the change in dislocation substructure and microtexture, particularly along shear bands initiated by the strain path change. In the H{1 1 0}〈0 1 1〉 and M{1 1 0}〈1 1 1〉 orientations, the flow stress increased by Taylor factor hardening then decreased by intense macroscopic shear band (MSB) formation. In the softer brass orientation and in the absence of Taylor factor hardening, more diffuse MSB formation occurred. The local rotations in the band were used to deduce the possible local slip systems initiated during the strain path change.     

In situ neutron diffraction study of texture evolution and variant selection during the α → β → α phase transformation in Ti–6Al–4V

In the present study, in situ phase transformation experiments have been carried out using neutron diffraction to monitor the texture evolution during the α → β → α phase transformation in Ti–6Al–4V with and without 0.4% yttrium additions. The aim of adding yttrium was to control β grain growth above the β transus by Zener pinning. First, both alloys were thermomechanically processed to generate a similar starting α texture and grain morphology. Subsequently, both materials were heat treated above the β transus up to 1250 °C followed by furnace cooling to 210 °C to promote diffusional phase transformation starting from β grain boundaries. In situ texture measurements were taken during α → β → α phase transformation starting at room temperature, 800 °C, 950 °C, above β transus (1050 and 1250 °C), and back to near room temperature. The degree of variant selection was determined by comparing the predicted transformation texture during heating and cooling based on the Burgers relationship and the assumption of no variant selection with the measured textures. It was found that during heating β grows from the pre-existing β and that the β texture evolved even before the β transus was exceeded. The β texture strengthened noticeably above the β transus in the case of conventional Ti–6Al–4V but not Ti–6Al–4V–0.4Y, which was related to β grain coarsening. The level of variant selection was clearly affected by grain coarsening and the formation of β texture components that contribute to the 〈1 1 1〉//normal direction (ND) γ fibre texture rotated about 10° away from ND.     

Orientations of recrystallization nuclei developed in columnar-grained Ni at triple junctions and a high-angle grain boundary

A directionally solidified, high-purity nickel sample with a strong 〈0 0 1〉 fiber texture was cold rolled to 40% reduction. Electron backscattered diffraction (EBSD) was used to identify triple junctions (grain edges) before annealing the sample at 430 °C, after which further EBSD was performed to identify 17 recrystallization nuclei at the initially characterized triple junctions on the rolling plane. In addition, a longitudinal section was cut on which a further seven recrystallization nuclei were found and characterized. This characterization of all nuclei revealed that the majority of nuclei could be broadly associated with a 40° 〈1 1 1〉 misorientation to the matrix in which they formed, while a much lower percentage were found to have orientations as those of the local deformation substructure. However, a substantial fraction (around one-third) could not be associated with either of these types. Mechanisms for the formation of nuclei with new orientations are discussed, as is evidence of reorientation of material ahead of the recrystallization front.     

In situ observation of texture evolution during α → β and β → α phase transformations in titanium alloys investigated by neutron diffraction

Texture changes during recrystallization and the α–β–α phase transformation in two titanium alloys were investigated in situ by time-of-flight neutron diffraction by heating in a vacuum furnace to 950 °C. In commercially pure titanium, a strong texture memory effect is observed. This effect is a direct consequence of an orientation-selective α → β transformation, favoring new orientations produced during nucleation and grain growth. The β–α transformation favors β orientations with minimal misorientations, resulting in a strong final α texture that emphasizes the grain growth component. In Ti–6Al–4V, the texture memory effect is less pronounced. The high-temperature β texture is obtained by growth of pre-existing β nuclei. In a similar way, during cooling, the growth of α domains is controlled by high-temperature α orientations inherited from the β grains with Burgers orientation relation.     

Characterization of the texture evolution during thermomechanical processing of an Fe–30 at% Al–6 at% Cr alloy

Texture and mesotexture analyses of samples obtained from an Fe–30 at% Al–6 at% Cr alloy during different steps of a thermomechanical processing route of hot and intercalated warm-rolling/isochronal annealing steps indicate a complex microstructural evolution depending on the strain and temperature paths that are taken. A strong 〈hkl〉 {111} fiber is obtained in warm-rolled samples, while almost random texture is obtained in recrystallized samples, independent of recrystallization temperature (20 min, 1073 K < T < 1372 K). The mesotexture of the recrystallized samples, however, shows the incidence of “clusters” of neighboring recrystallized grains with similar orientation, which are also present in the hot-rolled samples. Evidences are presented for the formation of these complex microstructures by a grain boundary rotation mechanism, at least for high temperature deformation conditions.     

Orientation dependence of local lattice rotations at precipitates: Example of κ-Fe3AlC carbides in a Fe3Al-based alloy

Local lattice rotations and in-grain orientation gradients at κ precipitates in matrix grains with orientations near the 45° rotated cube {0 0 1}〈1 1 0〉 (RC) and the γ-fiber components {1 1 1}〈1 1 2〉 were investigated in a Fe₃Al alloy warm-rolled to reductions of between 10% and 60%. Near-RC grains showed larger local lattice rotations at precipitates than γ-fiber grains. In RC-oriented grains the local lattice rotations about the transverse direction (TD) were dominant at low reductions, but rotations about the rolling direction (RD) also occurred at higher strains. In the γ-fiber grains the axes of the in-grain lattice rotations were scattered between TD and RD. The rotations around the particles and their orientation dependence were analyzed using 3-D crystal plasticity finite-element simulations of a spherical inclusion in a plane strain deformed matrix of different orientations, namely RC, {1 1 1}〈1 1 2〉 and {1 1 1}〈0 1 1〉.     

Texture evolution by shear on two planes during ECAP of a high-strength aluminum alloy

The evolution of texture was examined during equal-channel angular pressing (ECAP) of an Al–Zn–Mg–Cu alloy having a strong initial texture. An analysis of the local texture using electron backscatter diffraction demonstrates that shear occurs on two shear planes: the main shear plane (MSP) equivalent to the simple shear plane, and a secondary shear plane which is perpendicular to the MSP. Throughout most regions of the ECAP billet, the MSP is close to the intersection plane of the two channels but with a small (5°) deviation. Only the {1 1 1}〈1 1 0〉 and {0 0 1}〈1 1 0〉 shear systems were activated and there was no experimental evidence for the existence of other shear systems. In a small region at the bottom edge of the billet that passed through the zone of intersection of the channels, the observed textures were fully consistent with the rolling textures of Copper and Goss.     

Preferential orientation of fluorine-doped SnO2 thin films: The effects of growth temperature

Polycrystalline fluorine-doped SnO₂ thin films with a given thickness of about 250 nm have been grown by ultrasonic spray pyrolysis with a growth temperature in the range of 360–480 °C. A texture transition from 〈1 0 1〉 to 〈1 0 0〉 and 〈3 0 1〉 crystallographic orientations has experimentally been found by X-ray diffraction measurements as growth temperature is raised, revealing that a process of abnormal grain growth has occurred. The texture effects have been investigated within a thermodynamic approach considering that grain growth is driven by the minimization of total free energy. The anisotropic character of the physical quantities and the effects of growth temperature have been shown both on the surface energy per unit volume through its dependence on the oxygen chemical potential and on the strain energy density through its variation with the elastic strain and biaxial modulus. Importantly, it is demonstrated by thermodynamic simulations that the oxygen chemical potential increases with growth temperature in the spray pyrolysis conditions, showing that the atmosphere is less and less reducing. For low growth temperature, it is revealed that the 〈1 0 1〉 preferred orientation is due to surface energy minimization since the (1 0 1) reduced surfaces have a surface energy lower than the (1 0 0) reduced surfaces. In contrast, as growth temperature is raised, the 〈1 0 0〉 crystallographic orientation becomes predominant owing to strain energy minimization. A texture map is finally determined, revealing the expected texture as a function of elastic strain and oxygen chemical potential.     

Dislocation structure evolution induced by irradiation and plastic deformation in the Zr–2.5Nb nuclear structural material determined by neutron diffraction line profile analysis

Zr–2.5Nb samples removed after 7 years of service from a nuclear power reactor were investigated by traditional mechanical testing and whole pattern neutron diffraction line profile analysis of the irradiated and deformed materials. A significant increase in yield strength and subsequent strain softening are observed in the as-irradiated material. The line profile analysis allows the change in mechanical properties to be directly related to evolution of the microstructure. A fourfold increase in overall dislocation density accomplished entirely by an increase in the 〈a〉 Burgers vectors dislocations, and profound change in the dislocation network arrangement, are found to be created by the fast neutron irradiation. Comparison to the microstructural evolution during plastic deformation of the unirradiated sample shows a similar increase in dislocation density, but the increase is equally distributed amongst 〈a〉 and 〈c + a〉-type dislocations. Finally, plastic deformation of the previously irradiated material again increases the dislocation density significantly but, in contrast, does so through a 10-fold increase in the 〈c + a〉 dislocation density relative to the as-irradiated material, while the 〈a〉 Burgers vector density does not change. The different evolution of the 〈a〉 and 〈c + a〉 Burgers vector ratios in the unirradiated and irradiated Zr–2.5Nb during plastic deformation can perhaps be explained by the strain localization effect previously reported in irradiated Zircaloy subjected to deformation.     

Microstructure and texture evolution in a twinning-induced-plasticity steel during uniaxial tension

A combination of electron back-scattering diffraction and X-ray diffraction was used to track the evolution of the microstructure and texture of a fully recrystallized Fe–24 Mn–3 Al–2 Si–1 Ni–0.06 C twinning-induced-plasticity steel during interrupted uniaxial tensile testing. Texture measurements returned the characteristic double fibre texture for face-centred cubic materials, with a relatively stronger 〈1 1 1〉 and a weaker 〈1 0 0〉 partial fibre parallel to the tensile axis. The interaction with the stable 〈1 1 1〉 oriented grains results in preferential plastic flow in the unstable 〈1 1 0〉 oriented grains. Consequently, the grains oriented along the 〈1 1 0〉 and 〈1 0 0〉 fibres record the highest and lowest values of intragranular local misorientation, respectively. The viscoplastic self-consistent model was used to simulate the macroscopic stress–strain response as well as track the evolution of bulk crystallographic texture by detailing the contributions of perfect and/or partial slip, twinning and latent hardening. The simulations revealed the dominant role of perfect slip and the limited volume effect of twinning on the texture development. The effects of initial orientation and grain interaction on the overall orientation stability during uniaxial tension showed that while the 〈1 0 0〉 fibre remains stable and does not affect the unstable orientations along the 〈1 1 0〉 fibre, the orientations along the stable 〈1 1 1〉 fibre strongly affect the unstable 〈1 1 0〉 orientations.     

Nucleation and variant selection of secondary α plates in a β Ti alloy

The microtexture of secondary α plates in Ti–4.5Fe–6.8Mo–1.5Al has been investigated by electron backscatter diffraction (EBSD) to obtain more insight in the nucleation and variant selection of these α plates. A statistical analysis of the EBSD data shows that for most β grain boundaries the variant selection of the α plates is in agreement with a commonly used variant selection criterion yielding that the α-{0 0 0 1} pole is nearly parallel to the closest β-{1 1 0} poles of the two adjacent β grains. For a small angle between the β-{1 1 0} poles nucleation is predominantly observed at both sides of the grain boundary, while with increasing angle some β grain boundaries exhibit nucleation of α plates at only one side. In the β grain interior many so-called Type 2 α–α grain boundaries are observed which are thought to originate from autocatalytic nucleation when a new α plate is formed at an existing α–β interface.