Diffraction with high-energy synchrotron radiation is a new experimental method to determine textures of materials, which due to the special properties of this radiation, in the future may have advantages in terms of accuracy of local texture measurements in comparison to established methods like Electron back scatter diffraction (EBSD). In the present study NiAl polycrystals with two different initial textures have been deformed in torsion at 727°C and 1000°C and their texture development has been measured with highenergy synchrotron radiation. Torsion enables the study of texture formation with strain as well as the exploration of large strains without changing the shape of the samples. The pole figures indicate the preferred alignment of ‹100› with the shear direction and {110} with the shear plane. High pressure torsion may also open new possibilities in terms of grain refinement and texture formation and thus ductilization of NiAl.
Triaxial strain scanning has been performed on a 7mm thick 7150-aluminium alloy Variable Polarity Plasma Arc (VPPA) weld using synchrotron X-rays. It has been demonstrated that the use of specific advantageous ( hkl ) peaks that occur in this highly textured aerospace alloy plate permits fast deep measurements in reflection as well as in transmission. The sin2ψ method was also utilised to monitor the variation in deviatoric stress component (σ11−σ33) across the weld in both the test-piece and a comb like reference specimen used to map the changes in stress-free lattice spacings over the weld. The results suggest that microstresses have little effect on macrostress determination, particularly in the Heat Affected Zones (HAZ). Though small in magnitude, the macrostresses still present in the reference specimen can be allowed for to correct the stress tensor in the plate. Maximum tensile longitudinal stress values remain unchanged, whereas the stress condition in some parts of the HAZ is well described as biaxial after the proposed correction.
Using finite elements over Rodrigues space, methods are developed for the formation and inversion of pole figures. The methods take advantage of the properties of Rodrigues space, particularly the fact that geodesics corresponding to pole figure projection paths are straight lines. Both discrete and continuous pole figure data may be inverted to obtain orientation distribution functions (ODFs) in Rodrigues space, and we include sample applications for both types of data.
This paper describes the so-called meso-scale simulations of sintering a particulate body. Computations were made using 3D structure-imitation computer model of evolution of a powder compact during sintering. It was demonstrated, that in powder bodies the effect of zonal isolation (forming separate groups of particles during sintering) determines features of shrinkage and internal structure of a compact. In case of the diffusion- viscous flow of particles the fact was proved that the zonal isolation is predetermined by ratio of viscosity and free surface energy. It was verified, that there is a critical value of the above ratio with respect to which the balance of internal structure- creating processes is determined.
The deformation mechanisms of a superplastic Al–Li 2090 alloy have been investigated by means of texture analysis. It has been found that both crystallographic slip (CS) and grain boundary sliding (GBS) operate in response to the applied stress over a wide range of deformation, conditions. This is in contrast to well-accepted creep models, which predict that only one mechanism should operate and that the transition from one mechanism to another is abrupt and takes place over a narrow range of deformation conditions. Additionally, according to geometric (Taylor-type) models of uniaxial deformation for CS, the 〈110〉, 〈111〉, or 〈001〉 fibers should appear when 4, 6, or 8 slip systems operate. Here, however, CS contributes to stabilize orientations belonging to the α and β fibers.
Heavily cold drawn in situ Cu–Nb composites have been investigated by transmission electron microscopy (TEM) and X-ray analysis. Dislocation density in the copper matrix has been shown to change only slightly in the investigated drawing ratio range because of the development of stage IV of deformation. In Nb filaments dislocation density in the investigated range at first increases with deformation and then drops at the highest drawing ratio. At intermediate deformation niobium grains consist of fine blocks separated by low-angle dislocation boundaries. At drawing, fibre texture develops in both phases, with 〈111〉 and 〈100〉 axis for the copper matrix and 〈110〉 axis for niobium filaments. Besides, niobium filaments acquire ribbon-like form, and their grains possess certain orientation, namely, in interlacing grains crystallographic {311}, {100} and {111} planes are parallel to each other and to the filament plane, i.e. , the rolling texture with {311}〈110〉, {100}〈110〉 and {111}(110) components is forming within every filament.
The examples discussed in this paper illustrate the role that texture research plays in improving properties of films and coatings. Without texture studies, the failure mechanisms and changes of mechanical and physical properties of films cannot be properly understood. The optimization of electronic, magnetic and mechanical properties of thin films must also include a textural analysis, as texture plays an important role in property optimization in anisotropic media. Research on film texture will most likely focus on a better understanding of texture processing and control, with a final goal of optimizing and improving the properties and performance of films and coatings. These materials, which have special optical, magnetic, electronic, and mechanical properties, have contributed decisively to the information and communication revolution which we are experiencing at the end of this century. They will play an even more important role in the future design of computers, displays, recording media, communication equipment and various other electronic devices. Texture research should contribute to and play a more active role in the development of new films and coatings.
Improvement in the understanding of the influence of crystallographic texture on the diffusion behavior of protective oxides, formed at high temperatures on metallic substrates, is being sought through the study of a simple model system such as nickel–nickel oxide. Examples of textures in metallurgical nickel products and the correlation between the substrate and oxide textures, are discussed. Techniques of surface texturing are suggested and the texture leading to the highest oxidation resistance is selected on the basis of existing experimental evidence.
The frequency of occurrence of differently misoriented grain boundaries in growth selection experiments in silicon–iron was reported by Ibe and Lücke and has been the basis of many texture models. However, this pattern of behaviour bears much similarity to misorientation frequencies calculated from random textures. A comparison of the experimental and computed frequency distribution shows that there are statistically significant differences and therefore that some possibilities for growth selection do exist
Steel rolling within the temperature range intermediate between hot and cold rolling represents today a very economical and technically viable operation. The present work investigates the microstructure and the texture developed in a Ti microalloyed IF steel by rolling at 400°C and 600°C. Reductions of 40% and 60% were applied to a set of as hot rolled strip specimens part of which was subsequently annealed at 800°C for 5 minutes. Both the microstructure and the texture were examined by scanning electron microscopy. The texture was analysed by Electron Back Scattering Diffraction (EBSD) and Orientation Image Microscopy (OIM), and represented via the ODF method. The plastic anisotropy was also characterised. It was found that the textures developed by warm rolling are similar to those obtained by cold rolling, the intensities being also of comparable value. The microstructure is characterised by the presence of many shear banded grains whose amount was also quantified.
Films consisting of Mo, Cr, and Ta have all been found to display well-defined biaxial textures when grown under certain conditions. A well-defined out-of-plane texture evolves within the first ~ 100 nm of the film, followed by the evolution of a preferred crystallographic orientation in the plane of the film. These effect were studied using X-ray pole figure analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), transmission electron diffraction (TED), and high resolution grazing incidence X-ray scattering (GIXS). It has been found that in-plane texture evolves only when there is, on average, oblique adatom flux incident onto the substrate. Further, the type of out-of-plane texture can be controlled by altering the deposition conditions. Parameters including cathode-to-substrate distance, deposition rate, average angle of adatom incidence, and sputter gas pressure, have been shown to determine the type out-of-plane texture, as well as the rate of in-plane texture evolution. The studies conducted have shown that it is possible to create and control biaxially textured films and multilayers made of a variety of materials. A recent model which describes this phenomena is discussed.
The development of texture in thin films under ion bombardment is believed to occur due to the preferential growth of the aligned grains in the film relative to the unaligned grains. The difference in growth rates between aligned and unaligned grains results in the development of texture with increasing thickness. Both out-of-plane (fiber) and in-plane texture can be controlled during ion bombardment. Experiments were performed to create a (110) out-of-plane texture in thin aluminum films and to create a (110) in-plane texture in niobium films. Results showed that the texture in both cases increases in strength with depth, and that for 500 nm Al films, the (110) texture was stronger than the thermodynamically-preferred (111) texture obtained by physical vapor deposition. Results confirm a texturing mechanism based on ion channeling and preferential sputtering.
Solid state information from coherent neutron scattering can be extracted from transmission experiments on polycrystalline materials. The transmission technique has been applied to dynamic structural and phase change investigations and will be developed to cover the fields of strain mapping and structural tomography.
Austenitic stainless steels are widely used because of their high corrosion resistance and toughness. The influence of the applied cyclic load on the mechanical properties of the material is of great current interest. In order to investigate residual stress evolution a series of the austenitic steel samples (X6CrNiTi1810) with different degrees of low cycle fatigue was studied. Martensitic phase formation was observed at different degrees of low cycle fatigue. Residual stresses, microstresses in both phases, as well as martensitic precipitation volume fractions, were estimated. Usually after plastic deformation the martensite phase produces a structure of oriented plates or laths. Therefore martensite texture formation during phase transition can be expected. Indeed the registered neutron diffraction spectra from austenitic fatigued samples show texture presence and its variation in dependence of the fatigue degree. The attempt to consider the texture evolution in dependence of fatigue degree and its influence on the residual stresses was made.
The microstructural and quantitative texture analyses of a naturally deformed calcite mylonite, a dolomite mylonite and a dolomitic calcite mylonite reveal different texture asymmetries for comparable deformation conditions. Calcite shows a c-axis maximum rotated against the shear sense with regard to the main shear plane. In contrast, the dolomite shows a c-axis maximum rotated with the shear sense. In accordance with the experimental and simulated textures from the literature, this difference proves e-twinning and r-slip for calcite and f-twinning and c-slip for dolomite as the main deformation mechanisms. The dolomitic calcite mylonite shows for both the calcite and the dolomite a c-axis maximum rotated against the shear sense. On account of the microstructure of this sample, the dolomite texture has been passively overtaken from the deformation texture of calcite during a late-deformative dolomitization. The results significantly contribute to the interpretation that the sampled shear zone is a transpressive strike–slip fault.
The residual stress state and the texture of cold forward extruded full and hollow steel bodies as well as a hot extruded AlSi25Cu4Mg1 tube are studied by X-ray, high energy synchrotron and neutron diffraction. The experimental results reveal that all samples are fibre textured and that there are characteristic distributions of the residual stresses vs. sample diameter. In case of the cold forward extruded samples at low degrees of natural strain, the rod kernel is under compressive residual stresses which are balanced by tensile residual stresses in the outer part of the sample. In contrast to this, the outer part of the hot extruded sample is under compressive macroscopic stresses which are balanced by tensile macroscopic residual stresses in the inner part of the sample.
The de la Vallée Poussin standard orientation density function ν κ ( ω ) = C ( κ )cos 2 κ ( ω /2) is discussed with emphasis on the finiteness of its harmonic series expansion which, advantageously distinguishes it from other known standard functions. Given its halfwidth, the de la Vallée Poussin standard orientation density function allows, for example, to tabulate the degree of series expansion into harmonics required for its exact representation.
In our previous paper (Luzin, 1997. Proc. of Workshop “Neutron Textures and Stress Analysis” ) the basic principles of the quantitative approach to optimize the texture measurements were outlined. This paper is the report of advances in this direction. The quantitative approach is used to solve the smoothing problem. Smoothing by singular integrals with an integral kernel used by Nikolayev and Ullemeyer (1996). Proc. of Workshop “Math. Methods of Texture Analysis”, Textures and Microstructures 25 , 149– 158 is used in this paper. It is shown how the optimal smoothing parameter depends on the grain statistics, i.e. the number of grains in the sample. The algorithm for optimal smoothing of real pole density data (pole figures) is proposed. Also, the application of optimal smoothing for solving the central problem of quantitative texture analysis (QTA), i.e. orientation distribution function (ODF) reproduction, is discussed.
Goss texture development in silicon steels has been studied through EBSP measurements and various computer simulations and calculations. The results of these studies suggest the possible role of high energy grain boundaries (HEGB) in the abnormal growth of Goss grains. The Goss orientation has a fraction of HEGBs that is higher than any other commonly observed orientations in the primary recrystallized silicon steels. The HEGBs have high GB diffusion coefficients which cause rapid coarsening of precipitates on these HEGBs and release them earlier, at the time when other GBs are still pinned. A difference in the mobility between the HEGBs and the other GBs favours the abnormal growth of Goss grains. The Monte-Carlo methods that have been developed and used to validate this assumption have generated abnormally growing Goss grains. The experimentally observed grain boundary character distributions (GBCD) around the growing Goss grains have been reproduced in simulation by assuming high mobility to HEGBs. Apart from the high mobility differences between different GBs, the importance of the fraction of GBs with high mobility around growing Goss grains is realized.
We investigated the effect of high hydrostatic pressure on the normal grain growth in 2-D aluminium foils. The time dependence of the mean grain area was obtained. It was shown that normal grain growth takes place both at atmospheric pressure and under high hydrostatic pressure. The grain growth rate decreases by a factor 1.3 under high pressure. The activation volume for grain growth was 0.13 of the atomic volume. It was shown that high pressure strongly influences the ratio oflow angle boundaries and general boundaries at the early stages of secondary recrystallization.
