Materials Science Forum Vols. 638-642

Abstract: Prediction of microstructure evolution and properties of ultrafine-grained materials is one of the most significant, current problems in materials science. Recently, an interest to apply the cellular automata (CA) to the simulation of different phenomena in materials has been rising constantly. The main asset of the CA is the ability for accurate modeling of the microstructure. Deformation in micro-scale shows anisotropy, which is related with the different crystallographic orientation of the grains in the polycrystalline material. To improve the accuracy of modeling, CA and FEM must be combined with crystal plasticity theory. In present model, deformation in macro-scale is transferred to meso-scale, where a representative element contains several, score or hundreds grains, and then is applied in micro-scale to each grain. Strain and strain rate are decomposed into the crystallographic directions. For each crystallographic direction, development of dislocation and subgrain boundaries are considered. In each grain development of dislocation structure is distinctive because their orientation is unique. Creation of low-angle boundaries and their development into high-angle boundaries are simulated by the cellular automata on the base of calculations using finite element method and crystal plasticity theory. Some algorithms implemented into CA are described in the paper, as well as simulation results.

Abstract: An AC magnetic field (0.5Tesla) is applied with the field direction perpendicular to the rolling direction during annealing of a 76% cold-rolled IF steel sheet. Microstructure and texture evolution in the as-annealed specimens were determined using SEM based OIM technique. It is found that the recrystallization is noticeably retarded by AC magnetic field annealing. At the early stage of recrystallization (annealing at 650°C for 30min), the development of (111) <123> orientations was favored by the AC magnetic field. With progress of recrystallization (annealing at 700°C and 750°C for 30min), the applied AC magnetic field suppressed the development of γ-fiber recrystallization textures to some extent.

Abstract: The solidification structure of a hot-dip Zn-11%Al-3%Mg-0.2%Si coating with a Ti addition on a steel substrate was investigated. Steel sheet was coated using a laboratory hot-dip galvanizing simulator. The coating was subsequently characterized via optical and high resolution scanning electron microscopy with EBSD and high temperature X-ray diffractometry. The hot-dip coating consisted of a combination of a Zn/Al/MgZn2 ternary eutectic structure, primary Al phase and MgZn2 phase. TiAl3 acts as a heterogeneous nucleation site for Al, which was shown to have perfect lattice coherency with TiAl3 as epitaxial Al growth from the TiAl3 was found. The growth direction of Al is along <110> and has a random texture, whereas Zn has a rather strong ND//<0001> fiber texture.

Abstract: The evolution of crystallographic texture with equivalent strain, eq, was studied in low carbon steel bars fabricated using multi-pass warm caliber rolling. Finite element analysis was carried out to evaluate eq accumulated and strain components introduced with each pass through the rolled bars. The texture at characteristic deformation sites on the cross section in the bars was analyzed using the electron back-scattered diffraction method. Although the texture in the area around the center was dominated by a strong RD//<101>, in the other two areas, a RD//<101> texture was not produced. It is clarified that this difference results from three deformation modes during rolling. Consequently, the areas around the corners, where eq of over 5.7 is introduced, are filled with ultrafine ferrite grains of below 680 nm, and the texture in the areas is random regardless of the increase of eq.

Abstract: An IF steel sample was cold rolled to a reduction of 80% and subsequently submitted to annealing treatment at 650°C, 710°C and 770°C for various durations, respectively. The grain size and evolution of partial texture of small, medium and large grains were investigated during grain growth. It was found that the growth rate and partial texture characteristic were absolutely distinct at different annealing temperature, both were temperature dependent. At same annealing temperature, partial texture for various annealing time was similar, but its intensity increases with an increment of duration. And the relation between partial texture of different grains assembly and its mean grain size can be expressed by an empirical formula from experiment data.

Abstract: Those materials with an one dimensional phase-aligned structure have a large amount of potentiality as engineering materials because of their exceptional optical, electrical and anisotropically mechanical properties. Many researchers are now working determinedly to explore the methods for fabricating this kind of material. Recently, high magnetic fields have been used to fabricate non-magnetic materials with textured structure where anisotropic magnetic energy should be strong enough to induce preferred crystal orientation. Based on this mechanism, we developed an in situ process for fabricating phase-aligned composites using high magnetic fields. In this work, hypoeutectic Mn-Sb and hypereutectic Al-Ni alloys were solidified in various magnetic fields. The primary MnSb dendrites in the solidified Mn-Sb alloys were found to be macrostructurally aligned along the field direction, while the primary Al3Ni phases in the Al-Ni alloys were found to be macrostructurally aligned perpendicular to the field direction. The X-ray diffraction (XRD) measurement results suggested that these two phases were also oriented by the magnetic field. It was believed that the above-mentioned alignment is based on the crystal orientation and relevant to the heat flux direction, the preferred growth direction and the concentration field around crystallized crystals.

Abstract: The crystallographic texture formation in low carbon steel during asymmetric rolling was studied experimentally and analysed numerically. Modelling of plastic deformation was done in two scales: in the macro-scale using the finite element method ( FEM) and in crystallographic scale using the polycrystalline deformation model (LW model). The stress distribution in the rolling gap was calculated using FEM and next these stresses were applied in LW model of polycrystalline plastic deformation. In general, the predicted textures agree very well with experimental ones.

Abstract: In this work the nucleation of the Cube recrystallised grains in AA6111 was investigated. The alloys were cold rolled to 85% and then annealed at different temperatures in an air circulation furnace. X-ray diffraction was used to obtain global textures and for specific area of interest, Electron-Back Scattered Pattern (EBSP) was used. In order to observe the microstructures after rolling and partially annealing, Scanning Electron Microscopy (SEM) was used. It was found that the recrystallisation textures are strongly related to the annealing temperature. The recrystallisation texture after low temperature annealing gives a strong retained rolling texture and at high temperature, a fairly random texture with weak Cube and rotated Cube components. The difference in the volume fraction of Cube with different alloys and annealing temperature are related to the deformation microstructures. Cube bands are observed to be deformation bands on the rolling plane. During annealing, precipitates are formed on the deformation band boundaries and Cube nuclei which are formed in the deformation Cube band are restricted to growth due to the precipitates.

Abstract: In response to the development of new materials and the application of materials and components in new technologies the direct measurement, calculation and evaluation of textures and residual stresses has gained worldwide significance in recent years. Non-destructive analysis for phase specific residual stresses and textures is only possible by means of diffraction methods. The determination of global texture and the local variation of texture for example by inhomogeneous deformation are very important due to the coherence between the texture and the physical and mechanical properties of materials.

Abstract: The ferromagnetic properties of ferritic steels are known to strongly depend on the direction of magnetization. The <100> are the axes of spontaneous magnetic moments and hence the directions of easy magnetization. Materials displaying a <100>//ND texture are ideal not only for transformer but also for rotating machines due to their isotropic magnetic character. In the present study the potential of severe plastic rolling deformation is investigated. The cold rolling and annealing microstructures and textures are identified with increasing rolling strains to a maximum vM equivalent of 8.0. It is shown that excessive rolling reduction is capable of producing non-conventional texture components with promising potential for magnetic applications.