Materials Science Forum Vols. 539-543

Abstract: Textured Mg alloys exhibit tension – compression strength asymmetry due to mechanical twinning. The distinction arises as the material deforms primarily by slip in one direction and by twinning in the other. In-situ neutron diffraction during cyclic loading in tension and compression of extruded bar allows study of the effect of twinning on subsequent load reversals. The diffraction data reveal the texture evolution and internal stress development as a function of deformation. De-twinning resulted in complete texture reversal during initial cycles, but eventually “fatigued” resulting in some residual twin component.

Abstract: Theories of the pencil glide theory for bcc metal and MPG(modified pencil glide) theory for fcc metal are reviewed. Interest is focused to both analogy and difference in derivation of the theories. Some visualization figures using them are introduced. At last, it is informed that the authors have opened both the bcc pencil glide theory and MPG(fcc) theory on website publication which calls everybody to look and download the fundamentals, applications, visualization , procedure of calculation and C program for calculation for the both pencil glide theories.

Abstract: Thermoelectric oxide Bi1.5Pb0.5Sr1.7Y0.5Co2O9- δ is produced by sintering method. Uniaxial compression deformation is performed on the oxide under various strain rates at 1113K, close to the melting temperature. After deformation, density, microstructure, texture and thermoelectric characteristics such as specific electric resistance and Seebeck coefficient, are experimentally studied. Deformation mechanism is examined by stress change test. It is found that the oxide plastically deforms mainly by the motion of dislocations at the present temperature, resulting in an increase in density as well as the development of texture. It is concluded that the specific electric resistance extensively decreases by the high temperature compression deformation through densification and texture development.

Abstract: The influences of different rolling modes and speed ratios on cold rolling texture development, and the characteristics of recrystallization textures after ordinary annealing as well as magnetic annealing have been investigated for non-oriented silicon steel. Results show that the through-thickness deformation textures were effectively changed by asymmetric cold rolling even in the case of small speed ratios, and the recrystallization textures were modified with the enhanced favorable {100} and η (<100>//RD) texture components by magnetic annealing. Much improved magnetic properties can be obtained through optimization of asymmetric rolling and annealing parameters. Thus, application of asymmetric cold rolling and magnetic annealing might open up new possibilities for texture control in high-grade silicon steel production.

Abstract: The evolution of the microstructure, macrotexture, microtexture and mesotexture has been studied during the annealing at 760°C after temper rolling (9% thickness reduction) of a non-oriented electrical steel sheet containing 2 wt. % Si. Results showed that the coarse grained microstructure, obtained on annealing, is produced through a recrystallization mechanism that advances from the surface to the interior of the sheet. However, starting of this process is delayed due to the presence of Si. The majority of experiments carried out in this work have been repeated for a low-carbon steel (C = 0.0385; Mn = 0.18%) containing only 0.03% Si and the results obtained were practically identical to those observed in the steel containing 2% Si. The main difference observed between both steels was that the process of formation of the exaggeratedly large grains was slower in the steel containing 2% Si.

Abstract: Crystallographic macrotexture of pure niobium cold rolled to 30, 60, 80 and 90% reduction was analyzed by X-ray diffraction and compared with low carbon steel texture. Annealed samples from 800oC, to 1200oC were investigated by X-ray diffraction and electron back scattering diffraction (EBSD). The texture of cold rolled polycrystalline niobium is characterized by a component {001}<110> that increases in intensity with the cold work percentage. After annealing, the component {001}<110> spreads out about 20o.

Abstract: TiNi shape memory alloy thin sheets were produced from titanium and nickel metal sheets by a new processing consisting of repetitive roll-bonding and diffusional heat treatment. TiNi sheets after heat treatment at a relatively low temperature for a long time exhibited fairly isotropic and high shape-recoverable strain, because a near {111} B2-phase texture such as {223}<110> and {332}<113> was developed through reactive diffusion during heat treatment. In the early stage of reactive diffusion, intermetallic layers of Ti2Ni, TiNi and Ni3Ti were formed at once at the Ti/Ni interfaces of the roll-bonded laminate and then growth of a TiNi phase took place with the progress of interdiffusion. Texture of the final TiNi thin sheets, therefore, is derived from that of TiNi layers generated at the Ti/Ni interfaces, which is considered to have inherited rolling textures of Ni and Ti layers in the Ti/Ni laminate prior to reactive diffusion under orientation relationships on close-packed plane and direction between parent and product phases.

Abstract: Due to the deformation mechanisms and the typical basal texture rolled magnesium sheets show a significant asymmetry of flow stress in tension and compression. In order to avoid this undesired behavior it is necessary to achieve non-basal texture during rolling, or at least, to reduce the intensity of the basal texture component. The reduction of the anisotropy caused by the basal texture is very important for subsequent forming processes. This project aims at optimizing the hot rolling process with special consideration of texture effects. The development of the model is carried out in close cooperation with the experimental work on magnesium alloy AZ31 .The experimental results are required for the determination of model parameters and for the verification of the model. Deformation-induced texture is described by the visco-plastic self-consistent (VPSC) model of Lebensohn and Tomé. The combination of deformation and recrystallization texture models is applied to hot compression tests on AZ31, and it is found, that the model describes the observed texture and hardening/softening behavior well. In some cases rotation recrystallization occurs in AZ31 which appears to be a possibility to reduce the undesired basal rolling texture.

Abstract: Finite element models for metal forming are used to design and optimise industrial forming processes. The limit strain in sheet metal forming can be predicted for monotonic loading or strain paths with changes. Models like these should be as accurate as possible in order to be useful, and hence take the texture, microstructure and substructure (dislocation patterns) into account. To achieve this, a hierarchical type of modelling is proposed in order to maintain the balance between calculation speed (required for engineering applications) and accuracy. In that case, FE models to be used at the engineering length scale work with an analytical constitutive model, the parameters of which are identified using results of multilevel models (meso-scale with an homogenisation procedure). The analytical model to be used at macro-scale will be discussed, as well as the identifications procedure. The later make use of meso-scale models. Finally an example will be given (formability of a sheet material).

Abstract: Magnetostrictive Galfenol (Fe-Ga) is a promising and mechanically robust actuator material. Single crystals of Galfenol have been shown to exhibit up to 400 ppm magnetostrictive strains with saturating fields of several hundred oersteds. However, due to the high conductivity of Galfenol, it needs to be in thin sheet form for many device applications to avoid eddy current loses. One of the main challenges in producing engineering components from these materials is shaping of these materials while retaining a preferred crystallographic texture to optimize the magnetostrictive performance of the polycrystals. In this work, the effects of rolling on texture evolution of polycrystalline Galfenol are being investigated. Results from hot rolling experiments showed that careful control of rolling conditions can minimize the formation of cracks. They also suggested that significant dynamic recovery and recrystallization occurred during the deformation process, resulting in a large number of grain orientations with very little texture. Preliminary results also showed that the specimens can be successfully warm rolled to a thickness of less than 0.5 mm.