Materials Science Forum Vols. 495-497

Abstract: Industrially processed doped-tungsten wires in the as-drawn condition have essentially a <110>-fibre texture with attractive mechanical properties. The main objectives of the present work are to investigate (I) if any textural changes occur as the wire diameter decreases and (II) if such changes influence the mechanical behaviour of the wire. A wire of about ∅1.5mm is drawn to about ∅0.15mm following a standard industrial route and samples were collected from five intermediate drawing passes. Bulk texture measurements using X-radiations were then carried on the transverse sections of the wires and texture characteristics such as volume fraction of textural components and sharpness index were quantified with respect to the wire diameter. It was observed that the texture in the as-drawn wires remains chiefly the same <110>-fibre as the wire diameter decreases. However, the sharpness of texture reaches a maximum at a certain diameter and decreases with further decrease in the wire diameter. An explanation is offered based on the concept of deformation zone geometry. An attempt was also made to determine if texture weakening has any effect on the mechanical properties of the wire at room temperature.

Abstract: The crystallographic texture of electrolytic tough pitch copper has been investigated by neutron diffraction after deformation by cold wire-drawing (reduction of area between 51 and 94 %) and after static recrystallization. The deformation texture characterized by a strong <111> fiber is reinforced with increasing strain, while the volume fraction of <100> fiber is reduced. In turn, we show that the <100> fiber is strongly reinforced after recrystallization when intensity of the <100> maxima increases with the level of deformation. Since the <111> fiber disappears first during annealing, the static recrystallization has been followed “in situ” by measurements of the diffracted intensity evolution in the center of the {111} pole figure. From these experimental data and taking into account the Arrhenius equation, the activation energy of the recrystallization process has been determined for each deformation rate.

Abstract: Two methods of automatically determining boundary alignments from EBSD maps are discussed and shown to produce comparable results. Measurements of Al-0.1Mg and IF steel, deformed at room temperature, confirm that the alignment of low angle boundaries is primarily a function of the deformation mode, rather than the crystallography. During the high temperature deformation of aluminium, the lagbs maintain a large angle of inclination to the rolling direction (>35o) even at large strains, which is consistent with the boundaries being of transient character during deformation.

Abstract: Crystal plasticity FEM simulations of plane strain compression were performed. The Texture Component Crystal Plasticity-FEM was used for the texture mapping. Two different starting textures (random and hot rolling texture) were studied using four different FE meshes and two different sets of boundary conditions. While for the random starting texture the evolution of the texture with deformation was found to be rather similar in all cases studied, the simulations using an experimental hot rolling texture as staring texture are much more sensitive to the boundary conditions and probably also to changes in the mesh geometry.

Abstract: An attempt to model the nucleation of fragment boundaries during cold plastic deformation of f.c.c. metals is presented. The paper focuses on intrinsic nucleation in the grain interior due to elementary processes on the dislocation level. Since orientation fragmentation seems to be linked to slip banding and the underlying mechanisms should be the same, the model is based on the elementary process of double cross-slip. Simulations were carried out for Cu, Ni and Al. Fragment boundary spacings and misorientations could be predicted in reasonable agreement with experiment for Cu. For Ni, comparable results were obtained, when a stacking fault energy at the lower end of the range of literature data was chosen. The resulting rate equation for the generation of partial disclinations as carriers of orientation fragmentation can be implemented into an earlier model for the coupled substructure and texture development during cold plastic deformation.

Abstract: In this contribution we present how to implement the calculation of average field fluctuations inside the grains of a thermoelastic aggregate in terms of the derivatives of the stress potential given by the standard linear self-consistent (SC) model, and how this statistical information can be used to generate second-order estimates for the mechanical behavior of nonlinear viscoplastic polycrystals, by means of a rigorous non-linear homogenization procedure. To illustrate the differences between this second-order (SO) self-consistent approach and the classical first-order SC approximations, we compare them in terms of their predictions of the effective behavior of random fcc polycrystals as a function of their rate-sensitivity, and of the texture evolution in hcp ice polycrystals under uniaxial compression. In the latter case, the SO approximation is the only one able to predict a substantial accommodation of deformation by basal slip, even when the basal poles become strongly aligned with the compression direction and the basal slip systems became unfavorably oriented.

Abstract: A rate-independent polycrystal model, allowing for the shape and spatial coordination of neighboring constitutive crystals and for the plastic strain distribution among them, has been used to simulate the local texture evolution in an Al polycrystal under compression. The simulation results compare favourably to relevant experimental data and show the reorientation path of each crystal to strongly depend on orientations of its immediate neighbors.

Abstract: Using a processing path model based on the conservation principle in the orientation space explicit solutions can be formed linking any final (desired) microstructure to a given initial state for polycrystalline materials. The model uses texture coefficients in spherical harmonics expansion to as materials descriptors to represent the texture state of polycrystalline materials. In this work, the effect of increasing the maximum number of texture coefficients used in the series expansion (represented by Lmax) on the prediction of texture and its accuracy is fully studied.

Abstract: The method is described which enables to determine the microtexture that is the orientation distribution within individual grains of a polycrystal. The microtexture is evaluated on the base of X-ray pole distributions measured for separate reflections, referred to as microscopic pole figures (MPF). The procedure for treatment of experimental MPF and the following computation of orientation distribution function is described in detail. Precision of the microtexture evaluation and possible ways of its improvement are discussed. As an example of the method application, orientation distribution within a single grain of aluminum polycrystal deformed by uniaxial compression up to 50% has been examined.