Materials Science Forum Vols. 702-703

Abstract: The viscoplastic Φ-model belongs to the same class of self-consistent models but it is based on a new theory without the Eshelby scheme. The Φ-model, by varying the parameter Φ, can predict a very large range of the texture components: from the lower (Φ →1) to the upper (Φ→0 ) bounds results. In this work, we adapt the Φ-model to take into account the mechanical twinning. This extended Φ-model is used to predict textures in FCC metals under plane strain compression test. We show that the deformation twinning plays an important role in the formation of brass-type texture.

Abstract: This paper deals with the study of plastic heterogeneity. It aims to study the role of both grain size and orientation distributions in the development of such heterogeneity. The considered material is an IF steel. EBSD maps have been made on the same areas before and after several degrees of extension. Parameters such as GOS (Grain Orientation Spread) or GOS/D (D the diameter of the grain) or GND (Geometrically Necessary Dislocation) densities have been determined for the whole set of grains as well as for subpopulations (smallest grains, largest grains for example). It appears that the character of neighboring grains plays a more important role than any of these parameters alone.

Abstract: A novel experimental investigation of both high and medium stacking fault energy bi-crystals of aluminum and copper, respectively, show that orientation, grain interaction and material are all key factors in the stability of some ideal rolling texture components. Ideal {110} or {112} orientations obtained from high purity aluminum or copper single crystals were embedded within a {110} crystal orientation of the same material and reduced 60 percent by channel die compression at room temperature. Spatial misorientations developed inside the deformation bands were analyzed using SEM-based EBSD. The presence of long-range orientation gradients in some of the crystals revealed the interacting nature of polycrystalline deformation. From the results it is proposed that f.c.c. polycrystalline grains can be classified according to their stability and susceptibility to deformation: (i) stable and interacting; (ii) unstable and interacting; (iii) stable and non-interacting; (iv) unstable and non-interacting.

Abstract: The development of orientation spreads within individual grains of a polycrystal submitted to large deformations is analysed by both experiment and simulation. In the experiment, 176 grains on an internal surface of a split sample were followed by detailed EBSD measurements, at successive strains up to 1.2. In parallel, a high-resolution finite element simulation has been carried out on the same polycrystal configuration. For both experiment and simulation, hundreds to thousands of orientation values were obtained in each grain. Most grains showed a “unimodal” rotation, composed of an average rotation and an orientation spread. The experimental and simulated orientation spreads were compared through different statistical metrics. The average lattice disorientations are found to increase rapidly at the beginning of the deformation and to saturate at high strains. The orientation spreads are also analysed in terms of anisotropy along the sample axes. It is shown that the orientation spreads are aligned preferably along TD at the beginning of the deformation, then tend to move to RD in the experiment, and RD or ND in the simulation.

Abstract: Texture evolution in plastically deformed HCP metals is strongly influenced by the nucleation and growth of deformation twins and twin variant selection. Statistically based EBSD analyses of deformed microstructures in HCP metals indicate that the nucleation of deformation twins depends on, among other factors, the local stress fields arising from neighboring grain interactions at grain boundaries [1]. Inspired by these findings a probability model for twin nucleation was developed [2,3], based on the activation of defect sources statistically occurring in grain boundaries. This nucleation model was implemented in a Visco-Plastic Self-Consistent (VPSC) code. Because the latter is based on an Effective Medium assumption and the inclusion formalism, it only provides average stress values in the grains, and the nature of local stress fields at grain boundaries had to be considered in a heuristic manner. In order to have better insight on the effect of local textures on twin nucleation, in this work we employ a viscoplastic full field Fast Fourier Transform (FFT) method as a numerical tool for conducting virtual experiments to study the role of crystal orientation and local neighbor grain interactions on stress localization close to the interfaces and, consequently, on twin nucleation in hexagonal materials, such as Zr and Mg.

Abstract: From an EBSD map made on a polycrystal one can define a set of grains using a criterion of misorientation between the adjacent pixels. Once such a list of grains is obtained, various quantities can be associated to each grain such as its size, (mean) orientation, GOS (Grain Orientation Spread) etc... The GOS associated to one grain is the mean value of the misorientations between all the pixels of the grain and the mean orientation of the grain. This value is quite sensitive to the state of the material (degree of plastic deformation, degree of recrystallization for example). Therefore it can help in interpreting the evolution of a microstructure during thermomechanical treatments. It is the purpose of this presentation to provide GOS values for an IF steel after several degrees of plastic deformation as well as after several annealing treatments which lead to partially or totally recrystallized states. The sources of influence on GOS values (as grain detection limit or grain size) are analyzed. The link between the values and the state of the material will be discussed at a global stage for a given population of grains.

Abstract: The through-thickness textures of different variants of AA6111 T4 sheets were investigated by using X-ray pole figure technique, scanning electron microscopy (SEM), and electron back scattering diffraction (EBSD) technique in SEM. The roping behaviors of the sheets were determined and corelated to the through-thickness texture inhomogeneity. It has been demonstrated that (i) roping is due to through-thickness texture inhomogeneity, (ii) roping occurs in AA6111 when the cube and Goss texture components segregate along the rolling direction (RD) and alternate in the transverse direction (TD), (iii) the texture alignment from sheet surface to 1/5 thickness is most critical to roping behavior, while the effect of texture in the sheet centre is masked by the surface layer, and (iv) the texture alignment can be attributed to the stability of cube and Goss in rolling, and the nucleation and grain growth advantage of cube and Goss during heat treatments.

Abstract: The stability of a unique single, rotated Brass-{110}á556ñ component developed in a Al-Zn-Mg-Cu based 7010 alloy, during long term thermal annealing and cold rolling deformation has been systematically investigated. It is observed that this component remains stable during annealing at 465 °C over the period of 96 hrs and up to a uniaxial cold rolling reduction of 60%. The thermal and mechanical stability of the single component texture is discussed in terms of preferential growth advantage of recrystallized grains and confinement of slip activity in two major slip systems, respectively.

Abstract: Abstract. Features of the texture development in Zr-based alloys under compression at tempera-tures of the (α+β)-region of the Zr-Nb phase diagram indicate that the plastic deformation shifts temperatures of phase transformations due to accompanying thermal effects and the decrease of lattice stability, whereas formation of the fine-grained structure by phase transformation promotes activation of the non-crystallographic deformation mechanism of slip by interphase boundaries.

Abstract: Formability and mechanical properties of metal sheets are related to on their textures. It has been studied to improve the formability and change the texture of the AA 3003 Al alloy sheets after asymmetric rolling. Asymmetrically rolled Al sheets are shown the high intensity of the distorted cube texture, {001}, distorted rotated cube texture, {001}, weak γ-fiber, ND//, {123}, {120} and {120} components. After the asymmetrically rolled AA 3003 Al alloy sheets, the plastic strain ratios of the asymmetrically rolled Al alloy sheets were about 1.7 times higher than those of the initial Al sheets. The variation of plastic strain ratios of the asymmetrically rolled Al alloy sheets could be related to the change of texture components through asymmetrical rolling in AA 3003 Al sheet.