Materials Science Forum Vols. 495-497

Abstract: Intragranular misorientation reflects strain generated during deformation with dislocation glide. The SEM/EBSP (scanning electron microscope/ electron back scatter diffraction pattern) technique provides is “kernel average misorientation (KAM)” as the most appropriate quantity to evaluate the strain or the stored energy for a given point. The KAM is defined for a given point as the average misorientation of that point with all of its neighbors. In the present paper two analyses of the intragranular misorientation using the SEM/EBSP technique for a cyclic deformation at room temperature and a high temperature deformation in an Al-Mg-Mn alloy are reviewed.

Abstract: Due to their polycrystalline nature, metals develop intergranular stresses during elastic and inelastic deformation. These stresses are thought to play a role in the fatigue properties of metals and to significantly affect residual stress measurements. The development of intergranular stresses during deformation of interstial free steel was modelled using crystal plasticity finite element modelling. Predictions were compared with measurements made using fast synchrotron diffraction and good qualitative agreement was found. Effects of mesh size and shape, element packing and neighbourhood on the predicted mean elastic strains and their variance were investigated.

Abstract: A silicon steel single crystal with initial Goss orientation, i.e. the {110}<001> orientation, was cold rolled up to 89 % thickness reduction. Most of the crystal volume rotates into the two symmetrical equivalent {111}<112> orientations. However, a weak Goss component is still present after high strain, although the Goss orientation is mechanically instable under plane strain loading. Two types of Goss-oriented crystal volumes are found in the highly deformed material. We suggest that their origin is different. The Goss-oriented regions that are observed within shear bands form during the cold rolling process. In contrast, those Goss-oriented crystal volumes that are found inside of microbands survive the cold rolling.

Abstract: The local crystallography within shear bands (SB) has been examined in a single crystal of {112}<111> orientation of pure copper deformed at 77K by channel-die compression to strains of about 1. Setting up a system for making high-resolution orientation maps using transmission electron microscopy (TEM) has opened new advantageous circumstances for the analysis of orientation changes within SB. This method with spatial resolution higher than 10nm allows the examination of microstructure images composed of nanoscale subcells forming SB. It has been found that for well-developed shear bands, a crystal lattice rotation about <112> direction tends to dominate and this process is usually accompanied by activation of new slip systems. The present work shows that despite the plane strain deformation mode, the mechanism of lattice rotation within emerging SBs may lead to Goss and Brass texture components.

Abstract: A small number of crystal plasticity simulations and tensile tests are carried out with the aim of demonstrating that control of twinning can improve the uniform elongation of magnesium based alloys. It is suggested that this can be accomplished through texture manipulation because texture influences both the fraction of grains that undergo twinning and the strain required for the twinning reaction to go to completion.

Abstract: Two-stage sequences of simple shear and/or uniaxial tensile tests conducted on TRIP800 steel sheet and supplemented by texture measurements are reported. The purpose is a better understanding of the macroscopic work-hardening behaviour and its microstructural origin. According to the previously published work on single phase ferrite steel; the peculiar macroscopic transient effect in flow stress was mainly associated to the microstructural destabilization (e.g. reinforcement, dissolution or rearrangement of the previously formed dislocation walls). In addition, the macroscopic work-softening observed at the beginning of the second stage of cross-loading was attributed to the micro-band occurrence. Considering the actual multiphase steel, the main difference lies in the absence of the peculiar transient effect in flow stress upon cross-loading (where no macroscopic work-softening is observed) and the associated microstructural mechanisms (no formation of micro-bands). Besides, the initial texture for the actual multiphase steel is in some extent different to the previously investigated single phase steel mainly made up of the γ-fibre. Therefore, a detailed analysis of the measured deformed textures is carried out in order to investigate the contribution of the texture evolution on the macroscopic work-hardening. The computations of the orientation stability map as well as the predicted texture evolutions using the classical full constraint Taylor- Bishop-Hill (TBH) model are performed for a better understanding of the observed texture development. The influence of the texture evolution on the shape of the stress-strain curves, as well as on the remaining symmetries of the material, is also discussed. Explicitly, we show that despite the presence of a well developed texture in the as-received and deformed material, the contribution of the geometrical hardening (i.e. textural evolution) on the macroscopic behaviour remains small compared to the microstructural one.

Abstract: Although the Taylor-type models gives reasonable texture prediction of the monotonic cold deformation of annealed aluminum alloys both qualitatively and quantitatively, results are less satisfactory for the simple shear test when the alloy is heavily pre-deformed by cold rolling. The reason for this less good prediction originates from strain localization. A virtual stress-strain curve is proposed in which the texture aspects are dealt with by the FC Taylor simulation and the microstructure aspects by a model for the development of intragrain dislocations structure. This virtual yield law is used in a finite element simulation. A strain localization behavior is observed during the finite element simulation similar to that observed during experimental simple shear test. The strain profile of a specific global strain is discretized into a series of strain and the volume fractions of the regions deformed to these strain levels, using the statistical method of histogram. A secondary FC-Taylor simulation is performed, in order to generate the deformation textures, corresponding to this series of deformation strains. The global texture is generated by merging these textures with consideration of these volume fractions. Using this procedure of multi-level modeling, quite satisfactory texture prediction is observed, compared with the measured texture at this strain.