Abstract: The historical development of the two approaches to the interaction between solute atoms and a migrating interface, based on dissipation of Gibbs energy and on solute drag, are reviewed and compared. In the way the solute drag was formulated long ago for recrystallization and grain growth, it does not apply to phase transformations. With a new solute drag equation, which was recently proposed, it turns out that the two approaches are completely equivalent for phase transformations as well as grain boundary migration.
Abstract: In this paper we present results obtained in collaboration between NSC and Arcelor on the austenite of a multiphased steel and on a 70%Ni-30Fe alloy. The work concerns the formation of the crystallographic textures during the recrystallisation of austenite, since these textures have a strong influence, after the phase transformation, on the forming properties of the sheets. The microstructure and the textures of the austenite and the FeNi alloy were measured with X-Ray diffraction techniques and with EBSD on a high resolution FEG-SEM.
Abstract: The development of physically-based models of microstructural evolution during hot
deformation of metallic materials requires knowledge of the grain/subgrain structure and crystallographic texture characteristics over a range of processing conditions. A Fe-30wt%Ni based alloy, retaining a stable austenitic structure at room temperature, was used for modelling the development of austenite microstructure during hot deformation of conventional carbon-manganese steels. A series of plane strain compression tests was carried out at a temperature of 950 °C and strain rates of 10 s-1 and 0.1 s-1 to several strain levels. Evolution of the grain/subgrain structure and crystallographic texture was characterised in detail using quantitative light microscopy and highresolution electron backscatter diffraction. Crystallographic texture characteristics were determined separately for the observed deformed and recrystallised grains. The subgrain geometry and dimensions together with the misorientation vectors across sub-boundaries were quantified in detail across large sample areas and the orientation dependence of these characteristics was determined. Formation mechanisms of the recrystallised grains were established in relation to the deformation microstructure.
Abstract: The analysis of the microstructure deformation and the static recovery were
investigated by transmission electron microscopy (TEM) observations, after cold drawing in copper. The observed microstructures according to the orientation of grains are composed of dislocation cells, deformation bands and dense dislocation walls. In <001> grains, the cells are equiaxed, regular and surrounded by sharp walls, whereas in the <111> grains the cell creation is also in progress. During the annealing, the microstructure of <001> grains evolves to a stable configuration composed of very thin walls and coalesced cells that correspond to the first recrystallization nuclei.
Abstract: The description of the mechanical state of a polycrystal is presented in the
framework of the mean-field approaches and attention is paid to the fields heterogeneity. For nonlinear behaviours, the importance of the chosen model is emphasized with respect to relevant microstructural parameters for recrystallisation.
Abstract: This study has been conducted to evaluate the orientation-dependent stored energy of deformed grains from the data measured using electron back-scattered diffraction (EBSD) analysis. The stored energy in deformed grains is an important term as a driving force for static recrystallization of cold-rolled steels. Subgrain method based on subgrain structure is used for quantitative analysis of the stored energy developed in cold-rolled interstitial free (IF) steels to a reduction of 80%. The orientation dependent stored energy term was used in Monte Carlo technique to simulate static recrystallization of IF steels.
Abstract: In an investigation of nucleation of recrystallisation in an Interstitial Free steel it was
found that new crystals were almost always contained within the rolled-out hot band grain envelopes and were mostly equiaxed. At a later stage they grew and had an aspect ratio of 2:1 but at the completion of recrystallisation were again equiaxed. This is explained by the notion that nucleation occurs relatively frequently in certain grains, that these nuclei have very similar orientations and are thus orientation pinned within the solute and precipitate containing envelopes of the hot band grains. Provided the misorientation is small the impinged group are capable of spheroidisation provided the driving force across the pinned boundary is sufficient to overcome the pinning, because, by definition, this pinned boundary is of high angle character. The theory, as it is presented as coalescence, relies on a form of Östwald ripening and therefore provides a possible explanation of why grain growth kinetics obeys a time exponent of between 1/2 and 1/3. A similar observation of high aspect ratio grains has been made many times in the case of cold rolled copper which forms cube texture. Again, nuclei are formed in the cube bands, but these are prevented from lengthening because of orientation pinning. However, when the length of a group of such impinged nuclei is sufficient, spheroidisation will produce equiaxed grains.
Abstract: Wire-drawn copper has been investigated with Electron Back Scattered Diffraction
technique in a Scanning Electron Microscope after deformation by wire-drawing. In this paper, we show how to get qualitative informations about the deformation inhomogeneities related to the stored energy distribution, from the analysis of the quality index. Furthermore, the microstructural analysis in the wire diameter is completed using the quality index distribution approach. A relation between diameter of the wire and stored energy distribution is then qualitatively set. In order to validate the proposed method, the EBSD data are compared with the stored energy values obtained from neutron diffraction measurements.
Abstract: High resolution Electron Backscatter Diffraction (EBSD) in a field emission gun scanning electron microscope (FEGSEM) was used to study substructural development during the deformation by cold rolling of a single-phase Al-0.1Mg alloy with initial grain sizes between ~3µm and 120µm. In the coarse-grained material, bands of elongated cells aligned at approximately 35º to the rolling direction were formed at low strains. However, as the grain size was reduced, fewer of these aligned microstructural features were formed, and at the smallest grain sizes, there was little evidence of significant substructure within the deformed grains. The alignment of low angle boundaries was analysed from EBSD data and shown to be a function of grain size, strain and boundary misorientation.