THERMEC 2006

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Authors: Kim Verbeken, L. Barbé, Bruno C. De Cooman
Abstract: Phosphorus added TRIP steels were subjected to Electron BackScattering Diffraction (EBSD) measurements in order to study the texture of the three different phases and in order to evaluate the orientation relations that are active during the transformation of austenite to bainite. The retained austenite had a maximum intensity on the Brass component and the intensity gradually decreased along the alpha and the beta fibre. The intensity of both BCC phases was comparable, but the bainite texture displayed clear transformation products that could be related with the dominant Brass component of the intercritical austenite. A detailed evaluation of the crystallographic orientation relationships between about 360 retained austenite grains and their BCC neighbours was performed. Three relationships were considered, namely Kurdjumov-Sachs, Nishiyama-Wassermann and Pitsch. It was found that the majority of the austenite grains had at least one neighbour that could be related with one of the three orientation relationships. The Kurdjumov-Sachs relationship appeared to be dominant and no strong indication for variant selection could be retrieved from the studied data.
3347
Authors: Tetsuo Sakai, Hiroshi Utsunomiya, H. Koh, S. Minamiguchi
Abstract: Magnesium alloy sheets had to be rolled at elevated temperature to avoid cracking. The poor workability of magnesium alloy is ascribed to its hcp crystallography and insufficient activation of independent slip systems. Present authors have succeeded in 1-pass heavy rolling of AZ31 magnesium alloy sheet below 473K by raising rolling speed above 1000m/min. Heavy reduction larger than 60% can be applied by 1-pass high speed rolling even at room temperature. The improvement of workability at lower rolling temperature is due to temperature rise by plastic working. The texture of heavily rolled AZ31 magnesium alloy sheet is investigated in the present study. The texture of sheets rolled 60% at room temperature was <0001>//ND basal texture. At the rolling temperature above 373K, the peak of (0001) pole tilted ±10-15 deg toward RD direction around TD axisto form a double peak texture. The texture varied through thickness. At the surface, the (0001) peak tilted ±10-15 deg toward TD direction around RD axis to form a TD-split double peak texture. The direction of (0001) peak splitting rotated 90 deg from the surface to the center of thickness. Heavily rolled magnesium alloy sheets have non-basal texture. The sheets having non-basal texture are expected to show better ductility than sheets with basal texture.
3359
Authors: Valerie Randle, Gregory Owen
Abstract: Grain boundary engineering (GBE) has been carried out on copper and brass. A comparison of the resulting microstructure and grain boundary characteristics from the two specimens revealed that the brass specimen had approximately the same number fraction of Σ3s as the copper specimen (38%), but a lower number fraction of Σ9s and Σ27s and a markedly different microstructure. In the brass specimen twins were not incorporated into the grain boundary network, whereas in the copper specimen Σ3s replaced portions of the grain boundary network. These two mechanisms are discussed in detail.
3365
Authors: R. Quey, S. Ringeval, David Piot, Julian H. Driver
Abstract: Two relatively simple schemes are described for the interactions of grain deformations during large plastic deformations with the aim of evaluating their influence on texture development. The stress transfer model basically assumes that there is some degree of stress transfer across the boundaries proportional to the boundary area. The reduced stress incompatibility model minimizes the stress incompatibilities between each grain and their surrounding grains These models assume 3D topological schemes using evolving truncated octahedra for the spatial distributions of the grains. They are applied to the cases of hot rolled and cross forged Al alloys. Both give quite similar predictions for texture development which are moderate improvements on the Taylor models, confirming that the incorporation of grain interaction effects can be useful for texture modeling without major modifications. Moreover, they can yield interesting results for local orientation effects and their influence on orientation stability; an example of cube grains hot rolled in different crystallographic surroundings is also treated.
3371
Authors: Indrajit Charit, K. Linga Murty
Abstract: Zirconium (Zr) alloys are best known for their use in nuclear reactor applications. A hexagonally close-packed structure with a low c/a ratio and very limited slip systems leads to strong textures in these alloys during fabrication processes. These alloys are used in cladding applications for encapsulating fuel pellets, and undergo various stress conditions in-service. Hence, it is necessary to understand the creep properties of Zr alloys to predict the life of reactor claddings. Due to the unique texture, the creep deformation of these alloys is anisotropic in nature. The texture of Zircaloys was determined by X-ray diffraction experiments, and expressed in terms of pole figures and crystalline orientation distribution functions. Biaxial creep testing of thin walled tubing was used to study the creep anisotropy. Creep loci evaluation based on the experimental data and model predictions are compared. It is found that the models can predict the creep loci for recrystallized alloy very well. However, they fail to explain the behavior of the cold worked alloys. When stress enhancements due to the grain boundary sliding are taken into account, the predicted creep loci correlated well with that constructed from the experimental data.
3377
Authors: Irene J. Beyerlein, Carlos N. Tomé
Abstract: A constitutive model is applied to predict the flow stress of an fcc material up to 30% straining after rolling to reductions of 19%, 39%, and 50%. The model makes use of a single crystal hardening law which appreciates the directional anisotropy produced by planar dislocation boundaries, Bauschinger effects, and dissolution of substructure by new slip activity invoked by changes in strain path. Anisotropy between axial testing in the rolling (RD) versus the transverse direction (TD) and a tensioncompression stress- differential in RD are predicted. These and other characteristics of the flow curves are linked to changes in slip activity when deformation transitions from rolling to axial testing.
3383
Authors: Wei Guo Wang
Abstract: The progress of grain boundary engineering (GBE) is overviewed and the challenges for further investigations emphasized. It points out that, the electron backscatter diffraction (EBSD) reconstruction of grain boundaries, which gives the information of connectivity interruption of general high angle boundaries (HABs), is more significant than purely pursuing high frequency of so-called special boundaries. The criterion for the optimization of grain boundary character distribution (GBCD) needs to be established. The energy spectrum and the degradation susceptibility of grain boundaries of various characters including HABs and low Σ(Σ≤29) coincidence site lattice (CSL) needs to be studied and ascertained. And finally, the newly proposed model of non-coherent Σ3 interactions for GBCD optimization are discussed.
3389
Authors: Claude Esling, Yu Dong Zhang, Zhuo Chao Hu, Xiang Zhao, Liang Zuo
3395
Authors: Talal Al-Samman, Günter Gottstein
Abstract: Texture evolution and microstructure development of hot extruded pure magnesium and the magnesium alloy AZ31 deformed by plane strain deformation at select temperatures and strain rates were investigated using X-ray techniques, electron back scattered diffraction (EBSD) and optical microscopy. At a deformation temperature of 200 °C both materials showed a heterogeneous microstructure consisting of highly deformed zones appearing as huge grains or bands and of very small (~ 3 μm) grains. High temperature deformation (400 °C) gave rise to completely different microstructures. Changing of deformation conditions, i.e. the temperature and strain rate resulted in different final textures. At high deformation temperature and low strain rate the formation of a basal texture was suppressed.
3401

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