Papers by Keyword: Grain Subdivision

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Authors: Tomotsugu Shimokawa, Toshiyasu Kinari, Sukenori Shintaku
Abstract: The relationship between grain subdivision mechanisms of a crystalline metal and the strain gradient under severe plastic deformation is studied by using molecular dynamics simulations in quasi two dimensions. Two problems are simulated for single crystal models: (a) uniaxial tensile and compressive deformation and (b) localized shear deformation. In the case of uniaxial deformation, a large number of dislocation pairs with opposite Burgers vectors are generated under deformation, but most dislocations are vanished due to pair annihilation under relaxation. Therefore, no dislocation boundary can be formed. On the other hand, in case of localized shear deformation with large strain gradient, dislocation boundaries are formed between undeformed and deformed regions. These dislocations can be regarded as geometrically necessary dislocations. Consequently, the importance of the strain gradient to make grain boundaries under plastic deformation can be confirmed by atomic simulations.
Authors: Nobuhiro Tsuji, Naoya Kamikawa, Yoritoshi Minamino
Abstract: Ultra low-carbon interstitial free (IF) steel having ferrite (b.c.c.) single phase was deformed to various equivalent strains ranging from 0.8 to 5.6 by the accumulative roll bonding (ARB) process at 500°C. The microstructure and crystallographic feature of the deformed specimens were characterized mainly by FE-SEM/EBSD analysis. Grain subdivision during the plastic deformation up to very high strain was clarified quantitatively. After heavy deformation above 4.0 of strain, the specimens showed the lamellar boundary structure uniformly, in which the mean spacing of the lamellar boundaries was about 200nm and more than 80% of the boundaries were high-angle ones. Annealing behavior of the ARB processed IF steel strongly depended on the strain. The specimens deformed to medium strains exhibited discontinuous recrystallization characterized by nucleation and growth, while the specimens deformed above strain of 4.0 showed continuous recrystallization. The recrystallization behaviors are discussed on the basis of the microstructural and crystallographic parameters quantitatively measured in the as-deformed samples.
Authors: Naoki Ishida, Daisuke Terada, Keizo Kashihara, Nobuhiro Tsuji
Abstract: The sheet of pure Al (99.99%) single crystal having (1 12)[110] orientation was deformed up to equivalent strain of 6.4 by the accumulative roll-bonding (ARB) process. The microstructures and orientation of the single crystal ARB-processed by various cycles were characterized by the EBSP measurement. After 1cycle-ARB process, the crystal was macroscopically subdivided into two matrices (macroscopic grain subdivision). These matrices exhibits two different variants of brass orientation, which are (1 01)[121] and (011)[211]. In addition to the macroscopic grain subdivision, microscopic grain subdivision also occurred within the matrix to form an ultrafine grained structure in the single crystal specimen after high strains.
Authors: Nobuhiro Tsuji, Naoya Kamikawa, Bo Long Li
Abstract: Ultra-low carbon steel (ferritic steel), commercial purity aluminum and high purity copper were heavily deformed by the accumulative roll bonding (ARB) process, and the microstructural evolution during the ARB was analyzed. Significant grain refinement by grain subdivision mechanism was confirmed in all three kinds of materials. On the other hand, microstructure refinement slowed down with increasing strain and the grain size stayed in nearly a constant value in the ultrahigh strain region. The mechanism of the grain size saturation was discussed.
Authors: Niels Hansen, Dorte Juul Jensen
Authors: Aries Setiawan, Daisuke Terada, Nobuhiro Tsuji
Abstract: An ultra-low carbon IF steel was heavily deformed up to an equivalent strain of 36 at various high temperatures of ferrite single-phase region and various strain rates. Effects of temperature and strain rate on the microstructures evolved in torsion deformation were clarified. On the other hand, it was found that homogeneous ultrafine grained structures were not obtained by the present torsion deformation though very high strain was applied. The coarser grain sizes than those obtained by conventional severe plastic deformation (like ARB) were due to the deformation at higher temperature and lower strain rate, but lower fraction of high-angle grain boundaries in the torsion specimen was suggested to be attributed to the characteristics of monotonic torsion (or simple shear) deformation including the way of strain evaluation.
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