Papers by Keyword: Grain Boundary Sliding (GBS)

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Authors: Hachizo Muto, Mototsugu Sakai
Authors: Jean Jacques Blandin, B. Baudelet, R. Dendievel
Authors: Yong Nam Kwon, Young Seon Lee, S.W. Kim, Jung Hwan Lee
Abstract: Mg alloys could be the lightest alloys among the industrially applicable engineering alloys. Since wrought Mg alloy has limited applications due to the poor formability, casting is currently the main processing technique to fabricate Mg components even though wrought alloys are superior in terms of mechanical properties and reliability. While a lot of research and development has been focused on warm forming under the temperature condition of around 250°C where more formability could be expected, superplastic forming could be another way to get over the low formability of Mg alloys. Like other superplastic materials grain boundary sliding is the main deformation mechanism of Mg superplasticity. Accommodation of stress concentration around triple point of grain boundary should be done favorably if grain boundary sliding continues without any fracture. In the present study, superplastic behavior of AZ31 alloys with several grain sizes was examined firstly. Accommodation of grain boundary sliding of AZ31 alloy would be discussed on the basis of grain morphology and texture evolution after tensile deformation.
Authors: Buddhisagar Naik
Abstract: Different models have been put forward to explain superplasticity. Most of the models predict the independency of activation energy (Q) on stress. Superplasticity is observed in region II of creep curve (logε Vs σ/E). The most commonly considered mechanism for superplastic flow involves Grain Boundary Sliding (GBS), and it is necessary for an accommodation process to accompany GBS. The accommodation process might be grain boundary migration, recrystalisation, diffusional flow or some dislocation slip process. But the Arrhenius type of equation given by Becker gives the dependency of activation energy on stress. Here in this work we have considered this equation and relation between Q and σ is found out using genetic algorithm. The present model development studies the parameter optimization, where parameters appearing in the stress and energy relationship equation e.g. relationship between Q(σ) and σ for the Q(σ) equation given in present work as well as pre-exponential factors are optimized with the objective function being the error minimization of model predicted values and experimental data of strain are available from open literature.
Authors: Mamoru Mabuchi, Yasumasa Chino, Hajime Iwasaki
Abstract: Fine-grained 5083 Al alloy and AZ91 Mg alloy showed superplastic behavior. The plasticitycontrolled growth rates of cavities during superplastic deformation for the Al alloy and Mg alloy were investigated. The cavity volume fraction for the Mg alloy was larger than that for the Al alloy. However, the cavity growth rate for the Mg alloy was lower than that for the Al alloy.
Authors: Byung Nam Kim, Keijiro Hiraga, Koji Morita, Hidehiro Yoshida
Abstract: For steady-state deformation caused by grain-boundary diffusion and viscous grain-boundary sliding, the creep rate of regular polyhedral grains is analyzed by the energy-balance method. For the microstructure, the grain-grain interaction increases the degree of symmetry of diffusional field, resulting in a decrease of the effective diffusion distance. Meanwhile, the viscous grain-boundary sliding is found to decrease the creep rate. The present analysis reveals that the grain-size exponent is dependent on the grain size and the grain-boundary viscosity: the exponent becomes unity for small grain sizes and/or high viscosity, while it is three for large grain sizes and/or low viscosity.
Authors: Byung Nam Kim, Keijiro Hiraga, Koji Morita, Hidehiro Yoshida
Abstract: When the sliding of the grain boundary containing hexagonal particles is accommodated by grain-boundary diffusion, we evaluate the sliding rate and the stress distribution on the boundary, by taking the particle rotation and the intrinsic boundary viscosity into account. The sliding rate was obtained by the energy-balance method, and the particle-rotation rate by a condition of minimum energy-dissipation. With increasing boundary viscosity, the rotation rate increases and then decreases after a maximum. The sliding rate is enhanced by the particle rotation, and decreases with the boundary viscosity.
Authors: Chang Seog Kang, Sung Kil Hong
Abstract: An attempt has been made to measure the temperature dependence of dynamic Young's modulus together with the related variation of internal friction in polycrystalline copper. A mechanical spectroscopy study was used a standard servo hydraulic fatigue testing machine equipped with a scanning laser extensometer. Dynamic Young’s modulus and internal friction are measured over a temperature range of 298 to 873K at very low frequencies of 0.1, 0.05 and 0.01Hz. One internal friction peak was observed over the ranges 450K to 700K, together with marked decreases in the dynamic Young.s modulus in the same temperature ranges. From a quantitative analysis of the experimental data with the relaxation strength, relaxation time and activation energy, it is concluded that the peak phenomenon is due to grain-boundary sliding relaxation.
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