Papers by Keyword: Dislocation Slip

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Authors: Guo Sheng Duan, Bao Lin Wu, Xiang Zhao, Gang Zhao
Abstract: The strain-controlled fatigue tests on extruded AZ31B magnesium alloy were conducted under the uniaxial loading with strain ratio Rε=-∞, frequency of 0.1 Hz and strain amplitude of 2% at room temperature. The cyclic hardening behavior was investigated. It was found that, during the low cycle fatigue (LCF) process, as the number of cycles increases, the stress amplitude increases corresponding to the decrease of the plastic strain amplitude. The development of dislocation density can be described as the function of the number of fatigue cycles, and the behavior can be explained well based on the dislocation density development model.
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Authors: Chun Yan Wang, Hai Qun Qi, Kun Wu, Ming Yi Zheng
Abstract: The high temperature compressive tests of squeeze casting ZK60 magnesium alloy in the testing temperature range of 523-723K and strain rate range of 0.001-10s-1 were performed on Gleeble-1500D thermal simulator testing machine. Optical microscopy was performed to elaborate on the dynamic recrystallization (DRX) grain growth. TEM observation indicated that the mechanical twinning, dislocation slip, and dynamic recrystallization are the materials typical deformation features. Variations of flow behavior with deformation temperature as well as strain rate were analyzed. Analysis of the flowing deformation behavior and microstructure observations indicated that the flow localization was observed at lower testing temperature and higher strain rates. Dynamic recrystallization occurred at higher testing temperature and moderate strain rates, which improved the ductility of the material. The results indicated that at the testing temperatures lower than 573K and strain rates higher than 1s-1, the material exhibited flow instability manifesting as bands of flow localizations. These temperatures and strain rates should be avoided in processing the material. Dynamic recrystallization occurs in the temperature range 573-723K and the strain rate range 0.001-0.1s-1. The number of dynamic recrystallization grains is less at lower temperature and higher strain rate than higher temperature and lower strain rate. The dynamic recrystallization is inadequate at 573-623K while the dynamic recrystallization grain growth has been observed in the temperature range of 673-723K. Therefore it may be considered that the optimum processing parameters for hot working of squeeze casting ZK60 magnesium alloy are 648K and 0.001-0.01s-1, at which fine dynamic recrystallization microstructure can be obtained.
93
Authors: Chang Jian Geng, Bao Lin Wu, Yan Dong Wang
Abstract: Uni-axial tensile test was conducted at room temperature on a weak texture AZ31B magnesium alloy at different strain rate, from 2.8×10-5s-1 to 1.1×10-1s-1. The mechanical behavior was investigated. It was found that as strain rate is increased, flat character of the stress-strain curves can be found and {10-12} tension twinning is responsible for this phenomenon. The sample exhibites a brittle fracture at 1.1×10-1s-1 strain rate while exhibites a ductile fracture character at 2.8×10-5s-1 strain rate.
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Authors: Yulia Ivanisenko, Hans Jorg Fecht
Abstract: We suggest a simple method to study the mechanical behaviour of nanocrystalline (nc) samples in compression-torsion mode. High applied pressure prevents the fracture of sample, and quantitative parameters of sample response during torsion test can be compared with developed microstructure. Here we present and discuss the results of systematic investigation of mechanical behaviour of nc Pd with a mean grain size of 12 nm in a wide range of shear strains (0<γ<200) and at strain rates γ& = 3 10-1 s-1 and 3 10-2 s-1. We show that in the studied shear strain range the notable changes in the microstructure, namely a strain induced grain growth occurs, and that controls the relevant deformation mechanisms. For lower strains when the grain size is still small enough, the plastic flow governs by twinning and probably grain boundary sliding. The flow stresses are lower as compared with the later stages of deformation, when the grain size becomes larger and deformation is controlled exceptionally by dislocation glide. Finally, a steady stage is achieved, when the grain size, dislocation density and flow stress are saturated.
203
Authors: Michal Landa, Z. Prevorovský, František Chmelík, J. Dosoudil, Pavel Lukáč, Zuzanka Trojanová
407
Authors: Hector Basoalto, Paul L. Blackwell
Abstract: The conventional consensus has it that the magnitude of the strain rate sensitivity observed in superplastic materials is linked with grain boundary sliding. The grain boundary sliding mechanism is thought to theoretically produce a strain rate sensitivity exponent of 0.5, which is in good agreement with experimental data. The present paper argues that a rate sensitivity of 0.5 can be generated by dislocation slip under certain temperature and strain rate regimes that overlap with conditions representative of superplasticity. A physically based slip model that links the relevant microstructural parameters to the macroscopic strain rate is proposed.
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Authors: Remi Delville, Benoît Malard, Jan Pilch, Petr Šittner, Dominique Schryvers
Abstract: Transmission electron microscopy and mechanical testing were employed to investigate the evolution of microstructure and functional superelastic properties of 0.1mm diameter as-drawn Ni-Ti wires subjected to a non-conventional heat treatment by controlled electric pulse current. This method enables a finer control of the recovery and recrystallisation processes taking place during the heat treatment and accordingly a better control on the final microstructure. The best functional properties were obtained for heat-treated Ni-Ti wires having a nanograined microstructure (20-50 nm) partially recovered through polygonization and partially recrystallized. Such microstructure is highly resistant against dislocation slip upon cycling, while microstructures annealed for longer time and showing mostly recrystallized grains were prone to dislocation slip, particularly as the grain size exceeds 100 nm. The density of dislocation defects increased significantly with increasing grain size of the microstructure. The activity of three <100>/{011} slip systems was identified in the largest grains of 500-1200 nm. An additional mode of plastic deformation, {114} compound austenite twinning, was observed in the largest grains of fully recrystallized microstructures. It is proposed that dislocation slip (and possibly deformation twinning) occurring in superelastic cycling is coupled with the stress-induced martensitic transformation.
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