The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Farghalli A. Mohamed - One of the best experts on this subject based on the ideXlab platform.
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Correlation between microstructure evolution and cavity stringer formation in the superplastic Zn-22 wt% Al alloy
Philosophical Magazine A, 1999Co-Authors: Ahmadali Yousefiani, Farghalli A. MohamedAbstract:Abstract In the present investigation, microstructure evolution during the superplastic deformation of Zn–22 wt% Al was examined to provide insight into the origin of cavity stringers that form parallel to the Tensile Axis in the alloy. Substructural data show that groups of fine α (Al-rich) and β (Zn-rich) phases are encompassed by former α boundaries (FαcBs) which consist of fine elongated α grains and which divide the microstructure into equiaxed domains (FαB domains). By examining the correspondence between the behaviour of these boundaries and the development of cavity stringers, it is suggested that the alignment of cavities along the Tensile Axis can be explained in terms of two processes: firstly the preferential nucleation of cavities at FαBs during the initial stages of deformation, and secondly the tendency of FαBs and their associated cavities to change their orientation and align along the Tensile Axis during superplastic deformation. Evidence in support of this explanation is provided by pre...
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The effect of impurities on ductility and cavitation in the superplastic Zn-22%Al alloy
Materials Science and Engineering: A, 1994Co-Authors: Kyung-tae Park, S.t. Yang, James C. Earthman, Farghalli A. MohamedAbstract:Abstract An investigation of the effect of impurities on the ductility and cavitation behavior of a microduplex superplastic alloy was performed. Experiments were conducted in tension at 473 K on three grades of Zn-22%Al that contain different impurity contents. It is shown that a higher impurity content results in a drastic decrease in the ductility and an enhancement in the cavitation even when the deformation is considered superplastic. In addition, the orientation of the cavity stringers appears not to depend on the rolling direction but is always observed parallel to the Tensile Axis. The experimental observations are compared in terms of the strain rate sensitivity dependence of ductility. The results are also compared with the predictions of various theoretical models that attempt to describe cavity nucleation and growth. Finally, the mechanisms for the formation of cavity stringers parallel to the Tensile Axis are discussed.
Kyung-tae Park - One of the best experts on this subject based on the ideXlab platform.
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high strain rate superplasticity of submicrometer grained 5083 al alloy containing scandium fabricated by severe plastic deformation
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Kyung-tae Park, Duckyoung Hwang, Dong Hyuk ShinAbstract:Abstract High strain rate superplasticity (HSRS) was obtained in a commercial 5083 Al alloy by introducing a ultrafine grained structure of 0.3 μm through severe plastic deformation and by adding a dilute amount of scandium (Sc) as a microstructure stabilizer. Tensile tests were carried out on the as-processed sample at temperatures of 623–823 K and initial strain rates of 1×10 −3 –1×10 0 s −1 . The maximum elongation to failure of 740% was obtained at 773 K and 1×10 −2 s −1 . HSRS of the alloy was attributed to the combined effects of dynamic recrystallization and preservation of fine recrystallized grains by the presence of Sc. The mechanical behavior of the alloy at 773 K was characterized by a sigmoidal behavior in a plot of stress vs strain rate in the double logarithmic scale. The origin of the sigmoidal behavior was discussed in terms of microstructural evolution during superplastic deformation. An examination of the fractured samples revealed that failure occurred in a brittle manner related to cavitation rather than necking. Cavity stringers were formed parallel to the Tensile Axis by interlinkage of jagged-shaped isolated cavities along grain boundaries aligned to the Tensile Axis.
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The effect of impurities on ductility and cavitation in the superplastic Zn-22%Al alloy
Materials Science and Engineering: A, 1994Co-Authors: Kyung-tae Park, S.t. Yang, James C. Earthman, Farghalli A. MohamedAbstract:Abstract An investigation of the effect of impurities on the ductility and cavitation behavior of a microduplex superplastic alloy was performed. Experiments were conducted in tension at 473 K on three grades of Zn-22%Al that contain different impurity contents. It is shown that a higher impurity content results in a drastic decrease in the ductility and an enhancement in the cavitation even when the deformation is considered superplastic. In addition, the orientation of the cavity stringers appears not to depend on the rolling direction but is always observed parallel to the Tensile Axis. The experimental observations are compared in terms of the strain rate sensitivity dependence of ductility. The results are also compared with the predictions of various theoretical models that attempt to describe cavity nucleation and growth. Finally, the mechanisms for the formation of cavity stringers parallel to the Tensile Axis are discussed.
S.t. Yang - One of the best experts on this subject based on the ideXlab platform.
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The effect of impurities on ductility and cavitation in the superplastic Zn-22%Al alloy
Materials Science and Engineering: A, 1994Co-Authors: Kyung-tae Park, S.t. Yang, James C. Earthman, Farghalli A. MohamedAbstract:Abstract An investigation of the effect of impurities on the ductility and cavitation behavior of a microduplex superplastic alloy was performed. Experiments were conducted in tension at 473 K on three grades of Zn-22%Al that contain different impurity contents. It is shown that a higher impurity content results in a drastic decrease in the ductility and an enhancement in the cavitation even when the deformation is considered superplastic. In addition, the orientation of the cavity stringers appears not to depend on the rolling direction but is always observed parallel to the Tensile Axis. The experimental observations are compared in terms of the strain rate sensitivity dependence of ductility. The results are also compared with the predictions of various theoretical models that attempt to describe cavity nucleation and growth. Finally, the mechanisms for the formation of cavity stringers parallel to the Tensile Axis are discussed.
James C. Earthman - One of the best experts on this subject based on the ideXlab platform.
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The effect of impurities on ductility and cavitation in the superplastic Zn-22%Al alloy
Materials Science and Engineering: A, 1994Co-Authors: Kyung-tae Park, S.t. Yang, James C. Earthman, Farghalli A. MohamedAbstract:Abstract An investigation of the effect of impurities on the ductility and cavitation behavior of a microduplex superplastic alloy was performed. Experiments were conducted in tension at 473 K on three grades of Zn-22%Al that contain different impurity contents. It is shown that a higher impurity content results in a drastic decrease in the ductility and an enhancement in the cavitation even when the deformation is considered superplastic. In addition, the orientation of the cavity stringers appears not to depend on the rolling direction but is always observed parallel to the Tensile Axis. The experimental observations are compared in terms of the strain rate sensitivity dependence of ductility. The results are also compared with the predictions of various theoretical models that attempt to describe cavity nucleation and growth. Finally, the mechanisms for the formation of cavity stringers parallel to the Tensile Axis are discussed.
José Mendez - One of the best experts on this subject based on the ideXlab platform.
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Creep of a nickel-based single-crystal superalloy during very high-temperature jumps followed by synchrotron X-ray diffraction
Acta Materialia, 2015Co-Authors: Jean-briac Graverend, J. Cormier, Alain Jacques, Olivier Ferry, Thomas Schenk, José MendezAbstract:Complex thermomechanical loadings at high temperature (T >= 950 degrees C) on the AM1 single-crystal superalloy were studied by X-ray diffraction under synchrotron radiation. This technique enables in situ access to the evolutions of the lattice mismatch as well as the volume fraction and the dislocation density of the gamma and gamma' phases during high-temperature non-isothermal creep loadings. It is shown that the large microstructure evolutions through the growth/shrinkage of gamma/gamma' interfaces due to the gamma' volume fraction changes and the associated variations in the density of dislocations at these interfaces during temperature jumps are key parameters controlling the whole behavior (distribution of internal stresses and constitutive laws) of both phases. We propose an empirical constitutive law linking the strain rate of the y' phase to its stress state as well as a way to determine it. During our experiments, the plastic behavior of the gamma'-rafts is related to the entry of dislocations with Burgers vectors perpendicular to the Tensile Axis and controlled by the overcoming of a threshold stress corresponding to the internal stress components perpendicular to the Tensile Axis.
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Creep of a nickel-based single-crystal superalloy during very high-temperature jumps followed by synchrotron X-ray diffraction
Acta Materialia, 2015Co-Authors: Jean-briac Graverend, J. Cormier, Alain Jacques, Olivier Ferry, Thomas Schenk, José MendezAbstract:Abstract Complex thermomechanical loadings at high temperature ( T ⩾ 950 °C) on the AM1 single-crystal superalloy were studied by X-ray diffraction under synchrotron radiation. This technique enables in situ access to the evolutions of the lattice mismatch as well as the volume fraction and the dislocation density of the γ and γ′ phases during high-temperature non-isothermal creep loadings. It is shown that the large microstructure evolutions through the growth/shrinkage of γ/γ′ interfaces due to the γ′ volume fraction changes and the associated variations in the density of dislocations at these interfaces during temperature jumps are key parameters controlling the whole behavior (distribution of internal stresses and constitutive laws) of both phases. We propose an empirical constitutive law linking the strain rate of the γ′ phase to its stress state as well as a way to determine it. During our experiments, the plastic behavior of the γ′-rafts is related to the entry of dislocations with Burgers vectors perpendicular to the Tensile Axis and controlled by the overcoming of a threshold stress corresponding to the internal stress components perpendicular to the Tensile Axis.
