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Woo Jin Kim - One of the best experts on this subject based on the ideXlab platform.
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Variation of true strain-Rate Sensitivity Exponent as a function of plastic strain in the PM processed superplastic 7475Al + 0.7Zr alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: Woo Jin KimAbstract:The variation of strain Rate–stress relationship for the high-strain-Rate superplastic PM7475Al+0.7Zr alloy has been studied as a function of plastic strain. The increase of true strain-Rate Sensitivity Exponent, mt, from ∼0.3 to >0.5 was observed to occur with plastic strain when tested at an optimum strain Rate of 10−1 s−1 for superplasticity. In contrast, when tested at a lower strain Rate of 10−4 s−1 where only limited tensile elongation was obtained in the elongation-to-failure test, low mt values less than 0.5 were revealed throughout the test. The true activation energy for plastic flow was estimated for the dynamically recrystallized microstructure and found to be similar to that for lattice diffusion in pure aluminum and that for the same alloy with the initial microstructure with a high portion of low angle boundaries. Threshold stresses and its related activation energy for the recrystallized alloy were higher and lower, respectively, by comparison with those for the alloy with the initial microstructure. Tensile elongation behavior as a function of strain Rate could be explained in terms of true m value varying with strain.
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variation of true strain Rate Sensitivity Exponent as a function of plastic strain in the pm processed superplastic 7475al 0 7zr alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: Woo Jin KimAbstract:The variation of strain Rate–stress relationship for the high-strain-Rate superplastic PM7475Al+0.7Zr alloy has been studied as a function of plastic strain. The increase of true strain-Rate Sensitivity Exponent, mt, from ∼0.3 to >0.5 was observed to occur with plastic strain when tested at an optimum strain Rate of 10−1 s−1 for superplasticity. In contrast, when tested at a lower strain Rate of 10−4 s−1 where only limited tensile elongation was obtained in the elongation-to-failure test, low mt values less than 0.5 were revealed throughout the test. The true activation energy for plastic flow was estimated for the dynamically recrystallized microstructure and found to be similar to that for lattice diffusion in pure aluminum and that for the same alloy with the initial microstructure with a high portion of low angle boundaries. Threshold stresses and its related activation energy for the recrystallized alloy were higher and lower, respectively, by comparison with those for the alloy with the initial microstructure. Tensile elongation behavior as a function of strain Rate could be explained in terms of true m value varying with strain.
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Superplasticity of fine-grained ceramics and intermetallics
Metals and Materials, 1995Co-Authors: Woo Jin KimAbstract:The tensile elongation of fine-grained ceramics is shown to increase as a strong function of decreasing flow stress, even though the values of strain-Rate-Sensitivity Exponent remain high. The tensile ductility dependence on grain size was also investigated for many fine-grained ceramics either under a constant strain Rate condition or a constant stress condition. The large increase of tensile ductility with the decrease of grain size under a constant strain Rate, is primarily attributed to the decrease in flow stress accompanying grain size refinement. Tensile elongation behavior of some fine-grained intermetallic alloys appears similar to that typically observed in fine-grained ceramics, indicating similar failure mechanism snared by both materials.
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Superplastic Ceramics (With Emphasis on Iron Carbide)
1991Co-Authors: Oleg D. Sherby, J. Wolfenstine, Woo Jin KimAbstract:Abstract : Ultrafine grained iron carbide material was developed by an atomized powder process, utilizing hipping, pressing and extrusion procedures. The material was made superplastic and behaved like other superplastic ceramics. This observation lead to the following conclusions. Superplastic ceramics and metallic alloys exhibit different trends in tensile ductility in the range where the strain-Rate-Sensitivity Exponent, m, is high. The tensile ductility of superplastic metallic alloys (e.g. fine-grained zinc, aluminum, nickel and titanium alloys) is primarily a function of the strain-Rate-Sensitivity Exponent. In contrast, the tensile ductility of superplastic ceramic materials (e.g. zirconia, alumina, zirconia alumina composites and iron carbide) is not only a function of the strain Rate Sensitivity Exponent, but also a function of the parameter where the steady state strain Rate and Qc is the activation energy for superplastic flow. Superplastic ceramic materials exhibit a large decrease in tensile elongation with an increase. This trend in tensile elongation is explained based on a 'fracture-mechanics' model. The model predicts that tensile ductility increases with a decrease in flow stress, a decrease in grain size and an increase. The difference in the tensile ductility behavior of superplastic ceramics and metallic alloys can be related to their different failure mechanisms. Superplastic ceramics deform without necking and fail by intergranular cracks that propagate perpendicular to the applied tensile axis. In contrast, superplastic metallic alloys commonly fail by intergranular and transgranular (shearing) mechanisms with associated void formation in the neck region.
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Tensile ductility of superplastic ceramics and metallic alloys
Acta Metallurgica Et Materialia, 1991Co-Authors: Woo Jin Kim, J. Wolfenstine, Oleg D. SherbyAbstract:Superplastic ceramics and metallic alloys exhibit different trends in tensile ductility in the range where the strain-Rate-Sensitivity Exponent, m, is high (m⩾0.5). The tensile ductility of superplastic metallic alloys (e.g. fine-grained zinc, aluminium, nickel and titanium alloys) is primarily a function of the strain-Rate-Sensitivity Exponent. In contrast, the tensile ductility of superplastic ceramic materials (e.g. zirconia, alumina, zirconia-alumina composites and iron carbide) is not only a function of the strain-Rate-Sensitivity Exponent, but also a function of the parameter ⋗e exp (Qc/RT) where ⋗e is the steady-state strain Rate and Qc is the activation energy for superplastic flow. Superplastic ceramic materials exhibit a large decrease in tensile elongation with an increase in ⋗e exp (Qc/RT). This trend in tensile elongation is explained based on a “fracture-mechanics” model. The model predicts that tensile ductility increases with a decrease in flow stress, a decrease in grain size and an increase in the parameter (2γs−γgb), where γs is the surface energy and γgb is the grain boundary energy. The difference in the tensile ductility behavior of superplastic ceramics and metallic alloys can be related to their different failure mechanisms. Superplastic ceramics deform without necking and fail by intergranular cracks that propagate perpendicular to the applied tensile axis. In contrast, superplastic metallic alloys commonly fail by intergranular and transgranular (shearing) mechanisms with associated void formation in the neck region.
Shiao Pu - One of the best experts on this subject based on the ideXlab platform.
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evaluation of the hot workability corresponding to complex deformation mechanism evolution for ti 10v 2fe 3al alloy in a wide condition range
Journal of Materials Processing Technology, 2015Co-Authors: Guozheng Quan, Wenquan Lv, Jianting Liang, Shiao PuAbstract:Abstract The hot workability of as-forged Ti–10V–2Fe–3Al alloy was evaluated. Meanwhile, the intrinsic relationships between deformation mechanisms and processing parameters were determined by the processing maps on the basis of dynamic materials model (DMM) with the input stress–strain data collected from a series of isothermal compressions at temperatures of 948–1123 K (across β -transus) and strain Rates of 0.001–10 s −1 . At the beginning, at a set of discrete true strains the response maps of strain Rate Sensitivity Exponent ( m -value), power dissipation efficiency ( η -value) and instability parameter ( ξ -value) to temperatures and strain Rates were developed respectively. Following that, a processing map corresponding to each true strain was constructed by superimposing an instability map over a power dissipation map. According to m -criterion, η -criterion and ξ -criterion, the stable regions with higher power dissipation efficiency ( η > 0.3) and unstable regimes with negative strain Rate Sensitivity Exponent and instability parameter ( m ξ α + β -phase temperature range and DRV-predominant parameter domain in β -phase temperature range were identified and recommended. In a wide temperature range across β -transus and a large strain Rate range, the clarification of stable and unstable parameter regions corresponding to different deformation mechanisms contributes to design in the various hot forming processes of Ti–10V–2Fe–3Al alloy without resorting to time-consuming trial-and-error procedures.
Hong Li - One of the best experts on this subject based on the ideXlab platform.
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the variation of strain Rate Sensitivity Exponent and strain hardening Exponent in isothermal compression of ti 6al 4v alloy
Materials & Design, 2010Co-Authors: M Q Li, Weixin Yu, Hong LiAbstract:Abstract The deformation behavior in isothermal compression of Ti–6Al–4V alloy is investigated in the deformation temperatures ranging from 1093 K to 1303 K, the strain Rates ranging from 0.001 s −1 to 10.0 s −1 at an interval of an order magnitude and the height reductions ranging from 20% to 60% at an interval of 10%. Based on the experimental results in isothermal compression of Ti–6Al–4V alloy, the effect of processing parameters and grain size of primary α phase on the strain Rate Sensitivity Exponent m and the strain hardening Exponent n is in depth analyzed. The strain Rate Sensitivity Exponent m at a strain of 0.7 and strain Rate of 0.001 s −1 firstly tends to increase with the increasing of deformation temperature, and maximum m value is obtained at deformation temperature close to the beta-transus temperature, while at higher deformation temperature it drops to the smaller values. Moreover, the strain Rate Sensitivity Exponent m decreases with the increasing of strain Rate at the deformation temperatures below 1253 K, but the m values become maximal at a strain Rate of 0.01 s −1 and the deformation temperature above 1253 K. The strain Rate affects the variation of strain Rate Sensitivity Exponent with strain. Those phenomena can be explained reasonably based on the microstructural evolution. On the other hand, the strain hardening Exponent n depends strongly on the strain Rate at the strains of 0.5 and 0.7. The strain affects significantly the strain hardening Exponent n due to the variation of grain size of primary α phase with strain, and the competition between thermal softening and work hardening.
Guozheng Quan - One of the best experts on this subject based on the ideXlab platform.
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evaluation of the hot workability corresponding to complex deformation mechanism evolution for ti 10v 2fe 3al alloy in a wide condition range
Journal of Materials Processing Technology, 2015Co-Authors: Guozheng Quan, Wenquan Lv, Jianting Liang, Shiao PuAbstract:Abstract The hot workability of as-forged Ti–10V–2Fe–3Al alloy was evaluated. Meanwhile, the intrinsic relationships between deformation mechanisms and processing parameters were determined by the processing maps on the basis of dynamic materials model (DMM) with the input stress–strain data collected from a series of isothermal compressions at temperatures of 948–1123 K (across β -transus) and strain Rates of 0.001–10 s −1 . At the beginning, at a set of discrete true strains the response maps of strain Rate Sensitivity Exponent ( m -value), power dissipation efficiency ( η -value) and instability parameter ( ξ -value) to temperatures and strain Rates were developed respectively. Following that, a processing map corresponding to each true strain was constructed by superimposing an instability map over a power dissipation map. According to m -criterion, η -criterion and ξ -criterion, the stable regions with higher power dissipation efficiency ( η > 0.3) and unstable regimes with negative strain Rate Sensitivity Exponent and instability parameter ( m ξ α + β -phase temperature range and DRV-predominant parameter domain in β -phase temperature range were identified and recommended. In a wide temperature range across β -transus and a large strain Rate range, the clarification of stable and unstable parameter regions corresponding to different deformation mechanisms contributes to design in the various hot forming processes of Ti–10V–2Fe–3Al alloy without resorting to time-consuming trial-and-error procedures.
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Evaluation of the hot workability corresponding to complex deformation mechanism evolution for Ti–10V–2Fe–3Al alloy in a wide condition range
Journal of Materials Processing Technology, 2015Co-Authors: Guozheng Quan, Jianting Liang, Gui-chang Luo, Qing LiuAbstract:Abstract The hot workability of as-forged Ti–10V–2Fe–3Al alloy was evaluated. Meanwhile, the intrinsic relationships between deformation mechanisms and processing parameters were determined by the processing maps on the basis of dynamic materials model (DMM) with the input stress–strain data collected from a series of isothermal compressions at temperatures of 948–1123 K (across β -transus) and strain Rates of 0.001–10 s −1 . At the beginning, at a set of discrete true strains the response maps of strain Rate Sensitivity Exponent ( m -value), power dissipation efficiency ( η -value) and instability parameter ( ξ -value) to temperatures and strain Rates were developed respectively. Following that, a processing map corresponding to each true strain was constructed by superimposing an instability map over a power dissipation map. According to m -criterion, η -criterion and ξ -criterion, the stable regions with higher power dissipation efficiency ( η > 0.3) and unstable regimes with negative strain Rate Sensitivity Exponent and instability parameter ( m ξ α + β -phase temperature range and DRV-predominant parameter domain in β -phase temperature range were identified and recommended. In a wide temperature range across β -transus and a large strain Rate range, the clarification of stable and unstable parameter regions corresponding to different deformation mechanisms contributes to design in the various hot forming processes of Ti–10V–2Fe–3Al alloy without resorting to time-consuming trial-and-error procedures.
O.d. Sherby - One of the best experts on this subject based on the ideXlab platform.
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Superplasticity in a tool steel
Metals technology, 2013Co-Authors: J. Wadsworth, J. H. Lin, O.d. SherbyAbstract:AbstractA 01 tool steel has been studied for its superplastic characteristics for three different structures: (a) a coarse spheroidized-annealed structure; (b) a structure of fine spheroidized cementite particles and fine ferrite grains containing both high- and low-angle boundaries; and (c) a structure of fine spheroidized cementite particles and fine ferrite grains containing only high-angle boundaries. Optimum superplastic properties were obtained for the fine-grain-size steel containing high-angle boundaries. The 01 tool steel in this condition exhibited a strain-Rate-Sensitivity Exponent of 0·5 and a maximum elongation to failure of 1200% at 650°C.
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Development of ultrafine microstructures and superplasticity in Hadfield manganese steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1992Co-Authors: A. Goldberg, Oscar Antonio Ruano, O.d. SherbyAbstract:Abstract Ultrafine grains were developed in Hadfield manganese steels through appropriate thermomechanical processing. The steels contained from 1.2 to 1.7 wt.% C and 12.3–16.3 wt.% Mn. The austenite grains. 2–8 μm in size, were stabilized against grain growth by a dispersion of fine carbides, typically less than 1 μm. The processed materials were evaluated for superplastic properties at elevated temperatures (750–900 °C). Values for the strain Rate Sensitivity Exponent m in the expression σ=k dot e m ranged from 0.37 to 0.65. The value of m in the superplastic regime was found to depend on composition, grain size and temperature. At 23 °C, the fine-grain steels showed higher yield strengths and hardness values, but lower ductility, relative to values reported for commercially processed materials.
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Elevated temperature mechanical behaviour of an ultrahigh carbon steel/brass laminated composite
Composites, 1991Co-Authors: H.c. Tsai, J. Wolfenstine, O.d. SherbyAbstract:Abstract The mechanical properties of a laminated metal composite ( lmc ) based on ultrahigh carbon steel and brass were investigated from 710 to 840°C. A high strain Rate Sensitivity Exponent, m, of about 0.5 was observed at low strain Rates and decreased to about 0.15 at high strain Rates. The strain Rate vs. flow stress behaviour for the composite at low strain Rates correlates well with predicted behaviour based on the isostrain concept. The expected superplastic behaviour in the m=0.5 region was not realized because of severe cracking in the brass layers.
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Superplastic ceramics (with emphasis on iron carbide). Final report, 1 May 88-30 Apr 91
1991Co-Authors: O.d. Sherby, J. Wolfenstine, W.j. KimAbstract:Ultrafine grained iron carbide material was developed by an atomized powder process, utilizing hipping, pressing and extrusion procedures. The material was made superplastic and behaved like other superplastic ceramics. This observation lead to the following conclusions. Superplastic ceramics and metallic alloys exhibit different trends in tensile ductility in the range where the strain-Rate-Sensitivity Exponent, m, is high. The tensile ductility of superplastic metallic alloys (e.g. fine-grained zinc, aluminum, nickel and titanium alloys) is primarily a function of the strain-Rate-Sensitivity Exponent. In contrast, the tensile ductility of superplastic ceramic materials (e.g. zirconia, alumina, zirconia alumina composites and iron carbide) is not only a function of the strain Rate Sensitivity Exponent, but also a function of the parameter where the steady state strain Rate and Qc is the activation energy for superplastic flow. Superplastic ceramic materials exhibit a large decrease in tensile elongation with an increase. This trend in tensile elongation is explained based on a 'fracture-mechanics' model. The model predicts that tensile ductility increases with a decrease in flow stress, a decrease in grain size and an increase. The difference in the tensile ductility behavior of superplastic ceramics and metallic alloys can be related to their different failure mechanisms. Superplastic ceramicsmore » deform without necking and fail by intergranular cracks that propagate perpendicular to the applied tensile axis. In contrast, superplastic metallic alloys commonly fail by intergranular and transgranular (shearing) mechanisms with associated void formation in the neck region.« less
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The use of foil metallurgy processing to achieve ultrafine grained Mg-9 Li laminates and Mg-9Li-5B4C particulate composites
Journal of Materials Science, 1990Co-Authors: Gaspar González-doncel, J. Wolfenstine, P. Metenier, Oscar Antonio Ruano, O.d. SherbyAbstract:A foil metallurgy processing technique has been developed to prepare fine-grained laminates based on a two-phase Mg-9Li alloy and fine-grained particulate composites based on hard B4C powders embedded in the two-phase Mg-9Li alloy. The processing steps involve principally cold-rolling and low-temperature recovery processing for preparation of foils, and low-temperature press-bonding for preparation of laminates and composites. In this manner, contamination of the highly reactive alloy is minimized. Good tensile strength and ductility were achieved at room temperature with specific stiffness values of about 3.1 × 106 m3. Both the fine-grained laminates and the particulate composite are superplastic at 200 ° C, exhibiting a strain-Rate-Sensitivity Exponent,m, of 0.5.
