The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Ruslan Z. Valiev - One of the best experts on this subject based on the ideXlab platform.
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transition from poor ductility to room temperature Superplasticity in a nanostructured aluminum alloy
Scientific Reports, 2018Co-Authors: Kaveh Edalati, Zenji Horita, Ruslan Z. ValievAbstract:Recent developments of nanostructured materials with grain sizes in the nanometer to submicrometer range have provided ground for numerous functional properties and new applications. However, in terms of mechanical properties, bulk nanostructured materials typically show poor ductility despite their high strength, which limits their use for structural applications. The present article shows that the poor ductility of nanostructured alloys can be changed to room-temperature superplastisity by a transition in the deformation mechanism from dislocation activity to grain-boundary sliding. We report the first observation of room-temperature Superplasticity (over 400% tensile elongations) in a nanostructured Al alloy by enhanced grain-boundary sliding. The room-temperature grain-boundary sliding and Superplasticity was realized by engineering the Zn segregation along the Al/Al boundaries through severe plastic deformation. This work introduces a new boundary-based strategy to improve the mechanical properties of nanostructured materials for structural applications, where high deformability is a requirement.
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room temperature Superplasticity in an ultrafine grained magnesium alloy
Scientific Reports, 2017Co-Authors: Makoto Arita, Takahiro Masuda, Kaveh Edalati, Zenji Horita, Xavier Sauvage, Ruslan Z. Valiev, Mitsuaki FuruiAbstract:Superplasticity, a phenomenon of high tensile elongation in polycrystalline materials, is highly effective in fabrication of complex parts by metal forming without any machining. Superplasticity typically occurs only at elevated homologous temperatures, where thermally-activated deformation mechanisms dominate. Here, we report the first observation of room-temperature Superplasticity in a magnesium alloy, which challenges the commonly-held view of the poor room-temperature plasticity of magnesium alloys. An ultrafine-grained magnesium-lithium (Mg-8 wt.%Li) alloy produced by severe plastic deformation demonstrated 440% elongation at room temperature (0.35 T m) with a strain-rate sensitivity of 0.37. These unique properties were associated with enhanced grain-boundary sliding, which was approximately 60% of the total elongation. This enhancement originates from fast grain-boundary diffusion caused by the Li segregation along the grain boundaries and the formation of Li-rich interphases. This discovery introduces a new approach for controlling the room-temperature Superplasticity by engineering grain-boundary composition and diffusion, which is of importance in metal forming technology without heating.
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Room-Temperature Superplasticity in an Ultrafine-Grained Magnesium Alloy
Scientific Reports, 2017Co-Authors: Kaveh Edalati, Makoto Arita, Takahiro Masuda, Zenji Horita, Xavier Sauvage, Mitsuaki Furui, Ruslan Z. ValievAbstract:© 2017 The Author(s). Superplasticity, a phenomenon of high tensile elongation in polycrystalline materials, is highly effective in fabrication of complex parts by metal forming without any machining. Superplasticity typically occurs only at elevated homologous temperatures, where thermally-activated deformation mechanisms dominate. Here, we report the first observation of roomerature Superplasticity in a magnesium alloy, which challenges the commonly-held view of the poor roomerature plasticity of magnesium alloys. An ultrafine-grained magnesium-lithium (Mg-8 wt.%Li) alloy produced by severe plastic deformation demonstrated 440% elongation at room temperature (0.35 Tm) with a strain-rate sensitivity of 0.37. These unique properties were associated with enhanced grain-boundary sliding, which was approximately 60% of the total elongation. This enhancement originates from fast grain-boundary diffusion caused by the Li segregation along the grain boundaries and the formation of Li-rich interphases. This discovery introduces a new approach for controlling the roomerature Superplasticity by engineering grain-boundary composition and diffusion, which is of importance in metal forming technology without heating.
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Superplasticity in nanocrystalline Ni3Al
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: S. X. Mcfadden, Ruslan Z. Valiev, Amiya K. MukherjeeAbstract:Abstract Tensile testing at constant strain rate and temperature has shown that Superplasticity can be observed at lower temperatures in nanocrystalline materials than in the microcrystalline state. However, even at lower superplastic temperatures the onset of superplastic deformation in nanocrystalline materials coincides with microstructural instability. Consequently, ordered intermetallics such as Ni 3 Al are attractive systems for the study of nanocrystalline Superplasticity because grain growth kinetics is inhibited by preferred atomic pairing. Ni 3 Al was processed by severe plastic deformation to obtain nanocrystalline samples. The strain rate sensitivity, n , was estimated from strain rate jump tests to be 2.6. The grain size dependence of superplastic flow, p , was estimated by testing tensile specimens annealed to produce a range of grain size. The value of p was estimated to be 2.4–1.8. Several interesting features of nanocrystalline Superplasticity, such as strain hardening and high flow stresses, were investigated.
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high strain rate Superplasticity from nanocrystalline al alloy 1420 at low temperatures
Philosophical Magazine, 2001Co-Authors: Rajiv S. Mishra, Ruslan Z. Valiev, S. X. Mcfadden, Rinat K. Islamgaliev, A K MukherjeeAbstract:Abstract Superplasticity was investigated in nanocrystalline Al alloy 1420 to evaluate the scalability of conventional constitutive relationships in the nanocrystalline range. The parametric dependences of superplastic flow were obtained by constant-strain-rate tensile tests in the temperature range 200–300°C and a strain rate range of 3 × 10−4-5 × 10−1 s−1. The nanocrystalline alloy exhibits Superplasticity at low temperatures and higher strain rates compared with the microcrystalline alloy. The observation of high-strain-rate Superplasticity coincided with the temperature range for microstructural instability. A comparison with the theoretical models for Superplasticity and a constitutive relationship for Superplasticity in microcrystalline alloys shows a transition to slower deformation kinetics on a normalized basis. The transmission electron microscopy of deformed specimens supports the slip accommodation models for Superplasticity. It also shows a change in the intragranular dislocation density and ...
Yuji Kawamata - One of the best experts on this subject based on the ideXlab platform.
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High-Temperature Cycle Durability of Superplastic Al–Zn Eutectoid Solder Joints With Stress Relaxation Characteristics for SiC Power Semiconductor Devices
IEEE Electron Device Letters, 2019Co-Authors: Katsuaki Saito, Kunihiro Tamahashi, Jin Onuki, Takashi Inami, Mamoru Kobiyama, Yasushi Sasajima, Yuji KawamataAbstract:We have developed a new high-temperature Al-Zn lead-free soldering process that utilizes Superplasticity to realize SiC power devices with high-temperature cycle durability. The joining process consists of an Al-78wt.%Zn preparation being sandwiched by a SiC die and an insulation substrate, an interfacial cleaning process at approximately 250-270 °C, a heating stage to reach the solid-liquid coexisting temperature of 420-430 °C, the ejection of low-melting-temperature β(Zn) from the joining area by press stress, and the transformation to a superplastic composition, i.e., Al-70 wt.% Zn at 270-310 °C. Many lamellar phases that enable Superplasticity can be formed in this microstructure. This solder joint composition was proven to have a better stress-relaxation effect than eutectic Al-95wt.%Zn, and the composition shows a much higher damping capability at the maximum operating temperature of SiC devices (200 °C) than that of other joining candidates. The outstanding temperature cycle durability was verified in temperature cycle tests from -40 °C to 300 °C for 5000 cycles. This durability is due to the high-stress-relaxation effect from the Superplasticity transformation realized by the lamellar structures in the Al-Zn alloy solder.
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Highly reliable high-temperature superplastic Al-Zn eutectoid solder joining with stress relaxation characteristics for next generation SiC power semiconductor devices
2017 29th International Symposium on Power Semiconductor Devices and IC's (ISPSD), 2017Co-Authors: Jin Onuki, Akio Chiba, Kunihiro Tamahashi, Yoshinobu Motohashi, Mitsuo Kawakami, Yoshitaka Sugawara, Takashi Inami, Mamoru Kobiyama, Yuji KawamataAbstract:A new high-temperature lead-free solder joint which withstands temperatures up to 300°C and utilizes Superplasticity in an Al-Zn eutectoid alloy has been developed to realize SiC power semiconductor devices. The joining process consists of interfacial cleaning of the joint formed utilizing Superplasticity of the Al-Zn-eutectoid alloy at 250°C followed by bonding in the solid-liquid coexisting temperature range in order to control microstructures and to reduce occurrence of voids. The developed SiC/SiN substrate joints with void-free and stress relaxation effects show outstanding reliability in temperature cycle tests from -40°C to 300°C for 5000 cycles.
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A new lead-free solder joint utilizing superplastic Al-Zn eutectoid alloy for next generation SiC power semiconductor devices
Materials Science Forum, 2016Co-Authors: Jin Onuki, Akane Saitou, Akio Chiba, Kunihiro Tamahashi, Yoshinobu Motohashi, Yuji KawamataAbstract:A new high-temperature lead-free solder joint which withstands up to 300°C utilizing Superplasticity in the Al-Zn eutectoid alloy has been developed to realize SiC power semiconductor devices. The new solid state joining process consists of interfacial cleaning of joints utilizing Superplasticity of the Al-Zn-eutectoid alloy at 250°C followed by diffusion bonding between 350 and 390°C. The bonding strength of the new joints exhibits almost the same value at the temperature range from RT to 300°C, above which it decreases slightly with increasing temperature. It is also found that the bonding strength of the new joints is 8 times as high as those of a high-temperature Pb-5wt%Sn-1.5wt%Ag solder and the Al-Zn eutectoid alloy solder without utilizing Superplasticity at 250°C. The Al-Zn eutectoid alloy solder joint has shown high reliability in the temperature cycle testing between 50°C and 300°C up to 300 cycles.
Z Y - One of the best experts on this subject based on the ideXlab platform.
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exceptional high strain rate Superplasticity in mg gd y zn zr alloy with long period stacking ordered phase
Scripta Materialia, 2013Co-Authors: Qunbao Yang, B L Xiao, Quanxin Zhang, M Y Zheng, Z YAbstract:Friction stir processing (FSP) was applied to Mg–Gd–Y–Zn–Zr casting, producing a fine-grained structure of ∼3 μm with a long-period stacking ordered phase distributed within the grains and predominantly high-angle grain boundaries. This FSP alloy exhibited superior high-strain-rate Superplasticity at 350–500 °C. A maximum Superplasticity of 3570% was achieved at 425 °C and a strain rate of 3 × 10 −2 s −1 . Such superior Superplasticity is attributed to the thermally stable microstructure and good deformation compatibility.
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enhanced Superplasticity in friction stir processed mg gd y zr alloy
Journal of Alloys and Compounds, 2013Co-Authors: Qunbao Yang, B L Xiao, Z YAbstract:Abstract Fine-grained supersaturated Mg–10Gd–3Y–0.5Zr (GW103) alloy with predominant high-angle grain boundaries (HAGB) was prepared by friction stir processing (FSP). The FSP GW103 alloy was subjected to superplastic investigation at a small temperature range of 400–425 °C. Fine β-Mg 5 (Gd,Y) particles precipitated at the grain boundaries during heating before superplastic deformation, and their volume fraction decreased significantly with increasing the temperature from 400 to 425 °C. Superplasticity of the FSP GW103 alloy was sensitive to the testing temperature, and a maximum Superplasticity of 1110% was achieved at 1 × 10 −3 s −1 and a medium temperature of 415 °C. Grain boundary sliding was identified as the main deformation mechanism in FSP GW103 alloy. The high Superplasticity is attributed to the fine grains, high percentage of HAGBs, and a moderate volume fraction of β particles that precipitated at 415 °C.
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achieving high strain rate Superplasticity in mg zn y zr alloy produced by friction stir processing
Scripta Materialia, 2011Co-Authors: Qunbao Yang, B L Xiao, Z Y, Runsheng ChenAbstract:Friction stir processing was applied to hot-rolled Mg-Zn-Y-Zr alloy to produce a fine-grained structure 4.5 mu m in size with fine, uniformly distributed Mg(3)Zn(3)Y(2) particles and predominant high-angle grain boundaries (HAGBs) of 91%. A maximum Superplasticity of 1110% was achieved at a high strain rate of 1 x 10(-2) s(-1) and 450 degrees C. The superior Superplasticity at this high strain rate is attributed to the excellent thermal stability of the fine-grained structure and the high percentage of HAGBs. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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low temperature Superplasticity of al mg sc alloy produced by friction stir processing
Scripta Materialia, 2009Co-Authors: Z Y, L Q ChenAbstract:Ultrafine-grained (0.7 mu m) Al-Mg-Sc alloy with an approximately random misorientation distribution and predominantly high-angle boundaries of 97% was produced by friction stir processing. A ductility of 235% was obtained at 200 degrees C. Increasing temperature from 200 to 300 degrees C resulted in an increase in Superplasticity, optimum strain rate and strain rate sensitivity. Low temperature and high strain rate Superplasticity with a ductility of 620% was achieved at 300 degrees C and 3 x 10(-2) s(-1). Abnormal grain growth occurred at 350 degrees C, resulting in the disappearance of Superplasticity. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Kaveh Edalati - One of the best experts on this subject based on the ideXlab platform.
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transition from poor ductility to room temperature Superplasticity in a nanostructured aluminum alloy
Scientific Reports, 2018Co-Authors: Kaveh Edalati, Zenji Horita, Ruslan Z. ValievAbstract:Recent developments of nanostructured materials with grain sizes in the nanometer to submicrometer range have provided ground for numerous functional properties and new applications. However, in terms of mechanical properties, bulk nanostructured materials typically show poor ductility despite their high strength, which limits their use for structural applications. The present article shows that the poor ductility of nanostructured alloys can be changed to room-temperature superplastisity by a transition in the deformation mechanism from dislocation activity to grain-boundary sliding. We report the first observation of room-temperature Superplasticity (over 400% tensile elongations) in a nanostructured Al alloy by enhanced grain-boundary sliding. The room-temperature grain-boundary sliding and Superplasticity was realized by engineering the Zn segregation along the Al/Al boundaries through severe plastic deformation. This work introduces a new boundary-based strategy to improve the mechanical properties of nanostructured materials for structural applications, where high deformability is a requirement.
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room temperature Superplasticity in an ultrafine grained magnesium alloy
Scientific Reports, 2017Co-Authors: Makoto Arita, Takahiro Masuda, Kaveh Edalati, Zenji Horita, Xavier Sauvage, Ruslan Z. Valiev, Mitsuaki FuruiAbstract:Superplasticity, a phenomenon of high tensile elongation in polycrystalline materials, is highly effective in fabrication of complex parts by metal forming without any machining. Superplasticity typically occurs only at elevated homologous temperatures, where thermally-activated deformation mechanisms dominate. Here, we report the first observation of room-temperature Superplasticity in a magnesium alloy, which challenges the commonly-held view of the poor room-temperature plasticity of magnesium alloys. An ultrafine-grained magnesium-lithium (Mg-8 wt.%Li) alloy produced by severe plastic deformation demonstrated 440% elongation at room temperature (0.35 T m) with a strain-rate sensitivity of 0.37. These unique properties were associated with enhanced grain-boundary sliding, which was approximately 60% of the total elongation. This enhancement originates from fast grain-boundary diffusion caused by the Li segregation along the grain boundaries and the formation of Li-rich interphases. This discovery introduces a new approach for controlling the room-temperature Superplasticity by engineering grain-boundary composition and diffusion, which is of importance in metal forming technology without heating.
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Room-Temperature Superplasticity in an Ultrafine-Grained Magnesium Alloy
Scientific Reports, 2017Co-Authors: Kaveh Edalati, Makoto Arita, Takahiro Masuda, Zenji Horita, Xavier Sauvage, Mitsuaki Furui, Ruslan Z. ValievAbstract:© 2017 The Author(s). Superplasticity, a phenomenon of high tensile elongation in polycrystalline materials, is highly effective in fabrication of complex parts by metal forming without any machining. Superplasticity typically occurs only at elevated homologous temperatures, where thermally-activated deformation mechanisms dominate. Here, we report the first observation of roomerature Superplasticity in a magnesium alloy, which challenges the commonly-held view of the poor roomerature plasticity of magnesium alloys. An ultrafine-grained magnesium-lithium (Mg-8 wt.%Li) alloy produced by severe plastic deformation demonstrated 440% elongation at room temperature (0.35 Tm) with a strain-rate sensitivity of 0.37. These unique properties were associated with enhanced grain-boundary sliding, which was approximately 60% of the total elongation. This enhancement originates from fast grain-boundary diffusion caused by the Li segregation along the grain boundaries and the formation of Li-rich interphases. This discovery introduces a new approach for controlling the roomerature Superplasticity by engineering grain-boundary composition and diffusion, which is of importance in metal forming technology without heating.
Mamoru Mabuchi - One of the best experts on this subject based on the ideXlab platform.
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Superplasticity and grain boundary sliding in rolled az91 magnesium alloy at high strain rates
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Qijiang Wang, Hao Zhou, W J Ding, Yasumasa Chino, Mamoru MabuchiAbstract:Abstract The superplastic deformation characteristics and microstructure evolution of the rolled AZ91 magnesium alloys at temperatures ranging from 623 to 698 K (0.67–0.76 Tm) and at the high strain rates ranging from 10−3 to 1 s−1 were investigated with the methods of OM, SEM and TEM. An excellent Superplasticity with the maximum elongation to failure of 455% was obtained at 623 K and the strain rate of 10−3 s−1 in the rolled AZ91 magnesium alloys and its strain rate sensitivity m is high, up to 0.64. The dominant deformation mechanism in high strain rate Superplasticity is still grain boundary sliding (GBS), which was studied systematically in this study. The dislocation creep controlled by grain boundary diffusion was considered the main accommodation mechanism, which was observed in this study.
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realization of high strain rate Superplasticity at low temperatures in a mg zn zr alloy
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: Hiroyuki Watanabe, Mamoru Mabuchi, Toshiji Mukai, Koichi Ishikawa, Kenji HigashiAbstract:Abstract Possibility of combination of high-strain-rate Superplasticity and low-temperature Superplasticity was experimentally confirmed using extremely fine-grained magnesium alloy. In order to achieve such a superior superplastic behavior, the required grain size and the suitable processing was considered. It was suggested that the required grain size of ≤≈0.4 μm can be obtained through the processing from powder metallurgy route, using rapidly solidified powder. Therefore, superplastic behavior was examined using powder metallurgy processed Mg–Zn–Zr alloy (ZK61). Tensile tests revealed that high-strain-rate Superplasticity was obtained even at low temperatures of ≈473 K, which is corresponding to half the absolute melting point of the material. This was attributed to the fine grain size of 0.65 μm.
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low temperature Superplasticity in an az91 magnesium alloy processed by ecae
Scripta Materialia, 1997Co-Authors: Mamoru Mabuchi, Hajime Iwasaki, K Yanase, Kenji HigashiAbstract:An AZ91 alloy with a very small grain size of about 1 μm was processed by ECAE. The alloy showed a large elongation of 661% at a low temperature of 473 K, which is 0.5Tm. The strain rate sensitivity was about 0.3, suggesting that the low temperature Superplasticity for the AZ91 alloy is related to viscous-glide of dislocations. However, the mechanical properties strongly depended on the grain size and grain boundary sliding actively occurred. These facts are not in agreement with the viscous-glide controlled deformation mechanism. Further research is required to understand the origin of low temperature Superplasticity.
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high strain rate Superplasticity in metallic materials and the potential for ceramic materials
Isij International, 1996Co-Authors: Kenji Higashi, Mamoru Mabuchi, Terence G. LangdonAbstract:High-strain-rate Superplasticity (i.e., superplastic behavior at strain rates over 10-2s-1) has been observed in many meterials such as aluminum alloys and their matrix composites and it is associated with an ultra-fine grained stucture of less than about 3 μm. Its deformation mechanism appears to be different from that in conventional superplastic materials. Experimental investigations showed that a maximum elongation was attained at a temperature close to the partial melting temperature in many superplastic materials exhibiting high-strain-rate Superplasticity. Recently, a new model, which was considered from the viewpoint of the accommodation mechanism by an accommodatin helper such as a liquid or glassy phase, was proposed in which Superplasticity was critically controlled by the accommodation helper both to relax the stress concentration resulting from the sliding at grain boundaries and/or interfaces and to limit the build up of internal cavitation and subsequent failure. The critical conditions of the quantity and distribution of a liquid phase for optimizing superplastic deformation was discussed and then applied to consider the possibility of attaining high-strain-rate Superplasticity in ceramic materials.
