The Experts below are selected from a list of 8070 Experts worldwide ranked by ideXlab platform
Naoto Koshizaki - One of the best experts on this subject based on the ideXlab platform.
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Hexagonal Close Packed hierarchical amorphous tio2 nanocolumn arrays transferability enhanced photocatalytic activity and superamphiphilicity without uv irradiation
Journal of the American Chemical Society, 2008Co-Authors: Yue Li, Takeshi Sasaki, Yoshiki Shimizu, Naoto KoshizakiAbstract:A Hexagonal-Close-Packed (hcp), hierarchical amorphous TiO2 nanocolumn array was fabricated by pulsed laser deposition (PLD) using a PS colloidal monolayer as a template under a high pressure (6.7 Pa) of background oxygen gas. The formation mechanism was investigated, and a model of multidirection glancing deposition was proposed to explain the formation process. This strategy can be extended to the fabrication of similar structures using different materials. Interestingly, this nanostructured array could be transferred to almost any substrate, avoiding restriction of substrate types in fabrication of nanocolumn arrays, which is helpful in the design and creation of nanodevices on various desired substrates. This hierarchical nanocolumn array exhibits excellent superamphiphilicity with both water and oil contact angles of 0°, without further UV irradiation. More importantly, the amorphous TiO2 nanocolumn array demonstrates better performance in photocatalytic activity than an anatase nanocolumn array due ...
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Hexagonal Close Packed hierarchical amorphous tio2 nanocolumn arrays transferability enhanced photocatalytic activity and superamphiphilicity without uv irradiation
Journal of the American Chemical Society, 2008Co-Authors: Takeshi Sasaki, Yoshiki Shimizu, Naoto KoshizakiAbstract:A Hexagonal-Close-Packed (hcp), hierarchical amorphous TiO2 nanocolumn array was fabricated by pulsed laser deposition (PLD) using a PS colloidal monolayer as a template under a high pressure (6.7 Pa) of background oxygen gas. The formation mechanism was investigated, and a model of multidirection glancing deposition was proposed to explain the formation process. This strategy can be extended to the fabrication of similar structures using different materials. Interestingly, this nanostructured array could be transferred to almost any substrate, avoiding restriction of substrate types in fabrication of nanocolumn arrays, which is helpful in the design and creation of nanodevices on various desired substrates. This hierarchical nanocolumn array exhibits excellent superamphiphilicity with both water and oil contact angles of 0 degrees, without further UV irradiation. More importantly, the amorphous TiO2 nanocolumn array demonstrates better performance in photocatalytic activity than an anatase nanocolumn array due to its large surface area and special microstructures, suggesting that the surface area of the TiO2 is preferable to its crystal structure for enhancing photocatalytic activity. The combination of superamphiphilicity and photocatalytic activity gives the surface an excellent self-cleaning effect.
Rui Yang - One of the best experts on this subject based on the ideXlab platform.
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basal plane stacking fault energy of Hexagonal Close Packed metals based on the ising model
Acta Materialia, 2013Co-Authors: Qingmiao Hu, Rui YangAbstract:Abstract Stacking fault energy (SFE) plays an important role in the plastic deformation of metals. As compared to those of face-centered cubic metals, the SFEs of Hexagonal Close-Packed (hcp) metals are less reported in literature. In this paper, we derive the expressions of four types ( I 1 , I 2 , E and T 2 ) of basal plane SFEs of hcp metals in terms of the interlayer interaction energies within the framework of the Ising model. The SFEs of 14 kinds of hcp metals are then evaluated with the interlayer interaction energies extracted from the total energies of four prototypes calculated by using the first-principles full-potential augmented plane-wave method. We show that the hcp metals can be divided into three types according to their interlayer interaction energies. For all the hcp metals involved in this study, I 1 has the lowest SFE, whereas E has the highest. The metals (Mg, Co, Zn and Cd) with principal slip system (0 0 0 1) [ 1 1 2 ¯ 0 ] generally have low basal plane SFEs. The I 1 and T 2 SFEs increase linearly with the energy difference between double Hexagonal Close-Packed and hcp structures, whereas the I 2 and E SFEs increase linearly with the energy difference between the short-period twin and hcp structures, indicating a trivial contribution of the interaction energy between atomic layers over third nearest neighbors to the SFEs. The SFEs also correlate with the cohesive energy density (cohesive energy of unit volume) with the exception of Be, Co, Tc and Re.
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basal plane stacking fault energy of Hexagonal Close Packed metals based on the ising model
Acta Materialia, 2013Co-Authors: Rui YangAbstract:Abstract Stacking fault energy (SFE) plays an important role in the plastic deformation of metals. As compared to those of face-centered cubic metals, the SFEs of Hexagonal Close-Packed (hcp) metals are less reported in literature. In this paper, we derive the expressions of four types ( I 1 , I 2 , E and T 2 ) of basal plane SFEs of hcp metals in terms of the interlayer interaction energies within the framework of the Ising model. The SFEs of 14 kinds of hcp metals are then evaluated with the interlayer interaction energies extracted from the total energies of four prototypes calculated by using the first-principles full-potential augmented plane-wave method. We show that the hcp metals can be divided into three types according to their interlayer interaction energies. For all the hcp metals involved in this study, I 1 has the lowest SFE, whereas E has the highest. The metals (Mg, Co, Zn and Cd) with principal slip system (0 0 0 1) [ 1 1 2 ¯ 0 ] generally have low basal plane SFEs. The I 1 and T 2 SFEs increase linearly with the energy difference between double Hexagonal Close-Packed and hcp structures, whereas the I 2 and E SFEs increase linearly with the energy difference between the short-period twin and hcp structures, indicating a trivial contribution of the interaction energy between atomic layers over third nearest neighbors to the SFEs. The SFEs also correlate with the cohesive energy density (cohesive energy of unit volume) with the exception of Be, Co, Tc and Re.
C N Tome - One of the best experts on this subject based on the ideXlab platform.
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rolling induced face centered cubic titanium in Hexagonal Close Packed titanium at room temperature
Scientific Reports, 2016Co-Authors: Anil Kumar, C N Tome, Jun Wang, Z Zhang, Scott X MaoAbstract:Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline Hexagonal Close Packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: 〈0001〉hcp||〈001〉fcc and , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pure-shuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning.
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stochastic modeling of twin nucleation in polycrystals an application in Hexagonal Close Packed metals
International Journal of Plasticity, 2014Co-Authors: Stephen R Niezgoda, Irene J. Beyerlein, Anand K Kanjarla, C N TomeAbstract:Twinning in Hexagonal Close-Packed (hcp) metals is a multi-scale process that depends on the microstructural and mechanical response details at the polycrystalline aggregate, grain, micro, and atomic scales. Twinning can generally be regarded as a two-step process, a nucleation event followed by propagation and growth. This articles presents a stochastic model for the nucleation of deformation twins in hcp polycrystals. Twin nucleation is mod- eled through its dependence on lower length scale material details, such as the defect con- figurations at potential nucleation sites within grain boundaries, and mechanical details such as highly localized stress concentrations at the microscale in a probabilistic manner. These two aspects, the material and mechanical, must align for a successful nucleation event. The nucleation process is cast as a survival model parameterized by the local stress at the grain boundary. The model gives an explicit form for the probability distribution for the critical stress values required for twin nucleation. The model is implemented into a viscoplastic self-consistent (VPSC) crystal plasticity framework in order to test its predic- tive capability against previously reported statistical characterization in deformed zirco- nium at multiple temperatures. For implementation in VPSC, the stress concentrations are sampled from a distribution calibrated to full-field crystal plasticity simulations and a three-dimensional model of grain neighbors and distribution of grain boundary areas are implemented.
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anisotropy in Hexagonal Close Packed structures improvements to crystal plasticity approaches applied to magnesium alloy
Philosophical Magazine, 2013Co-Authors: A L Oppedal, C N Tome, Haitham El Kadiri, Sven C Vogel, M F HorstemeyerAbstract:AbstractDue to its polarity, twinning in strongly textured Hexagonal Close Packed (HCP) structures can be maximized or minimized under particular loading conditions. The resulting anisotropy can be dramatically demonstrated for magnesium with a fibre, for example. The stress–strain behaviour from compression loading parallel to the fibre produces a ‘parabolic’ stress–strain curve, but a ‘sigmoidal’ curve when loaded normal to the fibre. When modelling anisotropy in HCP structures with crystal plasticity, contemporary researchers usually fit hardening parameters to only these two extreme cases, i.e., maximized or minimized twinning activity, presuming that the same parameters would interpolate the correct behaviour under any other transitional stress direction. A comparison with experiments presented in this paper demonstrates that this assumption is not fully accurate, whether using the phenomenological Voce hardening model or the dislocation density based hardening model in the VPSC (visco-plastic self-...
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a crystal plasticity model for Hexagonal Close Packed hcp crystals including twinning and de twinning mechanisms
International Journal of Plasticity, 2013Co-Authors: Huamiao Wang, Jian Wang, C N TomeAbstract:Together with slip, deformation twinning and de-twinning are the plastic deformation mechanisms in Hexagonal Close Packed (HCP) crystals, which strongly affect texture evolution and anisotropic response. As a consequence, several twinning models have been proposed and implemented in the existing polycrystalline plasticity models. De-twinning is an inverse process with respect to twinning, which is relevant to cycling, fatigue and complex loads but is rarely incorporated into polycrystalline plastic models. In this paper, we propose a physics-based twinning and de-twinning (TDT) model that has the capability of dealing with both mechanisms during plastic deformation. The TDT model is characterized by four deformation mechanisms corresponding to twin nucleation, twin growth, twin shrinkage and re-twinning. Twin nucleation and twin growth are associated with deformation twinning, and twin shrinkage and re-twinning are associated with de-twinning. The proposed TDT model is implemented in the Elasto-Visco-Plastic Self-Consistent (EVPSC) model. We demonstrate the validity and the capability of the TDT model by simulating cyclic loading of magnesium alloys AZ31B plate and AZ31 bar. Comparison with the measurements indicates that the TDT model is able to capture the key features observed in experiments, implying that the mechanical response in the simulated materials is mainly associated with twinning and de-twinning.
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pure shuffle nucleation of deformation twins in Hexagonal Close Packed metals
Materials research letters, 2013Co-Authors: Jun Wang, S K Yadav, C N TomeAbstract:The propagation of deformation twins in Hexagonal-Close-Packed metals is commonly described by a conventional glide-shuffle mechanism. The widely accepted convention is that this process is also responsible for twin nucleation, but lacks direct confirmation. Using atomistic simulations, we identify an unconventional pure-shuffle mechanism for the nucleation of (1¯012) twins, which then grow through the conventional glide-shuffle mechanism entailing the glide of twinning disconnections. The pure-shuffle nucleation of twins at grain boundaries can be ascribed to a high-stress concentration and pre-existing grain boundary dislocations.
Takeshi Sasaki - One of the best experts on this subject based on the ideXlab platform.
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Hexagonal Close Packed hierarchical amorphous tio2 nanocolumn arrays transferability enhanced photocatalytic activity and superamphiphilicity without uv irradiation
Journal of the American Chemical Society, 2008Co-Authors: Yue Li, Takeshi Sasaki, Yoshiki Shimizu, Naoto KoshizakiAbstract:A Hexagonal-Close-Packed (hcp), hierarchical amorphous TiO2 nanocolumn array was fabricated by pulsed laser deposition (PLD) using a PS colloidal monolayer as a template under a high pressure (6.7 Pa) of background oxygen gas. The formation mechanism was investigated, and a model of multidirection glancing deposition was proposed to explain the formation process. This strategy can be extended to the fabrication of similar structures using different materials. Interestingly, this nanostructured array could be transferred to almost any substrate, avoiding restriction of substrate types in fabrication of nanocolumn arrays, which is helpful in the design and creation of nanodevices on various desired substrates. This hierarchical nanocolumn array exhibits excellent superamphiphilicity with both water and oil contact angles of 0°, without further UV irradiation. More importantly, the amorphous TiO2 nanocolumn array demonstrates better performance in photocatalytic activity than an anatase nanocolumn array due ...
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Hexagonal Close Packed hierarchical amorphous tio2 nanocolumn arrays transferability enhanced photocatalytic activity and superamphiphilicity without uv irradiation
Journal of the American Chemical Society, 2008Co-Authors: Takeshi Sasaki, Yoshiki Shimizu, Naoto KoshizakiAbstract:A Hexagonal-Close-Packed (hcp), hierarchical amorphous TiO2 nanocolumn array was fabricated by pulsed laser deposition (PLD) using a PS colloidal monolayer as a template under a high pressure (6.7 Pa) of background oxygen gas. The formation mechanism was investigated, and a model of multidirection glancing deposition was proposed to explain the formation process. This strategy can be extended to the fabrication of similar structures using different materials. Interestingly, this nanostructured array could be transferred to almost any substrate, avoiding restriction of substrate types in fabrication of nanocolumn arrays, which is helpful in the design and creation of nanodevices on various desired substrates. This hierarchical nanocolumn array exhibits excellent superamphiphilicity with both water and oil contact angles of 0 degrees, without further UV irradiation. More importantly, the amorphous TiO2 nanocolumn array demonstrates better performance in photocatalytic activity than an anatase nanocolumn array due to its large surface area and special microstructures, suggesting that the surface area of the TiO2 is preferable to its crystal structure for enhancing photocatalytic activity. The combination of superamphiphilicity and photocatalytic activity gives the surface an excellent self-cleaning effect.
Jian Wang - One of the best experts on this subject based on the ideXlab platform.
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a crystal plasticity model for Hexagonal Close Packed hcp crystals including twinning and de twinning mechanisms
International Journal of Plasticity, 2013Co-Authors: Huamiao Wang, Jian Wang, C N TomeAbstract:Together with slip, deformation twinning and de-twinning are the plastic deformation mechanisms in Hexagonal Close Packed (HCP) crystals, which strongly affect texture evolution and anisotropic response. As a consequence, several twinning models have been proposed and implemented in the existing polycrystalline plasticity models. De-twinning is an inverse process with respect to twinning, which is relevant to cycling, fatigue and complex loads but is rarely incorporated into polycrystalline plastic models. In this paper, we propose a physics-based twinning and de-twinning (TDT) model that has the capability of dealing with both mechanisms during plastic deformation. The TDT model is characterized by four deformation mechanisms corresponding to twin nucleation, twin growth, twin shrinkage and re-twinning. Twin nucleation and twin growth are associated with deformation twinning, and twin shrinkage and re-twinning are associated with de-twinning. The proposed TDT model is implemented in the Elasto-Visco-Plastic Self-Consistent (EVPSC) model. We demonstrate the validity and the capability of the TDT model by simulating cyclic loading of magnesium alloys AZ31B plate and AZ31 bar. Comparison with the measurements indicates that the TDT model is able to capture the key features observed in experiments, implying that the mechanical response in the simulated materials is mainly associated with twinning and de-twinning.
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twinning and de twinning via glide and climb of twinning dislocations along serrated coherent twin boundaries in Hexagonal Close Packed metals
Materials research letters, 2013Co-Authors: Jian Wang, C N Tome, L Liu, S X Mao, S K GongAbstract:The (1¯012) twin boundaries experimentally observed in Hexagonal-Close-Packed metals are often serrated rather than fully coherent. These serrated coherent twin boundaries (SCTBs) consist of sequential (1¯012) coherent twin boundaries and parallel basal–prismatic planes serrations (BPPS). We demonstrated that the formation of BPPS is geometrically and energetically preferred in the SCTBs, and an SCTB thus migrates by glide and climb of twinning dislocations, combined with atomic shuffling. Particularly, the climb mechanism, combined with the density and the height of BPPSs in the SCTBs, could be crucial in controlling twinning and de-twinning, and twinning-associated hardening.
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a constitutive model of twinning and detwinning for Hexagonal Close Packed polycrystals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2012Co-Authors: Huamiao Wang, C N Tome, Jian WangAbstract:Abstract A new constitutive model to describe twinning and detwinning for polycrystalline materials with the Hexagonal Close Packed (HCP) crystallographic structure is developed and implemented in the recently developed elastic viscoplastic self-consistent (EVPSC) polycrystal model. The new model is then applied to magnesium alloy Mg–3 Al–1 Zn (AZ31B) sheet under cyclic loadings and strain path changes. It is demonstrated that the new twinning model is able to capture key features associated with twinning and detwinning observed experimentally.
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atomic structures of symmetric tilt grain boundaries in Hexagonal Close Packed hcp crystals
Modelling and Simulation in Materials Science and Engineering, 2012Co-Authors: Jian Wang, Irene J. BeyerleinAbstract:Molecular dynamics simulation and interface defect theory are used to determine the relaxed equilibrium atomic structures of symmetric tilt grain boundaries (STGBs) in Hexagonal Close-Packed (hcp) crystals with a \( [0\bar{1}10] \) tilt axis. STGBs of all possible rotation angles θ from 0 deg to 90 deg are found to have an ordered atomic structure. They correspond either to a coherent, defect-free boundary or to a tilt wall containing an array of distinct and discrete intrinsic grain boundary dislocations (GBDs). The STGBs adopt one of six base structures, \( P_{B}^{(i)} \), i = 1, …, 6, and the Burgers vector of the GBDs is related to the interplanar spacing of the base structure on which it lies. The base structures correspond to the basal plane (θ = 0 deg, \( P_{B}^{(1)} \)); one of four minimum-energy, coherent boundaries, \( (\bar{2}111),\;(\bar{2}112),\;(\bar{2}114) \), and \( (\bar{2}116)\;\left( {P_{B}^{(2)} - P_{B}^{(5)} } \right) \); and the \( \left( {11\bar{2}0} \right) \) plane (θ = 90 deg, \( P_{B}^{(6)} \)). Based on these features, STGBs can be classified into one of six possible structural sets, wherein STGBs belonging to the same set i contain the same base boundary structure \( P_{B}^{(i)} \) and an array of GBDs with the same Burgers vector \( b_{\text{GB}}^{(i)} \), which vary only in spacing and sign with θ. This classification is shown to apply to both Mg and Ti, two metals with different c/a ratios and employing different interatomic potentials in simulation. We use a simple model to forecast the misorientation range of each set for hcp crystals of general c/a ratio, the predictions of which are shown to agree well with the molecular dynamics (MD) simulations for Mg and Ti.
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1 012 twinning nucleation mechanisms in Hexagonal Close Packed crystals
Acta Materialia, 2009Co-Authors: Jian Wang, J. P. Hirth, C N TomeAbstract:Abstract Mechanisms for ( 1 ¯ 0 1 2 ) twinning in Hexagonal-Close-Packed crystals at an atomic scale were studied using topological analysis and atomistic simulations. Two twinning mechanisms were found: a normal-twinning mechanism in which a stable twin nucleus is created by simultaneous nucleation of multiple twinning dislocations; and a zonal-twinning mechanism in which a stable twin nucleus is created by simultaneous nucleation of a partial dislocation and multiple twinning dislocations. The twinning direction, dependent on the ratio of lattice parameters c/a, is along [ 1 0 1 ¯ 1 ] when c / a 3 , but along the opposite direction when c / a > 3 . Atomistic simulations, using density function theory for Mg, Zr and Zn and an empirical potential for Mg, were performed to study the kinetics and energetics associated with the two twinning mechanisms. The results show that the zonal-twinning mechanism is energetically favorable relative to the normal-twinning mechanism, because the zonal dislocation has a smaller Burgers vector.