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Hiroyuki Kokawa - One of the best experts on this subject based on the ideXlab platform.
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Grain Structure evolution during friction-stir welding
Physical Mesomechanics, 2020Co-Authors: Sergey Mironov, Yutaka S. Sato, Hiroyuki KokawaAbstract:In this work, the current state of understanding of Grain Structure evolution during friction-stir welding is briefly reviewed. The broad aspects of this process and experimental techniques for its examination are critically addressed. The specific character of the microstructural evolutions in body-centered cubic, face-centered cubic and hexagonal close-packed metals are considered in details. In all cases, the Grain Structure evolution is shown to be a relatively complex process, which usually involves geometric effect of strain, continuous recrystallization and discontinuous recrystallization. Moreover, mechanical twinning, annealing twinning and Grain convergence may also occur in particular cases. It is also demonstrated that activation of a specific microstructural mechanism is primarily governed by crystal Structure and stacking fault energy but may also be influenced by welding temperature. Specifically, microStructure evolution in cubic metals with high stacking-fault energy is primarily governed by the continuous recrystallization whereas Grain Structure development in materials with low stacking-fault energy is mainly driven by the discontinuous recrystallization. In the case of transient stacking-fault energy, the materials may experience a transition from the continuous to the discontinuous mechanism. In hexagonal metals, microstructural changes are shown to be directly linked with crystallographic texture. Specifically, a formation of very sharp texture may promote the Grain convergence.
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Grain Structure and microtexture in friction stir welded commercial purity titanium
Science and Technology of Welding and Joining, 2010Co-Authors: Y Zhang, S H C Park, Yutaka S. Sato, Hiroyuki Kokawa, Satoshi HiranoAbstract:AbstractDefect free friction stir welds were produced in commercial purity titanium at rotational speeds between 200 and 400 rev min–1. Friction stir welding produced a finer Grain Structure in the stir zone than in the base material. Electron backscattered diffraction examination suggested that the fine Grains in the stir zone were formed through both continuous and discontinuous recrystallisation during friction stir welding. A torsion texture was observed in all welds and occupied most parts of the stir zone. Formation of this texture was attributed to the shear deformation along the tool shoulder during the stirring process.
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Grain Structure and texture evolution during friction stir welding of thin 6016 aluminum alloy sheets
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: U F H Suhuddin, Sergey Mironov, Y Sato, Hiroyuki KokawaAbstract:Abstract A “stop-action” technique was employed to study the Grain Structure and texture development during friction stir welding of thin 6016 aluminum sheets. The microstructural evolution ahead of the tool pin was found to be a complex process involving geometrical effects of strain as well as simultaneous development of continuous and discontinuous recrystallizations. At the circumference of the pin, the material flow was shown to be governed by the simple shear deformation induced by the rotating pin, which led to the formation of a pronounced {1 1 2} simple shear texture. Beyond the pin, the material experienced additional hot deformation, possibly caused by the influence of the tool shoulder, and limited static annealing during the weld cooling cycle. As a result, a well-recrystallized Grain Structure having a characteristic {1 0 0} cube texture finally developed in the stir zone.
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Grain Structure evolution during friction stir welding of az31 magnesium alloy
Acta Materialia, 2009Co-Authors: U F H Suhuddi, Yutaka S. Sato, Hiroyuki Kokawa, Sergey Mironov, Changwoo LeeAbstract:Abstract The high-resolution electron back-scatter diffraction technique was employed to study the Grain Structure evolution during friction-stir welding of AZ31 magnesium alloy. The material flow was found to be a very complex process associated mainly with basal slip. The Grain Structure development was demonstrated to be dictated by the texture evolution but also to involve { 1 0 1 ¯ 2 } twinning, geometrical effects of strain and limited discontinuous recrystallization.
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development of Grain Structure during friction stir welding of pure titanium
Acta Materialia, 2009Co-Authors: Sergey Mironov, Yutaka S. Sato, Hiroyuki KokawaAbstract:The microStructure evolution during friction stir welding of commercial purity titanium was studied. Material flow was found to be close to the simple-shear deformation and arose mainly from the prism slip. The Grain Structure evolution was shown to be a complex process including several stages. Far from the welding tool, the microstructural evolution was found to be governed by geometrical effects of strain and limited discontinuous recrystallization. In the stir zone, formation of a strong texture was shown to lead to texture-induced Grain convergence, and the Grain Structure development was thus closely related to the texture evolution.
Sergey Mironov - One of the best experts on this subject based on the ideXlab platform.
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Grain Structure evolution during friction-stir welding
Physical Mesomechanics, 2020Co-Authors: Sergey Mironov, Yutaka S. Sato, Hiroyuki KokawaAbstract:In this work, the current state of understanding of Grain Structure evolution during friction-stir welding is briefly reviewed. The broad aspects of this process and experimental techniques for its examination are critically addressed. The specific character of the microstructural evolutions in body-centered cubic, face-centered cubic and hexagonal close-packed metals are considered in details. In all cases, the Grain Structure evolution is shown to be a relatively complex process, which usually involves geometric effect of strain, continuous recrystallization and discontinuous recrystallization. Moreover, mechanical twinning, annealing twinning and Grain convergence may also occur in particular cases. It is also demonstrated that activation of a specific microstructural mechanism is primarily governed by crystal Structure and stacking fault energy but may also be influenced by welding temperature. Specifically, microStructure evolution in cubic metals with high stacking-fault energy is primarily governed by the continuous recrystallization whereas Grain Structure development in materials with low stacking-fault energy is mainly driven by the discontinuous recrystallization. In the case of transient stacking-fault energy, the materials may experience a transition from the continuous to the discontinuous mechanism. In hexagonal metals, microstructural changes are shown to be directly linked with crystallographic texture. Specifically, a formation of very sharp texture may promote the Grain convergence.
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Grain Structure and texture evolution during friction stir welding of thin 6016 aluminum alloy sheets
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010Co-Authors: U F H Suhuddin, Sergey Mironov, Y Sato, Hiroyuki KokawaAbstract:Abstract A “stop-action” technique was employed to study the Grain Structure and texture development during friction stir welding of thin 6016 aluminum sheets. The microstructural evolution ahead of the tool pin was found to be a complex process involving geometrical effects of strain as well as simultaneous development of continuous and discontinuous recrystallizations. At the circumference of the pin, the material flow was shown to be governed by the simple shear deformation induced by the rotating pin, which led to the formation of a pronounced {1 1 2} simple shear texture. Beyond the pin, the material experienced additional hot deformation, possibly caused by the influence of the tool shoulder, and limited static annealing during the weld cooling cycle. As a result, a well-recrystallized Grain Structure having a characteristic {1 0 0} cube texture finally developed in the stir zone.
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Grain Structure evolution during friction stir welding of az31 magnesium alloy
Acta Materialia, 2009Co-Authors: U F H Suhuddi, Yutaka S. Sato, Hiroyuki Kokawa, Sergey Mironov, Changwoo LeeAbstract:Abstract The high-resolution electron back-scatter diffraction technique was employed to study the Grain Structure evolution during friction-stir welding of AZ31 magnesium alloy. The material flow was found to be a very complex process associated mainly with basal slip. The Grain Structure development was demonstrated to be dictated by the texture evolution but also to involve { 1 0 1 ¯ 2 } twinning, geometrical effects of strain and limited discontinuous recrystallization.
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development of Grain Structure during friction stir welding of pure titanium
Acta Materialia, 2009Co-Authors: Sergey Mironov, Yutaka S. Sato, Hiroyuki KokawaAbstract:The microStructure evolution during friction stir welding of commercial purity titanium was studied. Material flow was found to be close to the simple-shear deformation and arose mainly from the prism slip. The Grain Structure evolution was shown to be a complex process including several stages. Far from the welding tool, the microstructural evolution was found to be governed by geometrical effects of strain and limited discontinuous recrystallization. In the stir zone, formation of a strong texture was shown to lead to texture-induced Grain convergence, and the Grain Structure development was thus closely related to the texture evolution.
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development of Grain Structure in β phase field during friction stir welding of ti 6al 4v alloy
Scripta Materialia, 2008Co-Authors: Sergey Mironov, Yutaka S. Sato, Yongjie Zhang, Hiroyuki KokawaAbstract:The electron backscattered diffraction technique was employed to examine the microstructural evolution in the high-temperature β-phase field during friction stir welding of a Ti–6Al–4V alloy. Reconstruction of the β-Grain Structure demonstrated that development of the Grain Structure is presumably governed by Grain elongation and transverse Grain subdivision. Orientation measurements in the retained β-phase showed that the material flow may be described in terms of a simple-shear deformation arising from the {1 1 0}〈1 1 1〉 slip.
Yutaka S. Sato - One of the best experts on this subject based on the ideXlab platform.
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Grain Structure evolution during friction-stir welding
Physical Mesomechanics, 2020Co-Authors: Sergey Mironov, Yutaka S. Sato, Hiroyuki KokawaAbstract:In this work, the current state of understanding of Grain Structure evolution during friction-stir welding is briefly reviewed. The broad aspects of this process and experimental techniques for its examination are critically addressed. The specific character of the microstructural evolutions in body-centered cubic, face-centered cubic and hexagonal close-packed metals are considered in details. In all cases, the Grain Structure evolution is shown to be a relatively complex process, which usually involves geometric effect of strain, continuous recrystallization and discontinuous recrystallization. Moreover, mechanical twinning, annealing twinning and Grain convergence may also occur in particular cases. It is also demonstrated that activation of a specific microstructural mechanism is primarily governed by crystal Structure and stacking fault energy but may also be influenced by welding temperature. Specifically, microStructure evolution in cubic metals with high stacking-fault energy is primarily governed by the continuous recrystallization whereas Grain Structure development in materials with low stacking-fault energy is mainly driven by the discontinuous recrystallization. In the case of transient stacking-fault energy, the materials may experience a transition from the continuous to the discontinuous mechanism. In hexagonal metals, microstructural changes are shown to be directly linked with crystallographic texture. Specifically, a formation of very sharp texture may promote the Grain convergence.
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Grain Structure and microtexture in friction stir welded commercial purity titanium
Science and Technology of Welding and Joining, 2010Co-Authors: Y Zhang, S H C Park, Yutaka S. Sato, Hiroyuki Kokawa, Satoshi HiranoAbstract:AbstractDefect free friction stir welds were produced in commercial purity titanium at rotational speeds between 200 and 400 rev min–1. Friction stir welding produced a finer Grain Structure in the stir zone than in the base material. Electron backscattered diffraction examination suggested that the fine Grains in the stir zone were formed through both continuous and discontinuous recrystallisation during friction stir welding. A torsion texture was observed in all welds and occupied most parts of the stir zone. Formation of this texture was attributed to the shear deformation along the tool shoulder during the stirring process.
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Grain Structure evolution during friction stir welding of az31 magnesium alloy
Acta Materialia, 2009Co-Authors: U F H Suhuddi, Yutaka S. Sato, Hiroyuki Kokawa, Sergey Mironov, Changwoo LeeAbstract:Abstract The high-resolution electron back-scatter diffraction technique was employed to study the Grain Structure evolution during friction-stir welding of AZ31 magnesium alloy. The material flow was found to be a very complex process associated mainly with basal slip. The Grain Structure development was demonstrated to be dictated by the texture evolution but also to involve { 1 0 1 ¯ 2 } twinning, geometrical effects of strain and limited discontinuous recrystallization.
-
development of Grain Structure during friction stir welding of pure titanium
Acta Materialia, 2009Co-Authors: Sergey Mironov, Yutaka S. Sato, Hiroyuki KokawaAbstract:The microStructure evolution during friction stir welding of commercial purity titanium was studied. Material flow was found to be close to the simple-shear deformation and arose mainly from the prism slip. The Grain Structure evolution was shown to be a complex process including several stages. Far from the welding tool, the microstructural evolution was found to be governed by geometrical effects of strain and limited discontinuous recrystallization. In the stir zone, formation of a strong texture was shown to lead to texture-induced Grain convergence, and the Grain Structure development was thus closely related to the texture evolution.
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development of Grain Structure in β phase field during friction stir welding of ti 6al 4v alloy
Scripta Materialia, 2008Co-Authors: Sergey Mironov, Yutaka S. Sato, Yongjie Zhang, Hiroyuki KokawaAbstract:The electron backscattered diffraction technique was employed to examine the microstructural evolution in the high-temperature β-phase field during friction stir welding of a Ti–6Al–4V alloy. Reconstruction of the β-Grain Structure demonstrated that development of the Grain Structure is presumably governed by Grain elongation and transverse Grain subdivision. Orientation measurements in the retained β-phase showed that the material flow may be described in terms of a simple-shear deformation arising from the {1 1 0}〈1 1 1〉 slip.
Jianguo Lin - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional virtual Grain Structure generation with Grain size control
Mechanics of Materials, 2012Co-Authors: P. Zhang, D.s. Balint, Morad Karimpour, Jianguo LinAbstract:Abstract A three-dimensional (3D) controlled Poisson Voronoi tessellation (CPVT) model has been developed for generating 3D polycrystalline Grain Structures for micromechanics simulations. A virtual Grain Structure generated using the CPVT model has the property that its Grain size distribution is statistically equivalent to the actual Grain Structure in term of the specified physical parameters: the mean Grain size, a small Grain size, a large Grain size, and the percentage of Grains within that range. Development of the CPVT model requires three steps: (1) Defining the regularity that specifies the uniformity of a tessellation, and deriving the control parameter based on the regularity, (2) establishing the mapping from the regularity to the distribution parameter of a one-parameter gamma distribution, (3) defining the mapping from the set of physical parameters to the distribution parameter. Relations between the regularity and distribution parameter, for a range of regularity values, are determined by a comprehensive set of statistical experiments, in which data fitting for the Grain size distribution model is in each case obtained by an evolutionary optimisation algorithm. A software system (VGrain) has been developed for implementing the proposed three-dimensional CPVT model to generate the Grain Structure for crystal plasticity finite element (CPFE) analysis. To demonstrate the proposed scheme and the VGrain system, CPFE analyses of compression of micro-pillars are performed, and the effects of both regularity and Grain size on the deformation are studied.
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An integrated scheme for crystal plasticity analysis: Virtual Grain Structure generation
Computational Materials Science, 2011Co-Authors: P. Zhang, D.s. Balint, Jianguo LinAbstract:Abstract An integrated scheme is developed based on the controlled Poisson Voronoi tessellation (CPVT) model to generate the polycrystalline Grain Structure for micromechanics simulations. The proposed model of CPVT involves a single control parameter that is used to produce the Grain Structure with regularity control, by which the yielded tessellation varies from the purely random Voronoi tessellation to the regular hexagonal tessellation. The system extends the standard CPVT model by the addition of two features: a one-parameter gamma distribution and a mapping from a set of quantitative metallographic measurements to the distribution parameter. Based on this scheme, a Grain Structure can be constructed such that the virtual tessellation is statistically equivalent to the expected Grain size distribution. To validate the modules that utilise the physical parameters that dictate the regularity, a series of theoretical investigations is performed. Efforts are devoted to proving the uniqueness of the mapping from the physical parameters to the distribution parameter and the regularity parameter. An efficient numerical algorithm is provided to facilitate the mapping solution process. A software system (VGrain) is developed implementing the proposed CPVT model to generate the Grain Structure for crystal plasticity finite element (CPFE) analysis. To demonstrate the proposed scheme and the VGrain system, a plane strain CPFE analysis is conducted. Two microStructures are generated with different regularities, and the deformation under uniaxial tension is simulated.
P. Zhang - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional virtual Grain Structure generation with Grain size control
Mechanics of Materials, 2012Co-Authors: P. Zhang, D.s. Balint, Morad Karimpour, Jianguo LinAbstract:Abstract A three-dimensional (3D) controlled Poisson Voronoi tessellation (CPVT) model has been developed for generating 3D polycrystalline Grain Structures for micromechanics simulations. A virtual Grain Structure generated using the CPVT model has the property that its Grain size distribution is statistically equivalent to the actual Grain Structure in term of the specified physical parameters: the mean Grain size, a small Grain size, a large Grain size, and the percentage of Grains within that range. Development of the CPVT model requires three steps: (1) Defining the regularity that specifies the uniformity of a tessellation, and deriving the control parameter based on the regularity, (2) establishing the mapping from the regularity to the distribution parameter of a one-parameter gamma distribution, (3) defining the mapping from the set of physical parameters to the distribution parameter. Relations between the regularity and distribution parameter, for a range of regularity values, are determined by a comprehensive set of statistical experiments, in which data fitting for the Grain size distribution model is in each case obtained by an evolutionary optimisation algorithm. A software system (VGrain) has been developed for implementing the proposed three-dimensional CPVT model to generate the Grain Structure for crystal plasticity finite element (CPFE) analysis. To demonstrate the proposed scheme and the VGrain system, CPFE analyses of compression of micro-pillars are performed, and the effects of both regularity and Grain size on the deformation are studied.
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An integrated scheme for crystal plasticity analysis: Virtual Grain Structure generation
Computational Materials Science, 2011Co-Authors: P. Zhang, D.s. Balint, Jianguo LinAbstract:Abstract An integrated scheme is developed based on the controlled Poisson Voronoi tessellation (CPVT) model to generate the polycrystalline Grain Structure for micromechanics simulations. The proposed model of CPVT involves a single control parameter that is used to produce the Grain Structure with regularity control, by which the yielded tessellation varies from the purely random Voronoi tessellation to the regular hexagonal tessellation. The system extends the standard CPVT model by the addition of two features: a one-parameter gamma distribution and a mapping from a set of quantitative metallographic measurements to the distribution parameter. Based on this scheme, a Grain Structure can be constructed such that the virtual tessellation is statistically equivalent to the expected Grain size distribution. To validate the modules that utilise the physical parameters that dictate the regularity, a series of theoretical investigations is performed. Efforts are devoted to proving the uniqueness of the mapping from the physical parameters to the distribution parameter and the regularity parameter. An efficient numerical algorithm is provided to facilitate the mapping solution process. A software system (VGrain) is developed implementing the proposed CPVT model to generate the Grain Structure for crystal plasticity finite element (CPFE) analysis. To demonstrate the proposed scheme and the VGrain system, a plane strain CPFE analysis is conducted. Two microStructures are generated with different regularities, and the deformation under uniaxial tension is simulated.
