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Siamak Soleymani Shishvan - One of the best experts on this subject based on the ideXlab platform.
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Discrete dislocation plasticity analysis of the high-temperature cyclic response of composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract Discrete dislocation plasticity (DDP) analysis of the high-temperature cyclic deformation of two-phase composites comprising a plastic matrix and elastic precipitates is presented. Deformation of the matrix is by climb-assisted glide of dislocations while the precipitates deform by a combination of bulk elasticity and stress-driven Interfacial Diffusion. The DDP calculations predict a cyclically softening response due to the formation of dislocation cell structures within the matrix. The dislocation cell sizes decrease with decreasing size of the unit cell (or equivalently matrix channels) and this results in an increased cyclic softening rate in composites with smaller unit cells. Interfacial Diffusion also enhances the formation of dislocation cell structures and thereby promotes cyclic softening. These results are consistent with predictions of the creep behaviour that indicate that the increase in the creep rate (i.e. tertiary creep) is also associated with the formation of dislocation cell structures within the matrix.
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discrete dislocation plasticity analysis of the effect of Interfacial Diffusion on the creep response of ni single crystal superalloys
Acta Materialia, 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract Discrete dislocation plasticity (DDP) analysis of the high temperature creep deformation of a single crystal Ni superalloy comprising Ni3Al precipitates ( γ ′ ) in a Ni matrix (γ) is presented. The γ ′ precipitates remain elastic but can also deform due to the stress-driven inter-Diffusion of the Al within the Ni on the γ / γ ′ interface while plastic deformation of the γ phase occurs by a combination of dislocation glide and dislocation climb coupled to the Diffusion of vacancies. At relatively low applied uniaxial tensile stresses, the creep strain rates are very low in the absence of Interfacial Diffusion. This is due to the stress-induced pile up of dislocations at γ / γ ′ interfaces that serves to inhibit further nucleation and suppresses continued plastic flow in the γ phase. When Interfacial Diffusion is permitted, the creep rates not only increase but the superalloy also exhibits distinct secondary and tertiary creep regimes. While this change in behaviour is a result of Interfacial Diffusion, the contribution of the average γ ′ strain to the deformation of the superalloy is small. Rather, the Diffusional deformation at the interface results in the development of a wavy interface which relaxes the back-stresses of dislocations piled-up at the γ / γ ′ interfaces. This permits continued dislocation activity within the γ phase with dislocations arranging themselves into low energy cell-structures in the γ phase via dislocation climb. The formation of these structures results in an increase in the creep strain rate and the onset of the tertiary creep regime. At high applied stresses, the high initial dislocation density within the γ phase results in the continued climb motion of dislocations and an evolving spatial distribution of vacancies within the superalloy. Thus, creep deformation occurs even in the absence of Interfacial Diffusion although the creep rates are significantly increased when Interfacial Diffusion is present. The DDP analysis presented here demonstrates the critical role of Interfacial Diffusion in controlling the creep rates of Ni superalloys and suggests that interface engineering to reduce Interfacial Diffusion rates will aid in improving the creep performance of these alloys.
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Interfacial Diffusion in high temperature deformation of composites a discrete dislocation plasticity investigation
Journal of The Mechanics and Physics of Solids, 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract We present a discrete dislocation plasticity (DDP) framework to analyse the high temperature deformation of multi-phase materials (composites) comprising a matrix and inclusions. Deformation of the phases is by climb-assisted glide of the dislocations while the particles can also deform due to stress-driven Interfacial Diffusion. The general framework is used to analyse the uniaxial tensile deformation of a composite comprising elastic particles with dislocation plasticity only present in the matrix phase. When dislocation motion is restricted to only glide within the matrix a strong size effect of the composite strength is predicted with the strength increasing with decreasing unit cell size due to dislocations forming pile-ups against the matrix/particle interface. Interfacial Diffusion decreases the composite strength as it enhances the elongation of the elastic particles along the loading direction. When dislocation motion occurs by climb-assisted glide within the matrix the size effect of the strength is reduced as dislocations no longer arrange high energy pile-up structures but rather form lower energy dislocation cell networks. While Interfacial Diffusion again reduces the composite strength, in contrast to continuum plasticity predictions, the elongation of the particles is almost independent of the Interfacial Diffusion constant. Rather, in DDP the reduction in composite strength due to Interfacial Diffusion is a result of changes in the dislocation structures within the matrix and the associated enhanced dislocation climb rates in the matrix.
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Discrete dislocation plasticity analysis of the effect of Interfacial Diffusion on the creep response of Ni single-crystal superalloys
'Organisation for Economic Co-Operation and Development (OECD)', 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tm Pollock, Deshpande VikramAbstract:© 2017 Acta Materialia Inc. Discrete dislocation plasticity (DDP) analysis of the high temperature creep deformation of a single crystal Ni superalloy comprising Ni3Al precipitates (γ′) in a Ni matrix (γ) is presented. The γ′ precipitates remain elastic but can also deform due to the stress-driven inter-Diffusion of the Al within the Ni on the γ/γ′ interface while plastic deformation of the γ phase occurs by a combination of dislocation glide and dislocation climb coupled to the Diffusion of vacancies. At relatively low applied uniaxial tensile stresses, the creep strain rates are very low in the absence of Interfacial Diffusion. This is due to the stress-induced pile up of dislocations at γ/γ′ interfaces that serves to inhibit further nucleation and suppresses continued plastic flow in the γ phase. When Interfacial Diffusion is permitted, the creep rates not only increase but the superalloy also exhibits distinct secondary and tertiary creep regimes. While this change in behaviour is a result of Interfacial Diffusion, the contribution of the average γ′ strain to the deformation of the superalloy is small. Rather, the Diffusional deformation at the interface results in the development of a wavy interface which relaxes the back-stresses of dislocations piled-up at the γ/γ′ interfaces. This permits continued dislocation activity within the γ phase with dislocations arranging themselves into low energy cell-structures in the γ phase via dislocation climb. The formation of these structures results in an increase in the creep strain rate and the onset of the tertiary creep regime. At high applied stresses, the high initial dislocation density within the γ phase results in the continued climb motion of dislocations and an evolving spatial distribution of vacancies within the superalloy. Thus, creep deformation occurs even in the absence of Interfacial Diffusion although the creep rates are significantly increased when Interfacial Diffusion is present. The DDP analysis presented here demonstrates the critical role of Interfacial Diffusion in controlling the creep rates of Ni superalloys and suggests that interface engineering to reduce Interfacial Diffusion rates will aid in improving the creep performance of these alloys
Robert M. Mcmeeking - One of the best experts on this subject based on the ideXlab platform.
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Discrete dislocation plasticity analysis of the high-temperature cyclic response of composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract Discrete dislocation plasticity (DDP) analysis of the high-temperature cyclic deformation of two-phase composites comprising a plastic matrix and elastic precipitates is presented. Deformation of the matrix is by climb-assisted glide of dislocations while the precipitates deform by a combination of bulk elasticity and stress-driven Interfacial Diffusion. The DDP calculations predict a cyclically softening response due to the formation of dislocation cell structures within the matrix. The dislocation cell sizes decrease with decreasing size of the unit cell (or equivalently matrix channels) and this results in an increased cyclic softening rate in composites with smaller unit cells. Interfacial Diffusion also enhances the formation of dislocation cell structures and thereby promotes cyclic softening. These results are consistent with predictions of the creep behaviour that indicate that the increase in the creep rate (i.e. tertiary creep) is also associated with the formation of dislocation cell structures within the matrix.
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discrete dislocation plasticity analysis of the effect of Interfacial Diffusion on the creep response of ni single crystal superalloys
Acta Materialia, 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract Discrete dislocation plasticity (DDP) analysis of the high temperature creep deformation of a single crystal Ni superalloy comprising Ni3Al precipitates ( γ ′ ) in a Ni matrix (γ) is presented. The γ ′ precipitates remain elastic but can also deform due to the stress-driven inter-Diffusion of the Al within the Ni on the γ / γ ′ interface while plastic deformation of the γ phase occurs by a combination of dislocation glide and dislocation climb coupled to the Diffusion of vacancies. At relatively low applied uniaxial tensile stresses, the creep strain rates are very low in the absence of Interfacial Diffusion. This is due to the stress-induced pile up of dislocations at γ / γ ′ interfaces that serves to inhibit further nucleation and suppresses continued plastic flow in the γ phase. When Interfacial Diffusion is permitted, the creep rates not only increase but the superalloy also exhibits distinct secondary and tertiary creep regimes. While this change in behaviour is a result of Interfacial Diffusion, the contribution of the average γ ′ strain to the deformation of the superalloy is small. Rather, the Diffusional deformation at the interface results in the development of a wavy interface which relaxes the back-stresses of dislocations piled-up at the γ / γ ′ interfaces. This permits continued dislocation activity within the γ phase with dislocations arranging themselves into low energy cell-structures in the γ phase via dislocation climb. The formation of these structures results in an increase in the creep strain rate and the onset of the tertiary creep regime. At high applied stresses, the high initial dislocation density within the γ phase results in the continued climb motion of dislocations and an evolving spatial distribution of vacancies within the superalloy. Thus, creep deformation occurs even in the absence of Interfacial Diffusion although the creep rates are significantly increased when Interfacial Diffusion is present. The DDP analysis presented here demonstrates the critical role of Interfacial Diffusion in controlling the creep rates of Ni superalloys and suggests that interface engineering to reduce Interfacial Diffusion rates will aid in improving the creep performance of these alloys.
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Interfacial Diffusion in high temperature deformation of composites a discrete dislocation plasticity investigation
Journal of The Mechanics and Physics of Solids, 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract We present a discrete dislocation plasticity (DDP) framework to analyse the high temperature deformation of multi-phase materials (composites) comprising a matrix and inclusions. Deformation of the phases is by climb-assisted glide of the dislocations while the particles can also deform due to stress-driven Interfacial Diffusion. The general framework is used to analyse the uniaxial tensile deformation of a composite comprising elastic particles with dislocation plasticity only present in the matrix phase. When dislocation motion is restricted to only glide within the matrix a strong size effect of the composite strength is predicted with the strength increasing with decreasing unit cell size due to dislocations forming pile-ups against the matrix/particle interface. Interfacial Diffusion decreases the composite strength as it enhances the elongation of the elastic particles along the loading direction. When dislocation motion occurs by climb-assisted glide within the matrix the size effect of the strength is reduced as dislocations no longer arrange high energy pile-up structures but rather form lower energy dislocation cell networks. While Interfacial Diffusion again reduces the composite strength, in contrast to continuum plasticity predictions, the elongation of the particles is almost independent of the Interfacial Diffusion constant. Rather, in DDP the reduction in composite strength due to Interfacial Diffusion is a result of changes in the dislocation structures within the matrix and the associated enhanced dislocation climb rates in the matrix.
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Discrete dislocation plasticity analysis of the effect of Interfacial Diffusion on the creep response of Ni single-crystal superalloys
'Organisation for Economic Co-Operation and Development (OECD)', 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tm Pollock, Deshpande VikramAbstract:© 2017 Acta Materialia Inc. Discrete dislocation plasticity (DDP) analysis of the high temperature creep deformation of a single crystal Ni superalloy comprising Ni3Al precipitates (γ′) in a Ni matrix (γ) is presented. The γ′ precipitates remain elastic but can also deform due to the stress-driven inter-Diffusion of the Al within the Ni on the γ/γ′ interface while plastic deformation of the γ phase occurs by a combination of dislocation glide and dislocation climb coupled to the Diffusion of vacancies. At relatively low applied uniaxial tensile stresses, the creep strain rates are very low in the absence of Interfacial Diffusion. This is due to the stress-induced pile up of dislocations at γ/γ′ interfaces that serves to inhibit further nucleation and suppresses continued plastic flow in the γ phase. When Interfacial Diffusion is permitted, the creep rates not only increase but the superalloy also exhibits distinct secondary and tertiary creep regimes. While this change in behaviour is a result of Interfacial Diffusion, the contribution of the average γ′ strain to the deformation of the superalloy is small. Rather, the Diffusional deformation at the interface results in the development of a wavy interface which relaxes the back-stresses of dislocations piled-up at the γ/γ′ interfaces. This permits continued dislocation activity within the γ phase with dislocations arranging themselves into low energy cell-structures in the γ phase via dislocation climb. The formation of these structures results in an increase in the creep strain rate and the onset of the tertiary creep regime. At high applied stresses, the high initial dislocation density within the γ phase results in the continued climb motion of dislocations and an evolving spatial distribution of vacancies within the superalloy. Thus, creep deformation occurs even in the absence of Interfacial Diffusion although the creep rates are significantly increased when Interfacial Diffusion is present. The DDP analysis presented here demonstrates the critical role of Interfacial Diffusion in controlling the creep rates of Ni superalloys and suggests that interface engineering to reduce Interfacial Diffusion rates will aid in improving the creep performance of these alloys
Qingquan Lei - One of the best experts on this subject based on the ideXlab platform.
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Interface Optimization and Electrical Properties of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 Thin Films Prepared by a Sol–Gel Process
The Journal of Physical Chemistry C, 2014Co-Authors: Qingguo Chi, Changhai Zhang, J. Sun, F. Y. Yang, Xin Wang, Qingquan LeiAbstract:In this work, 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (0.5BZT–0.5BCT) thin films were synthesized at 500 °C by introducing a seed layer. Low Interfacial Diffusion and high (100) orientation were simultaneously achieved. Minimal leakage current density, dielectric constant, and loss were obtained owing to low crystallization temperature and low Interfacial Diffusion. The pyroelectric coefficient remained relatively high because of the high orientation, which resulted in superior pyroelectric figures of merit compared with previously reported films. This study demonstrates that low-temperature crystallization can suppress Interfacial Diffusion and extend film applications by integrating the films with silicon substrates and that thin films annealed at 500 °C are good candidates for application in uncooled infrared detectors.
Xin Wang - One of the best experts on this subject based on the ideXlab platform.
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Low temperature growth of (100)-oriented Ba(Zr0.2Ti0.8)O3- 0.5(Ba0.7Ca0.3)TiO3 thin films using a LaNiO3 seed layer
Journal of Alloys and Compounds, 2016Co-Authors: Y. Chen, Xin Wang, T.y. Zhang, Chi Qingguo, J.q. Lin, Q.q. LeiAbstract:Abstract Low-temperature growth of Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) films, at temperatures as low as 550 °C, was successfully achieved by a sol–gel route using a LaNiO3 seed layer. The influence of the seed layer on the crystallization behavior and electric properties of the films was investigated in detail. It was found that low Interfacial Diffusion and high (100) orientation were simultaneously achieved by introducing a seed layer between films and substrates. Low leakage current density was obtained as a result of low-temperature crystallization and low Interfacial Diffusion, and the piezoelectric coefficient remained at a relatively high value because of the high orientation. This study showed that low-temperature crystallization suppresses Interfacial Diffusion and can extend film applications, for example, integrating them with silicon substrates.
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Interface Optimization and Electrical Properties of 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 Thin Films Prepared by a Sol–Gel Process
The Journal of Physical Chemistry C, 2014Co-Authors: Qingguo Chi, Changhai Zhang, J. Sun, F. Y. Yang, Xin Wang, Qingquan LeiAbstract:In this work, 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (0.5BZT–0.5BCT) thin films were synthesized at 500 °C by introducing a seed layer. Low Interfacial Diffusion and high (100) orientation were simultaneously achieved. Minimal leakage current density, dielectric constant, and loss were obtained owing to low crystallization temperature and low Interfacial Diffusion. The pyroelectric coefficient remained relatively high because of the high orientation, which resulted in superior pyroelectric figures of merit compared with previously reported films. This study demonstrates that low-temperature crystallization can suppress Interfacial Diffusion and extend film applications by integrating the films with silicon substrates and that thin films annealed at 500 °C are good candidates for application in uncooled infrared detectors.
Vikram Deshpande - One of the best experts on this subject based on the ideXlab platform.
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Discrete dislocation plasticity analysis of the high-temperature cyclic response of composites
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract Discrete dislocation plasticity (DDP) analysis of the high-temperature cyclic deformation of two-phase composites comprising a plastic matrix and elastic precipitates is presented. Deformation of the matrix is by climb-assisted glide of dislocations while the precipitates deform by a combination of bulk elasticity and stress-driven Interfacial Diffusion. The DDP calculations predict a cyclically softening response due to the formation of dislocation cell structures within the matrix. The dislocation cell sizes decrease with decreasing size of the unit cell (or equivalently matrix channels) and this results in an increased cyclic softening rate in composites with smaller unit cells. Interfacial Diffusion also enhances the formation of dislocation cell structures and thereby promotes cyclic softening. These results are consistent with predictions of the creep behaviour that indicate that the increase in the creep rate (i.e. tertiary creep) is also associated with the formation of dislocation cell structures within the matrix.
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discrete dislocation plasticity analysis of the effect of Interfacial Diffusion on the creep response of ni single crystal superalloys
Acta Materialia, 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract Discrete dislocation plasticity (DDP) analysis of the high temperature creep deformation of a single crystal Ni superalloy comprising Ni3Al precipitates ( γ ′ ) in a Ni matrix (γ) is presented. The γ ′ precipitates remain elastic but can also deform due to the stress-driven inter-Diffusion of the Al within the Ni on the γ / γ ′ interface while plastic deformation of the γ phase occurs by a combination of dislocation glide and dislocation climb coupled to the Diffusion of vacancies. At relatively low applied uniaxial tensile stresses, the creep strain rates are very low in the absence of Interfacial Diffusion. This is due to the stress-induced pile up of dislocations at γ / γ ′ interfaces that serves to inhibit further nucleation and suppresses continued plastic flow in the γ phase. When Interfacial Diffusion is permitted, the creep rates not only increase but the superalloy also exhibits distinct secondary and tertiary creep regimes. While this change in behaviour is a result of Interfacial Diffusion, the contribution of the average γ ′ strain to the deformation of the superalloy is small. Rather, the Diffusional deformation at the interface results in the development of a wavy interface which relaxes the back-stresses of dislocations piled-up at the γ / γ ′ interfaces. This permits continued dislocation activity within the γ phase with dislocations arranging themselves into low energy cell-structures in the γ phase via dislocation climb. The formation of these structures results in an increase in the creep strain rate and the onset of the tertiary creep regime. At high applied stresses, the high initial dislocation density within the γ phase results in the continued climb motion of dislocations and an evolving spatial distribution of vacancies within the superalloy. Thus, creep deformation occurs even in the absence of Interfacial Diffusion although the creep rates are significantly increased when Interfacial Diffusion is present. The DDP analysis presented here demonstrates the critical role of Interfacial Diffusion in controlling the creep rates of Ni superalloys and suggests that interface engineering to reduce Interfacial Diffusion rates will aid in improving the creep performance of these alloys.
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Interfacial Diffusion in high temperature deformation of composites a discrete dislocation plasticity investigation
Journal of The Mechanics and Physics of Solids, 2017Co-Authors: Siamak Soleymani Shishvan, Robert M. Mcmeeking, Tresa M. Pollock, Vikram DeshpandeAbstract:Abstract We present a discrete dislocation plasticity (DDP) framework to analyse the high temperature deformation of multi-phase materials (composites) comprising a matrix and inclusions. Deformation of the phases is by climb-assisted glide of the dislocations while the particles can also deform due to stress-driven Interfacial Diffusion. The general framework is used to analyse the uniaxial tensile deformation of a composite comprising elastic particles with dislocation plasticity only present in the matrix phase. When dislocation motion is restricted to only glide within the matrix a strong size effect of the composite strength is predicted with the strength increasing with decreasing unit cell size due to dislocations forming pile-ups against the matrix/particle interface. Interfacial Diffusion decreases the composite strength as it enhances the elongation of the elastic particles along the loading direction. When dislocation motion occurs by climb-assisted glide within the matrix the size effect of the strength is reduced as dislocations no longer arrange high energy pile-up structures but rather form lower energy dislocation cell networks. While Interfacial Diffusion again reduces the composite strength, in contrast to continuum plasticity predictions, the elongation of the particles is almost independent of the Interfacial Diffusion constant. Rather, in DDP the reduction in composite strength due to Interfacial Diffusion is a result of changes in the dislocation structures within the matrix and the associated enhanced dislocation climb rates in the matrix.