Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently bee... more Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently been recognized as a crucial mechanism in enhancing the ductility of solid-solution Mg alloys. In pure Mg, cross-slip is ineffective owing to the energy difference between the high energy pyramidal I and low energy pyramidal II 〈 c + a 〉 screw dislocations. A small addition of solutes, especially rare earth (RE) elements, can reduce this energy difference and accelerate cross-slip, thus enabling enhanced ductility. With increasing solute concentrations, the pyramidal I dislocation can become energetically favorable, which switches the primary 〈 c + a 〉 slip plane and alters the cross-slip process. Here, the transition path and energetics for double cross-slip of pyramidal I 〈 c + a 〉 dislocations are analysed in the regime where the pyramidal I dislocation is energetically more favorable than the pyramidal II. This is achieved using nudged elastic band simulations on a proxy MEAM potential for Mg designed to favor the pyramidal I over pyramidal II. The minimum energy transition path for pyramidal I double cross-slip is found to initiate with cross-slip onto a pyramidal II plane followed by cross-slip onto a pyramidal I plane parallel to the original pyramidal I plane. A previous mechanistic model for ductility is then extended to higher solute concentrations where pyramidal I is favorable. The model predicts an upper limit of solute concentrations beyond which ductility again becomes poor in Mg alloys. The model predictions are consistent with limited experiments of Mg-RE alloys at high concentrations and motivate further experimental studies in the high concentration regime.
Modelling and Simulation in Materials Science and Engineering, Jul 20, 2018
An interatomic potential for the Mg–Y binary system is developed within the framework of the seco... more An interatomic potential for the Mg–Y binary system is developed within the framework of the second-nearest-neighbor modified embedded-atom method (MEAM) based on a very good MEAM potential for pure Mg. The Mg–Y potential is fitted to a range of key physical properties, either experimental or computed by first-principles methods, including the Y interaction energy with basal and pyramidal stacking faults, and properties of the B2 Mg–Y intermetallic phase. Reasonable agreement is obtained—much better than existing potentials in the literature—but differences remain for subtle but important aspects of Y solutes in Mg. The predictions of the potential for Y misfit volume in Mg, Y solute interactions with the pyramidal II (c + a) edge dislocation and {1012} tension-twin boundary are then compared against recent density functional theory results, and reasonable accuracy is obtained. In light of the spectrum of results presented here, the applicability and limitations of this Mg–Y MEAM potential for investigating various plasticity phenomena in Mg–Y solid solution alloys are carefully discussed.
The Mg–Y binary system's potential has been developed within the framework of the second-near... more The Mg–Y binary system's potential has been developed within the framework of the second-nearest-neighbor modified embedded-atom method (MEAM) based on a potential for pure Mg. The potential fitting is done on a range of physical properties, either experimental or computed by first-principles methods. These include the Y interaction energy with basal and pyramidal stacking faults and properties of the B2 Mg–Y intermetallic phase. Using this model, one can make predictions generally in reasonable agreement with experiments and or DFT, but differences remain for subtle but important aspects of Y solutes in Mg.
Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently bee... more Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently been recognized as a crucial mechanism in enhancing the ductility of solid-solution Mg alloys. In pure Mg, cross-slip is ineffective owing to the energy difference between the high energy pyramidal I and low energy pyramidal II 〈 c + a 〉 screw dislocations. A small addition of solutes, especially rare earth (RE) elements, can reduce this energy difference and accelerate cross-slip, thus enabling enhanced ductility. With increasing solute concentrations, the pyramidal I dislocation can become energetically favorable, which switches the primary 〈 c + a 〉 slip plane and alters the cross-slip process. Here, the transition path and energetics for double cross-slip of pyramidal I 〈 c + a 〉 dislocations are analysed in the regime where the pyramidal I dislocation is energetically more favorable than the pyramidal II. This is achieved using nudged elastic band simulations on a proxy MEAM potential for Mg designed to favor the pyramidal I over pyramidal II. The minimum energy transition path for pyramidal I double cross-slip is found to initiate with cross-slip onto a pyramidal II plane followed by cross-slip onto a pyramidal I plane parallel to the original pyramidal I plane. A previous mechanistic model for ductility is then extended to higher solute concentrations where pyramidal I is favorable. The model predicts an upper limit of solute concentrations beyond which ductility again becomes poor in Mg alloys. The model predictions are consistent with limited experiments of Mg-RE alloys at high concentrations and motivate further experimental studies in the high concentration regime.
International Journal of Multicultural and Multireligious Understanding, 2020
This study aimed to examine the effect of strategic planning that is represented by three dimensi... more This study aimed to examine the effect of strategic planning that is represented by three dimensions (top management support, technology and strategic goals) on entrepreneurship strategy requirements that is represented by three dimensions (creative capabilities, risk taking,and entrepreneurial culture) related to the perspectives of employees at private hospitals in Iraqi Kurdistan Region Erbil city. A survey questionnaire has been used to collect data, and the questionnaires distributed randomly to (150) health staff comprising of a number of private hospitals, (146) of staff were able to fill and return the questionnaires however (142) of the questionnaires was suitable for the purpose of statically analyzing. The questionnaire encompassed two sections with 30 closed-ended questions. Data collected analyzed quantitatively by using SPSS program version 20. The results of study concluded that there is a moderate and positive correlation as well as a significant impact of strategic ...
Modelling and Simulation in Materials Science and Engineering
Taking advantage of the advances in generative deep learning, particularly normalizing flow, a fr... more Taking advantage of the advances in generative deep learning, particularly normalizing flow, a framework, called Boltzmann generator, has recently been proposed to generate equilibrium atomic configurations from the canonical ensemble and determining the associated free energy. In this work, we revisit Boltzmann generator to motivate the construction of the loss function from the statistical mechanical point of view and to cast the training of the normalizing flow model in a purely unsupervised manner that does not require any sample of the atomic configurations from the equilibrium ensemble. We further show that the normalizing flow framework furnishes a reference thermodynamic system, very close to the real thermodynamic system under consideration, that is suitable for the well-established free energy perturbation methods to determine accurate free energy of solids. We then apply the normalizing flow to two problems: temperature-dependent Gibbs free energy of perfect crystal and f...
Abstract Transitions of pyramidal ⟨ c + a ⟩ dislocations to sessile structures contribute to po... more Abstract Transitions of pyramidal ⟨ c + a ⟩ dislocations to sessile structures contribute to poor ductility in pure Mg. Mg-3 wt% Rare Earth (RE) alloys have good ductility, possibly due to ⟨ c + a ⟩ dislocation stabilization upon addition of RE solutes. Here, ⟨ c + a ⟩ stability is investigated in a model Mg-3 at.%Y random solid solution alloy using molecular dynamics simulations. Favorable fluctuations of Y solutes lower all dislocation energies and have no appreciable effects on the transition mechanism, energy barrier, or time. Enhanced ⟨ c + a ⟩ activity and improved ductility in Mg-3 wt%RE alloys are thus not likely associated with solute-stabilization of pyramidal ⟨ c + a ⟩ dislocations.
A framework for more ductile magnesium Development of ductile magnesium alloys is key to their us... more A framework for more ductile magnesium Development of ductile magnesium alloys is key to their use in reducing the weight of vehicles and other applications. Wu et al. tackle this issue by determining the underlying mechanisms in unprocessed magnesium alloys. Dilute amounts of solutes enhanced certain ductility-improving mechanisms over ones that cause brittle fracture. From this, the authors developed a theory that may be helpful for screening the large number of potential magnesium alloy compositions. Science , this issue p. 447
Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently bee... more Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently been recognized as a crucial mechanism in enhancing the ductility of solid-solution Mg alloys. In pure Mg, cross-slip is ineffective owing to the energy difference between the high energy pyramidal I and low energy pyramidal II 〈 c + a 〉 screw dislocations. A small addition of solutes, especially rare earth (RE) elements, can reduce this energy difference and accelerate cross-slip, thus enabling enhanced ductility. With increasing solute concentrations, the pyramidal I dislocation can become energetically favorable, which switches the primary 〈 c + a 〉 slip plane and alters the cross-slip process. Here, the transition path and energetics for double cross-slip of pyramidal I 〈 c + a 〉 dislocations are analysed in the regime where the pyramidal I dislocation is energetically more favorable than the pyramidal II. This is achieved using nudged elastic band simulations on a proxy MEAM potential for Mg designed to favor the pyramidal I over pyramidal II. The minimum energy transition path for pyramidal I double cross-slip is found to initiate with cross-slip onto a pyramidal II plane followed by cross-slip onto a pyramidal I plane parallel to the original pyramidal I plane. A previous mechanistic model for ductility is then extended to higher solute concentrations where pyramidal I is favorable. The model predicts an upper limit of solute concentrations beyond which ductility again becomes poor in Mg alloys. The model predictions are consistent with limited experiments of Mg-RE alloys at high concentrations and motivate further experimental studies in the high concentration regime.
Modelling and Simulation in Materials Science and Engineering, Jul 20, 2018
An interatomic potential for the Mg–Y binary system is developed within the framework of the seco... more An interatomic potential for the Mg–Y binary system is developed within the framework of the second-nearest-neighbor modified embedded-atom method (MEAM) based on a very good MEAM potential for pure Mg. The Mg–Y potential is fitted to a range of key physical properties, either experimental or computed by first-principles methods, including the Y interaction energy with basal and pyramidal stacking faults, and properties of the B2 Mg–Y intermetallic phase. Reasonable agreement is obtained—much better than existing potentials in the literature—but differences remain for subtle but important aspects of Y solutes in Mg. The predictions of the potential for Y misfit volume in Mg, Y solute interactions with the pyramidal II (c + a) edge dislocation and {1012} tension-twin boundary are then compared against recent density functional theory results, and reasonable accuracy is obtained. In light of the spectrum of results presented here, the applicability and limitations of this Mg–Y MEAM potential for investigating various plasticity phenomena in Mg–Y solid solution alloys are carefully discussed.
The Mg–Y binary system's potential has been developed within the framework of the second-near... more The Mg–Y binary system's potential has been developed within the framework of the second-nearest-neighbor modified embedded-atom method (MEAM) based on a potential for pure Mg. The potential fitting is done on a range of physical properties, either experimental or computed by first-principles methods. These include the Y interaction energy with basal and pyramidal stacking faults and properties of the B2 Mg–Y intermetallic phase. Using this model, one can make predictions generally in reasonable agreement with experiments and or DFT, but differences remain for subtle but important aspects of Y solutes in Mg.
Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently bee... more Abstract Solute accelerated cross-slip of pyramidal 〈 c + a 〉 screw dislocations has recently been recognized as a crucial mechanism in enhancing the ductility of solid-solution Mg alloys. In pure Mg, cross-slip is ineffective owing to the energy difference between the high energy pyramidal I and low energy pyramidal II 〈 c + a 〉 screw dislocations. A small addition of solutes, especially rare earth (RE) elements, can reduce this energy difference and accelerate cross-slip, thus enabling enhanced ductility. With increasing solute concentrations, the pyramidal I dislocation can become energetically favorable, which switches the primary 〈 c + a 〉 slip plane and alters the cross-slip process. Here, the transition path and energetics for double cross-slip of pyramidal I 〈 c + a 〉 dislocations are analysed in the regime where the pyramidal I dislocation is energetically more favorable than the pyramidal II. This is achieved using nudged elastic band simulations on a proxy MEAM potential for Mg designed to favor the pyramidal I over pyramidal II. The minimum energy transition path for pyramidal I double cross-slip is found to initiate with cross-slip onto a pyramidal II plane followed by cross-slip onto a pyramidal I plane parallel to the original pyramidal I plane. A previous mechanistic model for ductility is then extended to higher solute concentrations where pyramidal I is favorable. The model predicts an upper limit of solute concentrations beyond which ductility again becomes poor in Mg alloys. The model predictions are consistent with limited experiments of Mg-RE alloys at high concentrations and motivate further experimental studies in the high concentration regime.
International Journal of Multicultural and Multireligious Understanding, 2020
This study aimed to examine the effect of strategic planning that is represented by three dimensi... more This study aimed to examine the effect of strategic planning that is represented by three dimensions (top management support, technology and strategic goals) on entrepreneurship strategy requirements that is represented by three dimensions (creative capabilities, risk taking,and entrepreneurial culture) related to the perspectives of employees at private hospitals in Iraqi Kurdistan Region Erbil city. A survey questionnaire has been used to collect data, and the questionnaires distributed randomly to (150) health staff comprising of a number of private hospitals, (146) of staff were able to fill and return the questionnaires however (142) of the questionnaires was suitable for the purpose of statically analyzing. The questionnaire encompassed two sections with 30 closed-ended questions. Data collected analyzed quantitatively by using SPSS program version 20. The results of study concluded that there is a moderate and positive correlation as well as a significant impact of strategic ...
Modelling and Simulation in Materials Science and Engineering
Taking advantage of the advances in generative deep learning, particularly normalizing flow, a fr... more Taking advantage of the advances in generative deep learning, particularly normalizing flow, a framework, called Boltzmann generator, has recently been proposed to generate equilibrium atomic configurations from the canonical ensemble and determining the associated free energy. In this work, we revisit Boltzmann generator to motivate the construction of the loss function from the statistical mechanical point of view and to cast the training of the normalizing flow model in a purely unsupervised manner that does not require any sample of the atomic configurations from the equilibrium ensemble. We further show that the normalizing flow framework furnishes a reference thermodynamic system, very close to the real thermodynamic system under consideration, that is suitable for the well-established free energy perturbation methods to determine accurate free energy of solids. We then apply the normalizing flow to two problems: temperature-dependent Gibbs free energy of perfect crystal and f...
Abstract Transitions of pyramidal ⟨ c + a ⟩ dislocations to sessile structures contribute to po... more Abstract Transitions of pyramidal ⟨ c + a ⟩ dislocations to sessile structures contribute to poor ductility in pure Mg. Mg-3 wt% Rare Earth (RE) alloys have good ductility, possibly due to ⟨ c + a ⟩ dislocation stabilization upon addition of RE solutes. Here, ⟨ c + a ⟩ stability is investigated in a model Mg-3 at.%Y random solid solution alloy using molecular dynamics simulations. Favorable fluctuations of Y solutes lower all dislocation energies and have no appreciable effects on the transition mechanism, energy barrier, or time. Enhanced ⟨ c + a ⟩ activity and improved ductility in Mg-3 wt%RE alloys are thus not likely associated with solute-stabilization of pyramidal ⟨ c + a ⟩ dislocations.
A framework for more ductile magnesium Development of ductile magnesium alloys is key to their us... more A framework for more ductile magnesium Development of ductile magnesium alloys is key to their use in reducing the weight of vehicles and other applications. Wu et al. tackle this issue by determining the underlying mechanisms in unprocessed magnesium alloys. Dilute amounts of solutes enhanced certain ductility-improving mechanisms over ones that cause brittle fracture. From this, the authors developed a theory that may be helpful for screening the large number of potential magnesium alloy compositions. Science , this issue p. 447
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