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Advancing Atomistic Modeling of Defe...

Yang, Chaoming.

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Advancing Atomistic Modeling of Defects in Plastic Deformation of Metallic Crystalline Materials.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Advancing Atomistic Modeling of Defects in Plastic Deformation of Metallic Crystalline Materials./
作者:	Yang, Chaoming.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	213 p.
附註:	Source: Dissertations Abstracts International, Volume: 81-11, Section: B.
Contained By:	Dissertations Abstracts International81-11B.
標題:	Condensed matter physics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28006597
ISBN:	9798643184997

Advancing Atomistic Modeling of Defects in Plastic Deformation of Metallic Crystalline Materials.
Yang, Chaoming.

Advancing Atomistic Modeling of Defects in Plastic Deformation of Metallic Crystalline Materials. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 213 p.

Source: Dissertations Abstracts International, Volume: 81-11, Section: B.

Thesis (Ph.D.)--University of Michigan, 2020.

This item must not be sold to any third party vendors.

In crystalline metallic systems, plastic deformation originates from nucleation and evolution of crystal defects. There are two types of complexity that generate substantial obstacles for the simulations and understanding of these defects at the atomistic scale. One aspect is to precisely describe interatomic bonding characteristics originated from complex electronic structures. Another aspect is to construct the accurate and representative atomistic structures of defects for the investigations of plastic deformation. Thus, the main topic of this thesis is to develop and apply the theoretical and computational methods that can overcome these two types of barriers. For the aspect of the interatomic bonding, BCC refractory metals (W, Mo, Nb, Ta) and their alloys are typical investigation systems, which have partially filled d-band electrons that generate strong and directionally dependent interatomic bonds. Thus, ab initio calculations and continuum models were applied to investigate the occurrence of the elastic and phonon instability at extreme stress conditions, which reveals the characteristics of defects nucleation and the corresponding intrinsic ductility properties from the lattice instability perspective. A potential-fitting package based on a force-matching method was then developed to create a modified embedded atom method (MEAM) potential for these BCC metals. The MEAM potential of Nb was constructed to reflect both its intrinsic interatomic bonding characteristics under extreme stress conditions and its dislocation core attributes. This potential and other accurate MEAM potentials for BCC refractory metals and alloys can be used together to investigate the effects of interatomic bonding characteristics on the plastic deformation at the mesoscale. For the aspect of complex atomistic structures of defects, two-dimensional and three-dimensional defects such as grain boundary (GB) and precipitates are typical investigation systems, since it can be difficult to obtain their stable and metastable structures, which have significant impacts on the plastic deformation behavior. Thus, an evolution algorithm (EA) based package was developed to explore stable and metastable GB structures in FCC, BCC, and HCP metals. The GB structures generated in this package build a solid foundation for the investigations between GBs and other defects, such as dislocation and deformation twinning, in the future. Finally, collaborating with experimentalists, the effects of the ordered superlattices of precipitates on the precipitate-dislocation interactions in Mg-Nd alloys were investigated. A precipitation hardening model with parameters from ab initio calculations was constructed to predict the strengthening effects of the anti-phase boundaries (APB). Molecular dynamics (MD) simulations were performed to reveal the mechanism of dislocation cutting and cross-slip when interacting with precipitates. Understanding these dislocation-precipitate interaction mechanisms will be helpful in designing precipitate microstructures that can enhance the strength and ductility of Mg alloys simultaneously.

ISBN: 9798643184997Subjects--Topical Terms:

3173567
Condensed matter physics.
Subjects--Index Terms:

Molecular dynamics (MD)

Advancing Atomistic Modeling of Defects in Plastic Deformation of Metallic Crystalline Materials.
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300 $a 213 p.
500 $a Source: Dissertations Abstracts International, Volume: 81-11, Section: B.
500 $a Advisor: Qi, Liang.
502 $a Thesis (Ph.D.)--University of Michigan, 2020.
506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a In crystalline metallic systems, plastic deformation originates from nucleation and evolution of crystal defects. There are two types of complexity that generate substantial obstacles for the simulations and understanding of these defects at the atomistic scale. One aspect is to precisely describe interatomic bonding characteristics originated from complex electronic structures. Another aspect is to construct the accurate and representative atomistic structures of defects for the investigations of plastic deformation. Thus, the main topic of this thesis is to develop and apply the theoretical and computational methods that can overcome these two types of barriers. For the aspect of the interatomic bonding, BCC refractory metals (W, Mo, Nb, Ta) and their alloys are typical investigation systems, which have partially filled d-band electrons that generate strong and directionally dependent interatomic bonds. Thus, ab initio calculations and continuum models were applied to investigate the occurrence of the elastic and phonon instability at extreme stress conditions, which reveals the characteristics of defects nucleation and the corresponding intrinsic ductility properties from the lattice instability perspective. A potential-fitting package based on a force-matching method was then developed to create a modified embedded atom method (MEAM) potential for these BCC metals. The MEAM potential of Nb was constructed to reflect both its intrinsic interatomic bonding characteristics under extreme stress conditions and its dislocation core attributes. This potential and other accurate MEAM potentials for BCC refractory metals and alloys can be used together to investigate the effects of interatomic bonding characteristics on the plastic deformation at the mesoscale. For the aspect of complex atomistic structures of defects, two-dimensional and three-dimensional defects such as grain boundary (GB) and precipitates are typical investigation systems, since it can be difficult to obtain their stable and metastable structures, which have significant impacts on the plastic deformation behavior. Thus, an evolution algorithm (EA) based package was developed to explore stable and metastable GB structures in FCC, BCC, and HCP metals. The GB structures generated in this package build a solid foundation for the investigations between GBs and other defects, such as dislocation and deformation twinning, in the future. Finally, collaborating with experimentalists, the effects of the ordered superlattices of precipitates on the precipitate-dislocation interactions in Mg-Nd alloys were investigated. A precipitation hardening model with parameters from ab initio calculations was constructed to predict the strengthening effects of the anti-phase boundaries (APB). Molecular dynamics (MD) simulations were performed to reveal the mechanism of dislocation cutting and cross-slip when interacting with precipitates. Understanding these dislocation-precipitate interaction mechanisms will be helpful in designing precipitate microstructures that can enhance the strength and ductility of Mg alloys simultaneously.
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650 4 $a Materials science. $3 543314
650 4 $a Mechanical engineering. $3 649730
653 $a Molecular dynamics (MD)
653 $a Density-functional theory (DFT)
653 $a Metals and alloys
653 $a Crystal defects
653 $a Plastic deformation
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