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Atomic-level structure and structure...

Cheng, Yongqiang.

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Atomic-level structure and structure-property relationship in metallic glass.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	Atomic-level structure and structure-property relationship in metallic glass./
Author:	Cheng, Yongqiang.
Description:	268 p.
Notes:	Source: Dissertation Abstracts International, Volume: 71-05, Section: B, page: 3286.
Contained By:	Dissertation Abstracts International71-05B.
Subject:	Engineering, Mechanical. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3410171
ISBN:	9781124005379

Atomic-level structure and structure-property relationship in metallic glass.
Cheng, Yongqiang.

Atomic-level structure and structure-property relationship in metallic glass. - 268 p.

Source: Dissertation Abstracts International, Volume: 71-05, Section: B, page: 3286.

Thesis (Ph.D.)--The Johns Hopkins University, 2010.

One of the key tasks in material science is to understand the structure and structure-property relationship. The recently emerging bulk metallic glasses (BMGs) have demonstrated unique properties, especially intriguing mechanical properties such as their high strength and high propensity to localize deformation in shear bands. However, a comprehensive understanding of the structure of BMGs has been hindered by the complexity of these amorphous materials. Even more challenging is the structure-property correlation, which has been well established in crystals but has been seriously lacking for BMGs. This thesis presents a systematic study of the atomic-level structures of two representative BMGs, Cu-Zr and Cu-Zr-Al. The interpenetrating Cu-centered icosahedral clusters have been identified to be the primary structural feature. The fraction of icosahedra increases with increasing Cu or Al contents, and with decreasing cooling rate. The effect of Al in improving the icosahedral order is two-fold: the geometric effect due to the atomic-size mismatch and the chemical effect originated from the Cu-Al bond shortening. The resolved structure is used to study the structure-property relationship. The full icosahedra are found to be responsible for the dynamical slowdown of the supercooled liquid, which underlies the non-Arrhenius behavior, and explains the composition dependence of glass transition temperature, glass forming ability, and the room temperature strength. By simulated deformation, the initiation of plasticity and tendency for strain localization are also investigated. The full icosahedra are found to be the most rigid and resistant cluster with solid-like character, while the unstable clusters with liquid-like character serve as the fertile sites for initiating shear transformations. In addition, the elastic moduli are calculated and analyzed, and the origins of the different configurational dependence of shear modulus (G) and bulk modulus ( B) are explained. The Poisson's ratio, which scales with G/B, is then taken as a dimensionless indicator of the internal structural state. Combining the structure-plasticity and structure-elasticity relationships, the common structural origin of the elasticity-plasticity correlation is identified. More general implications are discussed by separating the effects of structural order and constituent elements (alloy composition), leading to a map that may guide the search for plastic BMGs.

ISBN: 9781124005379Subjects--Topical Terms:

783786
Engineering, Mechanical.

Atomic-level structure and structure-property relationship in metallic glass.
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245 1 0 $a Atomic-level structure and structure-property relationship in metallic glass.
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520 $a One of the key tasks in material science is to understand the structure and structure-property relationship. The recently emerging bulk metallic glasses (BMGs) have demonstrated unique properties, especially intriguing mechanical properties such as their high strength and high propensity to localize deformation in shear bands. However, a comprehensive understanding of the structure of BMGs has been hindered by the complexity of these amorphous materials. Even more challenging is the structure-property correlation, which has been well established in crystals but has been seriously lacking for BMGs. This thesis presents a systematic study of the atomic-level structures of two representative BMGs, Cu-Zr and Cu-Zr-Al. The interpenetrating Cu-centered icosahedral clusters have been identified to be the primary structural feature. The fraction of icosahedra increases with increasing Cu or Al contents, and with decreasing cooling rate. The effect of Al in improving the icosahedral order is two-fold: the geometric effect due to the atomic-size mismatch and the chemical effect originated from the Cu-Al bond shortening. The resolved structure is used to study the structure-property relationship. The full icosahedra are found to be responsible for the dynamical slowdown of the supercooled liquid, which underlies the non-Arrhenius behavior, and explains the composition dependence of glass transition temperature, glass forming ability, and the room temperature strength. By simulated deformation, the initiation of plasticity and tendency for strain localization are also investigated. The full icosahedra are found to be the most rigid and resistant cluster with solid-like character, while the unstable clusters with liquid-like character serve as the fertile sites for initiating shear transformations. In addition, the elastic moduli are calculated and analyzed, and the origins of the different configurational dependence of shear modulus (G) and bulk modulus ( B) are explained. The Poisson's ratio, which scales with G/B, is then taken as a dimensionless indicator of the internal structural state. Combining the structure-plasticity and structure-elasticity relationships, the common structural origin of the elasticity-plasticity correlation is identified. More general implications are discussed by separating the effects of structural order and constituent elements (alloy composition), leading to a map that may guide the search for plastic BMGs.
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