Publication Date
2021
Document Type
Dissertation
Committee Members
Raghavan Srinivasan, Ph.D. (Advisor); Ahsan Mian, Ph.D. (Committee Member); Daniel Young, Ph.D. (Committee Member); Joy Gockel, Ph.D. (Committee Member)
Degree Name
Doctor of Philosophy (PhD)
Abstract
Materials with a layered structure consist of crystalline layers that are bonded to each other with secondary bonds (van der Waals interactions). The bonding between crystalline layers is relatively weak compared to the interatomic bonding within the crystalline layers. This research hypothesizes that under appropriate conditions, such as elevated temperature, the deformation of layered materials occurs like the classic “deck of cards” with no preferred direction of slip on the slip planes. The motivation for this study is from the experimental texture evolution of one such material, Bismuth Telluride ,(Bi2Te3), commonly used materials for thermoelectric applications in the range of temperatures from −20°C to 150°C. Bismuth telluride has a trigonal crystal structure consisting of five layers of hexagonally close-packed Bi and Te atoms in an alternating sequence: {����(1) − ���� − ����(2) − ���� − ����(1)}. These quintuples are bonded with van der Waal interaction between adjacent layers of ����(1) atoms. Experimental results show that after deformation at 80 to 90% of the absolute melting temperature, this material develops characteristic textures depending on the type of deformation. For example, when (Bi2Te3), is subjected to rolling, the material develops a texture in which [0001] is oriented perpendicular to the rolling plane and〈11-20〉directions are randomly oriented in the plane of rolling, and when subjected to extrusion, the [0001] is oriented perpendicular to the extrusion axis and〈11-20〉directions are aligned in the extrusion direction. In this study, the texture development during the deformation of a layered material is modeled using relationships between the rotation of a slip-plane and the orientation of the loading axis relative to the slip plane normal and the slip direction. An orientation evolution matrix, which relates the applied principal (normal) strains to a change in slip plane orientation for a layered material, has been developed. Initial simulations under simple loading conditions – uniaxial compression, plane strain compression, and axisymmetric deformation – show that texture evolves with the slip plane normal rotating towards the compression direction. The goal of the research is to confirm the hypothesis stated earlier by combining finite element modeling of deformation and the orientation development matrix for other types of deformation and compare the results with experimental data that is available for (Bi2Te3) deformed by plane-strain rolling, round-to-round extrusion, and 3D channel die compression.
Page Count
188
Department or Program
Ph.D. in Engineering
Year Degree Awarded
2021
Copyright
Copyright 2021, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.
