Publication Date
2018
Document Type
Thesis
Committee Members
Hamed Attariani (Advisor), James Menart (Committee Member), Nikolai Priezjev (Committee Member)
Degree Name
Master of Science in Materials Science and Engineering (MSMSE)
Abstract
The advent of nanomaterials has opened a new avenue for designing and fabricating materials with unique properties, e.g., superior mechanical properties. Based on a common notion, the perfect structures are assumed to exhibit better mechanical properties, such as higher yield strength and Young's modulus. Therefore, researchers have devoted an extensive amount of time to decrease defect concentration by fabricating materials with the micro/nanoscale, e.g., nanowires (NWs) and nanobelts (NBs), to enhance the mechanical characteristics of the system. However, defects are a part of the fabrication process and precise control over synthesizing procedure is needed to eliminate them from the material. In this work, we showed, with the help of the classical molecular dynamics method, that these inherited defects can be employed as a microstructural feature to improve the mechanical properties of low dimensional nanomaterial, i.e., defect engineering. Our results indicate that the NWs with a high density of I1 stacking faults (I1-SFs) show higher compressive/tensile critical stress (14% increase), as well as Young's Modulus (37% increase), in comparison to the perfect structure over a wide range of temperature: ranged from 0 K to 500 K. Such an improvement is in agreement with the in-situ experimental measurements of highly defective GaAs NWs, and can be justified by interplay between surface stresses and the intrinsic stress field of locked SFs. The SF-induced stresses are partially relaxed by raising the temperature for this non-trivial strengthening. Moreover, a specific stress relaxation mechanism, twin boundary formation, was found to take place in highly defected NWs, which further postponed the phase transition from hexagonal (HX) to cubic and subsequently boosted the toughness of NWs; this phenomenon appears as a stress plateau in highly defected NWs. Numerous parametric studies on the system variables, such as cross-section geometry, aspect ratio, width, and SF distribution, were performed to find the optimum design. Our results demonstrated the promise and applicability of this strengthening method over a wide temperature range and geometrical features. This novel method, defects engineering, adds a new parameter to the design-space of materials and also paves the way to the fabrication of a new class of materials with superior mechanical properties, including higher stiffness, strength, and ductility.
Page Count
58
Department or Program
Department of Mechanical and Materials Engineering
Year Degree Awarded
2018
Copyright
Copyright 2018, all rights reserved. My ETD will be available under the "Fair Use" terms of copyright law.
