Degree Type

Dissertation

Date of Award

2017

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

Major

Mechanical Engineering

First Advisor

Gap-Yong Kim

Abstract

The mechanical properties of composite materials are mainly determined by their microstructures that depend on comprising phases and their properties, the shape and size of those phases, and their distribution. By controlling and optimizing the various aspects of the microstructure, composites with improved mechanical properties can be created. One of the challenges, however, is the lack of scalable fabrication method capable of making complex structures. The conventional fabrication techniques for MMCs have been limited to fabricating simple structures with homogeneous dispersion of constituents. In this work, various fabrication approaches that can control the microstructure in metal matrix reinforced with nanoparticles have been studied. Mechanical alloying (ball milling) was used to control the dispersion of graphene sheets in homogeneous reinforced aluminum composites. Spray assisted deposition of nanoparticles was used to fabricate layered composites with uniformly and hierarchically reinforced interfaces. Magnetic field assisted deposition was studied to manipulate and deposit nanoparticles into micro-patterns that can be used to create hierarchically layered composites.

Homogeneously reinforced aluminum alloy (Al6061) reinforced composites with graphene have been synthesized using mechanical alloying followed by semisolid sintering. The ball milling was used to control the dispersion as well as the cluster size of the graphene within the matrix. The effect of ball milling time on the fabricated composites was studied. A significant enhancement in the mechanical properties of the graphene reinforced composites was observed compared with the matrix material processed at the same condition.

Layered composites, which are uniformly or hierarchically reinforced at the interfaces, have been synthesized by implementing two processing concepts: spray assisted deposition and metallurgy (semi-solid sintering). Ultrasonic spray deposition creates nano-/micro-/meso-scale patterns on metallic sheets, which are then stacked together, densified, and synthesized into a composite through pressure assisted semi-solid sintering process. Silicon carbide (SiC) nanoparticle reinforced lightweight alloys (i.e. Magnesium Alloy (AZ31) and Al6061) have been synthesized. The synthesized composites showed an improvement in the strength with minor decrease on the total elongation.

Magnetic field directed manipulation of nanoparticles was demonstrated to self-assemble and deposit nanoparticles into user-defined micro-patterns on Al substrate for potential use in synthesis of hierarchically structure layered composites. The magnetic field was modulated by machining (e.g. micro-milling and laser machining) user-defined pattern of protrusions on the magnetic source surface. The deposition of magnetic particles as well as mixtures of magnetic and nonmagnetic nanoparticles was studied.

DOI

https://doi.org/10.31274/etd-180810-5902

Copyright Owner

Mina Bastwros

Language

en

File Format

application/pdf

File Size

142 pages

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