Materials Science and Engineering Commons^™

Chemistry, Design, And Processing Of Two-Stage Trip Steel, Daniel M. Field

Doctoral Dissertations

"A regular solution model was developed to calculate the chemical driving force for α-martensite formation, ΔG^{λ→ α}_Chem. A model for the strain energy, ΔG^λ→α_str, was formulated utilizing the Young’s modulus (E), lattice misfit squared (δ²), and molar volume (Ω) which opposed the chemical driving force for α-martensite formation. The M^α_S was determined at a temperature at which ΔG^λ→α_Chem + ΔG^λ→α_str = 0. In conjunction with a previously developed ε-martensite model, a means of predicting the volume fraction of λ-austenite was determined; and it was shown that for values …

Mitigation Of Environmental Hazards Of Sulfide Mineral Flotation With An Insight Into Froth Stability And Flotation Performance, Muhammad Badar Hayat

Doctoral Dissertations

"Today's major challenges facing the flotation of sulfide minerals involve constant variability in the ore composition; environmental concerns; water scarcity and inefficient plant performance. The present work addresses these challenges faced by the flotation process of complex sulfide ore of Mississippi Valley type with an insight into the froth stability and the flotation performance. The first project in this study was aimed at finding the optimum conditions for the bulk flotation of galena (PbS) and chalcopyrite (CuFeS₂) through Response Surface Methodology (RSM). In the second project, an attempt was made to replace toxic sodium cyanide (NaCN) with the biodegradable chitosan …

Multi-Scale Investigation Of Microstructure, Fiber-Matrix Bond, And Mechanical Properties Of Ultra-High Performance Concrete, Zemei Wu

Doctoral Dissertations

"The main objective of this study is to provide new insights into enhancing fiber-matrix bond and mechanical properties of ultra-high performance concrete (UHPC). Three main strategies were investigated: 1) use of supplementary cementitious materials; 2) use of nano-particles; and 3) use of deformed fibers. A multi-scale investigation involving the evaluation of non-fibrous UHPC mortar phase (matrix), fiber-matrix interface phase, and then UHPC composite material was undertaken to determine microstructural characteristics, fiber bond to matrix, and key mechanical properties of the UHPC matrix and UHPC. Test results indicate that the incorporation of 10%-20% silica fume effectively improved the fiber-matrix bond and …

High Temperature Polymer Composites Using Out-Of-Autoclave Processing, Sudharshan Anandan

Doctoral Dissertations

"High performance polymer composites possess high strength-to-weight ratio, corrosion resistance, and have design flexibility. Carbon/epoxy composites are commonly used aerospace materials. Bismaleimide based composites are used as a replacement for epoxy systems at higher service temperatures. Aerospace composites are usually manufactured, under high pressure, in an autoclave which requires high capital investments and operating costs. In contrast, out-of-autoclave manufacturing, specifically vacuum-bag-only prepreg process, is capable of producing low cost and high performance composites. In the current study, out-of-autoclave processing of high temperature carbon/bismaleimide composites was evaluated. The cure and process parameters were optimized. The properties of out-of-autoclave cured laminates compared …

Functionalized Nanoporous Carbon Scaffolds For Hydrogen Storage Applications, Christopher L. Carr

Doctoral Dissertations

"Recent efforts have demonstrated confinement in porous scaffolds at the nanoscale can alter the hydrogen sorption properties of metal hydrides, though not to an extent feasible for use in onboard hydrogen storage applications, proposing the need for a method allowing further modifications. The work presented here explores how the functionalization of nanoporous carbon scaffold surfaces with heteroatoms can modify the hydrogen sorption properties of confined metal hydrides in relation to non-functionalized scaffolds (FS). Investigations of nanoconfined LiBH₄ and NaAlH₄ indicate functionalizing the carbon scaffold surface with nitrogen can shift the activation energy of hydrogen desorption in excess of …

Soy-Based Polyurethane Foam For Insulation And Structural Applications, Gurjot S. Dhaliwal

Doctoral Dissertations

"Polyurethane (PU) foams are widely used as insulation materials due to their high insulation properties and low cost compared to conventional materials such as styrene and mineral wool. PU foams are traditionally fabricated with petroleum-based precursors. However, high crude price and higher carbon footprint has lead interest of researchers to synthesis PU foams using plant-based raw materials, that are inexpensive and renewable. In this dissertation, PU foams were fabricated using soy-based polyol and its thermal and mechanical properties were investigated. In the first part, of PU foam samples with different formulations were fabricated using soy-based polyol HB230, and varying amounts …

Micro-Slotting Technique For Measurement Of Local Residual Stress In Metallic Materials, Elizabeth Anne Burns

Doctoral Dissertations

"Micro-slotting, a micro-scale relaxation residual stress measurement technique, has been shown in recent years to be a reliable method for measuring local residual stresses in metallic materials. This technique employs an SEM-focused ion beam system for milling and imaging, digital image correlation software to track displacements due to residual stress relaxation, and finite element analysis for interpolation of the original local stress state. In this research, a micro-slotting procedure was established using finite element models and was used to obtain sub-surface residual stress measurements on machined and shot peened planar Ti-6Al-4V samples. These measurements were compared to macro-scale XRD residual …

Quantitative Phase-Field Modeling Of Crack Propagation In Multi-Phase Materials, Arezoo Emdadi

Doctoral Dissertations

”Research presented in this dissertation is focused on developing and validating a computational framework for study of crack propagation in polycrystalline composite ceramics capable of designing micro-architectures of phases to improve fracture toughness and damage tolerance of ZrB₂-based ultra-high temperature ceramics (UHTCs). A quantitative phase-field model based on the regularized formulation of Griffith’s theory is presented for crack propagation in homogenous and heterogeneous brittle materials. This model utilizes correction parameters in the total free energy functional and mechanical equilibrium equation within the crack diffusive area to ensure that the maximum stress in front of the crack tip is …

Experimental And Computational Investigation Of Multi-Principal Element Alloys, Mohsen Beyramali Kivy

Doctoral Dissertations

"Multi-principal element (MPE) alloys, unlike traditional alloys, consist of five or more principal elements with near equi-atomic compositions creating a large new compositional space for exploring new alloy possibilities. However, designing MPE alloys with the desired phases, microstructures and properties is challenging task, and there is a demand for basic research for a better understanding of structure-processing-property relations in these alloys.

In this Ph.D. research, different computational models and experiments were integrated to study phase formations, and mechanical properties of different MPE alloys. Density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations were used to determine crystal structures, …

Dirac Surface States Of Magnetic Topological Insulators, Seng Huat Lee

Doctoral Dissertations

"Magnetic topological insulator (TI) has been theoretically proposed to be a platform for inducing magnetic monopole and exhibit fascinating quantum phenomena, whereas topological superconductor can host Majorana fermions, particles that are their own antiparticles, which can be manipulated for topological quantum computing. In this dissertation, we experimentally demonstrated that by intercalation of different transition metals in the van der Waals gaps of Bi₂Se₃ TI, magnetism and even superconductivity can be induced. In Fe_xBi₂Se₃, antiferromagnetism is induced with a transition temperature at ~ 100 K. Coexistence of the Dirac surface state with …

Processing, Microstructure, And Mechanical Properties Of Zirconium Diboride-Molybdenum Disilicide Ceramics And Dual Composite Architectures, Ryan Joseph Grohsmeyer

Doctoral Dissertations

"This research had two objectives: characterization of processing-microstructure-mechanical property relationships of conventional ZrB₂-MoSi₂ ceramics at room temperature (RT) and 1500⁰C in air, and fabrication of ZrB₂-MoSi₂ dual composite architectures (DCAs) for use near 1500⁰C. Elastic moduli, fracture toughness, and flexure strength were measured at RT and 1500⁰C for 15 ZrB₂-MoSi₂ ceramics hot pressed using fine, medium, or coarse ZrB₂ starting powder with 5-70 vol.% MoSi₂, referred to as FX, MX, and CX respectively where X is the nominal MoSi₂ content. MoSi₂ decomposed during sintering, resulting in …

Understanding The Deformation Mechanisms In Nanostructured Metals By A Novel Discrete Crystal Plasticity Finite Element Model, Rui Yuan

Doctoral Dissertations

"Implementation of nanostructured metals and alloys for use in engineering applications requires a detailed knowledge of the underlying deformation mechanisms in these materials. It is well known that plastic deformation in metals and alloys is mainly mediated by dislocation activities. Nonetheless, TEM observations and atomistic simulations indicate that dislocation-mediated plasticity in nanostructured metals and alloys is significantly different from that in their coarse-grained counterparts. Therefore, this dissertation focuses on the exploration of the deformation mechanisms in nanostructured metals via crystal plasticity finite element modeling and simulation.

A statistical grain boundary dislocation source model accounting for dislocation nucleation and slip events …

Optimal Design And Freeform Extrusion Fabrication Of Functionally Gradient Smart Parts, Amir Ghazanfari

Doctoral Dissertations

"An extrusion-based additive manufacturing process, called the Ceramic On-Demand Extrusion (CODE) process, for producing three-dimensional ceramic components with near theoretical density was developed. In this process, an aqueous paste of ceramic particles with a very low binder content (<1 vol%) is extruded through a moving nozzle at room temperature. After a layer is deposited, it is surrounded by oil (to a level just below the top surface of most recent layer) to preclude non-uniform evaporation from the sides. Infrared radiation is then used to partially, and uniformly, dry the just-deposited layer so that the yield stress of the paste increases and the part maintains its shape. The same procedure is repeated for every layer until part fabrication is completed. Sample parts made of alumina and fully stabilized zirconia were produced using this process and their mechanical properties including density, strength, Young's modulus, Weibull modulus, toughness, and hardness were examined. Microstructural evaluation was also performed to measure the grain size, and critical flaw sizes were obtained. The results indicate that the proposed method enables fabrication of geometrically complex parts with superior mechanical properties. Furthermore, several methods were developed to increase the productivity of the CODE process and enable manufacturing of functionally graded materials with an optimum distribution of material composition. As an application of the CODE process, advanced ceramic components with embedded sapphire optical fiber sensors were fabricated and properties of parts and sensors were evaluated using standard test methods"--Abstract, page iv.

Studies On The Electrical Transport Properties Of Carbon Nanotube Composites, Taylor Warren Tarlton

Doctoral Dissertations

This work presents a probabilistic approach to model the electrical transport properties of carbon nanotube composite materials. A pseudo-random generation method is presented with the ability to generate 3-D samples with a variety of different configurations. Periodic boundary conditions are employed in the directions perpendicular to transport to minimize edge effects. Simulations produce values for drift velocity, carrier mobility, and conductivity in samples that account for geometrical features resembling those found in the lab. All results show an excellent agreement to the well-known power law characteristic of percolation processes, which is used to compare across simulations. The effect of sample …

Experimental And Numerical Evaluation Of A New Composite Pressure Pipe For A Trenchless Rehabilitation Technology, Xuanchen Yen

Doctoral Dissertations

The information presented in this dissertation is based on research work conducted at Trenchless Technology Center (TTC) at Louisiana Tech University. This work was performed through a contract with China University of Geoscience (CUG) for a gas company. China's gas pipelines need replacement or rehabilitation after 15 to 30 years of service. China's gas industry is looking for suitable techniques to transfer into their market.

When compared to conventional excavation pipeline renewal or replacement methods, there are obvious advantages of TRT for gas pipelines that can impact the triple bottom-line of economic, social and environmental benefits. An introduction of TRT …

Clay Nanotube Composites For Antibacterial Nanostructured Coatings, Christen J. Boyer

Doctoral Dissertations

A surging demand for the development of new antimicrobial nanomaterials exists due to the frequency of medical device-associated infections and the transfer of pathogens from highly touched objects. Naturally occurring halloysite clay nanotubes (HNTs) have shown to be ideal particles for polymer reinforcement, time-release drug delivery, nano-reactor synthesis, and as substrate material for nanostructured coatings.

This research demonstrates the feasibility of a novel method for coating HNTs with metals for antibacterial applications. The first ever ability to coat HNTs through electrolysis was developed for customizable and multi-functional antibacterial nanoparticle platforms. HNTs were investigated as substrate for the deposition of copper …

Multiphase Field Modeling Of The Formation Path Of Delta Hydrides In Zirconium, Jacob Luke Bair

Doctoral Dissertations

"Zirconium alloys are commonly used in nuclear fuel rod claddings due to their high ductility, good corrosion resistance, and low neutron absorption cross section. Among the most important weaknesses of zirconium alloys is their affinity for hydrogen, resulting in formation of hydrides in the cladding, and leading to embrittlement and mechanical failure. Despite numerous studies on hydride precipitation in zirconium alloys, the nucleation and formation path of stable δ hydrides in α zirconium matrix are not yet fully understood.

In this Ph.D. research project, two novel quantitative phase-field models were developed and utilized to advance our understanding of mechanisms of …

Nanostructured Materials Prepared By Atomic Layer Deposition For Catalysis And Lithium-Ion Battery Applications, Rajankumar Patel

Doctoral Dissertations

"Atomic/molecular layer deposition (ALD/MLD) has emerged as an important technique for depositing thin films in both scientific research and industrial applications. In this dissertation, ALD/MLD was used to create novel nanostructures for two different applications, catalysis and lithium-ion batteries.

MLD was used to prepare ultra-thin dense hybrid organic/inorganic polymer films. Oxidizing the hybrid films removed the organic components and produced the desired nanoporous films. Both porous alumina and titania films can be prepared by such a way. A novel nanostructured catalyst (Pt/SiO₂) with an ultra-thin porous alumina shell obtained from the thermal decomposition of an aluminium alkoxide film …

Dft Investigations Of Hydrogen Storage Materials, Gang Wang

Doctoral Dissertations

"Hydrogen serves as a promising new energy source having no pollution and abundant on earth. However the most difficult problem of applying hydrogen is to store it effectively and safely, which is smartly resolved by attempting to keep hydrogen in some metal hydrides to reach a high hydrogen density in a safe way. There are several promising metal hydrides, the thermodynamic and chemical properties of which are to be investigated in this dissertation.

Sodium alanate (NaAlH₄) is one of the promising metal hydrides with high hydrogen storage capacity around 7.4 wt. % and relatively low decomposition temperature of …

Development Of Implants Composed Of Bioactive Materials For Bone Repair, Wei Xiao

Doctoral Dissertations

"The purpose of this Ph.D. research was to address the clinical need for synthetic bioactive materials to heal defects in non-loaded and loaded bone. Hollow hydroxyapatite (HA) microspheres created in a previous study were evaluated as a carrier for controlled release of bone morphogenetic protein-2 (BMP2) in bone regeneration. New bone formation in rat calvarial defects implanted with BMP2-loaded microspheres (43%) was significantly higher than microspheres without BMP2 (17%) at 6 weeks postimplantation. Then hollow HA microspheres with a carbonate-substituted composition were prepared to improve their resorption rate. Hollow HA microspheres with ~12 wt. % of carbonate showed significantly higher …

Modeling And Evaluation Of Moisture Diffusion In Polymer Composite Materials, Zhen Huo

Doctoral Dissertations

"Fiber-reinforced polymer composites have extensive applications due to their high specific strength, improved product performance, low maintenance and design flexibility. However, moisture absorbed by polymer composites during the service life plays a detrimental role in both the integrity and durability of composite structure. It is essential to understand the moisture diffusion behavior and induced damage in polymer matrix composites under varying hygrothermal conditions. In Part I, the moisture diffusion characteristics in hybrid composites using moisture concentration-dependent diffusion method have been investigated. Also, a multi-stage diffusion model was proposed to explain the deviation of moisture diffusion behavior for sandwich composites from …

Microwave Material Characterization Of Alkali-Silica Reaction (Asr) Gel In Cementitious Materials, Ashkan Hashemi

Doctoral Dissertations

"Since alkali-silica reaction (ASR) was recognized as a durability challenge in cement-based materials over 70 years ago, numerous methods have been utilized to prevent, detect, and mitigate this issue. However, quantifying the amount of produced ASR byproducts (i.e., ASR gel) in-service is still of great interest in the infrastructure industry. The overarching objective of this dissertation is to bring a new understanding to the fundamentals of ASR formation from a microwave dielectric property characterization point-of-view, and more importantly, to investigate the potential for devising a microwave nondestructive testing approach for ASR gel detection and evaluation. To this end, a comprehensive …

Synthesis And Functionalization Of A Triaryldiamine-Base Photoconductive/Photorefractive Composite, And Its Application To Aberrated Image Restoration, Yichen Liang

Doctoral Dissertations

"Organic photorefractive (PR) composites have recently emerged as an important class of materials for applications including high-density data storage, optical communication, and biomedical imaging. In an effort to further improve their performance, this study focused on the utilization of functionalized semiconductor nanocrystals to photosensitize triaryamine (TPD)-based PR composites, as well as the application of TPD-based PR composites in the restoration of aberrated optical information. A novel approach to functionalize CdSe quantum dot (QCdSe) was firstly introduced where the sulfonated triarydiamine (STPD) was used as charge-transporting ligand to passivate QCdSe. TPD-based photoconductive and PR composites were photosensitized with the STPD-passivated QCdSe …

On The Spheroidal Graphite Growth And The Austenite Solidification In Ductile Irons, Jingjing Qing

Doctoral Dissertations

"Evolutions of austenite and nodular/spheroidal graphite particles during solidifications of ductile irons were experimentally investigated. Spheroidal graphite particle and austenite dendrite were found nucleated independently in liquid. Austenite dendrite engulfed the spheroidal graphite particles after contact and an austenite shell formed around a spheroidal graphite particle. The graphite diameter at which the austenite shell closed around nodule was determined. Statistically determined graphite size distributions indicated multiple graphite nucleation events during solidification.

Structures in a graphite nodule varied depending on the growth stages of the nodule in ductile iron. Curved graphene layers appearing as faceted growth ledges swept circumferentially around the …

Metallurgical Optimization Of High Strength Cast Steels With Stage I Tempering, Terrell Owen Webb Jr.

Doctoral Dissertations

“Eglin steel was developed by the U.S. Air Force and Ellwood National Forge Company as a cost-effective, ultrahigh strength steel for use in armament, aerospace, and commercial applications. Eglin steel has been successfully substituted for high alloy steels, such as AF1410 and HP-9-4-20/30, to produce the casing for “bunker buster” bombs where penetration of concrete barriers and rock at high velocity ( > 1000 ft/sec) is desired. Unlike AF1410 and HP-9-4-20/30, Eglin steel is low nickel (nominal 1 wt.%) and contains no cobalt. Given the successful performance of Eglin steel in the casings applications, the Department of Defense has directed that …

Dissolution Of Borate Glasses And Precipitation Of Phosphate Compounds, Jaime Lynn George

Doctoral Dissertations

"Borate glasses have been developed for biomedical applications such as scaffolds for soft tissue and bone repair. The dissolution processes of borate glasses in phosphate-containing aqueous solutions were studied by µ-Raman spectroscopy which provided information about the types and concentrations of borate species released into the solution as a function of time and characterized the formation of calcium phosphate reaction products on the glass surface. Boric acid molecules (H₃BO₃) and borate anions (B(OH)₄^-) can be detected in solution and their relative concentrations depend on the solution pH.

Static and dynamic single-pass flow-through experiments …

Fusion Welding Of Diboride-Carbide Ceramic Composites, Derek Scott King

Doctoral Dissertations

"Plasma and pulsed plasma arc welding (PAW and PPAW) processes were used to fusion weld ZrB₂ containing 20 vol% ZrC. Varying welding parameters resulted in changes in weld pool shape and size, and the size of ZrB₂ grains within the fusion zone. For PAW processes that resulted in a keyhole fusion zone (full penetration), the arc to workpiece power transfer efficiency was estimated to be 2 grain lengths were observed to decrease between binary PAW FZs (~1 mm in length), and binary PPAW FZs (~0.8 mm in length), and an increasing aspect ratio for ZrB₂ grains in …

Containment Materials For Thin-Strip Casting Of Steel, Abhishek Kumar

Doctoral Dissertations

"The focus of this research was to investigate the corrosion behavior of BN-based and ZrO₂-C refractories by molten steel. These refractories are used as side-dam and core-nozzle in the thin-strip casting of steel. The improvement and development of these refractory components will increase the process efficiency by prolonging the refractory service life.

The first part of this study focused on interaction of BN-ZrO₂-SiC side-dams with steel-inclusion system in a laboratory setup under argon gas environment. It was observed that corrosion of this ceramic was severe in contact with steel compared to slag/inclusion.

The second part of …

Inclusion Engineering In Mn-Si De-Oxidized Steel For Thin-Strip Casting, Vivek Thapliyal

Doctoral Dissertations

"The focus of this research was to understand inclusion formation and evolution in Mn-Si de-oxidized steels used in thin-strip casting. Inclusions formation and evolution in ultra-low carbon low-alloyed steels were studied. Inclusion engineering can be used to remove or modify detrimental inclusions, which cause casting issues.

The first part of this study focused on inclusion formation as a result of ferro-alloy addition. De-oxidation reaction in steels are the primary source of the typical oxide inclusion formed in steel. For Mn-Si de-oxidized steels ferro-silicon and ferro-manganese are the two ferro-alloys used for de-oxidation. Inclusion formation and evolution during the early stages …

Resistance Switching Of Electrodeposited Cuprous Oxide, Sanaz Yazdanparast

Doctoral Dissertations

In this work, the resistance switching behavior of electrodeposited cuprous oxide (Cu₂O) thin films in Au/Cu₂O/top electrode (Pt, Au-Pd, Al) cells was studied. After an initial FORMING process, the fabricated cells show reversible switching between a low resistance state (16.6 Ω) and a high resistance state (0.4 x 10⁶ Ω). Changing the resistance states in cuprous oxide films depends on the magnitude of the applied voltage which corresponds to unipolar resistance switching behavior of this material. The endurance and retention tests indicate a potential application of the fabricated cells for nonvolatile resistance switching random access …