UNT Theses and Dissertations - 60 Matching Results

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Additive Manufacturing of Metastable Beta Titanium Alloys

Description: Additive manufacturing processes of many alloys are known to develop texture during the deposition process due to the rapid reheating and the directionality of the dissipation of heat. Titanium alloys and with respect to this study beta titanium alloys are especially susceptible to these effects. This work examines Ti-20wt%V and Ti-12wt%Mo deposited under normal additive manufacturing process parameters to examine the texture of these beta-stabilized alloys. Both microstructures contained co… more
Date: August 2017
Creator: Yannetta, Christopher James
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Atomistic Computer Simulations of Diffusion Mechanisms in Lithium Lanthanum Titanate Solid State Electrolytes for Lithium Ion Batteries

Description: Solid state lithium ion electrolytes are important to the development of next generation safer and high power density lithium ion batteries. Perovskite-structured LLT is a promising solid electrolyte with high lithium ion conductivity. LLT also serves as a good model system to understand lithium ion diffusion behaviors in solids. In this thesis, molecular dynamics and related atomistic computer simulations were used to study the diffusion behavior and diffusion mechanism in bulk crystal and gra… more
Date: August 2014
Creator: Chen, Chao-Hsu
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Atomistic Studies of Point Defect Migration Rates in the Iron-Chromium System

Description: Generation and migration of helium and other point defects under irradiation causes ferritic steels based on the Fe-Cr system to age and fail. This is motivation to study point defect migration and the He equation of state using atomistic simulations due to the steels' use in future reactors. A new potential for the Fe-Cr-He system developed by collaborators at the Lawrence Livermore National Laboratory was validated using published experimental data. The results for the He equation of state ag… more
Date: August 2010
Creator: Hetherly, Jeffery
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Biocompatible Hybrid Nanomaterials Involving Polymers and Hydrogels Interfaced with Phosphorescent Complexes and Toxin-Free Metallic Nanoparticles for Biomedical Applications

Description: The major topics discussed are all relevant to interfacing brightly phosphorescent and non-luminescent coinage metal complexes of [Ag(I) and Au(I)] with biopolymers and thermoresponsive gels for making hybrid nanomaterials with an explanation on syntheses, characterization and their significance in biomedical fields. Experimental results and ongoing work on determining outreaching consequences of these hybrid nanomaterials for various biomedical applications like cancer therapy, bio-imaging and… more
Date: August 2011
Creator: Marpu, Sreekar B.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Carrier Mobility, Charge Trapping Effects on the Efficiency of Heavily Doped Organic Light-Emitting Diodes, and EU(lll) Based Red OLEDs

Description: Transient electroluminescence (EL) was used to measure the onset of emission delay in OLEDs based on transition metal, phosphorescent bis[3,5-bis(2-pyridyl)-1,2,4-triazolato] platinum(ΙΙ) and rare earth, phosphorescent Eu(hfa)3 with 4'-(p-tolyl)-2,2":6',2" terpyridine (ttrpy) doped into 4,4'-bis(carbazol-9-yl) triphenylamine (CBP), from which the carrier mobility was determined. For the Pt(ptp)2 doped CBP films in OLEDs with the structure: ITO/NPB (40nm)/mcp (10nm)/65% Pt(ptp)2:CBP (2… more
Date: August 2010
Creator: Lin, Ming-Te
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Compostable Soy-Based Polyurethane Foam with Kenaf Core Modifiers

Description: Building waste and disposable packaging are a major component in today's landfills. Most of these are structural or thermally insulative polymer foams that do not degrade over a long period of time. Currently, there is a push to replace these foams with thermoplastic or biodegradable foams that can either be recycled or composted. We propose the use of compostable soy-based polyurethane foams (PU) with kenaf core modifiers that will offer the desired properties with the ability to choose respon… more
Date: August 2016
Creator: Hoyt, Zachary
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Computational Studies on Structures and Ionic Diffusion of Bioactive Glasses

Description: Bioactive glasses are a class of synthetic inorganic material that have wide orthopedics, dentistry, tissue engineering and other biomedical applications. The origin of the bioactivity is closely related to the atomic structures of these novel glass materials, which otherwise lack long range order and defies any direct experimental measurements due to their amorphous nature. The structure of bioactive glasses is thus essential for the understanding of bioactive behaviors and eventually rational… more
Date: August 2014
Creator: Xiang, Ye
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Computational Study of Dislocation Based Mechanisms in FCC Materials

Description: Understanding the relationships between microstructures and properties of materials is a key to developing new materials with more suitable qualities or employing the appropriate materials in special uses. In the present world of material research, the main focus is on microstructural control to cost-effectively enhance properties and meet performance specifications. This present work is directed towards improving the fundamental understanding of the microscale deformation mechanisms and mechan… more
Date: August 2014
Creator: Yellakara, Ranga Nikhil
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Corrosion Protection of Aerospace Grade Magnesium Alloy Elektron 43™ for Use in Aircraft Cabin Interiors

Description: Magnesium alloys exhibit desirable properties for use in transportation technology. In particular, the low density and high specific strength of these alloys is of interest to the aerospace community. However, the concerns of flammability and susceptibility to corrosion have limited the use of magnesium alloys within the aircraft cabin. This work studies a magnesium alloy containing rare earth elements designed to increase resistance to ignition while lowering rate of corrosion. The microst… more
Date: August 2013
Creator: Baillio, Sarah S.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Definition of Brittleness: Connections Between Mechanical and Tribological Properties of Polymers.

Description: The increasing use of polymer-based materials (PBMs) across all types of industry has not been matched by sufficient improvements in understanding of polymer tribology: friction, wear, and lubrication. Further, viscoelasticity of PBMs complicates characterization of their behavior. Using data from micro-scratch testing, it was determined that viscoelastic recovery (healing) in sliding wear is independent of the indenter force within a defined range of load values. Strain hardening in sliding we… more
Date: August 2008
Creator: Hagg Lobland, Haley E.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Design of a Polymeric Coating for Protecting Thermoelectric Materials from Sublimation and Oxidation

Description: Thermoelectric (TE) devices can undergo degradation from reactions in corrosive environments and at higher operating temperatures by sublimation and oxidation. To prevent the degradation, we have applied two high temperature polymers (HTPs) as coatings for TE materials. Sintering temperatures were from 250°C to 400°C. We explain why dip coating is better technique in our study and had two potential HTPs for tests. By applying TGA (thermogravimetric analysis), we were able to figure out which HT… more
Date: August 2019
Creator: Chen, I Kang
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Determination of Wear in Polymers Using Multiple Scratch Test.

Description: Wear is an important phenomenon that occurs in all the polymer applications in one form or the other. However, important links between materials properties and wear remain illusive. Thus optimization of material properties requires proper understanding of polymer properties. Studies to date have typically lacked systematic approach to all polymers and wear test developed are specific to some polymer classes. In this thesis, different classes of polymers are selected and an attempt is made to us… more
Date: August 2004
Creator: Damarla, Gowrisankar
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Developing Precipitation Hardenable High Entropy Alloys

Description: High entropy alloys (HEAs) is a concept wherein alloys are constructed with five or more elements mixed in equal proportions; these are also known as multi-principle elements (MPEs) or complex concentrated alloys (CCAs). This PhD thesis dissertation presents research conducted to develop precipitation-hardenable high entropy alloys using a much-studied fcc-based equi-atomic quaternary alloy (CoCrFeNi). Minor additions of aluminium make the alloy amenable for precipitating ordered intermetallic … more
Date: August 2017
Creator: Gwalani, Bharat
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Device Engineering for Enhanced Efficiency from Platinum(II) Phosphorescent OLEDs

Description: Phosphorescent organic light emitting diodes (PHOLEDs) based on efficient electrophosphorescent dopant, platinum(II)-pyridyltriazolate complex, bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) (Pt(ptp)2) have been studied and improved with respect to power efficiency, external efficiency, chromacity and efficiency roll-off. By studying the electrical and optical behavior of the doped devices and functionality of the various constituent layers, devices with a maximum EQE of 20.8±0.2 % and p… more
Date: August 2010
Creator: Li, Minghang
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Dislocation Dynamics Simulations of Plasticity in Cu Thin Films

Description: Strong size effects in plastic deformation of thin films have been experimentally observed, indicating non-traditional deformation mechanisms. These observations require improved understanding of the behavior of dislocation in small size materials, as they are the primary plastic deformation carrier. Dislocation dynamics (DD) is a computational method that is capable of directly simulating the motion and interaction of dislocations in crystalline materials. This provides a convenient approach t… more
Date: August 2013
Creator: Wu, Han
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Electrical and Structure Properties of High-κ Barium Tantalite and Aluminum Oxide Interface with Zinc Oxide for Applications in Transparent Thin Film Transistors

Description: ZnO has generated interest for flexible electronics/optoelectronic applications including transparent thin film transistors (TFTs). For this application, low temperature processes that simultaneously yield good electrical conductivity and optical transparency and that are compatible with flexible substrates such as plastic, are of paramount significance. Further, gate oxides are a critical component of TFTs, and must exhibit low leakage currents and self-healing breakdown in order to ensure opt… more
Date: August 2011
Creator: Kuo, Fang-Ling
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Evolution of Precipitates and Their Influence on the Mechanical Properties of β-Titanium Alloys

Description: Over the last few decades, body-centered-cubic (bcc) beta (β) titanium alloys have largely been exploited as structural alloys owing to the richness in their microstructural features. These features, which lead to a unique combination of high specific strength and ductility, excellent hardenability, good fatigue performance, and corrosion resistance, make these alloys viable candidates for many applications, including aerospace, automobile, and orthopedic implants. The mechanical properties of … more
Date: August 2017
Creator: Mantri, Srinivas Aditya
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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First Principles Calculations of the Site Substitution Behavior in Gamma Prime Phase in Nickel Based Superalloys

Description: Nickel based superalloys have superior high temperature mechanical strength, corrosion and creep resistance in harsh environments and found applications in the hot sections as turbine blades and turbine discs in jet engines and gas generator turbines in the aerospace and energy industries. The efficiency of these turbine engines depends on the turbine inlet temperature, which is determined by the high temperature strength and behavior of these superalloys. The microstructure of nickel based sup… more
Date: August 2012
Creator: Chaudhari, Mrunalkumar
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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First Principles Study of Metastable Beta Titanium Alloys

Description: The high temperature BCC phase (b) of titanium undergoes a martensitic transformation to HCP phase (a) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed b phase separates into a + b upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in as-quenched b microstructure creates nanoscale precipitates of a new simple he… more
Date: August 2015
Creator: Gupta, Niraj
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Friction Stir Welding of High Strength Precipitation Strengthened Aluminum Alloys

Description: Rising demand for improved fuel economy and structural efficiency are the key factors for use of aluminum alloys for light weighting in aerospace industries. Precipitation strengthened 2XXX and 7XXX aluminum alloys are the key aluminum alloys used extensively in aerospace industry. Welding and joining is the critical step in manufacturing of integrated structures. Joining of precipitation strengthened aluminum alloys using conventional fusion welding techniques is difficult and rather undesirab… more
Date: August 2016
Creator: Sidhar, Harpreet
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys

Description: The Al-Zn-Mg-Cu (7XXX series) alloys are amongst the strongest aluminum available. However, they are considered unweldable with conventional fusion techniques due to the negative effects that arise with conventional welding, including hydrogen porosity, hot cracking, and stress corrosion cracking. For this reason, friction stir welding has emerged as the preferred technique to weld 7XXX series alloys. Aluminum 7449 is one of the highest strength 7XXX series aluminum alloy. This is due to its hi… more
Date: August 2016
Creator: Martinez, Nelson Y
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Gamma Prime Precipitation Mechanisms and Solute Partitioning in Ni-base Alloys

Description: Nickel-base superalloys have been emerged as materials for gas turbines used for jet propulsion and electricity generation. The strength of the superalloys depends mainly from an ordered precipitates of L12 structure, so called gamma prime (γ’) dispersed within the disorder γ matrix. The Ni-base alloys investigated in this dissertation comprise both model alloy systems based on Ni-Al-Cr and Ni-Al-Co as well as the commercial alloy Rene N5. Classical nucleation and growth mechanism dominates the… more
Date: August 2014
Creator: Rojhirunsakool, Tanaporn
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

High Temperature Sliding Wear Behavior and Mechanisms of Cold-Sprayed Ti and Ti-TiC Composites

Description: Ti and Ti-based alloys are used in many aerospace and automotive components due to their high strength-to-weight ratio and corrosion resistance. However, room and elevated temperature wear resistance remain an issue, thus requiring some form of secondary hard phase, e.g., refractory carbides and oxides, as well as solid lubrication to mitigate wear. In this study, Ti-TiC (14, 24 and 35 vol% TiC) composite coatings were deposited on mild steel substrates using cold spray with comparisons made to… more
Date: August 2020
Creator: Koricherla, Manindra Varma
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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In-situ Analysis of the Evolution of Surfaces and Interfaces under Applied Coupled Stresses

Description: To study the effect of the substrate support on the nanoscale contact, three different regimes, i.e., graphene on rigid (ultra-crystalline diamond) and on elastic (Polydimethylsiloxane) supports and free-standing graphene, were considered. The contribution of the graphene support to the mechanical and electrical characteristics of the graphene/metal contact was studied using the conductive atomic force microscopy (AFM) technique.The results revealed that the electrical conductivity of the graph… more
Date: August 2020
Creator: Lee, Ji Hyung
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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