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Study of Novel Ion/surface Interactions Using Soft-landing Ion Mobility

Preparative mass spectrometry is a gas-phase ion deposition technique aimed at deposition of monodisperse ion beams on a surface. This is accomplished through the implementation of a soft-landing ion mobility system which allows for high ion flux of conformationally selected ion packets. The soft-landing ion mobility system has been applied to a number of unique chemical problems including the deposition of insulators on graphene, the preparation of reusable surface enhanced Raman spectroscop… more

Date: December 2012

Creator: Hoffmann, William Darryle

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Characterization and Mechanical Properties of Nanoscale Precipitates in Modified Al-Si-Cu Alloys Using Transmission Electron Microscopy and 3D Atom Probe Tomography.

Among the commercial aluminum alloys, aluminum 319 (Al-7wt%Si-4wt%Cu) type alloys are popularly used in automobile engine parts. These alloys have good casting characteristics and excellent mechanical properties resulting from a suitable heat treatment. To get a high strength in the 319 type alloys, grain refining, reducing the porosity, solid solution hardening, and precipitation hardening are preferred. All experimental variables such as solidification condition, composition, and heat treatme… more

Date: May 2007

Creator: Hwang, Junyeon

Item Type: Thesis or Dissertation

Partner: UNT Libraries

Origin of Unusually Large Hall-Petch Strengthening Coefficients in High Entropy Alloys

High entropy alloys (HEAs), also referred to as complex concentrated alloys (CCAs), are a relatively new class of alloys that have gained significant attention since 2010 due to their unique balance of properties that include high strength, ductility and excellent corrosion resistance. HEAs are usually based on five or more elements alloyed in near equimolar concentrations, and exhibit simple microstructures by the formation of solid solution phases instead of complex compounds. HEAs have great… more

Date: May 2021

Creator: Jagetia, Abhinav

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Workfunction tuning of AZO Films Through Surface Modification for Anode Application in OLEDs.

Widespread use of organic light emitting diodes (OLEDs) in solid state lighting and display technologies require efficiency and lifetime improvements, as well as cost reductions, inclusive of the transparent conducting oxide (TCO). Indium tin oxide (ITO) is the standard TCO anode in OLEDs, but indium is expensive and the Earth's reserve of this element is limited. Zinc oxide (ZnO) and its variants such as aluminum-doped ZnO (AZO) exhibit comparable electrical conductivity and transmissivity to … more

Date: August 2016

Creator: Jha, Jitendra

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Sliding Friction and Wear Behavior of High Entropy Alloys at Room and Elevated Temperatures

Structure-tribological property relations have been studied for five high entropy alloys (HEAs). Microhardness, room and elevated (100°C and 300°C) temperature sliding friction coefficients and wear rates were determined for five HEAs: Co0.5 Cr Cu0.5 Fe Ni1.5 Al Ti0.4; Co Cr Fe Ni Al0.25 Ti0.75; Ti V Nb Cr Al; Al0.3CoCrFeNi; and Al0.3CuCrFeNi2. Wear surfaces were characterized with scanning electron microscopy and micro-Raman spectroscopy to determine the wear mechanisms and tribochemical phase… more

Date: December 2016

Creator: Kadhim, Dheyaa

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Surface Modifications to Enhance the Wear Resistance and the Osseo-integration Properties of Biomedical Ti-alloy

The current study focuses on improving the wear resistance of femoral head component and enhancing the osseo-integration properties of femoral stem component of a hip implant made of a new generation low modulus alloy, Ti-35Nb-7Zr-5Ta or TNZT. Different techniques that were adopted to improve the wear resistance of low-modulus TNZT alloy included; (a) fabrication of graded TNZT-xB (x= 0, 1, 2 wt%) samples using LENS, (b) oxidation, and (c) LASER nitriding of TNZT. TNZT-1B and TNZT-O samples hav… more

Date: August 2013

Creator: Kami, Pavani

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Atomistic Simulations of Deformation Mechanisms in Ultra-Light Weight Mg-Li Alloys

Mg alloys have spurred a renewed academic and industrial interest because of their ultra-light-weight and high specific strength properties. Hexagonal close packed Mg has low deformability and a high plastic anisotropy between basal and non-basal slip systems at room temperature. Alloying with Li and other elements is believed to counter this deficiency by activating non-basal slip by reducing their nucleation stress. In this work I study how Li addition affects deformation mechanisms in Mg usi… more

Date: May 2015

Creator: Karewar, Shivraj

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Tribological Behavior of Spark Plasma Sintered Tic/graphite/nickel Composites and Cobalt Alloys

Monolithic composites are needed that combine low friction and wear, high mechanical hardness, and high fracture toughness. Thin films and coatings are often unable to meet this engineering challenge as they can delaminate and fracture during operation ceasing to provide beneficial properties during service life. Two material systems were synthesized by spark plasma sintering (SPS) and were studied for their ability to meet these criteria. A dual hybrid composite was fabricated and consisted of… more

Date: December 2013

Creator: Kinkenon, Douglas

Item Type: Thesis or Dissertation

Partner: UNT Libraries

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

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: Thesis or Dissertation

Partner: UNT Libraries

open access

Polyethylene-layered double hydroxide and montmorillonite nanocomposites: Thermal, mechanical and flame retardance properties.

The effect of incorporation two clays; layered double hydroxides (LDH) and montmorillonite layered silicates (MLS) in linear low density polyethylene (PE) matrix was investigated. MLS and LDH were added of 5, 15, 30 and 60 weight percent in the PE and compounded using a Brabender. Ground pellets were subsequently compression molded. Dispersion of the clays was analyzed using optical microscopy, SEM and XRD. Both the layered clays were immiscible with the PE matrix and agglomerates formed with i… more

Date: May 2008

Creator: Kosuri, Divya

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Electrical and Structure Properties of High-κ Barium Tantalite and Aluminum Oxide Interface with Zinc Oxide for Applications in Transparent Thin Film Transistors

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: Thesis or Dissertation

Partner: UNT Libraries

Processing-Structure-Property Relationships of Reactive Spark Plasma Sintered Boron Carbide-Titanium Diboride Composites

Sintering parameter effects on the microstructure of boron carbide and boron carbide/titanium diboride composites are investigated. The resulting microstructure and composition are characterized by scanning electron microscopy (SEM), x-ray microscopy (XRM) and x-ray diffraction (XRD). Starting powder size distribution effects on microstructure are present and effect the mechanical properties. Reactive spark plasma sintering introduces boron nitride (BN) intergranular films (IGF's) and their eff… more

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Date: August 2019

Creator: Lide, Hunter

Item Type: Thesis or Dissertation

Partner: UNT Libraries

Materials properties of ruthenium and ruthenium oxides thin films for advanced electronic applications.

Ruthenium and ruthenium dioxide thin films have shown great promise in various applications, such as thick film resistors, buffer layers for yttrium barium copper oxide (YBCO) superconducting thin films, and as electrodes in ferroelectric memories. Other potential applications in Si based complementary metal oxide semiconductor (CMOS) devices are currently being studied. The search for alternative metal-based gate electrodes as a replacement of poly-Si gates has intensified during the last few … more

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Date: May 2006

Creator: Lim, ChangDuk

Item Type: Thesis or Dissertation

Partner: UNT Libraries

Linking Enhanced Fatigue Life to Design by Modifying the Microstructure

Structural material fatigue is a leading cause of failure and has motivated fatigue-resistant design to eliminate risks to human lives. Intrinsic microstructural features alter fatigue deformation mechanisms so profoundly that, essentially, fatigue properties of structural materials become deviant. With this in mind, we initiated this project to investigate the microstructural effect on fatigue behavior of potential structural high entropy alloys. With a better understanding of the effect of mi… more

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Date: August 2019

Creator: Liu, Kaimiao

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Precession Electron Diffraction Assisted Characterization of Deformation in α and α+β Titanium Alloys

Ultra-fine grained materials with sub-micrometer grain size exhibit superior mechanical properties when compared with conventional fine-grained material as well as coarse-grained materials. Severe plastic deformation (SPD) techniques have been shown to be an effective way to modify the microstructure in order to improve the mechanical properties of the material. Crystalline materials require dislocations to accommodate plastic strain gradients and maintain lattice continuity. The lattice curvat… more

Date: August 2015

Creator: Liu, Yue

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Evolution of Precipitates and Their Influence on the Mechanical Properties of β-Titanium Alloys

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: Thesis or Dissertation

Partner: UNT Libraries

open access

Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys

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: Thesis or Dissertation

Partner: UNT Libraries

open access

Growth, Structure and Tribological Properties of Atomic Layer Deposited Lubricious Oxide Nanolaminates

Friction and wear mitigation is typically accomplished by introducing a shear accommodating layer (e.g., a thin film of liquid) between surfaces in sliding and/or rolling contacts. When the operating conditions are beyond the liquid realm, attention turns to solid coatings. Solid lubricants have been widely used in governmental and industrial applications for mitigation of wear and friction (tribological properties). Conventional examples of solid lubricants are MoS2, WS2, h-BN, and graphite;… more

Date: December 2010

Creator: Mensah, Benedict Anyamesem

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Laser Additive Manufacturing of Magnetic Materials

A matrix of variably processed Fe-30at%Ni was deposited with variations in laser travel speeds as well and laser powers. A complete shift in phase stability occurred as a function of varying laser travel speed. At slow travel speeds, the microstructure was dominated by a columnar fcc phase. Intermediate travel speeds yielded a mixed microstructure comprised of both the columnar fcc and a martensite-like bcc phase. At the fastest travel speed, the microstructure was dominated by the bcc phase. T… more

Date: August 2017

Creator: Mikler, Calvin V.

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Solid Lubrication Mechanisms in Laser Deposited Nickel-titanium-carbon Metal Matrix Composites

A Ni/TiC/C metal matrix composite (MMC) has been processed using the laser engineered net shaping (LENS) process from commercially available powders with a Ni-3Ti-20C (atomic %) composition. This processing route produces the in-situ formation of homogeneously distributed eutectic and primary titanium carbide and graphite precipitates throughout the Ni matrix. The composite exhibits promising tribological properties when tested in dry sliding conditions with a low steady state coefficient of fr… more

Date: December 2012

Creator: Mogonye, Jon-Erik

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Stable Nanocrystalline Au Film Structures for Sliding Electrical Contacts

Hard gold thin films and coatings are widely used in electronics as an effective material to reduce the friction and wear of relatively less expensive electrically conductive materials while simultaneously seeking to provide oxidation resistance and stable sliding electrical contact resistance (ECR). The main focus of this dissertation was to synthesize nanocrystalline Au films with grain structures capable of remaining stable during thermal exposure and under sliding electrical contact stress… more

Date: May 2016

Creator: Mogonye, Jon-Erik

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

Tribological Improvements of Carbon-Carbon Composites by Infiltration of Atomic Layer Deposited Lubricious Nanostructured Ceramic Oxides

A number of investigators have reported enhancement in oxidation and wear resistant of carbon-carbon composites (CCC) in the presence of protective coating layers. However, application of a surface and subsurface coating system that can preserve its oxidation and wear resistance along with maintaining lubricity at high temperature remains unsolved. To this end, thermodynamically stable protective oxides (ZnO/Al2O3/ZrO2) have been deposited by atomic layer deposition (ALD) to infiltrate porous … more

Date: August 2011

Creator: Mohseni, Hamidreza

Item Type: Thesis or Dissertation

Partner: UNT Libraries

open access

The Role of Crystallographic Texture in Achieving Low Friction Zinc Oxide Nanolaminate Films

Metal oxide nanolaminate films are potential high temperature solid lubricants due to their ability to exhibit significant plasticity when grain size is reduced to the nanometer scale, and defective growth structure is achieved by condensation of oxygen vacancies to form intrinsic stacking faults. This is in contrast to conventional microcrystalline and single crystal oxides that exhibit brittle fracture during loading in a sliding contact. This study emphasizes the additional effect of growt… more

Date: December 2015

Creator: Mojekwu, Nneoma

Item Type: Thesis or Dissertation

Partner: UNT Libraries

Process-Structure-Property Relationships in Friction Stir Welded Precipitation Strengthened Aluminum Alloys

Through a series of carefully designed experiments, characterization and some modeling tools, this work is aimed at studying the role of thermal profiles on different microstructural zones and associated properties like strength and corrosion through a variation of weld parameters, thermal boundary conditions and material temper. Two different alloys belonging to the Al-Cu and Al-Cu-Li system in different temper conditions- peak aged (T8) and annealed (O) were used. A 3D-thermal pseudo mechanic… more

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Date: May 2019

Creator: Mondal, Barnali

Item Type: Thesis or Dissertation

Partner: UNT Libraries