UNT Theses and Dissertations - 119 Matching Results

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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

In-situ Electrochemical Surface Engineering in Additively Manufactured CoCrMo for Enhanced Biocompatibility

Description: Laser-based additive manufacturing is inherently associated with extreme, unprecedented, and rapid thermokinetics which impact the microstructural evolution in a built component. Such a unique, near to non-equilibrium microstructure/phase evolution in laser additively manufactured metallic components impact their properties in engineering application. In light of this, the present work investigates the unique microstructural traits as a result of process induced spatial and temporal variation i… more
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Date: May 2023
Creator: Mazumder, Sangram
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Comparative Coarsening Kinetics of Gamma Prime Precipitates in Nickel and Cobalt Base Superalloys

Description: The increasing technological need to push service conditions of structural materials to higher temperatures has motivated the development of several alloy systems. Among them, superalloys are an excellent candidate for high temperature applications because of their ability to form coherent ordered precipitates, which enable the retention of high strength close to their melting temperature. The accelerated kinetics of solute diffusion, with or without an added component of mechanical stress, le… more
Date: August 2014
Creator: Meher, Subhashish
Item Type: Refine your search to only Thesis or Dissertation
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Integration, Stability, and Doping of Mono-Elemental and Binary Transition Metal Dichalcogenide Van der Waals Solids for Electronics and Sensing Devices

Description: In this work, we have explored 2D semiconducting transition metal dichalcogenides (TMDs), black phosphorus (BP), and graphene for various applications using liquid and mechanical exfoliation routes. The topical areas of interest that motivate our work include considering factors such as device integration, stability, doping, and the effect of gasses to modulate the electronic transport characteristics of the underlying 2D materials. In the first area, we have integrated solution-processed trans… more
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Date: May 2022
Creator: Mehta, Ravindra K
Item Type: Refine your search to only Thesis or Dissertation
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Growth, Structure and Tribological Properties of Atomic Layer Deposited Lubricious Oxide Nanolaminates

Description: 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: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Stable Nanocrystalline Au Film Structures for Sliding Electrical Contacts

Description: 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: Refine your search to only Thesis or Dissertation
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Tribological Improvements of Carbon-Carbon Composites by Infiltration of Atomic Layer Deposited Lubricious Nanostructured Ceramic Oxides

Description: 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: Refine your search to only Thesis or Dissertation
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Process-Structure-Property Relationships in Friction Stir Welded Precipitation Strengthened Aluminum Alloys

Description: 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: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Structure Evolution and Nano-Mechanical Behavior of Bulk Metallic Glasses and Multi-Principal Element Alloys

Description: Bulk metallic glasses and multi-principal element alloys represent relatively new classes of multi-component engineering materials designed for satisfying multiple functionalities simultaneously. Correlating the microstructure with mechanical behavior (at the microstructural length-scales) in these materials is key to understanding their performance. In this study, the structure evolution and nano-mechanical behavior of these two classes of materials was investigated with the objective of funda… more
Date: May 2017
Creator: Mridha, Sanghita
Item Type: Refine your search to only Thesis or Dissertation
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High Strain Rate Deformation Behavior of Single-Phase and Multi-Phase High Entropy Alloys

Description: Fundamental understanding of high strain rate deformation behavior of materials is critical in designing new alloys for wide-ranging applications including military, automobile, spacecraft, and industrial applications. High entropy alloys, consisting of multiple elements in (near) equimolar proportions, represent a new paradigm in structural alloy design providing ample opportunity for achieving excellent performance in high strain rate applications by proper selection of constituent elements a… more
Date: May 2021
Creator: Muskeri, Saideep
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Formation and Quantification of Corrosion Deposits in the Power Industry

Description: The presence of deposits on the secondary side of pressurized water reactor (PWR) steam generator systems is one of the main contributors to the high maintenance costs of these generators. Formation and transport of corrosion products formed due to the presence of impurities, metals and metallic oxides in the secondary side of the steam generator units result in formation of deposits. This research deals with understanding the deposit formation and characterization of deposits by studying the s… more
Date: May 2007
Creator: Namduri, Haritha
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Titanium Boride Formation and Its Subsequent Influence on Morphology and Crystallography of Alpha Precipitates in Titanium Alloys

Description: Over the last two decades there has been an increased interest in understanding the influence of trace boron additions in Ti alloys. These additions refine the prior β grain size in as-cast Ti alloys along with increasing their modulus and yield strength due to the precipitation of TiB. TiB also acts as a heterogeneous nucleation site for α precipitation and has been shown to influence the α phase morphology. B is completely soluble in liquid Ti but has a negligible solubility in both body cent… more
Date: December 2013
Creator: Nandwana, Peeyush
Item Type: Refine your search to only Thesis or Dissertation
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Structural, Thermal and Acoustic Performance of Polyurethane Foams for Green Buildings

Description: Decreasing the carbon footprint through use of renewable materials has environmental and societal impact. Foams are a valuable constituent in buildings by themselves or as a core in sandwich composites. Kenaf is a Southeast USA plant that provides renewable filler. The core of the kenaf is porous with a cell size in a 5-10 micrometer range. The use of kenaf core in foams represents a novel multiscalar cellular structural composite. Rigid polyurethane foams were made using free foaming expansion… more
Date: December 2014
Creator: Nar, Mangesh
Item Type: Refine your search to only Thesis or Dissertation
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Tuning of Microstructure and Mechanical Properties in Additively Manufactured Metastable Beta Titanium Alloys

Description: The results from this study, on a few commercial and model metastable beta titanium alloys, indicate that the growth restriction factor (GRF) model fails to interpret the grain growth behavior in the additively manufactured alloys. In lieu of this, an approach based on the classical nucleation theory of solidification incorporating the freezing range has been proposed for the first time to rationalize the experimental observations. Beta titanium alloys with a larger solidification range (liquid… more
This item is restricted from view until June 1, 2024.
Date: May 2022
Creator: Nartu, Mohan Sai Kiran Kumar Yadav
Item Type: Refine your search to only Thesis or Dissertation
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Fatigue Behavior of A356 Aluminum Alloy

Description: Metal fatigue is a recurring problem for metallurgists and materials engineers, especially in structural applications. It has been responsible for many disastrous accidents and tragedies in history. Understanding the micro-mechanisms during cyclic deformation and combating fatigue failure has remained a grand challenge. Environmental effects, like temperature or a corrosive medium, further worsen and complicate the problem. Ultimate design against fatigue must come from a materials perspective … more
Date: May 2016
Creator: Nelaturu, Phalgun
Item Type: Refine your search to only Thesis or Dissertation
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Growth Mechanisms, and Mechanical and Thermal Properties of Junctions in 3D Carbon Nanotube-Graphene Nano-Architectures

Description: Junctions are the key component for 3D carbon nanotube (CNT)-graphene seamless hybrid nanostructures. Growth mechanism of junctions of vertical CNTs growing from graphene in the presence of iron catalysts was simulated via quantum mechanical molecular dynamics (QM/MD) methods. CNTs growth from graphene with iron catalysts is based on a ‘‘base-growth’’ mechanism, and the junctions were the mixture of C-C and Fe-C covalent bonds. Pure C-C bonded junctions could be obtained by moving the catalyst … more
Date: December 2014
Creator: Niu, Jianbing
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Processing, structure property relationships in polymer layer double hydroxide multifunctional nanocomposites

Description: Dan Beaty (1937-2002) was a prolific composer, pianist, researcher, educator, and writer. His large compositional output included chamber works, choral works, songs, orchestral pieces, electronic music, and keyboard works. Beaty was well versed in traditional Western music as well as the more avant-garde and perplexing idioms of the twentieth century. Beaty's compositions reflect the many fascinating, if not always popular, musical trends of his time. His music encompasses styles from serial … more
Date: August 2009
Creator: Ogbomo, Sunny Minister
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Functionalization and characterization of porous low-κ dielectrics.

Description: The incorporation of fluorine into SiO2 has been shown to reduce the dielectric constant of the existing materials by reducing the electrical polarizability. However, the incorporation of fluorine has also been shown to decrease film stability. Therefore, new efforts have been made to find different ways to further decrease the relative dielectric constant value of the existing low-k materials. One way to reduce the dielectric constant is by decreasing its density. This reduces the amount of p… more
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Date: May 2005
Creator: Orozco-Teran, Rosa Amelia
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Effects of Plasma, Temperature and Chemical Reactions on Porous Low Dielectric Films for Semiconductor Devices

Description: Low-dielectric (k) films are one of the performance drivers for continued scaling of integrated circuit devices. These films are needed in microelectronic device interconnects to lower power consumption and minimize cross talk between metal lines that "interconnect" transistors. Low-k materials currently in production for the 45 and 65 nm node are most often organosilicate glasses (OSG) with dielectric constants near 2.8 and nominal porosities of 8-10%. The next generation of low-k materials wi… more
Date: December 2010
Creator: Osei-Yiadom, Eric
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Thermomechanical Processing, Additive Manufacturing and Alloy Design of High Strength Mg Alloys

Description: The recent emphasis on magnesium alloys can be appreciated by following the research push from several agencies, universities and editorial efforts. With a density equal to two-thirds of Al and one-thirds of steel, Mg provides the best opportunity for lightweighting of metallic components. However, one key bottleneck restricting its insertion into industrial applications is low strength values. In this respect, Mg-Y-Nd alloys have been promising due to their ability to form strengthening precip… more
Date: May 2016
Creator: Palanivel, Sivanesh
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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Thermokinetics-Dependent Microstructural Evolution and Material Response in Laser-Based Additive Manufacturing

Description: Laser-based additive manufacturing offers a high degree of thermokinetic flexibility that has implications on the structure and properties of the fabricated component. However, to exploit the flexibility of this process, it is imperative to understand the process-inherent thermokinetic evolution and its effect on the material characteristics. In view of this, the present work establishes a fundamental understanding of the spatiotemporal variation of thermokinetics during the fabrication of the … more
Date: December 2021
Creator: Pantawane, Mangesh V
Item Type: Refine your search to only Thesis or Dissertation
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First Principles Study of the Effect of Local Bonding on Diffusion Mechanisms in Alloys

Description: This work demonstrates how local, randomized tailoring of bond stiffness can affect the activation energy of diffusion in model alloys using density functional theory-based computations. This work is organized into two parts. The first part deals with the vacancy diffusion mechanism, and it compares the in–plane (IP) vs out-of-plane (OOP) diffusion paths in prototypical binary Mg-X (Ca, Y, and Gd) and ternary Mg-X (Ca, Y, and Gd)-Zn alloys. We examine how vacancy formation, migration, and solut… more
Date: December 2021
Creator: Paranjape, Priyanvada Madhukar
Item Type: Refine your search to only Thesis or Dissertation
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Fabrication of Large-Scale and Thickness-Modulated Two-Dimensional Transition Metal Dichalcogenides [2D TMDs] Nanolayers

Description: This thesis describes the fabrication and characterization of two-dimensional transition dichalcogenides (2D TMDs) nanolayers for various applications in electronic and opto-electronic devices applications. In Chapter 1, crystal and optical structure of TMDs materials are introduced. Many TMDs materials reveal three structure polytypes (1T, 2H, and 3R). The important electronic properties are determined by the crystal structure of TMDs; thus, the information of crystal structure is explained. … more
Date: May 2019
Creator: Park, Juhong
Item Type: Refine your search to only Thesis or Dissertation
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Corrosion Behavior of High Entropy Alloys in Molten Chloride and Molten Fluoride Salts

Description: High entropy alloys (HEAs) or complex concentrated alloys (CCAs) represent a new paradigm in structural alloy design. Molten salt corrosion behavior was studied for single-phase HEAs such as TaTiVWZr and HfTaTiVZr, and multi-phase HEAs such as AlCoCrFeNi2.1. De-alloying with porosity formation along the exposed surface and fluxing of unstable oxides were found to be primary corrosion mechanisms. Potentiodynamic polarization study was combined with systematic mass–loss study for TaTiVWZr, HfTaT… more
This item is restricted from view until June 1, 2024.
Date: May 2022
Creator: Patel, Kunjalkumar Babubhai
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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