UNT Theses and Dissertations - 245 Matching Results

Search Results

prev Results: 91 - 114 next
open access

Integrated Computational and Experimental Approach to Control Physical Texture During Laser Machining of Structural Ceramics

Description: The high energy lasers are emerging as an innovative material processing tool to effectively fabricate complex shapes on the hard and brittle structural ceramics, which previously had been near impossible to be machined effectively using various conventional machining techniques. In addition, the in-situ measurement of the thermo-physical properties in the severe laser machining conditions (high temperature, short time duration, and small interaction volume) is an extremely difficult task. As a… more
Date: December 2013
Creator: Vora, Hitesh D.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Mist and Microstructure Characterization in End Milling Aisi 1018 Steel Using Microlubrication

Description: Flood cooling is primarily used to cool and lubricate the cutting tool and workpiece interface during a machining process. But the adverse health effects caused by the use of flood coolants are drawing manufacturers' attention to develop methods for controlling occupational exposure to cutting fluids. Microlubrication serves as an alternative to flood cooling by reducing the volume of cutting fluid used in the machining process. Microlubrication minimizes the exposure of metal working fluids to… more
Date: August 2013
Creator: Shaikh, Vasim
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Mechanics and Mechanisms of Creep and Ductile Fracture

Description: The main aim of this dissertation is to relate measurable and hopefully controllable features of a material's microstructure to its observed failure modes to provide a basis for designing better materials. The understanding of creep in materials used at high temperatures is of prime engineering importance. Single crystal Ni-based superalloys used in turbine aerofoils of jet engines are exposed to long dwell times at very high temperatures. In contrast to current theories, creep tests on Ni-base… more
Date: August 2013
Creator: Srivastava, Ankit
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

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
Partner: UNT Libraries
open access

Nano-crystallization Inhibition in 5 Nm Ru Film Diffusion Barriers for Advanced Cu-interconnect

Description: As the semiconductor industries are moving beyond 22 nm node technology, the currently used stacked Ta/TaN diffusion barrier including a copper seed will be unable to fulfill the requirements for the future technologies. Due to its low resistivity and ability to perform galvanic copper fill without a seed layer, ruthenium (Ru) has emerged as a potential copper diffusion barrier. However, its crystallization and columnar nanostructure have been the main cause of barrier failures even at low proc… more
Date: December 2013
Creator: Sharma, Bed P.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Investigations in the Mechanism of Carbothermal Reduction of Yttria Stabilized Zirconia for Ultra-high Temperature Ceramics Application and Its Influence on Yttria Contained in It

Description: Zirconium carbide (ZrC) is a high modulus ceramic with an ultra-high melting temperature and, consequently, is capable of withstanding extreme environments. Carbon-carbon composites (CCCs) are important structural materials in future hypersonic aircraft; however, these materials may be susceptible to degradation when exposed to elevated temperatures during extreme velocities. At speeds of exceeding Mach 5, intense heating of leading edges of the aircraft triggers rapid oxidation of carbon in C… more
Date: May 2014
Creator: Sondhi, Anchal
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Exploring the Synergistic Effects of MXene-based Nanocomposites for Superlubricity and Friction/Wear Reduction on Rough Steel Surfaces

Description: The aim of this thesis is to advance the field of solid lubrication science by developing coatings that provide reliable performance in ambient conditions, work on rough surfaces, and are amenable to industrial size and design complexities. Two different coating systems, Ti3C2Tx-MoS2 and Ti3C2Tx-Graphene Oxide blends, were studied in this work. The Ti3C2Tx-MoS2 nanocomposites were spray-coated onto rough 52100-grade steel surfaces, and their tribological performance was evaluated in a ball-on-d… more
Date: July 2023
Creator: Macknojia, Ali Zayaan
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Next Generation Friction Stir Welding Tools for High Temperature Materials

Description: The historical success of friction stir welding (FSW) on materials such as aluminum and magnesium alloys is associated with the absence of melting and solidification during the solid-state process. However, commercial adoption of FSW on steels and other non-ferrous high-strength, high-temperature materials such as nickel-base and titanium-base alloys is limited due to the high costs associated with the process. In this dissertation, the feasibility of using an FSW approach to fabricate certain … more
This item is restricted from view until August 1, 2028.
Date: July 2023
Creator: Gaddam, Supreeth
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Tribocatalytically-Active Coatings for Enhanced Tribological Performance and Carbon-Based Tribofilm Formation

Description: In this study, we investigate the fundamental mechanisms defining the approach for addressing tribological challenges in mechanical systems via the use of the tribocatalytically active coating. The coating is designed using an electrodeposition process and consists of a hard amorphous cobalt-phosphorous matrix with the incorporation of tribocatalytically-active nickel and copper. Our focus is on understanding the effect of the tribocatalytic elements, Cu vs Ni, on the coating's performance in h… more
Date: July 2023
Creator: Al Sulaimi, Rawan
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
This item is restricted from view until June 1, 2024.
Date: May 2023
Creator: Mazumder, Sangram
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Laser Powder Bed Fusion of H13 Tool Steel: Experiments, Process Optimization and Microstructural Characterization

Description: This work focused on laser powder bed fusion (LPBF) of H13 tool steel to examine microstructure and melt pool morphology. Experiments were conducted with varying laser power (P) in the range of 90-180 W and scan speed (v) in the range of 500-1000 mm/s. layer thickness (l) and hatch spacing (h) were kept constant. Volumetric energy density (γ) was calculated using the above process parameters. In order to find a relation between the recorded density and top surface roughness with changing proces… more
Date: May 2023
Creator: Channa Reddy, Sumanth Kumar Reddy
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Structures of Multicomponent Silicate and Borosilicate Glasses from Molecular Dynamics Simulations: Effects of Iron Redox Ratio and Cation Field Strength

Description: Multicomponent silicate and borosilicate glasses find wide technological applications ranging from optical fibers, biomedicine to nuclear waste disposal. As a common component of earth's mantle and nuclear waste, iron is a frequent encounter in silicate and borosilicate melts and glasses. The redox ratio in glass matrix defined by the ratio of ferrous and ferric ions is dependent on factors such as temperature, pressure, and oxygen fugacity. Understanding their roles on the short- and medium-ra… more
This item is restricted from view until June 1, 2024.
Date: May 2023
Creator: Tuheen, Manzila Islam
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

The Influence of Particle Morphology and Heat Treatment on the Microstructural Evolution of Silver Inks for Additively Manufactured RF Applications: A Comparison between Nanoflake and Reactive Inks

Description: In recent years, advancements in additive manufacturing (AM) technologies have paved the way for 3D-printed flexible hybrid electronics (FHE) and created opportunities for extending these gains to RF applications. However, printed metal interconnects and devices are typically characterized by high porosity and chemical impurities that significantly limit their electrical conductivity and RF performance compared to bulk equivalents. Using direct ink writing (DIW), two silver inks, a nanoflake su… more
Date: May 2023
Creator: Summers, Jason Masao
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Small Scale Fracture Mechanisms in Alloys with Varying Microstructural Complexity

Description: Small-scale fracture behavior of four model alloy systems were investigated in the order of increasing microstructural complexity, namely: (i) a Ni-based Bulk Metallic Glass (Ni-BMG) with an isotropic amorphous microstructure; (ii) a single-phase high entropy alloy, HfTaTiVZr, with body centered cubic (BCC) microstructure; (iii) a dual-phase high entropy alloy, AlCoCrFeNi2.1, with eutectic FCC (L12) -BCC (B2) microstructure; and (iv) a Medium-Mn steel with hierarchical microstructure. The micro… more
This item is restricted from view until August 1, 2025.
Date: July 2023
Creator: Jha, Shristy
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Switchable and Memorable Adhesion of Gold-Coated Microspheres with Electrochemical Modulation

Description: Switchable adhesives using stimuli-responsive systems have many applications, including transfer printing, climbing robots, and gripping in pick and place processes. Among these adhesives, electroadhesive surface can spontaneously adjust their adhesion in response to an external electric field. However, electroadhesives usually need high voltage (e.g. kV) and the adhesion disappears upon turning off the signal. These limitations make them complicated and costly. In this research, we demonstrate… more
Date: May 2021
Creator: Wang, Jie (Materials scientist)
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

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
Partner: UNT Libraries
open access

Enhancement of Light Emission from Metal Nanoparticles Embedded Graphene Oxide

Description: A fully oxidized state of graphene behaves as a pure insulating while a pristine graphene behaves as a pure conducting. The in-between oxide state in graphene which is the controlled state of oxide behaves as a semiconducting. This is the key condition for tuning optical band gap for the better light emitting property. The controlling method of oxide in graphene structure is known as reduction which is the mixed state of sp2 and sp3 hybrid state in graphene structure. sp2 hybridized domains cor… more
Date: May 2016
Creator: Karna, Sanjay K.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Design and Manufacture of Molding Compounds for High Reliability Microelectronics in Extreme Conditions

Description: The widespread use of electronics in more avenues of consumer use is increasing. Applications range from medical instrumentation that directly can affect someone's life, down hole sensors for oil and gas, aerospace, aeronautics, and automotive electronics. The increased power density and harsh environment makes the reliability of the packaging a vital part of the reliability of the device. The increased importance of analog devices in these applications, their high voltage and high temperature … more
Date: December 2016
Creator: Garcia, Andres
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Crystallization and Lithium Ion Diffusion Mechanism in the Lithium-Aluminum-Germanium-Phosphate Glass-Ceramic Solid Electrolytes

Description: NASCION-type lithium-aluminum-germanium-phosphate (LAGP) glass-ceramic is one of the most promising solid electrolyte (SEs) material for the next generation Li-ion battery. Based on the crystallization of glass-ceramic material, the two-step heat treatment was designed to control the crystallization of Li-ion conducting crystal in the glass matrix. The results show that the LAGP crystal is preferred to internally crystalize, Tg + 60%∆T is the nucleation temperature that provides the highest ion… more
Date: May 2021
Creator: Kuo, Po Hsuen
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Self-Healing Ceramics for High Temperature Application

Description: Ceramics have a wide variety of applications due to their unique properties; however, the low fracture toughness leads the formation and propagation of unpredictable cracks, and reduces their reliability. To solve this problem, self-healing adaptive oxides were developed. The aim of the work is to gain new insights into self-healing mechanisms of ceramics and their application. Binary oxide systems were investigated that are at least partially healed through the extrinsic or intrinsic addition … more
Date: August 2021
Creator: Gu, Jingjing
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

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
Access: Restricted to UNT Community Members. Login required if off-campus.
Date: May 2019
Creator: Mondal, Barnali
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

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
Partner: UNT Libraries

The Effect of Processing Conditions on the Surface Morphology of Few-Layered WS2 Thin Films

Description: Recent progress in layered transition metal dichalcogenides (TMDs) has led to various promising electronic and optoelectronic applications. However, the structure of materials plays a critical role in electronic and optoelectronic devices, and determines performance. Electronic and optoelectronic devices typically consist of multiple layers that form electrical homojunctions or heterojunctions. Therefore, in a device it can be expected that a WS2 layer may serve as the substrate for a subseque… more
Access: Restricted to UNT Community Members. Login required if off-campus.
Date: May 2019
Creator: Cai, Bimin
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Surface Chemistry and Work Function of Irradiated and Nanoscale Thin Films Covered Indium Tin Oxides

Description: In this study, we used UV-ozone Ar sputtering, X-ray photoelectron and ultra-violet photoelectron spectroscopies and sputtering based depositions of RuO2 and Se nano-layers on indium tin oxides (ITOs). We elucidated the effect of Ar sputtering on the composition and chemistry of Sn rich ITO surface. We demonstrated that while a combination of UV-ozone radiation and Ar sputtering removes most of the hydrocarbons responsible for degrading the work function of ITO, it also removes significant amou… more
Date: May 2018
Creator: Che, Hui
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
Back to Top of Screen