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Additive Friction Stir Deposition of Al-Ce Alloys for Improved Strength and Ductility

Description: Additive friction stir deposition (AFSD) is a solid-state additive manufacturing (AM) technique that breaks down large constituent particles into more refined and uniformly disturbed microstructure. AFSD was used to print Al-Ce alloys. Current commercial Al-alloys upon elevated temperatures go through dissolution and coarsening of strengthening precipitates causing mechanical degradation of these alloys. Al-Ce alloys do not have this issue as cerium's low solubility restricts dissolution into t… more
This item is restricted from view until January 1, 2029.
Date: December 2023
Creator: Davis, Devin Fredric
open access

Additive Manufacturing of AZ31B Magnesium Alloy via Friction Stir Deposition

Description: Additive friction stir deposition (AFSD) of AZ31B magnesium alloy was conducted to examine evolution of grain structure, phases, and crystallographic texture. AFSD was carried out using a hollow tool made from tool steel at a constant rotational velocity of 400 rpm on the AZ31B base plate. Bar stock of AZ31B was utilized as a feed material. The linear velocity of the tool was varied in the range of 4.2-6.3 mm/s. The feed rate of the material had to be maintained at a half value compared to the … more
Date: December 2021
Creator: Patil, Shreyash Manojkumar
open access

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

Advanced Cathodes for High Energy Density Lithium Sulfur Battery

Description: A systematic development of 2D alloy catalyst with synergistic performance of high lithium polysulfide (LiPS) binding energy and efficient Li+ ion/electron conduction is presented. The first section of work found that Li+ ions can flow through the percolated ion transport pathway in polycrystalline MoS2, while Na+ and K+ ions can easily flow through the percolated 1D ion channel near the grain boundaries. An unusually high ionic conductivity of extrinsic Li+, Na+, and K+ ions in 2D MoS2 film ex… more
Date: December 2021
Creator: Bhoyate, Sanket
open access

Advanced Technology for Source Drain Resistance Reduction in Nanoscale FinFETs

Description: Dual gate MOSFET structures such as FinFETs are widely regarded as the most promising option for continued scaling of silicon based transistors after 2010. This work examines key process modules that enable reduction of both device area and fin width beyond requirements for the 16nm node. Because aggressively scaled FinFET structures suffer significantly degraded device performance due to large source/drain series resistance (RS/D), several methods to mitigate RS/D such as maximizing contact … more
Date: May 2008
Creator: Smith, Casey Eben

Alloy Design, Processing and Deformation Behavior of Metastable High Entropy Alloys

Description: This dissertation presents an assortment of research aimed at understanding the composition-dependence of deformation behavior and the response to thermomechanical processing, to enable efficient design and processing of low stacking fault energy (SFE) high entropy alloy (HEAs). The deformation behavior and SFE of four low SFE HEAs were predicted and experimentally verified using electron microscopy and in-situ neutron diffraction. A new approach of employing a minimization function to refine … more
Date: May 2021
Creator: Frank, Michael (Materials science researcher)
open access

Alloy Development and High-Energy X-Ray Diffraction Studies of NiTiZr and NiTiHf High Temperature Shape Memory Alloys

Description: NiTi-based shape memory alloys (SMAs) offer a good combination of high-strength, ductility, corrosion resistance, and biocompatibility that has served them well and attracted the attention of many researchers and industries. The alloys unique thermo-mechanical ability to recover their initial shape after relatively large deformations by heating or upon unloading due to a characteristic reversible phase transformation makes them useful as damping devices, solid state actuators, couplings, etc. H… more
Date: May 2018
Creator: Carl, Matthew A
open access

Amorphization and De-vitrification in Immiscible Copper-Niobium Alloy Thin Films

Description: While amorphous phases have been reported in immiscible alloy systems, there is still some controversy regarding the reason for the stabilization of these unusual amorphous phases. Direct evidence of nanoscale phase separation within the amorphous phase forming in immiscible Cu-Nb alloy thin films using 3D atom probe tomography has been presented. This evidence clearly indicates that the nanoscale phase separation is responsible for the stabilization of the amorphous phase in such immiscible sy… more
Date: May 2007
Creator: Puthucode Balakrishnan, Anantharamakrishnan
open access

Angular Analysis of a Wide-Band Energy Harvester based on Mutually Perpendicular Vibrating Piezoelectric Beams

Description: The recent advancements in electronics and the advents of small scaled instruments has increased the attachment of life and functionality of devices to electrical power sources but at the same time granted the engineers and companies the ability to use smaller sources of power and batteries. Therefore, many scientists have tried to come up with new solutions for a power alternatives. Piezoelectric is a promising material which can readily produce continuous electric power from mechanical inputs… more
Date: December 2016
Creator: Mirzaabedini, Sohrab
open access

Anisotropic Nature of Radially Strained Metal Tubes

Description: Metal pipes are sometimes swaged by a metal cone to enlarge them, which increases the strain in the material. The amount of strain is important because it affects the burst and collapse strength. Burst strength is the amount of internal pressure that a pipe can withstand before failure, while collapse strength is the amount of external pressure that a pipe can withstand before failure. If the burst or collapse strengths are exceeded, the pipe may fracture, causing critical failure. Such an … more
Date: December 2015
Creator: Strickland, Julie N.
open access

An Assessment of Uncommon Titanium Binary Systems: Ti-Zn, Ti-Cu, and Ti-Sb

Description: The current study focuses on phase stability and evolution in the titanium-zinc titanium-copper and titanium-antimony systems. The study utilized the Laser Engineering Net Shaping (LENS™) processing technique to deposit compositionally graded samples of three binary system in order to allow the assessment of phase stability and evolution as a function of composition and temperature the material is subjected to. Through LENS™ processing it was possible to create graded samples from Ti-xSb (up … more
Date: May 2015
Creator: Brice, David
open access

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
open access

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

Description: 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
open access

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

Barrier and Long Term Creep Properties of Polymer Nanocomposites.

Description: The barrier properties and long term strength retention of polymers are of significant importance in a number of applications. Enhanced lifetime food packaging, substrates for OLED based flexible displays and long duration scientific balloons are among them. Higher material requirements in these applications drive the need for an accurate measurement system. Therefore, a new system was engineered with enhanced sensitivity and accuracy. Permeability of polymers is affected by permeant solubility… more
Access: Restricted to the UNT Community Members at a UNT Libraries Location.
Date: December 2004
Creator: Ranade, Ajit

Bio-Inspired Material Surfaces with Self-cleaning, Micromanipulation and Water Collection

Description: Geckos are famous for the skill of switchable adhesion that they use to stick on various surface while keep their fingers super clean. In the dissertation, a unique mechanism was discovered to explain gecko self-cleaning phenomena. Using atomic force microscopy (AFM), we managed to compare the microparticle-substrate adhesion and the microparticle-seta adhesion with a single seta bonded to the AFM cantilever. A dynamic effect was approved that high pulling-off speed could increase the micropart… more
Access: Restricted to UNT Community Members. Login required if off-campus.
Date: May 2019
Creator: Wan, Yiyang
open access

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.
open access

Biodegradable Poly(hydroxy Butyrate-co-valerate) Nanocomposites And Blends With Poly(butylene Adipate-co-terephthalate) For Sensor Applications

Description: The utilization of biodegradable polymers is critical for developing “cradle to cradle” mindset with ecological, social and economic consequences. Poly(hydroxy butyrate-co-valerate) (PHBV) shows significant potential for many applications with a polypropylene equivalent mechanical performance. However, it has limitations including high crystallinity, brittleness, small processing window, etc. which need to be overcome before converting them into useful products. Further the development of biode… more
Date: December 2011
Creator: Vidhate, Shailesh
open access

Bioresorbable Polymer Blend Scaffold for Tissue Engineering

Description: Tissue engineering merges the disciplines of study like cell biology, materials science, engineering and surgery to enable growth of new living tissues on scaffolding constructed from implanted polymeric materials. One of the most important aspects of tissue engineering related to material science is design of the polymer scaffolds. The polymer scaffolds needs to have some specific mechanical strength over certain period of time. In this work bioresorbable aliphatic polymers (PCL and PLLA) were… more
Date: May 2011
Creator: Manandhar, Sandeep
open access

Bulk and Interfacial Effects on Density in Polymer Nanocomposites

Description: The barrier properties of polymers are a significant factor in determining the shelf or device lifetime in polymer packaging. Nanocomposites developed from the dispersion of nanometer thick platelets into a host polymer matrix have shown much promise. The magnitude of the benefit on permeability has been different depending on the polymer investigated or the degree of dispersion of the platelet in the polymer. In this dissertation, the effect of density changes in the bulk and at the polymer-pl… more
Date: May 2007
Creator: Sahu, Laxmi Kumari

Carbon Nanotubes and Molybdenum Disulfide Protected Electrodes for High Performance Lithium-Sulfur Battery Applications

Description: Lithium-sulfur (Li-S) batteries are faced with practical drawbacks of poor cycle life and low charge efficiency which hinder their advancements. Those drawbacks are primarily caused by the intrinsic issues of the cathodes (sulfur) and the anodes (Li metal). In attempt to resolve the issues found on the cathodes, this work discusses the method to prepare a binder-free three-dimensional carbon nanotubes-sulfur (3D CNTs-S) composite cathode by a facile and a scalable approach. Here, the 3D structu… more
Access: Restricted to UNT Community Members. Login required if off-campus.
Date: August 2019
Creator: Cha, Eunho
open access

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
open access

Catalytic Properties and Mechanical Behavior of Metallic Glass Powders

Description: Lack of crystalline order and microstructural features such as grain/grain-boundary in metallic glasses results in a suite of remarkable attributes including very high strength, close to theoretical elasticity, high corrosion and wear resistance, and soft magnetic properties. By altering the morphology and tuning of composition, MGs may be transformed into high-performance catalytic materials. In this study, the catalytic properties of metallic glass powders were demonstrated in dissociating to… more
Date: May 2017
Creator: Garrison, Seth
open access

Characterization and Chemical Analysis of Fundamental Components for Lead Acid Batteries

Description: Although markets for alternative batteries, such as Li-ion, are growing, Pb-alloy batteries still dominate the market due to their low cost and good functionality. Even though these Pb-alloy batteries have been around since their discovery in 1859, little research involving advanced characterization techniques, such as synchrotron radiation X-ray diffraction (SR-XRD) and transmission electron diffraction (TEM) have been performed on Pb-alloys and sulfation, a failure mode in lead acid batteries… more
Date: May 2022
Creator: Wall, Michael T
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