Non-Isothermal Laser Treatment of Fe-Si-B Metallic Glass (open access)

Non-Isothermal Laser Treatment of Fe-Si-B Metallic Glass

Metallic glasses possess attractive properties, such as high strength, good corrosion resistance, and superior soft magnetic performance. They also serve as precursors for synthesizing nanocrystalline materials. In addition, a new class of composites having crystalline phases embedded in amorphous matrix is evolving based on selective crystallization of metallic glasses. Therefore, crystallization of metallic glasses and its effects on properties has been a subject of interest. Previous investigations from our research group related to laser assisted crystallization of Fe-Si-B metallic glass (an excellent soft magnetic material by itself) showed a further improvement in soft magnetic performance. However, a fundamental understanding of crystallization and mechanical performance of laser treated metallic glass was essential from application point of view. In light of this, the current work employed an integrated experimental and computational approach to understand crystallization and its effects on tensile behavior of laser treated Fe-Si-B metallic glass. The time temperature cycles during laser treatments were predicted using a finite element thermal model. Structural changes in laser treated Fe-Si-B metallic glass including crystallization and phase evolution were investigated with the aid of X-ray diffraction, differential scanning calorimetry, resistivity measurements, and transmission electron microscopy. The mechanical behavior was evaluated by uniaxial tensile tests with …
Date: December 2017
Creator: Joshi, Sameehan Shrikant
System: The UNT Digital Library
Modeling of High Strain Rate Compression of Austenitic Shape Memory Alloys (open access)

Modeling of High Strain Rate Compression of Austenitic Shape Memory Alloys

Shape memory alloys (SMAs) exhibit the ability to absorb large dynamic loads and, therefore, are excellent candidates for structural components where impact loading is expected. Compared to the large amount of research on the shape memory effect and/or pseudoelasticity of polycrystalline SMAs under quasi-static loading conditions, studies on dynamic loading are limited. Experimental research shows an apparent difference between the quasi-static and high strain rate deformation of SMAs. Research reveals that the martensitic phase transformation is strain rate sensitive. The mechanism for the martensitic phase transformation in SMAs during high strain rate deformation is still unclear. Many of the existing high strain rate models assume that the latent heat generated during deformation contributes to the change in the stress-strain behavior during dynamic loading, which is insufficient to explain the large stress observed during phase transformation under high strain rate deformation. Meanwhile, the relationship between the phase front velocity and strain rate has been studied. In this dissertation, a new resistance to phase transformation during high strain rate deformation is discussed and the relationship between the driving force for phase transformation and phase front velocity is established. With consideration of the newly defined resistance to phase transformation, a new model for …
Date: December 2017
Creator: Yu, Hao
System: The UNT Digital Library
Effects of HALSs and Nano-ZnO Worked as UV Stabilizers of Polypropylene (open access)

Effects of HALSs and Nano-ZnO Worked as UV Stabilizers of Polypropylene

This work reports the outdoor weathering performance of ultraviolet (UV)-stabilized polypropylene (PP) products (using PP resins from Encore Wire). Different hindered amine light stabilizers (HALSs) and nano-ZnO were used to stabilize PP-film-based formulations that were exposed under UV light for 6 weeks simulating for in harsh outdoor weather of Dallas, Texas, USA in 2016. Characterization of the exposed PP film products was done in terms of mechanical and friction spectroscopic properties. The PP film formulations were divided into 15 categories based on the type of HALS and nano-ZnO incorporated. This was done to derive meaningful comparison of the various film formulations. Following exposure under UV light, the lifetimes of certain formulations were determined. On the basis of the mechanical and friction properties, it was determined that generally, the HALS or nano-ZnO stabilized PP film give better properties and if those two kinds of UV stabilizers can work together.
Date: December 2017
Creator: Lu, Xinyao
System: The UNT Digital Library
Solid Lubrication Mechanisms in Laser Deposited Nickel-titanium-carbon Metal Matrix Composites (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 friction (CoF) of ~0.1 and lower wear rates in comparison to LENS deposited pure Ni. The as deposited and tribologically worn composite has been characterized using Auger electron spectroscopy, scanning electron microscopy (SEM), X-ray diffraction, high resolution transmission electron microscopy (HRTEM) with energy dispersive spectroscopy (EDS), dual beam focused ion beam SEM (FIB/SEM) serial sectioning and Vickers micro-hardness testing. The evolution of subsurface stress states and precipitate motion during repeated sliding contact has been investigated using finite element analysis (FEA). The results of FIB/SEM serial sectioning, HRTEM, and Auger electron spectroscopy in conjunction with FEA simulations reveal that the improved tribological behavior is due to the in-situ formation of a low interfacial shear strength amorphous carbon tribofilm that is extruded to the surface via refined Ni grain boundaries.
Date: December 2012
Creator: Mogonye, Jon-Erik
System: The UNT Digital Library
Effects of Plasma, Temperature and Chemical Reactions on Porous Low Dielectric Films for Semiconductor Devices (open access)

Effects of Plasma, Temperature and Chemical Reactions on Porous Low Dielectric Films for Semiconductor Devices

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 will require k values 2.6 and below for the 45 nm device generation and beyond. The continuous decrease in device dimensions in ultra large scale integrated (ULSI) circuits have brought about the replacement of the silicon dioxide interconnect dielectric (ILD), which has a dielectric constant (k) of approximately 4.1, with low dielectric constant materials. Lowering the dielectric constant reduces the propagation delays, RC constant (R = the resistance of the metal lines; C = the line capacitance), and metal cross-talk between wires. In order to reduce the RC constants, a number of low-k materials have been studied for use as intermetal dielectrics. The k values of these dielectric materials can be lowered by replacing oxide films with carbon-based polymer films, incorporating hydrocarbon functional groups into oxide films (SiOCH …
Date: December 2010
Creator: Osei-Yiadom, Eric
System: The UNT Digital Library
Growth, Structure and Tribological Properties of Atomic Layer Deposited Lubricious Oxide Nanolaminates (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; however, these and some others mostly perform best only for a limited range of operating conditions, e.g. ambient air versus dry nitrogen and room temperature versus high temperatures. Conversely, lubricious oxides have been studied lately as good potential candidates for solid lubricants because they are thermodynamically stable and environmentally robust. Oxide surfaces are generally inert and typically do not form strong adhesive bonds like metals/alloys in tribological contacts. Typical of these oxides is ZnO. The interest in ZnO is due to its potential for utility in a variety of applications. To this end, nanolaminates of ZnO, Al2O3, ZrO2 thin films have been deposited at varying sequences and thicknesses on silicon substrates and high temperature (M50) bearing steels by atomic layer deposition (ALD). The top lubricious, nanocrystalline ZnO layer was structurally-engineered …
Date: December 2010
Creator: Mensah, Benedict Anyamesem
System: The UNT Digital Library
Microstructure Evolution in Laser Deposited Nickel-Titanium-Carbon in situ Metal Matrix Composite (open access)

Microstructure Evolution in Laser Deposited Nickel-Titanium-Carbon in situ Metal Matrix Composite

Ni/TiC metal matrix composites have been processed using the laser engineered net shaping (LENS) process. As nickel does not form an equilibrium carbide phase, addition of a strong carbide former in the form of titanium reinforces the nickel matrix resulting in a promising hybrid material for both surface engineering as well as high temperature structural applications. Changing the relative amounts of titanium and carbon in the nickel matrix, relatively low volume fraction of refined homogeneously distributed carbide precipitates, formation of in-situ carbide precipitates and the microstructural changes are investigated. The composites have been characterized in detail using x-ray diffraction, scanning electron microscopy (including energy dispersive spectroscopy (XEDS) mapping and electron backscatter diffraction (EBSD)), Auger electron spectroscopy, and transmission (including high resolution) electron microscopy. Both primary and eutectic titanium carbides, observed in this composite, exhibited the fcc-TiC structure (NaCl-type). Details of the orientation relationship between Ni and TiC have been studied using SEM-EBSD and high resolution TEM. The results of micro-hardness and tribology tests indicate that these composites have a relatively high hardness and a steady-state friction coefficient of ~0.5, both of which are improvements in comparison to LENS deposited pure Ni.
Date: December 2010
Creator: Gopagoni, Sundeep
System: The UNT Digital Library
Dynamic Precipitation of Second Phase Under Deformed Condition in Mg-nd Based Alloy (open access)

Dynamic Precipitation of Second Phase Under Deformed Condition in Mg-nd Based Alloy

Magnesium alloys are the lightweight structural materials with high strength to weigh ratio that permits their application in fuel economy sensitive automobile industries. Among the several flavors of of Mg-alloys, precipitation hardenable Mg-rare earth (RE) based alloys have shown good potential due to their favorable creep resistance within a wide window of operating temperatures ranging from 150°C to 300°C. A key aspect of Mg-RE alloys is the presence of precipitate phases that leads to strengthening of such alloys. Several notable works, in literature, have been done to examine the formation of such precipitate phases. However, there are very few studies that evaluated the effect stress induced deformation on the precipitation in Mg-RE alloys. Therefore, the objective of this work is to examine influence of deformation on the precipitation of Mg-Nd based alloys. To address this problem, precipitation in two Mg-Nd based alloys, subjected to two different deformation conditions, and was examined via transmission electron microscopy (TEM) and atom probe tomography (APT). In first deformation condition, Md-2.6wt%Nd alloy was subjected to creep deformation (90MPa / 177ºC) to failure. Effect of stress-induced deformation was examined by comparing and contrasting with precipitation in non-creep tested specimens subjected to isothermal annealing (at 177ºC). In …
Date: December 2013
Creator: Dendge, Nilesh Bajirao
System: The UNT Digital Library
Tribological Behavior of Spark Plasma Sintered Tic/graphite/nickel Composites and Cobalt Alloys (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 a nickel matrix for fracture toughness, TiC for hardness and graphite for solid/self‐lubrication. An in‐situ reaction during processing resulted in the formation of TiC from elemental Ti and C powders. The composition was varied to determine its effects on tribological behavior. Stellite 21, a cobalt‐chrome‐molybdenum alloy, was also produced by SPS. Stellite 21 has low stacking fault energy and a hexagonal phase which forms during sliding that both contribute to low interfacial shear and friction. Samples were investigated by x‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x‐ray spectroscopy (EDS), and electron back‐scattered diffraction (EBSD). Tribological properties were characterized by pin on disc tribometry and wear rates were determined by profilometry and abrasion testing. Solid/self‐lubrication in the TiC/C/Ni system was investigated by Raman and Auger …
Date: December 2013
Creator: Kinkenon, Douglas
System: The UNT Digital Library
Laser Surface Modification on Az31b Mg Alloy for Bio-wettability (open access)

Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Laser surface modification of AZ31B Magnesium alloy changes surface composition and roughness to provide improved surface bio-wettability. Laser processing resulted in phase transformation and grain refinement due to rapid quenching effect. Furthermore, instantaneous heating and vaporization resulted in removal of material, leading the textured surface generation. A study was conducted on a continuum-wave diode-pumped ytterbium laser to create multiple tracks for determining the resulting bio-wettability. Five different laser input powers were processed on Mg alloy, and then examined by XRD, SEM, optical profilometer, and contact angle measurement. A finite element based heat transfer model was developed using COMSOL multi-physics package to predict the temperature evolution during laser processing. The thermal histories predicted by the model are used to evaluate the cooling rates and solidification rate and the associated changes in the microstructure. The surface energy of laser surface modification samples can be calculated by measuring the contact angle with 3 different standard liquid (D.I water, Formamide, and 1-Bromonaphthalen). The bio-wettability of the laser surface modification samples can be conducted by simulated body fluid contact angle measurement. The results of SEM, 3D morphology, XRD, and contact angle measurement show that the grain size and roughness play role for wetting behavior of …
Date: December 2013
Creator: Ho, YeeHsien
System: The UNT Digital Library
Synchrotron Radiation X-Ray Diffraction of Nickel-Titanium Shape Memory Alloy Wires During Mechanical Deformation (open access)

Synchrotron Radiation X-Ray Diffraction of Nickel-Titanium Shape Memory Alloy Wires During Mechanical Deformation

Shape memory alloys (SMAs) are a new generation material which exhibits unique nonlinear deformations due to a phase transformation which allows it to return to its original shape after removal of stress or a change in temperature. It shows a shape memory effect (martensitic condition) and pseudoelasticity (austenitic condition) properties depends on various heat treatment conditions. The reason for these properties depends on phase transformation through temperature changes or applied stress. Many technological applications of austenite SMAs involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity, but are limited due to poor fatigue life. In this thesis, I investigated two important mechanical feature to fatigue behavior in pseudoelastic NiTi SMA wires using high energy synchrotron radiation X-ray diffraction (SR-XRD). The first of these involved simple bending and the second of these involved relaxation during compression loading. Differential scanning calorimetry (DSC) was performed to identify the phase transformation temperatures. Scanning electron microscopy (SEM) images were collected for the initial condition of the NiTi SMA wires and during simple bending, SEM revealed that micro-cracks in compression regions of the wire propagate with increasing bend angle, while tensile regions tend to not exhibit crack propagation. SR-XRD patterns were analyzed …
Date: December 2015
Creator: Zhang, Baozhuo
System: The UNT Digital Library
Improving the Long-term Performance of PVC Compositions (open access)

Improving the Long-term Performance of PVC Compositions

PVC are extensively applied in many fields, such as cables, pipes, vehicles, shoes, toys and infusion bags. Generally, plasticizers are blended with PVC to improve the ability of process in industrial production; however, the toxic plasticizers will gradually migrate to the surface of products and such a leakage results in brittleness of plasticized PVC and environmental pollution. In other words, humans are frequently exposed to the potential risks. According to previous researches, cross-linked PVC was proved that it was able to hinder the migration of plasticizer. Thus, in this research, we selected some commercially used cross-linking agents and employed six different tests based on mechanical, tribological and microscopy analysis in order to seek the best solution against plasticizer migration. Thus, we expected to develop a cross-linked flexible PVC which performed improved long-term performance and extended lifetime.
Date: December 2016
Creator: Yang, Yu Chia
System: The UNT Digital Library
Sliding Friction and Wear Behavior of High Entropy Alloys at Room and Elevated Temperatures (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 phases, respectively. It was determined that the two HEAs Co0.5 Cr Cu0.5 Fe Ni1.5 Al Ti0.4 and Ti V Nb Cr Al exhibit an excellent balance of high hardness, low friction coefficients and wear rates compared to 440C stainless steel, a currently used bearing steel. This was attributed to their more ductile body centered cubic (BCC) solid solution phase along with the formation of tribochemical Cr oxide and Nb oxide phases, respectively, in the wear surfaces. This study provides guidelines for fabricating novel, low-friction, and wear-resistant HEAs for potential use at room and elevated temperatures, which will help reduce energy and material losses in friction and wear applications.
Date: December 2016
Creator: Kadhim, Dheyaa
System: The UNT Digital Library
Trapping of hydrogen in Hf-based high κ dielectric thin films for advanced CMOS applications. (open access)

Trapping of hydrogen in Hf-based high κ dielectric thin films for advanced CMOS applications.

In recent years, advanced high κ gate dielectrics are under serious consideration to replace SiO2 and SiON in semiconductor industry. Hafnium-based dielectrics such as hafnium oxides, oxynitrides and Hf-based silicates/nitrided silicates are emerging as some of the most promising alternatives to SiO2/SiON gate dielectrics in complementary metal oxide semiconductor (CMOS) devices. Extensive efforts have been taken to understand the effects of hydrogen impurities in semiconductors and its behavior such as incorporation, diffusion, trapping and release with the aim of controlling and using it to optimize the performance of electronic device structures. In this dissertation, a systematic study of hydrogen trapping and the role of carbon impurities in various alternate gate dielectric candidates, HfO2/Si, HfxSi1-xO2/Si, HfON/Si and HfON(C)/Si is presented. It has been shown that processing of high κ dielectrics may lead to some crystallization issues. Rutherford backscattering spectroscopy (RBS) for measuring oxygen deficiencies, elastic recoil detection analysis (ERDA) for quantifying hydrogen and nuclear reaction analysis (NRA) for quantifying carbon, X-ray diffraction (XRD) for measuring degree of crystallinity and X-ray photoelectron spectroscopy (XPS) were used to characterize these thin dielectric materials. ERDA data are used to characterize the evolution of hydrogen during annealing in hydrogen ambient in combination with preprocessing in …
Date: December 2007
Creator: Ukirde, Vaishali
System: The UNT Digital Library
Synthesis and characterization of crystalline assembly of poly Nisopropylacry-lamide)-co-acrylic acid nanoparticles. (open access)

Synthesis and characterization of crystalline assembly of poly Nisopropylacry-lamide)-co-acrylic acid nanoparticles.

In this study, crystalline poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAm-co-AAc) nanoparticle network in organic solvents was obtained by self assembling precursor particles in acetone/epichlorohydrin mixture at room temperature followed by inter-sphere crosslinking at ~98 °C. The crystals thus formed can endure solvent exchanges or large distortions under a temporary compressing force with the reoccurrence of crystalline structures. In acetone, the crystals were stable, independent of temperature, while in water crystals could change their colors upon heating or changing pH values. By passing a focused white light beam through the crystals, different colors were displayed at different observation angles, indicating typical Bragg diffraction. Shear moduli of the gel nanoparticle crystals were measured in the linear stress-yield ranges for the same gel crystals in both acetone and water. Syntheses of particles of different sizes and the relationship between particle size and the color of the gel nanoparticle networks at a constant solid content were also presented. Temperature- and pH- sensitive crystalline PNIPAm-co-AAc hydrogel was prepared using osmosis crosslinking method. Not only the typical Bragg diffraction phenomenon was observed for the hydrogel but also apparent temperature- and pH- sensitive properties were performed. The phase behavior of PNIPAm nanoparticles dispersed in water was also investigated using a …
Date: December 2004
Creator: Zhou, Bo
System: The UNT Digital Library
Low Temperature Polymeric Precursor Derived Zinc Oxide Thin Films (open access)

Low Temperature Polymeric Precursor Derived Zinc Oxide Thin Films

Zinc oxide (ZnO) is a versatile environmentally benign II-VI direct wide band gap semiconductor with several technologically plausible applications such as transparent conducting oxide in flat panel and flexible displays. Hence, ZnO thin films have to be processed below the glass transition temperatures of polymeric substrates used in flexible displays. ZnO thin films were synthesized via aqueous polymeric precursor process by different metallic salt routes using ethylene glycol, glycerol, citric acid, and ethylene diamine tetraacetic acid (EDTA) as chelating agents. ZnO thin films, derived from ethylene glycol based polymeric precursor, exhibit flower-like morphology whereas thin films derived of other precursors illustrate crack free nanocrystalline films. ZnO thin films on sapphire substrates show an increase in preferential orientation along the (002) plane with increase in annealing temperature. The polymeric precursors have also been used in fabricating maskless patterned ZnO thin films in a single step using the commercial Maskless Mesoscale Materials Deposition system.
Date: December 2006
Creator: Choppali, Uma
System: The UNT Digital Library
Study of lead sorption on magnetite at high temperatures. (open access)

Study of lead sorption on magnetite at high temperatures.

Lead's uptake on magnetite has been quantitatively evaluated in the present study at a temperature of 200°C and pH of 8.5 with lead concentrations ranging from 5 ppm to175 ppm by equilibrium adsorption isotherms. The pH independent sorption behavior suggested lead sorption due to pH independent permanent charge through weak electrostatic, non-specific attraction where cations are sorbed on the cation exchange sites. The permanent negative charge could be a consequence of lead substitution which is supported by increase in the lattice parameter values from the X-ray diffraction (XRD) results. Differential scanning calorimetry (DSC/TGA) results showed an increase of exothermic (magnetite to maghemite transformation) peak indicating substitution of lead ions due to which there is retardation in the phase transformation. Presence of outer sphere complexes and physical sorption is further supported by Fourier transformed infrared spectroscopy (FTIR). None of the results suggested chemisorption of lead on magnetite.
Date: December 2006
Creator: Paliwal, Vaishali
System: The UNT Digital Library
Micro and nano composites composed of a polymer matrix and a metal disperse phase. (open access)

Micro and nano composites composed of a polymer matrix and a metal disperse phase.

Low density polyethylene (LDPE) and Hytrel (a thermoplastic elastomer) were used as polymeric matrices in polymer + metal composites. The concentration of micrometric (Al, Ag and Ni) as well as nanometric particles (Al and Ag) was varied from 0 to 10 %. Composites were prepared by blending followed by injection molding. The resulting samples were analyzed by scanning electron microscopy (SEM) and focused ion beam (FIB) in order to determine their microstructure. Certain mechanical properties of the composites were also determined. Static and dynamic friction was measured. The scratch resistance of the specimens was determined. A study of the wear mechanisms in the samples was performed. The Al micro- and nanoparticles as well as Ni microparticles are well dispersed throughout the material while Ag micro and nanoparticles tend to form agglomerates. Generally the presence of microcomposites affects negatively the mechanical properties. For the nanoparticles, composites with a higher elastic modulus than that of the neat materials are achievable. For both micro- and nanocomposites it is feasible to lower the friction values with respective to the neat polymers. The addition of metal particles to polymers also improves the scratch resistance of the composites, particularly so for microcomposites. The inclusion of Ag …
Date: December 2007
Creator: Olea Mejia, Oscar Fernando
System: The UNT Digital Library
Supercritical CO2 foamed biodegradable polymer blends of polycaprolactone and Mater-Bi. (open access)

Supercritical CO2 foamed biodegradable polymer blends of polycaprolactone and Mater-Bi.

Supercritical CO2 foam processing of biopolymers represents a green processing route to environmentally friendly media and packaging foams. Mater-Bi, a multiconstituent biopolymer of polyester, starch and vegetable oils has shown much promise for biodegradation. The polymer, however, is not foamable with CO2 so blended with another polymer which is. Polycaprolactone is a biopolymer with potential of 4000% change in volume with CO2. Thus we investigate blends of Mater-Bi (MB) and polycaprolactone (PCL) foamed in supercritical CO2 using the batch process. Characterization of the foamed and unfoamed samples were done using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Micrographs of the samples from the SEM revealed that the cell size of the foams reduced and increased with increase in MB concentration and increase in the foaming temperature respectively. Mechanical tests; tensile, compression, shear and impact were performed on the foamed samples. It was noted that between the 20-25% wt. MB, there was an improvement in the mechanical properties. This suggests that at these compositions, there is a high interaction between PCL and MB at the molecular level compared to other compositions. The results indicate that green processing of polymer blends is viable.
Date: December 2007
Creator: Ogunsona, Emmanuel Olusegun
System: The UNT Digital Library
Long Term Property Prediction of Polyethylene Nanocomposites (open access)

Long Term Property Prediction of Polyethylene Nanocomposites

The amorphous fraction of semicrystalline polymers has long been thought to be a significant contributor to creep deformation. In polyethylene (PE) nanocomposites, the semicrystalline nature of the maleated PE compatibilizer leads to a limited ability to separate the role of the PE in the nanocomposite properties. This dissertation investigates blown films of linear low-density polyethylene (LLDPE) and its nanocomposites with montmorillonite-layered silicate (MLS). Addition of an amorphous ethylene propylene copolymer grafted maleic anhydride (amEP) was utilized to enhance the interaction between the PE and the MLS. The amorphous nature of the compatibilizer was used to differentiate the effect of the different components of the nanocomposites; namely the matrix, the filler, and the compatibilizer on the overall properties. Tensile test results of the nanocomposites indicate that the addition of amEP and MLS separately and together produces a synergistic effect on the mechanical properties of the neat PE Thermal transitions were analyzed using differential scanning calorimetry (DSC) to determine if the observed improvement in mechanical properties is related to changes in crystallinity. The effect of dispersion of the MLS in the matrix was investigated by using a combination of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Mechanical measurements were correlated to …
Date: December 2008
Creator: Shaito, Ali Al-Abed
System: The UNT Digital Library
Structure and Low-temperature Tribology of Lubricious Nanocrystalline ZnO/Al2O3  Nanolaminates and ZrO2 Monofilms Grown by Atomic Layer Deposition (open access)

Structure and Low-temperature Tribology of Lubricious Nanocrystalline ZnO/Al2O3 Nanolaminates and ZrO2 Monofilms Grown by Atomic Layer Deposition

Currently available solid lubricants only perform well under a limited range of environmental conditions. Unlike them, oxides are thermodynamically stable and relatively inert over a broad range of temperatures and environments. However, conventional oxides are brittle at normal temperatures; exhibiting significant plasticity only at high temperatures (>0.5Tmelting). This prevents oxides' use in tribological applications at low temperatures. If oxides can be made lubricious at low temperatures, they would be excellent solid lubricants for a wide range of conditions. Atomic layer deposition (ALD) is a growth technique capable of depositing highly uniform and conformal films in challenging applications that have buried surfaces and high-aspect-ratio features such as microelectromechanical (MEMS) devices where the need for robust solid lubricants is sometimes necessary. This dissertation investigates the surface and subsurface characteristics of ALD-grown ZnO/Al2O3 nanolaminates and ZrO2 monofilms before and after sliding at room temperature. Significant enhancement in friction and wear performance was observed for some films. HRSEM/FIB, HRTEM and ancillary techniques (i.e. SAED, EELS) were used to determine the mechanisms responsible for this enhancement. Contributory characteristics and energy dissipation modes were identified that promote low-temperature lubricity in both material systems.
Date: December 2008
Creator: Romanes, Maia Castillo
System: The UNT Digital Library
Determining the Emissivity of Roofing Samples: Asphalt, Ceramic and Coated Cedar (open access)

Determining the Emissivity of Roofing Samples: Asphalt, Ceramic and Coated Cedar

The goal is to perform heat measurements examine of selected roofing material samples. Those roofing materials are asphalt shingles, ceramics, and cedar. It’s important to understand the concept of heat transfer, which consists of conduction, convection, and radiation. Research work was reviewed on different infrared devices to see which one would be suitable for conducting my experiment. In this experiment, the main focus was on a specific property of radiation. That property is the emissivity, which is the amount of heat a material is able to radiate compared to a blackbody. An infrared measuring device, such as the infrared camera was used to determine the emissivity of each sample by using a measurement formula consisting of certain equations. These equations account for the emissivity, transmittance of heat through the atmosphere and temperatures of the samples, atmosphere and background. The experiment verifies how reasonable the data is compared to values in the emissivity table. A blackbody method such as electrical black tape was applied to help generate the correct data. With this data obtained, the emissivity was examined to understand what factors and parameters affect this property of the materials. This experiment was conducted using a suitable heat source to heat …
Date: December 2015
Creator: Adesanya, Oludamilola
System: The UNT Digital Library
Anisotropic Nature of Radially Strained Metal Tubes (open access)

Anisotropic Nature of Radially Strained Metal Tubes

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 event could cost the owners and their customers millions of dollars in clean up, repair, and lost time, in addition to the potential environmental damage. Therefore, a reliable way of estimating the burst and collapse strength of strained pipe is desired and valuable. The sponsor currently rates strained pipes using the properties of raw steel, because those properties are easily measured (for example, yield strength). In the past, the engineers assumed that the metal would be work-hardened when swaged, so that yield strength would increase. However, swaging introduces anisotropic strain, which may decrease the yield strength. This study measured the yield strength of strained material in the transverse and axial direction and compared them to raw material, to determine …
Date: December 2015
Creator: Strickland, Julie N.
System: The UNT Digital Library
An Initial Study of Binary and Ternary Ti-based Alloys Manufactured Using Laser Engineered Net Shaping (LENSTM) (open access)

An Initial Study of Binary and Ternary Ti-based Alloys Manufactured Using Laser Engineered Net Shaping (LENSTM)

In this study an initial assessment of the composition – microstructure – property relationships in binary and ternary Ti – based systems are made possible using LENSTM technology. Laser Engineering Net Shaping (LENSTM), a rapid prototyping, directed laser deposition methodology of additive manufacturing (AM) was used to create bulk homogenous specimens that are compositionally graded. Compositionally graded specimens were made possible by incorporating elemental blends of powder during the LENSTM process. While there have been numerous studies assessing the influence of common elements (e.g., V, Mo, Al, and Cr) on the resulting microstructure in titanium alloys, other elements have been neglected. A systematic study of the Ti – Fe – Al ternary system based upon varying compositions of the eutectoid former, Fe with Al to stabilize the a and b phases respectively has also been neglected. This research effort focuses on exploiting the LENSTM process by rapidly assessing the composition – microstructure – property relationships in a combinatorial approach for the Ti – W, Ti – Fe, and Ti – Fe – Al systems. Compositionally graded specimens of Ti – xW (0<x<40wt.%(14.79at.%)), Ti – xFe (0<x<35wt.%(36.37at.%)), and Ti – xFe – yAl (0<x<40wt.%(36.37at.%)), y=5,10, 15wt.%) have been heat treated to …
Date: December 2015
Creator: Gray, Alyn M.
System: The UNT Digital Library