Engineering Commons^™

Friction Stir Processing Of Laser Metal Deposited Ti-6al-4v, Romy Francis

Masters Theses

"Laser metal deposition (LMD) can form near net shaped components for aerospace applications. Ti-6Al-4V is a widely used aerospace alloy and fabrication of this alloy using LMD is gaining popularity. Improved mechanical properties are always a requirement in aerospace alloys and research is constantly being conducted to improve the properties of components formed from this alloy. Friction Stir Processing (FSP) in the past has been used as a method to change the surface properties of materials through microstructural modifications. The changes in properties can include hardness, corrosion resistance, fatigue strength, etc. The first section of this thesis is based on …

Synthesis Of Surface Composites Using Friction Stir Processing, Bharat Gattu

Masters Theses

"Composite materials have an edge over monolithic materials due to higher strength/stiffness - to - density ratios, improved fatigue and wear resistance and better high temperature properties. Surface composites provide improved tribological properties such as wear resistance, friction coefficient and corrosion resistance. Friction stir processing (FSP) which originated from friction stir welding (FSW - a method for joining aluminum alloys) is a solid state technique to modify the microstructure of the alloys. During FSP the frictional heat generated at the tool - work piece interface plasticizes the material allowing it to flow around the pin. The combined effect of the …

Investment Shell Cracking, Edward A. Druschitz

Masters Theses

"Shell cracking is the single greatest problem affecting investment casters. A clearer understanding of the factors affecting the melt profile of the wax can be gained using computational fluid dynamics (CFD) to model the interaction among 1) the thermal conductivity of the wax, 2) the thermal conductivity of the shell, and 3) the temperature of the autoclave during the autoclave de-waxing cycle. The most favorable melt profile results from a high autoclave temperature (438⁰K to 458⁰K) and saturated thermal conductivity of the shell (1.36 to 1.40 Wm⁻¹k⁻¹) in conjunction with a low wax thermal conductivity (0.33 Wm⁻¹k⁻¹). These parameters reduce …

Fatigue Of Friction Stir Welded Lap Joints With Sealants, Kenneth Doering

Masters Theses

"A lack of understanding of corrosion fatigue in friction stir welded aluminum joints prevents friction stir welding from being implemented in aerospace applications. Fatigue testing reveals a 60-75% reduction in the fatigue life of friction stir welded aluminum lap joints immersed in 3.5% NaCl solution (corrosion fatigue) compared with that of lap joints tested in ambient air. The loss in fatigue life is attributed to accelerated fatigue cracking due to hydrogen environment embrittlement. Two polymer sealant candidates are investigated: silicone rubber and nylon-11. Both sealant candidates can be applied prior to welding and seal the faying surface gaps in lap …

The Corrosion Of Ni₃Si Alloys In Sulfuric Acid, Christopher Marc Larson

Masters Theses

"Hydrogen production from water, the world's most renewable natural resource, can provide an economical and sustainable form of energy for the future. One means to achieve this is with a nuclear reactor-based sulfur-iodine (S-I) thermochemical cycle. Currently there are few materials available, other than precious metals like gold and platinum, that possess the corrosion resistance and mechanical properties required for the sulfuric acid decomposition loop of the S-I process. However, alloys based on Ni₃Si show promise to be a more affordable, corrosion resistant materials option for this technology. In this study, the corrosion behavior of NiSi₂₂ and NiSi₂₀(Nb,Ti)₃ alloys in …

Fabrication And Characterization Of Zirconium Oxide Thin Films, Vemnkata Rama Sesha Ravi Kumar Vemuri

Open Access Theses & Dissertations

Zirconium oxide (ZrO2) is an important material with a potential for a wide range of technological applications. The outstanding chemical stability, electrical and mechanical properties, high dielectric constant, and wide band gap of ZrO2 make it suitable for several industrial applications in the field of optics, electronics, magneto-electronics, and optoelectronics. ZrO2 is frequently used as a high refractive index material in multilayer optical coatings in high power laser systems. ZrO2 is employed in super plastic structural ceramics that demonstrate excellent strength and fracture toughness. ZrO2 has been considered as a promising dielectric to replace SiO2 in advanced metal oxide semiconductor …

Maxwell Garnett Rule For Dielectric Mixtures With Statistically Distributed Orientations Of Inclusions, Marina Koledintseva, Richard E. Dubroff, Robert W. Schwartz

Electrical and Computer Engineering Faculty Research & Creative Works

An analytical model of an effective permittivity of a composite taking into account statistically distributed orientations of inclusions in the form of prolate spheroids will be presented. In particular, this paper considers the normal Gaussian distribution for either zenith angle, or azimuth angle, or for both angles describing the orientation of inclusions. The model is an extension of the Maxwell Garnett (MG) mixing rule for multiphase mixtures. The resulting complex permittivity is a tensor in the general case. The formulation presented shows that the parameters of the distribution law for orientation of inclusions affect the frequency characteristics of the composites, …

Vibrational And Mechanical Properties Of 10 Mol % Sc2o3-1 Mol % Ceo2- Zro2 Electrolyte Ceramics For Solid Oxide Fuel Cells, Svetlana Lukich

Electronic Theses and Dissertations

Solid Oxide Fuel Cells (SOFCs) are emerging as a potential breakthrough energy conversion technology for clean and efficient production of electricity and heat from hydrogen and hydrocarbon fuels. Sc0.1Ce0.01ZrO2 electrolytes for Solid Oxide Fuel Cells are very promising materials because their high ionic conductivity in the intermediate temperature range 700°C-800°C. The vibration response of cubic and rhombohedral (β) 10 mol%Sc2O3 - 1 mol%CeO2 - ZrO2(Sc0.1Ce0.01ZrO2 ) both at room and high-temperatures is reported. The in-situ heating experiments and ex-situ indentation experiments were performed to characterize the vibrational behavior of these important materials. A temperature and stress-assisted phase transition from cubic …

An Analysis Of Silver Candlesticks From A Casting Point Of View: Originals, Copies, Forgeries, Jaromir Audy, Emil Evin

Research outputs pre 2011

Collecting silver artefacts has traditionally been a very popular hobby. Silver is addictive, therefore the number of potential collectors and investors appears to grow each year. Unfortunately, increases in the interest and buying potentials resulted in a number of forgeries manufactured and introduced to the open antique market. The items such as early silver candlesticks dictate a very high price, for many high quality fakes show very good appearances and matching similarities with originals. Such copies are traditionally manufactured by casting using the original items as patterns. Small details and variances in design features, position and shape of hallmarks, including …

Multicomponent Interdiffusion In Austenitic Ni-, Fe-Ni-Base Alloys And L12-Ni3al Intermetallic For High-Temperature Applications, Narayana Garimella

Electronic Theses and Dissertations

Interdiffusion in multicomponent-multiphase alloys is commonly encountered in many materials systems. The developments of multicomponent-multiphase alloys require control of microstructure through appropriate heat treatment, involving solid-state transformations, precipitation processes, and surface modification, where the interdiffusion processes play a major role. In addition, interdiffusion processes often control degradation and failure of these materials systems. Enhanced performance and reliable durability always requires a detailed understanding of interdiffusion. In this study, ternary and quaternary interdiffusion in Ni-Cr-X (X = Al, Si, Ge, Pd) at 900°C and 700°C, Fe-Ni-Cr-X (X = Si, Ge) at 900°C, and Ni3Al alloyed with Ir, Ta and Re at …

Formation Of Lyotropic Liquid Crystals Through The Self-Assembly Of Bile Acid Building Blocks, Karan Tamhane

Electronic Theses and Dissertations

Liquid crystalline materials (LCMs) have gained much popularity over the past century. The thermotropic forms of these materials have been extensively studied and employed in a range of innovative applications. The lyotropic liquid crystal systems that have been studied in the past have often been formed by the organization of natural and synthetic small molecules in solutions. In this study, we use self-assembled supramolecular structures as building blocks to fabricate lyotropic liquid crystals. We investigate the self-assembly of a naturally occurring bile acid called lithocholic acid (LCA), to form supramolecular fibrous and tubular structures in basic aqueous solutions. We control …

Electronic Properties And Microstructures Of Amorphous Sicn Ceramics Derived From Polymer Precursors, Tao Jiang

Electronic Theses and Dissertations

Polymer-derived ceramics (PDCs) are a new class of high-temperature materials synthesized by thermal decomposition of polymeric precursors. These materials possess many unique features as compared with conventional ceramics synthesized by powder metallurgy based processing. For example, PDCs are neither amorphous nor crystalline. Instead, they possess nano-domain structures. Due to the direct chemical-to-ceramic processing, PDCs can be used for making components and devices with complex shapes. Thus, understanding the properties and structures of these materials are of both fundamental and practical interest. In this work, the structures and electronic behavior of polymer-derived amorphous silicon carbonitrides (SiCNs) were investigated. The materials were …

Characterization And Aqueous Colloidal Processing Of Tungsten Nano-Powders, Zhengtao Yang

Electronic Theses and Dissertations

Extensive attention has been paid to consolidate nanoparticles into nanocrystalline components that possess better properties than their coarse-grained counterparts. Nanocrystalline monolithic tungsten (W) has been envisaged to possess better properties than coarse-grained tungsten and to improve the performance of many military components. Commercially available nano-W powders were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and Brunauer, Emmett, and Teller (BET) measurement. While the bulk of nano-W powders consisted of bcc-W as confirmed by XRD and TEM, much of their surface consisted of WO3 with traces of …

Sintering Additives For Nanocrystalline Titania And Processing Of Porous Bone Tissue Engineering Scaffolds, Arun Menon

Electronic Theses and Dissertations

Titania (Titanium dioxide, TiO2) has been researched as a promising biomaterial due to its excellent biocompatibility. However, the main limitation of titania is its poor mechanical properties which limit its use in many load-bearing applications. In this thesis report, the properties of titania were improved by doping with small quantities of MgO, ZnO and SiO2 as sintering additives. Nanocrystalline powder was selected, as it possesses outstanding properties over conventional coarse-grained powders due to reduced grain size. Nanocrystalline anatase powder of size 5-15 nm was synthesized via a simple sol-gel technique. Small quantities of dopants were introduced into pure titania powder, …

Classical Size Effect In Copper Thin Films: Impact Of Surface And Grain Boundary Scattering On Resistivity, Tik Sun

Electronic Theses and Dissertations

Surface and grain boundary electron scattering contribute significantly to resistivity as the dimensions of polycrystalline metallic conductors are reduced to, and below, the electron mean free path. A quantitative measurement of the relative contributions of surface and grain boundary scattering to resistivity is very challenging, requiring not only the preparation of suitably small conductors having independent variation of the two relevant length scales, namely, the sample critical dimension and the grain size, but also independent experimental quantification of these two length scales. In most work to date the sample grain size has been either assumed equal to conductor dimension or …

Impacting Testing Of High Temperature Ceramics Through The Use Of A Vitiated Heater For Hot And Cold Fire Collisions, Adrian Trejo

Open Access Theses & Dissertations

Material testing is a crucial step during the design process as particular materials serve as safety and life saving conditions. In this study, a MoSi2 is chosen as the target specimen to undergo impact under high temperatures. An impact apparatus is designed and constructed for the purpose of propelling alumina particles at high velocities. A nozzle using compressed nitrogen gas is used to fire the particle at the desired velocities. Due to the possibility of thermal shock occurring at higher temperatures, a separate nozzle utilizing vitiation heating is designed to fire the particle at equally higher temperatures to prove the …

Quench Factor Analysis Of Wrought And Cast Aluminum Alloys, Vishwanath Gandikota

Masters Theses

"Mechanical property variation across the cross section of heat treatable aluminum alloys is a major concern. To minimize such variation, a proper understanding of kinetic transformations and estimation of mechanical properties is required. The Jominy end quench test has been used successfully to study the effect of quench rate on the final heat treated properties of wrought and cast aluminum alloys. This test produces varying cooling rates along the length of a cylindrical sample cooled with water at one end. Jominy bars of wrought and cast aluminum alloys were solutionized, endquenched, and aged to T6 temper condition after delays of …

Oxidation Modeling By Means Of Molecular Dynamics, Chaiyod Soontrapa

UNLV Theses, Dissertations, Professional Papers, and Capstones

Oxidation modeling is normally engineered to study systems at macroscopic scales, mostly in analytical forms based on diffusion theories. The associated time scale is usually in months, days, or minutes, and the length scale is in the order of microns. In this dissertation, oxidation modeling is performed at atomistic scale with the time and length scales in picoseconds and angstroms, respectively, using molecular dynamics. Molecular dynamics simulations generate trajectories of each atom or particle in a system according to the laws of physics. Studying oxidations under the atomistic point of view can offer new insights on atomic behaviors and influencing …

Fracture Toughness, Crack-Growth-Rate And Creep Studies Of Alloy 276, Joydepp Pal

UNLV Theses, Dissertations, Professional Papers, and Capstones

Austenitic nickel-base Alloy 276 had been proposed to be a candidate structural material within the purview of the nuclear hydrogen initiative program. A mechanistic understanding of high temperature tensile deformation of this alloy has already been presented in an earlier investigation. The current investigation has been focused on the evaluation of crack-growth behavior, fracture toughness, stress-corrosion-cracking and creep deformation of this alloy as functions of different metallurgical and mechanical variables. The results of crack-growth study under cyclic loading indicate that this alloy exhibited greater cracking tendency with increasing temperature at a constant load ratio (R). However, the effect of temperature …

Tensile Strength And Failure Criterion Of Analog Lithophysal Rock, James A. Nott

UNLV Theses, Dissertations, Professional Papers, and Capstones

This project determines the tensile strength of lithophysal analog rock and presents failure criteria that can be used by geotechnical engineers to evaluate underground structures in rock. The physical and mechanical properties that are related to the failure criterion, such as porosity, compressive strength and modulus of elasticity, are also discussed. Experimental tensile tests were made using direct uniaxial and indirect Brazilian tests. Three 4-inch specimens were fabricated and tested in direct uniaxial tensile tests using Hydro-Stone TB. The results showed that the elastic tensile modulus of elasticity was within two percent of existing data for the compressive modulus of …

Study Of Corrosion Of Materials In The Sulfur-Iodine Hydrogen Production Cycle, Thao Trung Ho

UNLV Theses, Dissertations, Professional Papers, and Capstones

Hydrogen is of great interest since the availability of traditional fossil fuels is in decline. Strictly speaking, hydrogen is not a primary source of energy but is an energy carrier, since energy typically must be used from another source (electricity, natural gas, coal, etc.) to produce it. Of hydrogen production techniques, the Sulfur-Iodine thermochemical water splitting process (S-I cycle), which was proposed by General Atomics (GA), is promising with its simplicity and high efficiency. Most of the chemicals are recycled except water. However, the S-I cycle operates in a harsh, corrosive environment in the presence of a mixture of iodine …

Effects Of Mechanical And Metallurgical Variables On Creep, Fracture Toughness And Crack Growth Behavior Of Alloy 617, Muhammad Hasibul Hasan

UNLV Theses, Dissertations, Professional Papers, and Capstones

Nickel base Alloy 617 has been identified to be a suitable structural material for heat exchanger applications in both hydrogen and electricity generation using nuclear heat. A maximum operating temperature of 950°C has been specified by department of energy (DOE) for both applications to achieve a maximum possible efficiency. Therefore, an extensive investigation has been pursued to evaluate time-dependent-deformation (Creep) of this alloy as functions of temperature and applied load. The results indicate that this alloy exhibited severe creep deformation, characterized by development of an instantaneous tertiary creep region at 850 and 950°C under applied stresses corresponding to its 35% …

Spectroscopic Investigation Of Palladium-Copper Bimetallic Systems For Pem Fuel Cell Catalysts, Timo Hofmann

UNLV Theses, Dissertations, Professional Papers, and Capstones

One of the main barriers to commercialization of polymer electrolyte membrane fuel cells systems is cost, which is largely due to the need of platinum (Pt)-containing catalysts. In this thesis we investigate bimetallic systems consisting of a base metal (copper) and a noble metal (palladium) that, as an alloy on the nanoscale, mimic the electronic properties that make Pt desirable as a catalyst.

We present a detailed investigation of the electronic structure of carbon-supported Pd/Cu nanoparticle catalysts, model bilayer thin film systems, alloys, and various metal reference samples. We have investigated the valence band structure of the catalysts using a …

Morphology And Cathode Optimization For Efficient Polymer Bulk Heterojunction Solar Cells, Yi Yang

Material Science and Engineering Theses - Archive

Efficiency of polymer bulk heterojunction solar cell is highly dependent on the active layer morphology and can be controlled by specific experimental conditions. In this work, the influences of P3HT:PCBM blend composition, solution concentration, and the thermal annealing on the cell performance are presented. The maximum of Jsc and FF are reached when the weight percentage of PCBM in the blend is 60 % under which both high density of donor and accepter interfaces expecting the formation of efficient percolated electron transport paths. 36 mg/ml is found to be the optimum solution concentration for P3HT:PCBM blend and it can be …

Effect Of Aging On The Transformation Of Phases In Solder Joint Of Pbga Packaging, Jeong-Min Kim

Material Science and Engineering Theses - Archive

This study investigates the microstructural characteristics of 3.0Ag-0.5Cu-Sn (SAC305) solder joint as in assembled state, and their evolution with aging treatment at 100 and 150°C for various hours. Specific aim of the study is 1) to understand thermodynamic stability of as-reflowed microstructure (β-Sn dendrite, inner dendrite Cu6Sn5 intermetallic (IMC) compound, and the eutectic structure), 2) to find direction of their change with aging, and 3) to relate interfacial reaction to such evolution in microstructures. This investigation is spurred by the findings made in a separate study where fatigue resistance of solder joint and failure location shows markedly keen dependence on …

Structural, Magnetic And Surface Properties Of Rf Magnetron Sputtered Undoped Lanthanum Mangnite Thin Films, Varad Rajan Sakhalkar

Material Science and Engineering Theses - Archive

In the present study, polycrystalline and epitaxial undoped Lanthanum Manganite (LMO) thin films were deposited by using RF magnetron sputtering on three substrates, Si (100), MgO (100) and LaAlO₃ (100) to study the influence of the misfit strain at the substrate/film interface. The effect of processing conditions on the synthesis of LMO films was studied by conducting deposition on Si wafer. Films were characterized by X-Ray Diffraction (XRD), Atomic Force Microscope (AFM), Energy Dispersive Spectroscopy (EDS) and Superconducting Quantum Interference Device (SQUID) to investigate the influence of processing parameters on their structure and properties. Based on the initial study on …

Low-Temperature Growth Of Inn On Si(100) By Femtosecond Pulsed Laser Deposition, M. A. Hafez, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

InN films were grown on Si(100) using femtosecond pulsed laser deposition. Laser induced breakdown of ammonia was used to generate atomic nitrogen for InN growth. An indium buffer layer was initially deposited on the Si substrate at low temperature followed by an InN intermediate layer. The crystal quality and surface morphology were investigated by reflection high-energy electron diffraction during growth and atomic force microscopy and x-ray diffraction after growth. The results showed that the In (2×1) initial buffer layer improved the quality of the InN film. High quality InN films were grown at a temperature of ∼350 °C.

Yttrium And Hydrogen Superstructure And Correlation Of Lattice Expansion And Proton Conductivity In The Bazr0.9y0.1o2.95 Proton Conductor, A. Braun, A. Ovalle, V. Pomjakushin, A. Cervellino, S. Erat, Wayne C. Stolte, T. Graule

Chemistry and Biochemistry Faculty Research

Bragg reflections in Y-resonant x-ray diffractograms of BaZr_0.9Y_0.1O_2.95 (BZY10) reveal that Y is organized in a superstructure. Comparison with neutron diffraction superstructure reflections in protonated/deuterated BZY10 suggests that both superstructures are linked, and that protons move in the landscape imposed by the Y. The thermal lattice expansion decreases abruptly for protonated BZY10 at T≥648±20 K, coinciding with the onset of lateral proton diffusion and suggesting a correlation of structural changes and proton conductivity. The chemical shift in the Y L₁-shell x-ray absorption spectra reveals a reduction from Y³⁺ toward Y²⁺ upon …

The Effect Of Near-Surface Metallurgy On The Machinability Of Cast Iron, William Dewey Peach

Masters Theses

"The increasing performance and durability of cutting tool inserts have created metallurgical challenges for production foundries to produce near-net shaped castings within strict dimensional tolerances. In order for foundries to take full advantage of the increased cutting speed capabilities, it becomes necessary to reduce machining allowances and produce much more stable casting surfaces. To accomplish this, a better understanding of the complex microstructures formed within the first 0.120 in. (3 mm) of the mold/metal interface (as-cast surface) is necessary. The goal of the work presented here was to examine the microstructures formed in the near-surface region of gray iron castings, …

Friction Stir Processing Of Magnesium Alloys, Gaurav Bhargava

Masters Theses

"Magnesium alloys have been fast catching up their attention in applications where both lightweight and exceptional strength is desired. But magnesium alloys suffer formability issues which limit their use to cast applications when designing complicated shapes. Friction stir processing (FSP) is technique for, imparting a fine-grained, homogeneous microstructure by which both strength and ductility can be enhanced. The results from the first part of present work showed that AZ31 alloy when employed the use of FSP, yielded significant strength and ductility gains but on the cost of anisotropy. The cause of anisotropy was investigated to be correlated to texture evolution …