Engineering Commons^™

Processing, Microstructures, And Properties Of Aluminide-Strengthened Ferritic Steels, Zhenke Teng

Doctoral Dissertations

NiAl-strengthened ferritic steel is a material of interest for steam turbine applications due to their promising creep resistance, high thermal conductivity, low cost and thermal expansion coefficient. However, there are two critical issues restricting their applications: low room temperature ductility and limited creep resistance at temperatures higher than 600°C. The reasons for these behaviors have not been fully understood, especially the processing-microstructure-property relationship has not been clearly identified.

The alloys were designed, fabricated, and processed, according to the required microstructures and properties. The matrix and precipitates can be thoroughly characterized by a combination of techniques, including atom probe tomography, neutron …

Computational And Experimental Study Of Structure-Property Relationships In Nial Precipitate-Strengthened Ferritic Superalloys, Shenyan Huang

Doctoral Dissertations

Ferritic superalloys strengthened by coherent ordered NiAl B2-type precipitates are promising candidates for ultra-supercritical steam-turbine applications, due to their superior resistance to creep, coarsening, oxidation, and steam corrosion as compared to Cr ferritic steels at high temperatures. Combined computational and experimental tools have been employed to investigate the interrelationships among the composition, microstructure, and mechanical behavior, and provide insight into deformation micromechanisms at elevated temperatures.

Self and impurity diffusivities in a body-centered-cubic (bcc) iron are calculated using first-principles methods. Calculated self and impurity diffusivities compare favorably with experimental measurements in both ferromagnetic and paramagnetic states of bcc Fe. The calculated …

Shear-Band Formation And Thermal Activation In Metallic Glasses, Lu Wang

Doctoral Dissertations

Metallic glasses (MGs) usually have high strength, high hardness and high elastic strain limit. However, the deformation mode and mechanism in metallic glasses are radically different from those in conventional crystalline materials with a long-range ordered structure. For crystalline materials, the intrinsic relationship between their mechanical properties and crystal structures has been well described by dislocation theory. In contrast, for amorphous materials, theories on the structures and controlling factors of localized shear-band formation are far from being complete.

In this thesis, shear-banding behavior of MGs under nanoindentation was first reviewed. The hardness of MGs was found to be independent on …

Micromechanical Studies Of Intergranular Strain And Lattice Misorientation Fields And Comparisons To Advanced Diffraction Measurements, Lili Zheng

Doctoral Dissertations

Inhomogeneous deformation fields arising from the grain-grain interactions in polycrystalline materials have been evaluated using a crystal plasticity finite element method and extensively compared to neutron diffraction measurements under fatigue crack growth conditions. The roles of intergranular deformation anisotropy, grain boundary damage, and non-common deformation mechanisms (such as twinning for hexagonal close packed crystals) are systematically evaluated. The lattice misorientation field can be used to determine the intragranular deformation behavior in polycrystals or to describe the deformation inhomogeneity due to dislocation plasticity in single crystals. The study of indentation-induced lattice misorientation fields in single crystals sheds lights on the understanding …

Nanoscale Metal Thin Film Dewetting Via Nanosecond Laser Melting: Understanding Instabilities And Materials Transport In Patterned Thin Films, Yueying Wu

Doctoral Dissertations

Nanoscale metal thin film dewetting via laser treatment is studied in this dissertation. The purpose is to understand: 1) the spatial and temporal nature of intrinsic instabilities; and 2) mass transportation involved in dewetting pattern evolution in metal thin films as well as in lithographically patterned nanostructures; and finally 3) to explore advanced control of metallic nanostructure fabrication via the confluence of top down nanolithography and pulsed laser induced dewetting. This study includes three sections. In first section, thin film Cu-Ni alloys ranging from 2-8nm were synthesized and laser irradiated. The evolution of the spinodal dewetting process is investigated as …

Failure Analysis Of Leaking Stainless Steel Pump Casing, Mary E. Parker

Chancellor’s Honors Program Projects

No abstract provided.

Study Of Mechanical Behaviors And Structures Of Bulk Metallic Glasses With High-Energy Synchrotron X-Ray Diffraction, Feng Jiang

Doctoral Dissertations

This dissertation addresses two critical issues in the mechanical behaviors and structures of bulk-metallic glasses (BMGs): (1) the effect of composition, fabrication method, and pretreatment of plastic deformation on mechanical properties and structures of BMGs; (2) the mechanical response and structural evolution of BMGs in the elastic and plastic region.

(Cu₅₀Zr₅₀)₉₄Al₆ and (Cu₅₀Zr₅₀)₉₂Al₈ amorphous alloys were used to study the effect of composition on mechanical properties and structures of BMGs. The (Cu₅₀Zr₅₀)₉₄Al₆ alloy exhibits lower yield stress and Young’s …

Strong Spin Orbital Coupling Effect On Magnetic Field Response Generated By Intermolecular Excited States In Organic Semiconductors, Liang Yan

Doctoral Dissertations

It has been found that non-magnetic organic semiconductors can show some magnetic responses in low magnetic field (<100 >mT). When applying magnetic field, the electroluminescence, electrical current, photocurrent, and photoluminescence could change with magnetic field, which are called magnetic field effects.

Magnetic field effects are generated through spin-dependent process affected by the internal magnetic interaction. In nonmagnetic materials, hyperfine interaction has been supposed to dominantly affect the spin-dependent process recently. But the conclusion was made in weak spin-orbital coupling organic semiconductor. The hyperfine interaction might not be the main reason responsible for magnetic field effects in strong spin-orbital coupling materials. …

Acoustic Emission And X-Ray Diffraction Techniques For The In Situ Study Of Electrochemical Energy Storage Materials, Kevin James Rhodes

Doctoral Dissertations

Current demands on lithium ion battery (LIB) technology include high capacity retention over a life time of many charge and discharge cycles. Maximizing battery longevity is still a major challenge partly due to electrode degradation as a function of repeated cycling. The intercalation of lithium ions into an active material causes the development of stress and strain in active electrode materials which can result in fracture and shifting that can in turn lead to capacity fade and eventual cell failure. The processes leading to active material degradation in cycling LIBs has been studied using a combination of acoustic emission (AE) …

Magnetic Field Dependent Electroluminescence And Charge Transport In Organic Semiconductors, Ming Shao

Doctoral Dissertations

It has been found that a small magnetic field (<300 mT) can substantial change the electroluminescence, photoluminescence, photocurrent, electrical injection current in nonmagnetic organic semiconductors. It is generally believed that these magnetic field effects (MFE) are related to the spin dependent processes in organic semiconductor. However, the origin of MFE is still not well understood. In this dissertation, we investigate the underlying mechanism for magnetic field effects on electroluminescence (MFE_EL) and magnetoresistance (MR) and demonstrate the complete tuning of MFE_EL and MR based on our theoretical understanding.

We consider MFE arising from magnetic field sensitive intersystem crossing (ISC) and triplet charge reaction. Magnetic field can increase the singlet ratios through ISC, accounting for positive MFE_EL. Magnetic field modulated ISC strongly depends on the electron-hole pair separation distance. MFE can be enhanced by increasing the electron hole pair distance through material mixing and interplaying the electric dipole-dipole interaction. Meanwhile, two possible mechanisms corresponding for negative MFE_{EL …}

Roles Of Polymer Crosslinking Density And Crystallinity In Regulating Surface Characteristics And Pre-Osteoblastic Mc3t3 Cell Behavior, Kan Wang

Doctoral Dissertations

This dissertation presents material design strategies to investigate cell-biomaterial interactions on specific biocompatible polymers and polymer blends by using mouse pre-osteoblastic MC3T3 cells aiming for potential applications in bone tissue engineering. Chapter 1 reviews some related background knowledge including polymeric biomaterials for tissue engineering, cell-biomaterial interaction, synthetic photo-crosslinkable and degradable polymers, and the effect of surface features on osteoblast cell responses. Chapter 2 presents photo-crosslinkable composites of poly(propylene fumarate) (PPF), an injectable and biodegradable polyester, and methacryl-polyhedral oligomeric silsesquioxane (mPOSS), which has eight methacryl groups tethered with a cage-like hybrid inorganic-organic nanostructure, for bone tissue engineering applications. Blending mPOSS with …

Discovery And Development Of Rare Earth Activated Binary Metal Halide Scintillators For Next Generation Radiation Detectors, Kan Yang

Doctoral Dissertations

This work focuses on discovery and development of novel binary halide scintillation materials for radiation detection applications. A complete laboratory for raw materials handling, ampoule preparation, material rapid synthesis screening, single crystal growth, sample cutting, polishing and packaging of hygroscopic halide scintillation materials has been established. Ce³⁺ and Eu²⁺ activated scintillators in three binary systems: Alkali Halide – Rare Earth Halide (AX–REX₃), Alkali Halide – Alkaline Earth Halide (AX–AEX₂) and Alkalin Earth Halide – Rare Earth Halide (AEX₂–REX₃) were systematically studied. Candidates for new scintillation materials in the three systems …

Pulsed Laser Deposition Of Boron And Boron Nitride Thin Film, Siwei Tang

Masters Theses

This thesis focuses on the preparation parameter and characterization of boron and boron nitride thin film. System is built composing of designing the geometry, substrate and target holder, pumping parts and plasma generated parts. Experiments with various conditions have been tried and the optimized condition is found for the film growth rate. Many ways of characterization includes: X-ray diffraction, Scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy have been tried to identify the material composition.

Elastic Properties Of Complex Transition Metal Oxides Studied By Resonant Ultrasound Spectroscopy, Yanbing Luan

Doctoral Dissertations

The elastic properties of novel transition metal oxides have been investigated, using a powerful technique known as Resonant Ultrasound Spectroscopy (RUS). Two sets of transition metal oxides have been studied. One is the ruthenate Ca_2-xSr_xRuO₄ series with a layered perovskite structure, a Mott transition system that connects the Mott insulator Ca₂RuO₄ with the unconventional superconductor Sr₂RuO₄. The other set contains geometrically frustrated materials, including vanadium spinels AV₂O₄ (A = Zn, Mn and Fe) and titanate pyrochlores A₂Ti₂O₇ (A= Y, Tb, …

Atomistic Modeling Of Hydrogen Storage In Nanostructured Carbons, Lujian Peng

Doctoral Dissertations

Nanoporous carbons are among the widely studied and promising materials on hydrogen storage for on-board vehicles. However, the nature of nanoporous carbon structures, as well as the relationship between local structure and hydrogen adsorption are still unclear, and hinder the design of carbon materials for optimum hydrogen storage. This dissertation presents a systematic modeling effort of hydrogen storage in nanoporous carbon materials. Tight binding molecular dynamics simulations are utilized to simulate the amorphous carbons over a wide range of density. The resulting structures are in good agreement with experimental data of ultra-microporous carbon (UMC), a wood-based activated carbon, as indicated …

Investigating Properties Of Pavement Materials Utilizing Loaded Wheel Tester (Lwt), Hao Wu

Doctoral Dissertations

Loaded wheel tester (LWT) is a common testing equipment usually used to test the permanent deformation and moisture susceptibility of asphalt mixtures by applying moving wheel loads on asphalt mixture specimens. It has been widely used in the United States since 1980s and practically each Department of Transportation or highway agency owns one or more LWT(s). Compared to other testing methods for pavement materials, LWT features movable wheel loads that allow more realistic situations existing on the actual pavement to be simulated in the laboratory. Due to its potential of creating a condition of repetitive loading, the concept of using …

Optimizing The Performance Of A Glass-Ceramic Storage Phosphor As An Imaging Plate For Medical Use, Manh Vu

Masters Theses

Europium-doped-fluorochlorozirconate glass ceramics, known as ZBLAN, were produced in a glove box which has a controlled environment of argon gas. For imaging applications BaCl₂ is used instead of BaF₂. Their properties after different thermal processing and different amounts of europium-doping were investigated. After annealing the ZBLAN glass, BaCl₂ nanoparticles are precipitated in the glass matrix. These glass ceramic storage phosphors are strong candidates for replacing traditional x-ray screen film system and commercial storage phosphors such as Agfa MD-30.

Differential scanning calorimetry (DSC) was used to determine the crystallization temperature of the hexagonal phase of BaCl_{2 …}