UNT Theses and Dissertations - 245 Matching Results

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Fractography and Mechanical Properties of Laminated Alumina and Yttria Stabilized Zirconia

Description: Yttria stabilized zirconia (YSZ) is a polymorph with possible phase transformation toughening occurring during impact. The fractography and mechanical properties of laminated alumina and YSZ were studied in this thesis. Five sample types were studied in this thesis: (5:5) Al2O3/YSZ (a sequence of 5 alumina tapes stacked on 5 YSZ tapes), (5:5) Al2O3/YSZ (1 wt.% Pure ZrO2), (7:3) Al2O3/YSZ, Al2O3, and YSZ. Scanning electron microscopy (SEM) and X-ray microscopy (XRM) were used to study morphology… more
Date: December 2021
Creator: Cotton, Shomari Johnny
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Structural and Magnetic Properties of Additively Manufactured Hiperco (FeCo-2V)

Description: The FeCo-V alloy, commercially referred to as Hiperco, is known for its great soft magnetic properties. However, the high cost of production has limited the usage of this alloy to small-scale applications, where the small volume and high magnetic performance are critical. Additive manufacturing (AM) has the potential to solve the production problems that exist in Hiperco manufacturing. The present research has focused on selective laser melting (SLM) based AM processing of Hiperco. The goal was… more
Date: December 2021
Creator: O'Donnell, Aidan James
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Self-Healing Ceramics for High Temperature Application

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

Synergistic Effects of Lattice Instability and Chemical Ordering on FCC Based Complex Concentrated Alloys

Description: The current work investigates how the interactions among constituent elements in high entropy alloys or complex concentrated alloys (HEA/CCAs) can lead to lattice instability and local chemical ordering which in turn affects the microstructure and properties of these alloys. Using binary enthalpies of mixing, the degree of ordering in concentrated multi-component solid solutions was successfully tailored by introducing Cr, Al and Ti in a CoFeNi HEA/CCA. CoFeNi was selected as the base alloy to … more
Date: August 2021
Creator: Dasari, Sriswaroop
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Defect-Engineered Two-Dimensional Transition Metal Dichalcogenides for High-Efficient Piezoelectric Sensor

Description: Piezoelectricity in two-dimensional (2D) transition metal dichalcogenides (TMDs) has attracted significant attention due to their unique crystal structure and the lack of inversion centers when the bulk TMDs thin down to monolayer. Although the piezoelectricity effect in atomic-thickness TMDs has been demonstrated, they are not scalable. Herein, we demonstrate a piezoelectric effect from large-scale, sputtered MoS2 and WS2 using a robust defect-engineering based on the thermal-solvent annealing… more
Date: May 2021
Creator: Kim, Junyoung
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

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

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

Optical Emission Spectroscopy Monitoring Method for Additively Manufactured Iron-Nickel and Other Complex Alloy Samples

Description: The method of optical emission spectroscopy has been used with Fe-Ni and other complex alloys to investigate in-situ compositional control for additive manufacturing. Although additive manufacturing of metallic alloys is an emerging technology, compositional control will be a challenge that needs to be addressed for a multitude of industries going forward for next-gen applications. This current scope of work includes analysis of ionized species generated from laser and metal powder interaction … more
Date: May 2021
Creator: Flannery, David A. (David Andrew)
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

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)
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Investigation of Porous Ceramic Structure by Freeze-Casting

Description: The design and fabrication of porous ceramic materials with anisotropic properties has, in recent years, gained popularity due to their potential application in various areas that include medical, energy, defense, space, and aerospace. Freeze-casting is an effective, low-cost, and safe method as a wet shaping technique to create these structures. To control the morphology of these materials, many critical factors were found to play an important role. In this dissertation, the processing paramet… more
Date: May 2021
Creator: Bakkar, Said Adnan
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Origin of Unusually Large Hall-Petch Strengthening Coefficients in High Entropy Alloys

Description: High entropy alloys (HEAs), also referred to as complex concentrated alloys (CCAs), are a relatively new class of alloys that have gained significant attention since 2010 due to their unique balance of properties that include high strength, ductility and excellent corrosion resistance. HEAs are usually based on five or more elements alloyed in near equimolar concentrations, and exhibit simple microstructures by the formation of solid solution phases instead of complex compounds. HEAs have great… more
Date: May 2021
Creator: Jagetia, Abhinav
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

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

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

Engineering the Uniform Lying Helical Structure in Chiral Nematic Liquid Crystal Phase: From Morphology Transition to Dimension Control

Description: Chiral nematic liquid crystals or cholesteric liquid crystals (CLC) can be obtained by adding a chiral dopant into a nematic liquid crystal. Liquid crystal molecules spontaneously rotate along a long axis to form helical structures in CLC system. Both pitch size and orientation of the helical structure is determined by the boundary conditions and can be further tuned by external stimuli. Particularly, the uniform lying helical structure of CLC has attracted intensive attention due to its beam s… more
Date: May 2021
Creator: Jia, Zhixuan
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

High Strain Rate Deformation Behavior of Single-Phase and Multi-Phase High Entropy Alloys

Description: Fundamental understanding of high strain rate deformation behavior of materials is critical in designing new alloys for wide-ranging applications including military, automobile, spacecraft, and industrial applications. High entropy alloys, consisting of multiple elements in (near) equimolar proportions, represent a new paradigm in structural alloy design providing ample opportunity for achieving excellent performance in high strain rate applications by proper selection of constituent elements a… more
Date: May 2021
Creator: Muskeri, Saideep
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Effects of Surface Texture and Porosity on the Corrosion Behavior and Biocompatibility of Pure Zinc Biomaterials for Orthopedic Applications

Description: In this dissertation, small and large NaCl particle-derived surfaces (Ra > 40 microns) were generated on 2D Zn materials, and the surfaces were carefully studied concerning topography, corrosion behavior, and bone cell compatibility. Increases in surface roughness accelerated the corrosion rate, and cell viability was maintained. This method was then extended to 3D porous scaffolds prepared by a hybrid AM/casting technique. The scaffolds displayed a near-net shape, an interconnected pore struct… more
Date: May 2021
Creator: Cockerill, Irsalan
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Tribo-Corrosion of High Entropy Alloys

Description: In this dissertation, tribo-corrosion behavior of several single-phase and multi-phase high entropy alloys were investigated. Tribo-corrosion of body centered cubic MoNbTaTiZr high entropy alloy in simulated physiological environment showed very low friction coefficient (~ 0.04), low wear rate (~ 10-8 mm3/Nm), body-temperature assisted passivation, and excellent biocompatibility with respect to stem cells and bone forming osteoblast cells. Tribo-corrosion resistance was evaluated for additively… more
Date: December 2020
Creator: Shittu, Jibril
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Processing, Pre-Aging, and Aging of NiTi-Hf (15-20 at.%) High Temperature Shape Memory Alloy from Laboratory to Industrial Scale

Description: The overarching goal of this research was to generate a menu of shape memory alloys (SMAs) actuator materials capable of meeting the demands of aerospace applications. Material requirements were recognized to meet the demand for high temperature SMAs with actuating temperatures above 85 °C and provide material options capable of performing over 100K actuation cycles. The first study is a preliminary characterization for the down selection of Ni-rich NiTiHf15 compositions chosen for a more in-de… more
Date: December 2020
Creator: Gantz, Faith
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

High Temperature Sliding Wear Behavior and Mechanisms of Cold-Sprayed Ti and Ti-TiC Composites

Description: Ti and Ti-based alloys are used in many aerospace and automotive components due to their high strength-to-weight ratio and corrosion resistance. However, room and elevated temperature wear resistance remain an issue, thus requiring some form of secondary hard phase, e.g., refractory carbides and oxides, as well as solid lubrication to mitigate wear. In this study, Ti-TiC (14, 24 and 35 vol% TiC) composite coatings were deposited on mild steel substrates using cold spray with comparisons made to… more
Date: August 2020
Creator: Koricherla, Manindra Varma
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

In-situ Analysis of the Evolution of Surfaces and Interfaces under Applied Coupled Stresses

Description: To study the effect of the substrate support on the nanoscale contact, three different regimes, i.e., graphene on rigid (ultra-crystalline diamond) and on elastic (Polydimethylsiloxane) supports and free-standing graphene, were considered. The contribution of the graphene support to the mechanical and electrical characteristics of the graphene/metal contact was studied using the conductive atomic force microscopy (AFM) technique.The results revealed that the electrical conductivity of the graph… more
Date: August 2020
Creator: Lee, Ji Hyung
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Synthesis, Phase Development, and the Mechanism for Negative Thermal Expansion in Aluminum Tungstate

Description: An in-depth study of Al2W3O12 negative thermal expansion (NTE) ceramic was performed, focused on synthesis, phase mappings, and the underlying mechanisms shown to be responsible for NTE. Review of the literature has shown inconsistencies in reported values of the dilatometry measured coefficients of thermal expansion, and the temperature for the known monoclinic to orthorhombic phase transition. Two synthesis techniques are introduced: an ionic-liquid non-hydrolytic sol-gel synthesis route; an… more
Date: May 2020
Creator: Rose, Kyle
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Thermo-Mechanical Processing and Advanced Charecterization of NiTi and NiTiHf Shape Memory Alloys

Description: Shape memory alloys (SMAs) represent a revolutionary class of active materials that can spontaneously generate strain based on an environmental input, such as temperature or stress. SMAs can provide potential solutions to many of today's engineering problems due to their compact form, high energy densities, and multifunctional capabilities. While many applications in the biomedical, aerospace, automotive, and defense industries have already been investigated and realized for nickel-titanium (Ni… more
Date: May 2020
Creator: Ley, Nathan A
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Nano-Manufacturing of Catalytic Amorphous Alloys

Description: In this dissertation, nano-manufacturing of amorphous alloys for electro-catalytic applications is reported and the role of chemistry and active surface area on catalytic behavior is discussed. The catalytic activity of recently developed platinum and palladium-based metallic glasses was studied using cyclic voltammetry and localized electrochemical techniques. The synergistic effect between platinum and palladium was shown for amorphous alloys containing both these elements. The mechanism for … more
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Date: December 2019
Creator: Hasannaeimi, Vahid
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Processing-Structure-Property Relationships of Reactive Spark Plasma Sintered Boron Carbide-Titanium Diboride Composites

Description: Sintering parameter effects on the microstructure of boron carbide and boron carbide/titanium diboride composites are investigated. The resulting microstructure and composition are characterized by scanning electron microscopy (SEM), x-ray microscopy (XRM) and x-ray diffraction (XRD). Starting powder size distribution effects on microstructure are present and effect the mechanical properties. Reactive spark plasma sintering introduces boron nitride (BN) intergranular films (IGF's) and their eff… more
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Date: August 2019
Creator: Lide, Hunter
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Charpy Impact Testing of Twinning Induced Plasticity and Transformation Induced Plasticity High Entropy Alloys

Description: High entropy alloys (HEAs) are a new class of solid solution alloys that contain multiple principal elements and possess excellent mechanical properties, from corrosion resistance to fatigue and wear resistance. Even more recently, twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) non-equiatomic high entropy alloys have been engineered, promising increased strength and ductility as compared to their equiatomic counterparts. However, impact and fracture resistance o… more
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Date: August 2019
Creator: Zellner, Samantha R
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Linking Enhanced Fatigue Life to Design by Modifying the Microstructure

Description: Structural material fatigue is a leading cause of failure and has motivated fatigue-resistant design to eliminate risks to human lives. Intrinsic microstructural features alter fatigue deformation mechanisms so profoundly that, essentially, fatigue properties of structural materials become deviant. With this in mind, we initiated this project to investigate the microstructural effect on fatigue behavior of potential structural high entropy alloys. With a better understanding of the effect of mi… more
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Date: August 2019
Creator: Liu, Kaimiao
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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