UNT Theses and Dissertations - 137 Matching Results

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Thermodynamics, Kinetics and Mechanical Behavior of Model Metallic Glasses

Description: The thermophysical properties and deformation behavior of a systematic series of model metallic glasses was investigated. For Zr-based metallic glasses with all metallic constituents, the activation energy of glass transition was determined to be in the range of 74-173 kJ/mol while the activation energy of crystallization was in the range of 155-170 kJ/mol. The reduced glass transition temperature was roughly the same for all the alloys (~ 0.6) while the supercooled liquid region was in the ran… more
This item is restricted from view until January 1, 2026.
Date: December 2023
Creator: Akhtar, Mst Alpona
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Small Scale Fracture Mechanisms in Alloys with Varying Microstructural Complexity

Description: Small-scale fracture behavior of four model alloy systems were investigated in the order of increasing microstructural complexity, namely: (i) a Ni-based Bulk Metallic Glass (Ni-BMG) with an isotropic amorphous microstructure; (ii) a single-phase high entropy alloy, HfTaTiVZr, with body centered cubic (BCC) microstructure; (iii) a dual-phase high entropy alloy, AlCoCrFeNi2.1, with eutectic FCC (L12) -BCC (B2) microstructure; and (iv) a Medium-Mn steel with hierarchical microstructure. The micro… more
This item is restricted from view until August 1, 2025.
Date: July 2023
Creator: Jha, Shristy
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Next Generation Friction Stir Welding Tools for High Temperature Materials

Description: The historical success of friction stir welding (FSW) on materials such as aluminum and magnesium alloys is associated with the absence of melting and solidification during the solid-state process. However, commercial adoption of FSW on steels and other non-ferrous high-strength, high-temperature materials such as nickel-base and titanium-base alloys is limited due to the high costs associated with the process. In this dissertation, the feasibility of using an FSW approach to fabricate certain … more
This item is restricted from view until August 1, 2028.
Date: July 2023
Creator: Gaddam, Supreeth
Item Type: Refine your search to only Thesis or Dissertation
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Electrochemical Behavior of Catalytic Metallic Glasses

Description: Metallic Glasses are multi-component alloys with disordered atomic structures and unique and attractive properties such as ultra-high strength, soft magnetism, and excellent corrosion/wear resistance. In addition, they may be thermoplastically processed in the supercooled liquid region to desired shapes across multiple length-scales. Recently developed metallic glasses based on noble metals (such as Pt and Pd) are highly active in catalytic reactions such as hydrogen oxidation, oxygen reduction… more
This item is restricted from view until August 1, 2025.
Date: July 2023
Creator: Mahajan, Chaitanya
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Structures of Multicomponent Silicate and Borosilicate Glasses from Molecular Dynamics Simulations: Effects of Iron Redox Ratio and Cation Field Strength

Description: Multicomponent silicate and borosilicate glasses find wide technological applications ranging from optical fibers, biomedicine to nuclear waste disposal. As a common component of earth's mantle and nuclear waste, iron is a frequent encounter in silicate and borosilicate melts and glasses. The redox ratio in glass matrix defined by the ratio of ferrous and ferric ions is dependent on factors such as temperature, pressure, and oxygen fugacity. Understanding their roles on the short- and medium-ra… more
This item is restricted from view until June 1, 2024.
Date: May 2023
Creator: Tuheen, Manzila Islam
Item Type: Refine your search to only Thesis or Dissertation
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In-situ Electrochemical Surface Engineering in Additively Manufactured CoCrMo for Enhanced Biocompatibility

Description: Laser-based additive manufacturing is inherently associated with extreme, unprecedented, and rapid thermokinetics which impact the microstructural evolution in a built component. Such a unique, near to non-equilibrium microstructure/phase evolution in laser additively manufactured metallic components impact their properties in engineering application. In light of this, the present work investigates the unique microstructural traits as a result of process induced spatial and temporal variation i… more
This item is restricted from view until June 1, 2024.
Date: May 2023
Creator: Mazumder, Sangram
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
open access

Developing Modern Atom Probe Tomography for Nonmetals

Description: Atom probe tomography as a 3D atomic-scale characterization tool has seen considerable development in the past decade, both in systems improvement and theoretical understanding. However, the time and expertise required from the outset of experimentation to analyzed results is highly asymmetric between metals and nonmetals. For complex oxides, this difficulty can be exemplified by GdBa2Cu3O7-x based high-temperature superconducting coated conductors. The objective of this dissertation is to furt… more
Date: December 2022
Creator: Smith, Jesse Daniel
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Processing-Structure-Property Correlation for Additively Manufactured Metastable High Entropy Alloy

Description: In the present study both fusion based - laser powder bed fusion (LPBF), and solid state - additive friction stir deposition (AFSD) additive manufacturing processes were employed for the manufacturing of a metastable high entropy alloy (HEA), Fe40Mn20Co20Cr15Si5 (CS-HEA). A processing window was developed for the LPBF and AFSD processings of CS-HEA. In case of LPBF, formation of solidification related defects such as lack of fusion pores (for energy density ≤ 31.24 J/mm3) and keyhole pores (for… more
Date: August 2022
Creator: Agrawal, Priyanshi
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Microstructure Evolution and Mechanical Response of Material by Friction Stir Processing and Modeling

Description: In this study, we have investigated the relationship between the process-microstructure to predict and modify the material's properties. Understanding these relationships allows the identification and correction of processing deficiencies when the desired properties are not achieved, depending on the microstructure. Hence, the co-relation between process-microstructure-properties helped reduce the number of experiments, materials & tool costs and saved much time. In the case of high entropy all… more
Date: August 2022
Creator: Gupta, Sanya
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Photophysical Interactions in Vapor Synthesized and Mechanically Exfoliated Two-Dimensional Conducting Crystallites for Quantum and Optical Sensing

Description: In the first study, superconducting 2D NbSe₂ was examined towards its prototypical demonstration as a transition-edge sensor, where photoexcitation caused a thermodynamic phase transition in NbSe₂ from the superconducting state to the normal state. The efficacy of the optical absorption was found to depend on the wavelength of the incoming radiation used, which ranged from the ultra-violet (405 nm), visible (660 nm), to the infrared (1060 nm). In the second case involving WSe₂, the UV-ozone tr… more
This item is restricted from view until September 1, 2024.
Date: August 2022
Creator: Jayanand, Kishan
Item Type: Refine your search to only Thesis or Dissertation
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Time-Dependent Deformation Mechanisms in Metallic Glasses as a Function of Their Structural State

Description: In this study, the time-dependent deformation behavior of several model bulk metallic glasses (BMGs) was studied. The BMGs were obtained in different structural states by thermal relaxation below their glass transition temperature, cryogenic thermal cycling, and chemical rejuvenation by micro-alloying. The creep behavior of Zr52.5Ti5Cu17.9Ni14.6Al10 BMG in different structural states was investigated as a function of peak load and temperature. The creep strain rate sensitivity (SRS) indicated a… more
This item is restricted from view until June 1, 2024.
Date: May 2022
Creator: Ghodki, Nandita
Item Type: Refine your search to only Thesis or Dissertation
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open access

Fabrication of the Novel Asymmetric Polymeric Materials via Bottom-Up Approach

Description: Asymmetric polymeric materials can be formed by either top-down or bottom-up methods. Bottom-up methods involve assembling the atoms and molecules to form small nanostructures by carefully controlled synthesis, which results in a reduction of some of the top-down limitations. In this dissertation, thermal, tribological and antireflective properties of polymeric materials have been enhanced by introducing structural asymmetry. The overall performance of commercial polymeric coatings, e.g. epoxy … more
Date: May 2022
Creator: Hnatchuk, Nataliia
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Corrosion Behavior of High Entropy Alloys in Molten Chloride and Molten Fluoride Salts

Description: High entropy alloys (HEAs) or complex concentrated alloys (CCAs) represent a new paradigm in structural alloy design. Molten salt corrosion behavior was studied for single-phase HEAs such as TaTiVWZr and HfTaTiVZr, and multi-phase HEAs such as AlCoCrFeNi2.1. De-alloying with porosity formation along the exposed surface and fluxing of unstable oxides were found to be primary corrosion mechanisms. Potentiodynamic polarization study was combined with systematic mass–loss study for TaTiVWZr, HfTaT… more
This item is restricted from view until June 1, 2024.
Date: May 2022
Creator: Patel, Kunjalkumar Babubhai
Item Type: Refine your search to only Thesis or Dissertation
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Integration, Stability, and Doping of Mono-Elemental and Binary Transition Metal Dichalcogenide Van der Waals Solids for Electronics and Sensing Devices

Description: In this work, we have explored 2D semiconducting transition metal dichalcogenides (TMDs), black phosphorus (BP), and graphene for various applications using liquid and mechanical exfoliation routes. The topical areas of interest that motivate our work include considering factors such as device integration, stability, doping, and the effect of gasses to modulate the electronic transport characteristics of the underlying 2D materials. In the first area, we have integrated solution-processed trans… more
This item is restricted from view until June 1, 2024.
Date: May 2022
Creator: Mehta, Ravindra K
Item Type: Refine your search to only Thesis or Dissertation
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open access

Characterization and Chemical Analysis of Fundamental Components for Lead Acid Batteries

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

Mechanically Driven Reconstruction of Materials at Sliding Interfaces to Control Wear

Description: To minimize global carbon emissions, having efficient jet engines and internal combustion engines necessitates utilizing lightweight alloys such as Al, Ti, and Mg-based alloys. Because of their remarkable strength/weight ratio, these alloys have received a lot of attention. Nonetheless, they have very poor tribological behavior, particularly at elevated temperatures beyond 200 °C, when most liquid lubricants begin to fail in lubrication. Over the last two decades, there has been a lot of intere… more
Date: May 2022
Creator: Shirani, Asghar
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Considerations in Designing Alloys for Laser-Powder Bed Fusion Additive Manufacturing

Description: This work identifies alloy terminal freezing range, columnar growth, grain coarsening, liquid availability towards the terminal stage of solidification, and segregation towards boundaries as primary factors affecting the hot-cracking susceptibility of fusion-based additive manufacturing (F-BAM) processed alloys. Additionally, an integrated computational materials engineering (ICME)-based approach has been formulated to design novel Al alloys, and high entropy alloys for F-BAM processing. The IC… more
This item is restricted from view until June 1, 2027.
Date: May 2022
Creator: Thapliyal, Saket
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

Tuning of Microstructure and Mechanical Properties in Additively Manufactured Metastable Beta Titanium Alloys

Description: The results from this study, on a few commercial and model metastable beta titanium alloys, indicate that the growth restriction factor (GRF) model fails to interpret the grain growth behavior in the additively manufactured alloys. In lieu of this, an approach based on the classical nucleation theory of solidification incorporating the freezing range has been proposed for the first time to rationalize the experimental observations. Beta titanium alloys with a larger solidification range (liquid… more
This item is restricted from view until June 1, 2024.
Date: May 2022
Creator: Nartu, Mohan Sai Kiran Kumar Yadav
Item Type: Refine your search to only Thesis or Dissertation
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Wear, Friction and High Shear Strain Deformation of Metallic Glasses

Description: In this work, wear and scratch behavior of four different bulk metallic glasses (BMGs) namely Zr41.2Cu12.5Ni10Ti13.8Be22.5 (LM 1), Zr57Cu15.4Ni12.6Al10Nb5 (LM 106), Ni60Pd20P17B3 (Ni-BMG), and Pt57.5Cu14.7Ni5.3P22.5 (Pt-BMG) were compared. Shear band formation on the edges of the scratch groove with spallation was found to be the primary failure mechanism in progressive scratch tests. The wear behavior and the scratch response of model binary Ni-P metallic glasses was systematically studied as … more
This item is restricted from view until June 1, 2024.
Date: May 2022
Creator: Pole, Mayur
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open access

Unraveling the Effect of Atomic Configurations and Structural Statistics on Mechanical Behavior of Multicomponent and Amorphous Alloys

Description: Multicomponent high-entropy and amorphous alloys represent relatively new classes of structural materials with complex atomic configurations and exceptional mechanical properties. However, there are several knowledge gaps in the relationships between their atomic structure and mechanical properties. Understanding these critical relationships will enable novel alloy design and tailoring of their mechanical properties for desired engineering applications. In this dissertation, first-principles ca… more
Date: December 2021
Creator: Yang, Yu Chia
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Materials Approaches for Transparent Electronics

Description: This dissertation tested the hypothesis that energy transferred from a plasma or plume can be used to optimize the structure, chemistry, topography, optical and electrical properties of pulsed laser deposited and sputtered thin-films of ZnO, a-BOxNy, and few layer 2H-WS2 for transparent electronics devices fabricated without substrate heating or with low substrate heating. Thus, the approach would be compatible with low-temperature, flexible/bendable substrates. Proof of this concept was demons… more
Date: December 2021
Creator: Iheomamere, Chukwudi E.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries

First Principles Study of the Effect of Local Bonding on Diffusion Mechanisms in Alloys

Description: This work demonstrates how local, randomized tailoring of bond stiffness can affect the activation energy of diffusion in model alloys using density functional theory-based computations. This work is organized into two parts. The first part deals with the vacancy diffusion mechanism, and it compares the in–plane (IP) vs out-of-plane (OOP) diffusion paths in prototypical binary Mg-X (Ca, Y, and Gd) and ternary Mg-X (Ca, Y, and Gd)-Zn alloys. We examine how vacancy formation, migration, and solut… more
Date: December 2021
Creator: Paranjape, Priyanvada Madhukar
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Partner: UNT Libraries
open access

Thermokinetics-Dependent Microstructural Evolution and Material Response in Laser-Based Additive Manufacturing

Description: Laser-based additive manufacturing offers a high degree of thermokinetic flexibility that has implications on the structure and properties of the fabricated component. However, to exploit the flexibility of this process, it is imperative to understand the process-inherent thermokinetic evolution and its effect on the material characteristics. In view of this, the present work establishes a fundamental understanding of the spatiotemporal variation of thermokinetics during the fabrication of the … more
Date: December 2021
Creator: Pantawane, Mangesh V
Item Type: Refine your search to only Thesis or Dissertation
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Advanced Cathodes for High Energy Density Lithium Sulfur Battery

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