Chalcogen-rich transition-metal dichalcogenide (TMD) magnetron sputtering targets were custom manufactured via ball milling and sintering in the interest of depositing p-type chalcogen-rich films. Room temperature radio frequency (RF) magnetron sputtering produced ultra-thin amorphous precursor of WSx and MoSx (where x is between 2-3) on several different substrates. The influence of working pressure on the MoS3 content of the amorphous films was explored with X-ray photoelectron spectroscopy (XPS), while the physical and chemical effects of sputtering were investigated for the WSx target itself. The amorphous precursor films with higher chalcogenide content were chosen for laser annealing, and their subsequent laser annealing induced phase transformations were investigated for the synthesis of polycrystalline 2H-phase semiconducting thin films. The role of laser fluence and the number of laser pulses during annealing on phase transformation and film mobility was determined from Raman spectroscopy and Hall effect measurement, respectively. Hall effect measurements were used to identify carrier type and track mobility between amorphous precursors and crystalline films. The p-type 2H-TMD films demonstrates the ability to produce a scalable processing criterion for quality ultra-thin TMD films on various substrates and in a method which is also compatible for flexible, stretchable, transparent, and bendable substrates.

To design high pressure fuel system components that resist wear and scuffing failure when operated in low viscosity fuels, a comprehensive study on the tribological performance of various existing coating materials is necessary. This thesis aims to provide the relative performance of a variety of coating materials across different fuel environments by testing them in conditions that model those experienced in fuel pumps. The relative performance of these coatings are then indexed across a variety of material properties, including hardness, elastic modulus, wettability, and the interaction between the surface and the various types of fuel molecules.

In this study, we observed the effects of the processing-induced method on two different shape memory alloys (SMAs). First, we compare the transformation behavior of a martensitic NiTi SMA during thermal cycling using wide angle synchrotron radiation X-ray diffraction (WAXS). Based on the thermal cycling results, three observations about processing-induced SGAs as compared to SMAs can be seen: (1) retention of distorted austenite at high and low temperatures, (2) broadening of diffraction peaks in WAXS and disappearance of the thermal peaks in DSC measurements both due to induced strain, and (3) gradual increase in the amount of the martensitic phase. Second, we applied a processing-induced method to a FeMnAlCrNi alloy to examine the possibility of forming a strain glass alloy in an Fe-based system through sufficient dislocation formation via plastic deformation. This alloy was subjected to various percentages of cold work and characterized using scanning electron microscopy, differential scanning calorimetry, Vickers hardness, WAXS data. The results indicate with 50% thickness reduction, stress-free thermal cycling no longer exhibits a measurable phase transformation, suggesting the successful formation of strain glass alloy through sufficient dislocation. The results of this research contribute significantly to the advancement of strain glass alloys (SGAs), especially with respect …

Shape memory alloys (SMAs) have gained much attention as a powerful source of actuation due to their improved performance, reduced size, and reduced complexity between components as well as having a high work output density. Their primary mechanism of actuation relies on a non-diffusional cyclic phase transformation from martensite to austenite, where the amount of thermal energy needed per cycle is directly associated with the hysteresis width between the austenite final and martensite final temperatures. Consequently, a narrower gap between those two temperature ranges requires a much lower energy demand to produce the actuation needed. Previous studies have indicated that the hysteresis width is linked to a strong coherence between the austenite/martensite interface. It has been shown that elemental additions to NiTi-based SMAs can further improve this coherency. Another huge challenge facing this unique technology is linked with its thermo-mechanical stability. Binary NiTi SMAs often exhibit significant transformation temperature shifts after each thermo-mechanical cycle, which can contribute to a shorter lifespan. The primary goal of this project is to identify and develop thermo-mechanically stable, low hysteresis shape memory alloys (LHSMAs) for actuator applications. To accomplish this goal, elemental additions of Cu, Co, Hf, and Pd were incorporated into NiTi-based SMAs …

Traditional lightweight armor ceramics such as boron carbide (B4C) and silicon carbide (SiC) are used alone or together in varying amounts to create monolithic protective plates. These materials exhibit relatively small differences in hardness, flexure strength, and fracture toughness. Many of the routes taken during the synthesis of the powder and sintering of the plates using traditional ceramic processing techniques have long processing times, tend to leave asperities within the microstructure, and have unwanted secondary phases that lower the performance of these materials. In lieu of the incremental changes in the above properties, it is thought that adding diamond particulates to the ceramic matrix will dramatically improve the mechanical properties and overall performance. With the reduced cost of synthetic diamond and the commercial development of more rapid spark plasma sintering (SPS), this work develops a novel reactive SPS process to fabricate near fully dense SiC-TiC-diamond composites at various processing temperatures with minimal graphitization and full adhesion to the ceramic matrix. It was found that samples with up to ~97% theoretical density can be fabricated with no quantifiable graphite content within the characterization ability using advanced X-ray diffraction and microscopy techniques.

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 a function of composition, with amorphous alloy formation over the narrow range of 10 at% to 20 at% phosphorus. Pulsed current electrodeposition was used to obtain these binary amorphous alloys, which offers a facile and versatile alternative to conventional melt quenching route. The electrodeposited metallic glasses (EMGs) showed hardness values in the range of 6.6-7.4 GPa, modulus in the range of 155-163 GPa, and friction coefficient around 0.50. Among the studied alloys, electrodeposited Ni80P20 showed the lowest wear rate. The wear mechanism was determined to be extensive plastic deformation along with mild ploughing, micro tears, and formation of discontinuous lubricious oxide patches. The effect of phosphorus content on the structure, mechanical properties, and the tribological response was systematically investigated for biocompatible Co-P metallic glasses. With increase in phosphorus content, there was …

Current ways to alter the microstructure of materials are usually through heat treatments, alloying, and other physical metallurgical methods. Recent efforts in the 21st century are focused on altering the microstructure of a material without physical contact which can be achieved through exposure to a magnetic field (MF). The motivation of this research is to study the quantum effects by subjecting solid-state metals to exposure of MFs. Many of the popular metals currently used in industry are paramagnetic. The ability to alter the microstructure and thus properties of these paramagnetic materials through a magnetic field would open new avenues to the field of research, including, potentially, a pollution-free, non-contact route. The effects of a magnetic field on the mechanical properties of paramagnetic materials were observed through compression testing of the pure paramagnetic material samples induced in a magnetic field. XRD and PPMS were used to relate flow stress to dislocation density and magnetic property of the samples when exposed to the presence of a static magnetic field. The effects of a magnetic field relative to alloyed paramagnetic materials were observed through the same procedure as pure paramagnetic elements. For this purpose, -Ti alloys were chosen as literature suggests a phase …

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 further establish the experimental and theoretical knowledge required to effectively, and compositionally, study nanoscale defects in nonmetals using atom probe tomography; specifically, those influencing the electromagnetic properties of RBa2Cu3O7-x high temperature superconducting coated conductors. The results from this dissertation can be applied to other complex oxides, nitrides, carbides, or other nonmetallic systems, through the creation and use of an extensive open-source Python package, APAV.

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 (liquidus minus solidus temperature) exhibited a more equiaxed grain morphology, while those with smaller solidification ranges exhibited columnar grains. Subsequently, the printability of two candidate beta titanium alloys containing eutectoid elements (Fe) that are prone to beta fleck in conventional casting, i.e., Ti-1Al-8V-5Fe (wt%) or Ti-185, and Ti-10V-2Fe-3Al (wt%) or Ti-10-2-3, is further investigated via two different AM processing routes. These alloys are used for high-strength applications in the aerospace industry, such as landing gears and fasteners. The Laser Engineered Net Shaping and Selective Laser Melting (the two AM techniques) results show that locally higher solidification rates in AM can prevent the problem of beta fleck and potentially produce β-titanium alloys with significantly enhanced mechanical properties over conventionally cast/forged counterparts. Further, the detailed investigation of microstructure-mechanical property …

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 ICME-based approach has led to heterogeneous nucleation-induced grain refinement, terminal eutectic solidification-enabled liquid availability, and segregation-induced coalescence of solidification boundaries during laser-powder bed fusion (L-PBF) processing. In addition to exhibiting a wide crack-free L-PBF processing window, the designed alloys exhibited microstructural heterogeneity and hierarchy (MHH), and thus could leverage the unique process dynamics of L-PBF to produce a fine-tunable MHH and mechanical behavior. Furthermore, alloy chemistry-based fine tuning of the stacking fault energy has led to transformative damage tolerant alloys. Such alloys can shield defects stemming from the stochastic powder bed in L-PBF, and consequently can prevent catastrophic failure despite the solidification defects. A modified materials systems approach that explicitly includes alloy chemistry as a means to modify the printability, properties and performance with F-BAM is also presented. Overall, this work is expected to facilitate application specific manufacture with …

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 transition from shear transformation zone (STZ) mediated deformation at room temperature to diffusion dominated mechanisms at high temperatures. The relaxation enthalpy of Zr47Cu46Al7 BMG was found to increase significantly with the addition of 1 at% Ti, namely for Zr47Cu45Al7Ti1. Comparison of their respective free volumes indicated that chemical rejuvenation had a more pronounced effect compared to cryogenic thermal rejuvenation. Micro-pillar compression tests supported the improved plasticity with increase in free volume from the rejuvenation effect. Effect of chemistry change on mechanical response and time-dependent deformation was investigated for topologically equivalent Pt-Pd BMGs, where the Pt atoms were systematically replaced with Pd atoms (Pt42.5-xPdx)Cu27Ni9.5P21: x=0, 7.5, 20, 22.5, 35, 42.5). The hardness and reduced modulus increased while the degree of plasticity decreased with increase in Pd-content, which was attributed to the increase in …

Magnetic field-assisted freeze-casting was used to create porous B4C ceramic preforms. An optimum slurry consisted of a mixture of B4C powders with 6 wt.% Er2O3 powder in an H2O-PVA solution and was cooled at a rate of 1 °C/min from room temperature to -30 °C resulting in porous green state ceramic preform with vertical channels. The Er2O3 powder was added to improve the magnetic response of the slurry. The preform was then sublimated to remove H2O and then sintered. The sintered ceramic preform was then infiltrated in the most vertically aligned channel direction with molten Al (A356) metal through a vacuum-assisted pump to create the metal matrix composite (MMC). Finite element analysis simulations were used to analyze and predict the anisotropic effect of B4C channel alignment on mechanical properties. The mechanical properties of the composite were then experimentally found via compression testing, which was compared with rule-of-mixtures and finite element modeling simulations, to analyze the effect of anisotropy due to magnetic field-assisted freeze-casting. This study reinforces the viability of cost-effective magnetic field-assisted freeze-casting as a method to create highly directional ceramic preforms, which can be subsequently metal infiltrated to produce MMCs with highly anisotropic toughness.

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 transparent conducting oxides (TCOs), specifically indium-doped tin oxide (ITO) with BP, which is a commonly used TCO for solar cell devices. Here we have found surface treatment of glass substrates with a plasma before spin-coating the solution-processed ITO, to be effective in improving coverage and uniformity of the ITO film by promoting wettability and film adhesion. The maximum transmittance obtained was measured to be ~75% in the visible region, while electrical measurements made on BP/ITO heterostructures showed improved transport characteristics compared to the bare ITO film. Within the integration realm, inkjet-printing of BP and MoS2 p-n hetero-junctions on standard ITO glass substrates in a vertical architecture was also demonstrated. To address the issue of stability which some 2D materials such as BP face, we experimented with ionic liquids (ILs) to passivation the …

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, with regards to thermally- and electrochemically-induced changes at the atomic and microstructural scale. Therefore, there is a need to close this scientific gap between research and the application of Pb-alloy battery material. The main objectives of this research are to examine the process of sulfation and its growth mechanisms as well as to study the effects of minor alloying additions in Pb-alloy material. In the first case, nucleation and growth mechanisms of PbSO4 nano- and micro-particles in various solutions are examined using TEM to potentially reduce or control the buildup of PbSO4 on battery electrodes over time. The time dependency of particle morphology was observed using various reaction conditions. This insight can provide avenues to reduce unwanted buildup of PbSO4 on battery electrodes over time which can extend battery life and …

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, HfTaTiVZr, and AlCoCrFeNi2.1 as a function of temperature. Electrochemical impedance spectroscopy (EIS) was used for monitoring the corrosion of TaTiVWZr and HfTaTiVZr in molten fluoride salt at 650 oC. TaTiVWZr and AlCoCrFeNi2.1 showed low corrosion rate in the range of 5.5-7.5 mm/year and low mass-loss in the range of 35-40 mg/cm2 in molten chloride salt at 650 oC. Both TaTiVWZr and HfTaTiVZr showed similar mass loss in the range of 31-33 mg/cm2, which was slightly higher than IN 718 (~ 28 mg/cm2) in molten fluoride salt at 650 oC. Ta-W rich dendrite region in TaTiVWZr showed higher corrosion resistance against dissolution of alloying elements in the molten salt environment. AlCoCrFeNi2.1 showed higher resistance to galvanic corrosion compared to Duplex steel 2205 in molten chloride salt environment. These results suggest the potential use …

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 and polyvinyl chloride, has been improved by conducting the blending methods, specifically, chemical modification (α,ω-dihydroxydimethyl(methyl-vinyl)oligoorganosiloxane), cross-linking (triallyl isocyanurate), and antioxidant (tris(nonylphenyl) phosphite) incorporation. The nonequilibrium polymeric structures (moth-eye and square array) have been developed for the ultrahigh molecular weight block copolymers via the short-term solvent vapor annealing self-assembly. The large domain size of the moth eye structure allows for improvement of the light transmittance particularly in the visible and near infrared ranges, while the square arrangement of the block copolymer opens the possibility of magnetic data storage application by the large magnetic nanoparticles' embedment or masking of the superconductors.

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 interest in protecting Al, and Ti-based alloys by developing multiphase solid lubricants with a hard sublayer that provide mechanical strength and maintain the part's integrity while providing lubricity. The development of novel coatings with superior lubricity, high toughness, and high-temperature tolerance remains a challenging and hot topic to research and provide new engineered solutions for. To address and provide solutions to protect light-weight, i.e., Al, and Ti alloys at high-temperature and bestow superior tribological properties to such alloys, three types of adaptive lubricious coatings have been studied in this thesis: Nb-Ag-O self-healing lubricious ternary oxide, PEO-chameleon a self-adaptive multi-phase coating, and Sb2O3-MSH-C lubricious adaptive coatings to address this challenge. The development of the Nb-Ag-O ternary resulted in a coefficient of friction as low as 0.2 at 600 °C …

Bioactive glass is a type of third generation bioactive material that can bond to both soft and hard tissue with applications ranging from bone defect repair, coatings for metallic implants, to scaffolds for tissue engineering. Design of bioactive glasses for these applications rely on a detailed understanding of the structures of these glasses which are complicated and multicomponent. In this thesis, I have applied molecular dynamics (MD) simulations with interatomic potentials developed in our group to understand the effect of modifier cation substitution on the structures and properties of two series of bioactive glasses. Particularly, MD simulations are used to understand K2O to Na2O and MgO to CaO substitution on the short and medium range structures (such as cation coordination number, pair distribution function, Qn distribution, and ring size distribution) and properties (such as bulk and Young's moduli and CTE) of 55S4.1 bioactive glasses. As Na2O is incrementally substituted with K2O in 55S4.1, a decrease of the glass transition temperature (Tg) and an increase of CTE was observed, as well as a decreasing trend in the moduli. For the MgO to CaO substitution series, Mg2+ is mainly four-fold coordinated that suggests that it can play a role as a network …