In 2015, the United States consumed about 140.43 billion gallons of gasoline, resulting in the emission of over 1 billion metric tons of carbon dioxide, according to the U.S. Energy Information Administration. Despite continued efforts to develop more efficient engines and cleaner fuels, a major barrier to reducing energy consumption and CO2 production is the mass of the vehicle. Replacing traditional automotive materials such as iron and steel with lighter-weight materials is a big step toward improving fuel economy. Magnesium has great potential for use in the automotive industry because of its low density, about 78% less than the density of steel, and high strength-to-weight ratio. Using cast magnesium instead of steel can reduce the overall weight of a vehicle, improving performance and increasing fuel efficiency. However, magnesium’s high susceptibility to corrosion limits its feasibility as a substitute for traditional materials.

This project aimed to understand the effects of composition and phase distribution on the corrosion behavior of magnesium-aluminum (Mg-Al) alloys in an ionic liquid electrolyte. The purpose of studying corrosion in nonaqueous ILs is to determine the anodic dissolution behaviors of the alloy phases without the interference of side reactions that occur in aqueous electrolytes, such as di-oxygen or water reduction. Three commercial Mg-Al alloys were studied: AZ91D (9% Al), AM60 (6% Al), and AZ31B (3% Al). An annealed alloy containing solid-solution α-phase Mg-Al with 5 at% aluminum content (Mg5Al) was also used. The ionic liquid chosen for this project was 1:2 molar ratio choline-chloride:urea (cc-urea), a deep eutectic solvent. After potentiostatic corrosion in cc-urea, the magnesium alloys were found to form a high surface area porous morphology as corrosion duration increased. This morphology consists of aluminum-rich ridges formed by Al nanowires surrounding an aluminum-poor base area, but with an overall increase in surface Al composition, indicating selective dealloying of the Mg in cc-urea and redistribution of the Al on the surface. Further work will focus on the development of hydrophobic coatings using ionic liquids.

Lithium-ion batteries are one of the most widely used energy storage solutions today. As renewable energy sources proliferate to meet growth in worldwide energy consumption, it is important that lithium-ion batteries be improved to help capture this energy for use when the demand arises. One way to boost the performance of lithium-ion batteries is to replace the electrode active materials with materials of higher specific capacity. Silicon is one material that has been widely touted as a potential replacement for the graphite used in commercial anodes with a theoretical capacity of 3500 mAh/g as opposed to graphite's 372 mAh/g. However, bulk silicon is known to pulverize after experiencing large strains during lithiation. Here, silicon clathrates are investigated as a potential structure for accommodation of these strains. Silicon clathrates consist of covalently bonded silicon host cages surrounding a guest alkali or alkaline earth metal ion. Previous work has looked at silicon clathrates for their superconducting and thermoelectric properties. In this study, electrochemical properties of type I and II silicon clathrates with sodium guest ions (NaxSi46 and NaxSi136) and type I silicon clathrates with copper framework substitution and barium guest ions (Ba8CuxSi46-x) are examined. Sodium clathrates showed very high capacities during initial lithiation (>2500 mAh/g), but rapidly lost capacity thereafter. X-ray diffraction after lithiation showed conversion of the clathrate phase to lithium silicide and then to amorphous silicon after delithiation, indicating destruction of the clathrate structure as a possible explanation for the rapid capacity fade. Ba8CuxSi46-x clathrates were found to have their structures completely intact after 50 cycles. However, they had very low reversible capacities (<100 mAh/g) and potentially might not be electrochemically active. Further work is needed to better understand exactly how lithium is inserted into clathrates and if copper impurities detected during wavelength-dispersive X-ray spectroscopy could be inhibiting lithium transport into the clathrates.

The use of solar energy to produce power has increased substantially in the past few decades. In an attempt to provide uninterrupted solar power, production plants may find themselves having to operate the systems at temperatures higher than the operational capacity of the materials used in many of their components, which affects the microstructural and mechanical properties of those materials. Failures in components that have been exposed to these excessive temperatures have been observed during operations in the turbine used by AORA Solar Ltd. A particular component of interest was made of a material similar to the Ni-based superalloy Inconel 718 (IN 718), which was observed to have damage that is believed to have been initiated by Foreign Object Damage (FOD) and worsened by the high temperatures in the turbine. The potential links among the observed failure, FOD and the high temperatures of operation are investigated in this study.

IN718 is a precipitation hardened nickel superalloy with resistance to oxidation and ability to withstand high stresses over a wide range of temperatures. Several studies have been conducted to understand IN 718 tensile and fatigue properties at elevated temperatures (600- 950°C). However, this study focuses on understanding the behavior of IN718 with FOD induced by a stream of 50 μm Alumina particles at a velocity of 200 m/s. under high cycle fatigue at an elevated temperature of 1050 °C. Tensile tests were conducted for both as-received and heat treated (1050 °C in air for 8hrs) samples at room and high temperature. Fatigue tests were performed at heat treated samples at 1050 °C for samples with and without ablation. The test conditions were as similar as possible to the conditions in the AORA turbine. The results of the study provide an insight into tensile properties, fatigue properties and FOD. The results indicated a reduction in fatigue life for the samples with ablation damage, where crack nucleation occurred either at the edge or inside the ablation region and multisite cracking was observed under far field stresses that were the same than for pristine samples, which showed single cracks. Fracture surfaces indicate intergranular fracture, with the presence of secondary cracks and a lack of typical fatigue features, e.g., beach marks which was attributed to environmental effects and creep.

Nanocrystalline (nc) thin films exhibit a wide range of enhanced mechanical properties compared to their coarse-grained counterparts. Furthermore, the mechanical behavior and microstructure of nc films is intimately related. Thus, precise control of the size, aspect ratio and spatial distribution of grains can enable the synthesis of thin films with exceptional mechanical properties. However, conventional bottom-up techniques for synthesizing thin films are incapable of achieving the microstructural control required to explicitly tune their properties. This dissertation focuses on developing a novel technique to synthesize metallic alloy thin films with precisely controlled microstructures and subsequently characterizing their mechanical properties using in situ transmission electron microscopy (TEM). Control over the grain size and distribution was achieved by controlling the recrystallization process of amorphous films by the use of thin crystalline seed layers. The novel technique was used to manipulate the microstructure of structural (TiAl) and functional (NiTi) thin films thereby exhibiting its capability and versatility. Following the synthesis of thin films with tailored microstructures, in situ TEM techniques were employed to probe their mechanical properties. Firstly, a novel technique was developed to measure local atomic level elastic strains in metallic glass thin films during in situ TEM straining. This technique was used to detect structural changes and anelastic deformation in metallic glass thin films. Finally, as the electron beam (e-beam) in TEMs is known to cause radiation damage to specimen, systematic experiments were carried out to quantify the effect of the e-beam on the stress-strain response of nc metals. Experiments conducted on Al and Au films revealed that the e-beam enhances dislocation activity leading to stress relaxation.

Dealloying, the selective electrochemical dissolution of an active component from an alloy, often results in nanoscale bi-continuous solid/void morphologies. These structures are attracting attention for a wide range of applications including catalysis, sensing and actuation. The evolution of these nanoporous structures has been widely studied for the case at low homologous temperature, TH, such as in Ag-Au, Cu-Au, Cu-Pt, etc. Since at low TH the solid-state mobility of the components is of order 10-30 cm2s-1 or less, percolation dissolution is the only mechanism available to support dealloying over technologically relevant time scales. Without the necessity of solid-state mass transport, percolation dissolution involves sharp transitions based on two key features, the parting limit and critical potential.

Dealloying under conditions of high TH, (or high intrinsic diffusivity of the more electrochemically reactive component) is considerably more complicated than at low TH. Since solid-state mass transport is available to support this process, a rich set of morphologies, including negative or void dendrites, Kirkendall voids and bi-continuous porous structures, can evolve. In order to study dealloying at high TH we have examined the behavior of Li-Sn and Li-Pb alloys. The intrinsic diffusivities of Li were measured in these alloys using electrochemical titration and time of flight measurements. Morphology evolution was studied with varying alloy composition, host dimension and imposed electrochemical conditions. Owing to diffusive transport, there is no parting limit for dealloying, however, there is a compositional threshold (pPD) as well as a critical potential for the operation of percolation dissolution and the formation of bi-continuous structures. Negative or void dendrite morphologies evolve at compositions below pPD and at large values of the applied electrochemical potential when the rate of dealloying is limited by solid-state mass transport. This process is isomorphic to dendrite formation in electrodeposition. Kirkendall voiding morphologies evolve below the critical potential over the entire range of alloy compositions.

We summarize our results by introducing dealloying morphology diagrams that we use to graphically illustrate the electrochemical conditions resulting in various morphologies that can form under conditions of low and high TH.

Structural stability and performance of structural materials is important for energy production, whether renewable or non renewable, to have uninterrupted energy supply, that is economically feasible and safe. High temperature metallic materials used in the turbines of AORA, an Israel-based clean energy producer, often experience high temperature, high stress and foreign object damage (FOD). In this study, efforts were made to study the effects of FOD on the fatigue life of these materials and to understand their failure mechanisms. The foreign objects/debris recovered by AORA were characterized using Powder X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) to identify composition and phases. To perform foreign object damage experiment a gas gun was built and results of XRD and EDS were used to select particles to mimic FOD in lab experiments for two materials of interest to AORA: Hastelloy X and SS 347. Electron Backscattering Diffraction, hardness and tensile tests were also performed to characterize microstructure and mechanical properties. Fatigue tests using at high temperature were performed on dog bone samples with and without FOD and the fracture surfaces and well as the regions affected by FOD were analyzed using Scanning Electron Microscopy (SEM) to understand the failure mechanism. The findings of these study indicate that FOD is causing multiple secondary cracks at and around the impact sites, which can potentially grow to coalesce and remove pieces of material, and the multisite damage could also lead to lower fatigue lives, despite the fact that the FOD site was not always the most favorable for initiation of the fatal fatigue crack. It was also seen by the effect of FOD on fatigue life that SS 347 is more susceptible to FOD than Hastelloy X.

Because of their favorable ionic and/or electronic conductivity, non-stoichiometric oxides are utilized for energy storage, energy conversion, sensing, catalysis, gas separation, and information technologies, both potential and commercialized. Charge transport in these materials is influenced strongly by grain boundaries, which exhibit fluctuations in composition, chemistry and atomic structure within Ångstroms or nanometers. Here, studies are presented that elucidate the interplay between macroscopic electrical conductivity, microscopic character, and local composition and electronic structure of grain boundaries in polycrystalline ceria-based (CeO2) solid solutions. AC impedance spectroscopy is employed to measure macroscopic electrical conductivity of grain boundaries, and electron energy-loss spectroscopy (EELS) in the aberration-correction scanning transmission electron microscope (AC-STEM) is used to quantify local composition and electronic structure. Electron diffraction orientation imaging microscopy is employed to assess microscopic grain boundary character, and links these macro- and nanoscopic techniques across length scales.

A model system, CaxCe1-xO2-x-δ, is used to systematically investigate relationships between nominal Ca2+ concentration, grain boundary ionic conductivity, microscale character, and local solute concentration. Grain boundary conductivity varied by several orders of magnitude over the composition range, and assessment of grain boundary character highlighted the critical influence of local composition on conductivity. Ceria containing Gd3+ and Pr3+/4+ was also investigated following previous theoretical work predicting superior ionic conductivity relative to state-of-the-art GdxCe1-xO2-x/2-δ. The grain boundary conductivity was nearly 100 times greater than expected and a factor four enrichment of Pr concentration was observed at the grain boundary, which suggested electronic conduction that was cited as the origin of the enhanced conductivity. This finding inspired the development of two EELS-based experimental approaches to elucidate the effect of Pr enrichment on grain boundary conductivity. One employed ultra-high energy resolution (~10 meV) monochromated EELS to characterize Pr inter-bandgap electronic states. Alternatively, STEM nanodiffraction orientation imaging coupled with AC-STEM EELS was employed to estimate the composition of the entire grain boundary population in a polycrystalline material. These compositional data were the input to a thermodynamic model used to predict electrical properties of the grain boundary population. These results suggest improved DC ionic conduction and enhanced electronic conduction under AC conditions.

There is a fundamental attractiveness about harnessing renewable energy in an age when sustainability is an ethical norm. Lithium ion batteries and hydrogen fuels are considered the most promising energy source instead of fossil fuels. This work describes the investigation of new cathode materials and devices architectures for lithium ion batteries, and photocatalysts for their usage in water splitting and waste water treatment.

LiCoO2 and LiNi1/3Mn1/3Co1/3O2 were exfoliated into nanosheets using electrochemical oxidation followed by intercalation of tetraethylammonium cations. The nanosheets were purified using dialysis and electrophoresis. The nanosheets were successfully restacked into functional cathode materials with microwave hydrothermal assistance, indicating that new cathodes can be obtained by reassembling nanosheets. This method can pave the way for the synthesis of materials with novel structures and electrochemical properties, as well as facilitate the fabrication of hybrid and composite structures from different nanosheets as building blocks.

Paper folding techniques are used in order to compact a Li-ion battery and increase its energy per footprint area. Full cells were prepared using Li4Ti5O12 and LiCoO2 powders deposited onto current collectors consisting of paper coated with carbon nanotubes. Folded cells showed higher areal capacities compared to the planar versions. Origami lithium-ion battery made in this method that can be deformed at an unprecedented high level, including folding, bending and twisting.

Spray pyrolysis was used to prepare films of AgInS2 with and without Sn as an extrinsic dopant. The photoelectrochemical performance of these films was evaluated after annealing under a N2 or S atmosphere with different amounts of the Sn dopant. Density Function Theory (DFT) was used to calculate the band structure of AgInS2 and understand the role of Sn doping in the observed properties.

Cr(VI) removal was investigated using multiple oxide photocatalyst and additives. The efficiency for Cr(VI) removal using these photocatalysts was investigated in synthetic neutral and alkaline water, as well as in cooling tower blowdown water. While sulfite alone can chemically reduce Cr(VI), sulfite in combination with a photocatalyst resulted in faster and complete removal of Cr(VI) in 10 min using a SO32−/Cr(VI) ratio >35 in pH ∼ 8 solutions.

Stress corrosion cracking (SCC) is a materials degradation phenomena resulting from a combination of stress and a corrosive environment. Among the alphabet soup of proposed mechanism of SCC the most important are film-rupture, film-induced cleavage and hydrogen embrittlement.

This work examines various aspects of film-induced cleavage in gold alloys for which the operation of hydrogen embrittlement processes can be strictly ruled out on thermodynamic grounds. This is so because in such alloys SCC occurs under electrochemical conditions within which water is stable to hydrogen gas evolution. The alloy system examined in this work is AgAu since the corrosion processes in this system occur by a dealloying mechanism that results in the formation of nanoporous gold. The physics behind the dealloying process as well as the resulting formation of nanoporous gold is today well understood.

Two important aspects of the film-induced cleavage mechanism are examined in this work: dynamic fracture in monolithic nanoporous gold and crack injection. In crack injection there is a finite thickness dealloyed layer formed on a AgAu alloy sample and the question of whether or not a crack that nucleates within this layer can travel for some finite distance into the un-corroded parent phase alloy is addressed. Dynamic fracture tests were performed on single edge-notched monolithic nanoporous gold samples as well as “infinite strip” sample configurations for which the stress intensity remains constant over a significant portion of the crack length. High-speed photography was used to measure the crack velocity. In the dynamic fracture experiments cracks were observed to travel at speeds as large as 270 m/s corresponding to about 68% of the Raleigh wave velocity. Crack injection experiments were performed on single crystal Ag77Au23, polycrystalline Ag72Au28 and pure gold, all of which had thin nanoporous gold layers on the surface of samples. Through-thickness fracture was seen in both the single crystal and polycrystalline samples and there was an indication of ~ 1 μm injected cracks into pure gold. These results have important implications for the operation of the film-induced cleavage mechanism and represent a first step in the development of a fundamental model of SCC.

Shock loading is a complex phenomenon that can lead to failure mechanisms such as strain localization, void nucleation and growth, and eventually spall fracture. The length scale of damage with respect to that of the surrounding microstructure has proven to be a key aspect in determining sites of failure initiation. Studying incipient stages of spall damage is of paramount importance to accurately determine initiation sites in the material microstructure where damage will nucleate and grow and to formulate continuum models that account for the variability of the damage process due to microstructural heterogeneity, which is the focus of this research. Shock loading experiments were conducted via flyer-plate impact tests for pressures of 2-6 GPa and strain rates of 105/s on copper polycrystals of varying thermomechanical processing conditions. Serial cross sectioning of recovered target disks was performed along with electron microscopy, electron backscattering diffraction (EBSD), focused ion beam (FIB) milling, and 3-D X-ray tomogrpahy (XRT) to gain 2-D and 3-D information on the spall plane and surrounding microstructure. Statistics on grain boundaries (GB) containing damage were obtained from 2-D data and GBs of misorientations 25° and 50° were found to have the highest probability to contain damage in as-received (AR), heat treated (HT), and fully recrystallized (FR) microstructures, while {111} Σ3 GBs were globally strong. The AR microstructure’s probability peak was the most pronounced indicating GB strength is the dominant factor for damage nucleation. 3-D XRT data was used to digitally render the spall planes of the AR, HT, and FR microstructures. From shape fitting the voids to ellipsoids, it was found that the AR microstructure contained greater than 55% intergranular damage, whereas the HT and FR microstructures contained predominantly transgranular and coalesced damage modes, respectively. 3-D reconstructions of large volume damage sites in shocked Cu multicrystals showed preference for damage nucleation at GBs between adjacent grains of a high Taylor factor mismatches as well as an angle between the shock direction and the GB physical normal of ~30°-45°. 3-D FIB sectioning of individual voids led to the discovery of uniform plastic zones ~25-50% the size of the void diameter and plastic deformation directions were characterized via local average misorientation maps. Incipient transgranular voids revealed from the sectioning process were present in grains of high Taylor factors along the shock direction, which is expected as materials with a low Taylor factor along the shock direction are susceptible to growth due their accomodation of plastic deformation. Fabrication of square waves using photolithography and chemical etching was developed to study the nature of plasticity at GBs away from the spall plane. Grains oriented close to <0 1 1> had half the residual amplitudes than grains oriented close to <0 0 1>.