Ti-6Al-4V anterior cervical plates (ACP) are used in spinal fusion surgeries to fixate cervical vertebrae during graft adhesion. However, documented cases of implant failure and the potential for ACP corrosion raise concerns regarding any degradation of material resulting from extended implantation. In addition, abrasion during implantation may damage a section of the protective oxide layer, potentially exposing surrounding tissues to the harmful effects of bare titanium, aluminum, and vanadium. Thermal oxidation has been shown to improve corrosion-resistance and wear-resistance, depending on temperature and time. To quantify the attributes of the thermally grown oxide layer, Ti-6Al-4V coupons underwent thermal oxidation treatments in an atmosphere environment at 600 and 675 ˚C for 1, 4, 8, and 16 hours. Two sample types were produced: non-abraded and abraded. Non-abraded samples underwent potentiodynamic polarization according to ASTM F2129, which included open circuit potential tests. Open circuit potentials (EOC) increased with increasing treatment time, indicating that longer treatment time resulted in thicker oxides. All samples treated at 675˚C displayed higher EOC than samples treated at 600˚C, indicating an increase in oxide thickness with higher temperature. During the first hour of treatment at 675˚C, the rate of oxide growth was greater than the rate of oxide growth of all samples treated at 600˚C. Samples treated at 600˚C for 4 and 8 hours displayed pitting during potentiodynamic polarization, but all other samples withstood the applied potentials and surfaces were further passivated. To simulate damage during surgery, a single abrasion was made across samples in the abraded group with a diamond-tip indenter under a load of 471g at 4.4 mm/s. Abraded samples were subjected to potential-step tests to assess repassivation ability after abrasion. All samples displayed repassivation ability, except for the sample treated at 600˚C for 4 hours. Surface roughness was measured with atomic force microscopy before and after thermal oxidation treatments. Lower surface roughness was desired to discourage osseointegration, or the growth of bone cells. No isothermal surface roughness trends were observed, as high surface roughness outliers were seen in samples treated at 675˚C for 8 hours and 600˚C for 4 hours. Rockwell hardness and Vickers microhardness were also measured to assess bulk changes in mechanical properties and hardness of the oxidized surfaces. No statistical change was seen in Rockwell hardness. Vickers hardness increased with increasing temperature and time, with the exception of the sample treated at 600˚C for 4 hours. Metallography of the thermally oxidized samples was analyzed to determine if a change in microstructure had occurred due to thermal processing. No major change in grain size or the amount of alpha and beta grains was seen in samples treated at 600˚C, but samples treated for extended times at 675˚C showed equiaxed enlarged alpha grains and a reduction in beta grains. The breakdown of samples treated at 600˚C exemplified possible differences in the alpha-beta oxide behavior during thermal oxidation and corrosion. Outlying surface roughness and microhardness values related to the thermal oxidation treatments and resulting oxide structure. Due to delamination of oxides grown at 675˚C for 4, 8, and 16 hours, the treatment parameters would not be effective in the ACP application. Therefore, through corrosion resistance, repassivation ability, low surface roughness, increased microhardness, and no microstructural change, thermal oxidation treatments at 600˚C for more than 16 hours, and 675˚C for 1 hour or less would be suitable treatments for anterior cervical plates.

NiTi components are commonly subjected to thermo-mechanical heat treatments during production and fabrication. This study investigates the effects of applied strain of 0-10% and heat treatments of 300-600ºC for times of 2-30 minutes during shape-setting of Ti–50.8 at% Ni wire with a nominal diameter of 0.495 mm and an initial transition temperature, Af, of 12ºC. Strain was applied prior to heat treatments by coiling NiTi wire, essentially producing coiled springs, around different diameter steel mandrels to obtain different strain levels. The samples of NiTi wire under applied strain were heat treated in a salt bath, followed by a rapid quench. Transformation temperatures and mechanical properties were characterized using the differential scanning calorimeter and tensile tests. Changes in the Af, UTS, and elastic modulus due to ageing processes and applied strain were observed. Following theory, precipitation rates of Ni-rich phases generally increased with increased temperature (up to a certain point), time and applied strain levels. Reaction rates to achieve a particular Af might be faster than expected if the sample is under strain during the shape-setting process. Due to precipitation strengthening, an increase in UTS with increased heat treatment time was observed between 300-450°C; annealing processes dominate at higher temperatures, resulting in a decrease in UTS above 500°C. A decrease in UTS with increasing level of applied strain was observed. Trends in elastic modulus were highly inconsistent in this study. As shown by this study, applied strain in NiTi during heat treatment affects the Af and mechanical properties.

A piezoelectric microspeaker device that could be used in a variety of acoustic applications was designed and fabricated using a thin film ZnO layer that was reactively DC sputtered onto a single crystalline n-type silicon substrate. When tested the microspeaker did not produce sound due to complications in the etching process, the thickness of the diaphragms, and clamping effects. Instead, a characterization approach was taken and the structural, optical, electrical, and piezoelectric properties of the ZnO were investigated. Scanning electron microscopy, x-ray diffraction, and atomic force microscopy were utilized to discover the ZnO’s structural properties. Using the XRD and SEM, the as-sputtered ZnO films were found to have highly c-axis oriented columnar crystals. Optical properties were determined from the reflectance spectrums obtained from a Filmetrics F20 reflectometer and were used to determine the film thickness, the optical constants, and the optical band gap of the ZnO thin films. Using a four-point probe, the as-sputtered ZnO films were found to be highly resistive and insulative, mainly due to voided growth boundaries between the crystals. To improve electrical conductivity and piezoelectric response, ZnO samples were annealed at varying temperatures in a nitrogen environment. The annealing process successfully increased the electrical conductivity and piezoelectric properties of the films. The local piezoelectric properties of the ZnO were discovered with an Asylum MFP-3D and a piezoresponse force microscopy (PFM) technique called DART-PFM. The ZnO films that were sputtered with 70 watts and an argon to oxygen gas ratio of 2:1 were found to have the highest d33 piezoelectric coefficients. The ZnO sample that was annealed at 600°C for 30 minutes had the highest overall d33 value of 4.0 pm/V, which means that the 600°C annealed ZnO films would have the best chance of making a functional microspeaker.

The bottom-up processing techniques used for making Microelectromechanical systems (MEMS) devices can produce material properties different from bulk processing. The material properties must be evaluated with the process parameters used and for changes in the process parameters. The mechanical properties are needed to design MEMS devices. A material of interest for MEMS devices is nickel titanium (NiTi) shape memory alloy (SMA) because of the high work output (~107 J/m3). This thesis will focus on the fabrication of thin film NiTi by DC magnetron sputtering deposition and testing mechanical properties of the fabricated films by nanoindentation. Thin film NiTi SMA was successfully created by DC magnetron sputtering deposition and high vacuum annealing in the Microfabrication Laboratory at California Polytechnic State University – San Luis Obispo. Characterization of the thin film by nanoindentation produced an elastic modulus of the thin film NiTi SMA with the developed processing parameters was 67.9 GPa with a hardness of 2.1 GPa. The measured thin film NiTi elastic modulus was greater than bulk NiTi of 40 GPa because of the residual stress from the deposition process. The shape memory effect was evaluated at the nanometer scale by measuring the nanoindents before and after thermally inducing a phase transformation. A maximum indentation depth recovery of 58% was measured upon the heat induced martensitic phase transformation. The low recovery was attributed to the high strain of 8% induced by the Berkovich tip. The effects of deposition power on the NiTi as-sputtered film stress, elastic modulus, hardness, and electrical conductivity were evaluated. At the highest sputtering deposition power of 450 Watts, an elastic modulus of 186 GPa with a hardness of 8.3 GPa was measured by nanoindentation. An increase in deposition power increased the residual film compressive stress, elastic modulus, and hardness while the electrical resistivity increased. The mechanisms for the measured properties are discussed in this thesis.

The objective of this project is to find which type of coating has the best performance characteristics for finishing firearms. This is accomplished by measuring and comparing several performance characteristics, such as: adhesion, hardness, wear resistance, friction control, and corrosion resistance. Appearance is not a factor since any exterior coating that is flashy can be subdued or camouflaged with special purpose paints, which have proven durable enough for such purposes. Cost will not be a limiting factor for this experiment, but will be discussed in the conclusion as a secondary concern. This data will be used to identify the best coating for steel and aluminum firearm parts. The goal is to lengthen a firearm’s life cycle while increasing performance and reliability by applying the best coating.

High energy density batteries have garnered much attention in recent years due to their demand in electric vehicles. Lithium-oxygen (Li-O2) batteries are becoming some of the most promising energy storage and conversion technologies due to their ultra-high energy density. They are still in the infancy stage of development and there are many challenges needing to be overcome before their practical commercial application. Some of these challenges include low round-trip efficiency, lower than theoretical capacity, and poor rechargeability. Most of these issued stem from the poor catalytic performance of the cathode that leads to a high overpotential of the battery. In this doctoral work, Li-O2 cathodes containing nanoparticles of palladium were used to alleviate this problem. Cathodes composed of palladium-coated and palladium-filled carbon nanotubes (CNTs) were prepared and investigated for their battery performance. The full discharge of batteries showed 6-fold increase in the first discharge of the Pdfilled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled CNTs also exhibited improved cyclability with 58 full cycles of 500 mAh·g-1 at current density of 250 mA·g-1 versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. The effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, XRD, UV/Vis spectroscopy, and visual inspection of the discharge products using scanning electron microscopy confirmed the increased stability of the electrolyte due catalyst shielding. The electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on carbon nanotubes (CNT) cathodes with palladium (Pd) catalyst, Pd-coated CNT and Pd-filled CNT, have been evaluated in an ether-based electrolyte solution to develop a lithium oxygen (Li−O2) battery with a high specific energy. The electrochemical properties of CNT cathodes were studied using electrochemical impedance spectroscopy (EIS). The infrared spectroscopy and SEM are employed to analyze the reaction products adsorbed on the electrode surface of the Li-O2 battery developed using Pd-coated and Pd-filled CNTs as cathode and an ether based electrolyte. vii Studies in this dissertation conclude that the use of nanocatalysts composed of palladium improved the overall performance of the Li-O2 batteries, while shielding these catalysts from direct contact with the electrolyte prolonged the life of the battery by stabilizing the electrolyte.

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) and in situ X-ray diffraction (XRD) techniques. Safe, low cost custom electrochemical cells were designed and developed for use in battery AE and XRD experiments. These tools were used to monitor the time of material fracture through AE and link these events to lattice strain and phase composition as determined by XRD. Both anode and cathode materials were studied with an emphasis on graphite, silicon, and Li(Mn1.5Ni0.5)O4, and tin. A thermal analogy model for lithiation/delithiation induced fracture of spherical particles capable of predicting when AE should be detected in a cell containing a composite silicon electrode. The results of this work were used to develop an understanding of when and how active materials are degrading as well as to suggest methods of improving their performance and operational longevity.

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 modulus, higher Poisson’s ratio, worse thermal stability, and better plasticity than (Cu50Zr50)92Al8. Both the topological and chemical effects of Al addition account for the differences of mechanical and physical properties between them. A Zr55Ni5Al10Cu30 glass-forming alloy with injection casting (the melting temperatures are 1,550 K and 1,250 K, respectively) and with suction casting was fabricated. The results indicate that despite their amorphous structures, the suction-casting samples exhibit a lower yield stress, lower Young’s modulus, and larger plastic strain than the injection-casting samples (the melting temperature is 1,550 K) due to more quenched-in free volumes in suction casting, which results from the higher cooling rate. The inhomogeneous plastic deformation in Zr50Cu40Al10 BMG samples was introduced by four-point-bend fatigue. There is almost no difference of the stress-strain behaviors between the deformed and undeformed samples. Elastostatic compression was used to introduce homogeneous deformation in Zr70Cu6Ni16Al8 BMG samples. The preloaded samples are softer with decreases of yield strength and Young’s moduli. Anisotropy was observed in the preloaded samples despite their small magnitudes, which even occurred at a relatively low temperature and applied stress level. The structural evolution of Zr70Cu6Ni16Al8 BMG in the elastic region was analyzed with anisotropic pair density function. The analysis of the first shell of Zr70Cu6Ni16Al8 glass confirms the structural changes in the elastic region. The bond reorientation leads to direction dependent changes in the chemical short-range order. The structural evolution in the plastic region of Zr70Cu6Ni16Al8 BMG is investigated as well. The serrations were observed for both the stress-displacement and full width at half maximum-displacement curves. The excess free volume was measured, which increases with increasing the displacement.

Tb6FeSb2 and Tb6FeBi2 are novel rare earth compounds with little prior research. These compounds show high and variable curie temperatures for rare-earth compounds. This has lead to a literature review which includes the discussion of: elasticity, resonance, and magnetism. This review is used to discuss the theory and methodology which can relate these various properties to each other. Furthermore, synthesis, x-ray analysis, and RUS sample preparation of Tb6FeSb2 and Tb6FeBi2 were completed. Resonant Ultrasound Spectroscopy (RUS) elastic studies were taken for Tb6FeSb2 and Tb6FeBi2 as a function temperature from 5-300K, in various magnetic fields ranging from 0-9T. Tb6FeSb2’s and Tb6FeBi2’s elastic moduli are related to their magnetic properties. Magnetization data, primarily M v. H, provides another measure the magnetic properties are used to help correlate the data to elasticity. Tb6FeSb2 and Tb6FeBi2 Curie temperatures are 253(3)K and 246(5)K respectively. The low temperature magnetic transition of Tb6FeSb2 is 65-90K and Tb6FeBi2 is 55-75K. RUS suggests that this low temperature transition is somehow related to a structural transition but this transition does not occur in these two compounds. Co-substitution of Tb6FeSb2 and Tb6FeBi2 seem to greatly affect this lower temperature transition in RUS. It does not greatly effect the curie temperature. Low temperature XRD shows that Co-substitution also creates a structural transition in this family of compounds.

Tb6FeSb2 and Tb6FeBi2 are novel rare earth compounds with little prior research. These compounds show high and variable curie temperatures for rare-earth compounds. This has lead to a literature review which includes the discussion of: elasticity, resonance, and magnetism. This review is used to discuss the theory and methodology which can relate these various properties to each other. Furthermore, synthesis, x-ray analysis, and RUS sample preparation of Tb6FeSb2 and Tb6FeBi2 were completed. Resonant Ultrasound Spectroscopy (RUS) elastic studies were taken for Tb6FeSb2 and Tb6FeBi2 as a function temperature from 5-300K, in various magnetic fields ranging from 0-9T. Tb6FeSb2’s and Tb6FeBi2’s elastic moduli are related to their magnetic properties. Magnetization data, primarily M v. H, provides another measure the magnetic properties are used to help correlate the data to elasticity. Tb6FeSb2 and Tb6FeBi2 Curie temperatures are 253(3)K and 246(5)K respectively. The low temperature magnetic transition of Tb6FeSb2 is 65-90K and Tb6FeBi2 is 55-75K. RUS suggests that this low temperature transition is somehow related to a structural transition but this transition does not occur in these two compounds. Co-substitution of Tb6FeSb2 and Tb6FeBi2 seem to greatly affect this lower temperature transition in RUS. It does not greatly effect the curie temperature. Low temperature XRD shows that Co-substitution also creates a structural transition in this family of compounds.