Haynes® 282® is a relatively new precipitation strengthened nickel-based superalloy typically used in the hotsections of jet engines. The alloy is most commonly used in its wrought form, however Haynes® 282® castings have been of interest in the industry lately as they can offer increased flexibility, e.g. ability to cast advanced geometries to final shapes, and cost advantages. As expected however, castings present challenges related toboth mechanical properties and manufacturing. In particular, the large grains and dendritic structure theypresent make it difficult to laser weld specimens thicker than 8 mm due to cracking in the heat affected zone. GKN has identified a heat treatment that improves the weldability and reduces cracking, however this improved pre-weld heat treatment has a relatively long duration.The purpose of this thesis is therefore to optimize the pre-weld heat treatment with regards to liquation cracking while also reducing total heat treatment time. The proposed heat treatment selection was based on a literature survey, discussions with experts as well as previous results at GKN. Heat treated cast plates with thickness 8 mm were laser welded (bead-on-plate) and subsequently examined metallographically. Three proposed heat treatments showed a potential improvement while two heat treatments seem to have achieved similar results as the GKN heat treatment however at a significantly reduced total heat treatment time. These results were complimented with microstructural analysis and hardness measurements to improve our understanding of pre-weld microstructure on hot cracking.

The major goal of the work is to develop effective additives for U-10Zr (wt.%) metallic fuel to mitigate the fuel-cladding chemical interactions (FCCIs) due to fission product lanthanides and to optimize the fuel phase mainly by lowering the gamma-onset temperature. The additives Sb, Mo, Nb, and Ti have been investigated. Metallic fuels with one or two of the additives and with or without lanthanide fission products were fabricated. In this study, Ce was selected as the representative lanthanide fission product. A series of tests and characterizations were carried out on the additive-bearing fuels, including annealing, diffusion coupling, scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and differential scanning calorimetry (DSC). Sb was investigated to mitigate FCCIs because available studies show its potential as a lanthanide immobilizer. This work extends the knowledge of Sb in U-10Zr, including its effect in the Zr-free region. Sb forms precipitates with fuel constituents, either U or Zr. However, it combines with the lanthanide fission product Ce when Ce is present. Those Sb-precipitates are found to be stable upon annealing, and are compatible with the cladding. The additive does not change the phase transition of U-10Zr. Mo, Nb, and Ti have been investigated for phase optimization based on the known characteristics shown in the binary phase diagrams. The quaternary alloys, i.e., two Mo-bearing alloys and two Nb-bearing alloys, were investigated. Compared to U-10Zr, a few weight percentages of Zr are replaced by those additives in the quarternary alloys. The solid-state phase transitions were determined (alpha and U2Ti transfer into gamma). The transition temperature varies depending on the compositions. The Mo-bearing alloys have lower -onset temperatures than the Nb-bearing alloys. All of them have lower gamma-onset temperatures than that of U-10Zr. Since low gamma-onset temperature is favorable, the results indicate that the fuel phase can be optimized by the replacement of a few weight percentages of Zr into those additives. All the experiments were out-of-pile tests. Therefore, in-pile experiments will be necessary to fully evaluate the performance of the additives in the future. / Doctor of Philosophy / Fuel is the "heart" of a nuclear reactor, and fuel development is a key to improving the performance and reliability of a nuclear reactor. This study investigated the effects of metallic fuel additives in a sodium-cooled fast reactor (SFR). SFRs are an advanced reactor design. Metallic fuel, e.g., U-10Zr (wt.%), is one of the common candidates for SFR fuel. The aim of this study is to develop effective additives for U-10Zr metallic fuel to improve fuel performance. The study has two main objectives. The first one is to mitigate the fuel-cladding chemical interactions (FCCIs), while the second one is to optimize the fuel phase. Four additives, i.e., Sb, Mo, Nb, and Ti have been investigated. The study is a pioneer for the application, thus, the experiments were performed without considering the irradiation effect. Metallic fuels with one or two additives were fabricated, with a series of tests being performed at a laboratory scale. The additive, Sb, was used to mitigate the FCCIs, since FCCIs are a limitation of fuel utilization (i.e., burnup). Lanthanides are produced during fuel operation and attack cladding, being one of the reasons for FCCIs. It is known that the additive Sb has the potential to bind lanthanides into stable precipitates. This work brings the investigation a step further, providing more evidence to demonstrate the stability of the precipitates and the compatibility with cladding. The results are favorable as they demonstrate that the lanthanides will not attack the cladding if they can be caught by the additive Sb in the fuel. The additives Mo, Nb, and Ti were investigated to optimize the phase. One of the favorable phase properties is the gamma-onset temperature - the lower the better. For example, the gamma-onset temperature is 776°C in pure U, while it is 680°C in U-10Zr (meaning that 10 wt.% Zr lowers the gamma-onset temperature by 96°C). In this work, the exploration moves forward by replacing a few percentages of Zr with Mo+Ti, or Nb+Ti. After the change, the gamma-onset temperatures are further decreased, with the temperatures decreasing more in the Mo-bearing fuels than in the Nb-bearing fuels. The significance of this work is twofold. Firstly, it extends the knowledge of Sb as an additive for mitigating FCCIs; secondly, it shows that Mo, Nb, and Ti can optimize the fuel to achieve a favorable phase property. The results provide strong reasons for additional irradiation tests in the future.

Thermal conductivity is a critical fuel performance property not only for current UO2 oxide fuel based light water reactors but also important for next-generation fast reactors that use U-Zr based metallic fuels. In this work, the thermal transport properties of both UO2 based oxide fuels and U-Zr based metallic fuels have been studied. At first, molecular dynamics (MD) simulations were conducted to study the effect of dispersed Xe fission gas atoms on the UO2 thermal conductivity. Numerous studies have demonstrated that xenon (Xe) fission gas plays a major role on fuel thermal conductivity degradation. Even a very low Xe concentration can cause significant thermal conductivity reduction. In this work, the effect of dispersed Xe gas atoms on UO2 thermal conductivity were studied using three different interatomic potentials. It is found that although these potentials result in significant discrepancies in the absolute thermal conductivity values, their normalized values are very similar at a wide range of temperatures and Xe concentrations. By integrating this unified effect into the experimentally measured thermal conductivities, a new analytical model is developed to predict the realistic thermal conductivities of UO2 at different dispersed Xe concentrations and temperatures. Using this new model, the critical Xe concentration that offsets the grain boundary Kapitza resistance effect on the thermal conductivity in a high burnup structure is studied. Next, the mechanisms on how Xe gas bubbles affect the UO2 thermal conductivity have been studied using MD. At a fixed total porosity, the effective thermal conductivity of the bubble-containing UO2 increases with Xe cluster size, then reaches a nearly saturated value at a cluster radius of 0.6 nm, demonstrating that dispersed Xe atoms result in a lower thermal conductivity than clustering them into bubbles. In comparison with empty voids of the same size, Xe-filled bubbles lead to a lower thermal conductivity when the number ratio of Xe atoms to uranium vacancies (Xe:VU ratio) in bubbles is high. Detailed atomic-level analysis shows that the pressure-induced distortion of atoms at bubble surface causes additional phonon scattering and thus further reduces the thermal conductivity. For metallic fuels, temperature gradient and irradiation induced constituent redistribution in U-Zr based fuels cause the variation in fuel composition and the formation of different phases that have different physical properties such as thermal conductivity. In this work, a semi-empirical model is developed to predict the thermal conductivities of U-Zr alloys for the complete composition range and a wide range of temperatures. The model considers the effects of (a) scattering by defects, (b) electron-phonon scattering, and (c) electron-electron scattering. The electronic thermal resistivity models for the two pure components are empirically determined by fitting to the experimental data. A new mixing rule is proposed to predict the average thermal conductivity in U-Zr alloys based on their nominal composition. The thermal conductivity predictions by the new model show good agreement with many available experimental data. In comparison with previous models, the new model has further improvement, in particular for high-U alloys that are relevant to reactor fuel compositions and at the low-temperature regime for the high-Zr alloys. The average thermal conductivity model for the binary U-Zr fuel is also coupled with finite element-based mesoscale modeling technique to calculate the effective thermal conductivities of the U-Zr heterogeneous microstructures. For a U-10wt.%Zr (U-10Zr) fuel at temperatures below the ɑ phase transition temperature, the dominant microstructures are lamellar δ-UZr2 and ɑ-U. Using the mesoscale modeling, the phase boundary thermal resistance R (Kapitza resistance) between δ-UZr2 and ɑ-U has been determined at different temperatures, which shows a T-3 dependence in the temperature range between 300K and 800K. Besides, the Kapitza resistance exhibits a strong dependence on the aspect ratio of the δ-UZr2 phase in the alloying system. An analytical model is therefore developed to correlate the temperature effect and the aspect ratio effect on the Kapitza resistance. Combining the mesoscale modeling with the newly developed Kapitza resistance model, the effective thermal conductivities of many arbitrary δ-UZr2 + ɑ-U heterogeneous systems can be estimated. / Doctor of Philosophy / Thermal transport in nuclear fuels is critical for both energy conversion efficiency and nuclear energy safety. Therefore, understanding the thermal transport properties such as thermal conductivity of nuclear fuels is not only important for current UO2 oxide fuel-based light water reactors but also critical for next-generation fast reactors that use U-Zr based metallic fuels. The thermal transport mechanisms in the two fuel types are fundamentally different: the predominant heat carriers in UO2 are phonons while they are electrons in U-Zr. This work studies the thermal transport properties for both types of nuclear fuels. At first, molecular dynamics (MD) simulations were conducted to study the effect of dispersed xenon (Xe) fission gas atoms on the UO2 thermal conductivity, because Xe is the major fission gas product and even a small concentration of Xe can cause significant fuel thermal conductivity reduction. In this work, three different interatomic potentials were used to study the Xe effect. It is found that although these potentials result in significant discrepancies in the absolute thermal conductivity values, the normalized values are very similar at a wide range of temperatures and Xe concentrations. By integrating this unified effect into the experimentally measured thermal conductivities, a new analytical model is developed to predict the thermal conductivities of UO2 at different Xe concentrations and temperatures. Then this new model is used to study how dispersed Xe influences the effective thermal conductivity of heterogeneous UO2 microstructures with different grain sizes. Next, we focused on how the presence of Xe bubbles degrades the effective UO2 thermal conductivity using MD. The effects of both Xe gas bubble size and pressure were examined. Our results show that dispersed Xe gas atoms or small Xe clusters result in a lower thermal conductivity than clustering them into larger bubbles if the total porosity is fixed. In comparison with empty voids of the same sizes, a Xe-filled bubble leads to a lower thermal conductivity when the bubbles pressure is high, because the distorted bubble surface can cause additional phonon scattering effect. Besides the UO2 based oxide fuels, U-Zr based metallic fuels are promising fuel forms for next-generation fast reactors due to their high thermal conductivity. In this work, a semi-empirical model with a single set of parameters is developed to predict the average thermal conductivities of U-Zr alloys for the complete composition range and a wide range of temperatures. The thermal conductivities predicted by the new model have good agreement with many available experimental data, even if some experimental data are not included in the model fitting. The above thermal conductivity model for the binary U-Zr alloy has been coupled with finite element-based mesoscale modeling to calculate the effective thermal conductivities of U-Zr heterogeneous microstructures containing ɑ-U and δ-UZr2 lamellar phases. Using the mesoscale modeling, the phase boundary thermal resistance R (Kapitza resistance) between δ-UZr2 and ɑ-U has been determined for a wide range of temperatures as well as the aspect ratio of the lamellar δ-UZr2 phase. An analytical model is therefore developed to correlate the effects of temperature and aspect ratio on the Kapitza resistance. Combining the mesoscale modeling with the newly developed Kapitza resistance model, the effective thermal conductivities of many U-Zr heterogeneous systems can be accurately estimated.

Iron is one of the most common trace elements in natural water sources and an important component to living systems. The existence of iron may not only cause metallic flavor, it may also deeply impact health of human and animals by interacting with constituents in the related biological fluids such as saliva and milk. The overall goal of this study is to investigate the taste interaction between iron and sweeteners, and the interaction between iron and proteins in bovine milk and human saliva. Based on pairwise-ranking sensory test, we have found that sweetness of sweeteners was varied with different concentrations of minerals in water and with different types of sweeteners. Sweet-metallic taste interaction between sucrose and ferrous ions significantly (p<0.05) increased the acceptance of very hard water (3 mg Fe/L). The sweet-metallic interaction created a unique selection of the emotional term 'mild'. High iron concentration in bovine drinking water (2 mg Fe/L or higher), causing oxidative stress in dairy cattle, affected expression of both casein and whey proteins in the milk. Direct addition of iron above 5 mg Fe/L in processed whole commercial milk led to lipid oxidation during storage at 4°C. Oxidation level was positively associated with increasing concentration of added iron. Minerals (Mg, P, Na, K, Ca, Zn) in milk were not affected with the added iron in milk. Dietary supplementation with metal-binding protein significantly decreased (p<0.05) taste and smell abnormality score in cancer patients receiving chemotherapy, and this effect lasted at least 30 days after the treatment was ended. Although supplementation did not effectively reduce (p>0.05) the metallic taste intensity stimulated by ferrous sulfate solution (1 mg Fe/L), it significantly (p<0.05) decreased salivary Fe for both healthy subjects and cancer patients. The production of metallic taste perception both induced by chemotherapy and ferrous sulfate solution, might be associated with the decreased expression of low-abundance proteins (pH 5.5-8.5, MW 25-75kDa), which were mainly immune proteins in saliva. Supplementation may improve taste disorder by recovering low-abundance salivary proteins in cancer patients. / Ph. D.

A test fixture for combined tension-compression cyclic testing of unidirectional composites was designed and characterized using 606l-O aluminum specimens. The elastoplastic response of graphite/aluminum l5° off-axis and 90° specimens under tension-compression cyclic loading was subsequently investigated at three temperatures, -l50°F, room temperature and 250°F. The test results showed that the tensile response was predominantly elastoplastic, whereas the compressive response could not be characterized exclusively on the basis of the classical plasticity theory. Secondary dissipative mechanisms caused by inherent voids in the material's microstmcture had an apparent influence on the elastoplastic behavior in compression. At different test temperatures, the initial yield stress in tension and compression were translated in the tension direction with increasing temperature. This is believed to be caused by residual stresses induced in each phase of the composite. The micromechanics model proposed by Aboudi was subsequently employed to correlate the experimental and analytical results at room temperature. A semi-inverse methodology was incorporated to determine the in-situ properties of the constituents. Comparison between the analytical and experimental results showed good agreement for monotonic tensile response. For tension-compression cyclic loading, fairly good correlation was obtained for l5° specimens, but poor for 90° specimens. The major cause of the discrepancy is suggested to be caused by the secondary dissipative mechanisms. / Master of Science

The feasibility of utilizing TiB₂-reinforced near-gamma TiAl intermetallic matrix composites (IMCs) as a reinforcing entity within a commercially pure Ti matrix was investigated. IMCs are "ceramic-like" at ambient to moderate temperatures, and “metallic-like" in their deformation behavior above their brittle-to-ductile transition temperature, thus IMCs create opportunities to create unique in-situ composite microstructures otherwise unattainable using conventional ceramic reinforcements. CP titanium composites reinforced with 20 vol% of near-gamma TiAl IMC were produced by powder blending and densifying via high temperature extrusion deformation processing. The microstructures of the in-situ processed composites were characterized in terms of size, aspect ratio and average spacing of the IMC reinforcement. The microstructural features were correlated to observed mechanical behavior of the composites relative to the unreinforced matrix. The results indicate that the strengthening is derived from microstructural changes within the matrix due to the presence of the IMC particles, and solid solution strengthening due to the diffusion of Al from the reinforcing IMC phase into the Ti matrix. The increase in flow strength due to the former contribution correlates with the inverse square root of the IMC interparticle spacing. / Master of Science

Ionomeric polymer transducers (IPTs) are an exciting new class of smart materials that can serve a dual purpose in engineering or biomedical applications as sensors or actuators. Most commonly they are used for mechanical actuation, as they have the ability to generate large bending strains and moderate stress under low applied voltages. Although the actuation capabilities of IPTs have been extensively studied, the sensing capabilities of these transducers have yet to be fully explored. The work presented herein aims to investigate the fundamental sensing characteristics of these transducers and apply the acquired knowledge toward the development of an electronic stethoscope for digital auscultation. The sensors were characterized both geometrically and electrically to determine their effectiveness in resolving a signal from sub 1 Hz to 2 kHz. Impedance spectroscopy was used to interrogate the sensing mechanism. Following the characterization of the transducer, a bio–acoustic sensor was designed and fabricated. The bio–acoustic sensor was placed over the carotid artery to resolve the arterial pressure waveform in situ and on the thorax to measure the S1 and S2 sounds generated by the heart. The temporal response and spectral content was compared with previously known data and a commercially available electronic stethoscope to prove the acquisition of cardiovascular sounds. / Master of Science

Master of Science

Master of Science

This report analyzes the microstructural evolution of an AlSi10Mg sample fabricated through the Powder Bed Fusion—Laser Beam additive manufacturing process. The project aimed to interpret the microstructural changes occurring during the additive manufacturing process and their influence on thermal conductivity. This analysis was achieved using thermodynamic calculations supported with images obtained from a scanning electron microscope. The result showed that segregation had occurred. The phase exhibiting the most segregation occurs as the amount of silicon increases. Silicon extends the solidification interval, altering the primary solidification from α-Al (FCC)to a secondary fine cooperative eutectic (α-Al + Si) substructure. The images obtained from a scanning electron microscope show cellular grains in the build direction and a substructure between these grains. It can be confirmed that the substructure is lamellar eutectic. Furthermore, it is confirmed that the FCC phase impacts thermal conductivity. Finally, the eutectic structure was proven to influence thermal conductivity, and a finer structure elevates it. / Den här rapporten analyserar den mikrostrukturella utvecklingen av en AlSi10Mg-legering som tillverkats genom additiv tillverkning med pulverbäddsteknik. Projektets syfte är att tolka de mikrostrukturella förändringar som inträffar under en additiv tillverkningsprocess och dess inverkan på värmeledningsförmågan. Analysen utfördes med hjälp av termodynamiska beräkningar tillsammans med bilder från ett svepelektronmikroskop. Resultatet visade att segring hade uppstått. Fasen som uppvisar mest segregation uppstår när mängden kisel ökar. Kisel förlängde stelningsintervallet och gjorde att den primära stelningen övergår från α-Al (FCC) till en fin kooperativ eutektisk (α-Al + Si) substruktur. Bilderna från ett svepelektronmikroskop visade kolumnära korn i byggriktningen och en substruktur mellan dessa korn. Det kunde bekräftas att substrukturen var lamellär eutektisk. Vidare bekräftades det att FCC fasen påverkar värmeledningsförmågan. Slutligen visade det sig att den eutektiska strukturen påverkade värmeledningsförmågan, där en finare eutektisk struktur höjde den.