Master of Sciences (Engineering), Case Western Reserve University, 2012, Materials Science and Engineering

Current production techniques for large diameter 6061 alloy seamless pressure vessels can lead to cylinder heads with regions of large (1mm+) grains that fracture in a low ductility intergranular fashion along the circumference of the head during proof tests. This phenomena and fracture mode was reproduced in commercially produced cylinders by a combination of slow strain rate (10-6/s) 4-point bending and controlled surface strain experiments. As-spun heads were commercially produced and given solution heat treatments at CWRU via either a salt bath or an induction coil, the former followed by quenching at rates from 180°C/s to 18°C/s. The effects of these different heat treatments on the resulting grain size, crack resistance and fracture mode were compared to the standard commercial treatments. Induction heated samples produced grain sizes below 150 µm and exhibited a significantly higher crack resistance, fracturing in a transgranular ductile manner.

Committee: John Lewandowski PhD (Advisor); Gary Michal PhD (Committee Member); David Schwam PhD (Committee Member); Henry Holroyd PhD (Other) Subjects: Aerospace Materials; Materials Science; Metallurgy

Doctor of Philosophy, University of Akron, 2024, Chemical Engineering

The aim of this work is to draw links between 1-D pitting corrosion in literature and crevice corrosion in Alloy 625 and SS 316L in chloride-containing environments. Crevice corrosion initiation, propagation, and repassivation were studied using real-time optical imaging and UV spectroscopy, and the crevice corrosion mechanism was investigated for different cases with the ultimate goal of finding a unifying mechanism for crevice corrosion that is in line with 1-D pitting corrosion. In the first part of this work, crevice corrosion was investigated for LPBF AM Alloy 625 specimens in comparison to the conventionally wrought condition. The AM specimens tested were of two different orientations with respect to the build platform. In addition, the tests were carried out for specimens of the as made or not treated condition as well as specimens that were subject to post manufacturing heat treatments including stress relieving, solution annealing, and solution plus stabilization annealing. Hence, the effect of heat treatment and build orientation on the susceptibility of LPBF additively manufactured Alloy 625 to crevice corrosion was investigated. There was not sufficient evidence that build orientation affects crevice corrosion susceptibility. Nevertheless, it has been shown that heat treatment affects crevice corrosion susceptibility. In addition, though the crevice corrosion susceptibility of as made AM Alloy 625 was not remarkably different from that of wrought 625, solution annealing improves crevice corrosion performance of the AM specimens beyond that of the wrought condition. Crevice corrosion performance differences could be explained with microstructure reflected in the corrosion morphology. Nevertheless, the different AM alloys studied followed the same kinetics/mechanism as the wrought alloy with similar trends in current density and repassivation potential. Such kinetics/mechanisms appear in literature for 1D pits supporting the applicability of the “1D (open full item for complete abstract)

Committee: Robert Lillard (Advisor); Qixin Zhou (Committee Member); Dmitry Golovaty (Committee Member); Gregory Morscher (Committee Member); Linxiao Chen (Committee Member) Subjects: Chemical Engineering; Materials Science

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Materials Science

Co-Cr-Mo alloys are widely utilized in prosthetic devices due to their exceptional wear and corrosion resistance, mechanical properties, and biocompatibility. These attributes are highly dependent on the microstructure, primarily influenced by the γ-FCC to ε-HCP transformation, along with compositional control, processing, and heat treatment. This study investigates the γ-FCC to ε-HCP phase transformation in a laser powder bed fusion additively manufactured Co-29Cr-5Mo alloy through four distinct parts. In the first part, the γ-FCC to ε-HCP transformation was examined after direct aging heat treatment of the material in the as-built condition at temperatures between 750°C and 875°C for up to 100 hours. The microstructural changes were studied by XRD, SEM, and TEM. Crystallographic relations between the &gamma and ε phases were determined via EBSD in the SEM and electron diffraction in the TEM. The as-built material's microstructure was γ-FCC, characterized by a sub-micron dislocation cell structure and stacking faults, together with Cr23C6 carbides at the cell and grain boundaries. A rapid massive transformation to ε-HCP occurred within 0.5 hours at 1073 K, identified by composition invariance, grain face nucleation, and interface-controlled linear growth. This transformation is facilitated by reduced carbon content in the γ-FCC phase, partly due to carbide formation at grain and cell boundaries, and the varied grain structures and interfaces. The second part of the work focused on the kinetic and thermodynamic aspects of massive transformation. The LPBF process produced specimens with a distinctive microstructure featuring columnar grains oriented along the build direction, adorned with intergranular and intragranular precipitates, high dislocation density, and numerous stacking faults. Isothermal aging treatments transformed the γ-FCC phase to the ε-HCP phase at varying rates, with optimal kinetics observed at 850°C. The Johnson-Mehl-Avrami-Kolmogorov (JMA (open full item for complete abstract)

Committee: Vijay Vasudevan Ph.D. (Committee Chair); Dinc Erdeniz Ph.D. (Committee Member); Ashley Paz y Puente Ph.D. (Committee Member); Matthew Steiner Ph.D. (Committee Member) Subjects: Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2023, Mechanical Engineering

Additive Manufacturing (AM) methods are promising in applications where complex part geometries, exotic materials and small lot sizes are required. Aerospace manufacturing stands to use AM methods extensively in the future, and frequently requires temperature- and corrosion-resistant alloy materials such as Inconel 718. However, the microstructural evolution of Inconel 718 during additive manufacturing is poorly understood and depends on part size and shape. We studied the microstructure of Inconel 718 parts manufactured by Laser Powder Bed Fusion in order to further elucidate these dependencies. Microstructural analysis, SEM imaging, EBSD scans and Microhardness testing were performed.

Committee: Henry D. Young Ph.D. (Advisor); Dino Celli Ph.D. (Committee Member); Raghavan Srinivasan Ph.D., P.E. (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science, University of Akron, 2023, Polymer Engineering

Understanding the quasi-crystalline structure of carbon black (CB) has been an important area of research for decades. The dispersion of CB in rubber is influenced by the continuous graphitic planes on its surface that lead to agglomeration of filler. The first objective of this work was to establish a method for repeatable and accurate quantification of crystallinity in CB. We used X-Ray diffraction (XRD) and Raman spectroscopy and developed equations for measurement of the % crystallinity of CB. A comparison of Raman and XRD data revealed lower % crystallinity from XRD. A correction was made to crystallinity measurements from Raman spectroscopy to include amorphous carbon in CB. Next, we considered two treatment methods of as received CB -the ball milling process and the heat treatment process in limited air atmosphere -to control the graphitic nature and the crystal structure of CB. The ball milling process had minimum effect on crystallinity of CB but greatly increased the amount of surface oxygen. The heat treatment process significantly enhanced the fraction of graphitized CB and increased the defect density of CB particles. The treated CB grades were compounded with styrene-butadiene rubber (SBR) for tire tread application and compound properties were measured. A major emphasis was given on dispersion and dynamic properties of the rubber compounds. In conjunction, the mechanical and thermal properties and cure characteristics were evaluated. The dynamic properties revealed information on filler flocculation, Payne effect (energy losses), and rolling resistance. It was found that high surface area, high structure CB had poor dispersion in rubber compounds especially after filler treatment by the above two methods compared to low surface area, low structure grades of CB. The ball-milled CB produced an average of 46.5% reduction in rolling resistance and a significant reduction in Payne effect compared to control CB. An increase of CB crystallinity resulte (open full item for complete abstract)

Committee: Sadhan C. Jana (Advisor); Li Jia (Committee Member); Mark D. Soucek (Committee Chair) Subjects: Materials Science

Master of Science, The Ohio State University, 2022, Materials Science and Engineering

The processing parameters used during electron beam melting powder bed fusion (EBM-PBF) fabrication can create spatio-temporal variations in thermal gradients and solidification rates which impact the evolution of microstructure and mechanical properties in a material. Therefore, a systematic in-depth understanding of process structure property correlations for material in use is a prerequisite for wide industrial adoption of EBM-PBF fabrication. Haynes 282, a recently developed Ni based superalloy known for its high temperature applications in industrial gas turbine engines, is a promising candidate for fabrication via EBM-PBF on account of its good weldability. A rapid qualification of EBM-PBF manufactured Haynes 282 for industries requires a well tiered framework to quantify impact of variations in individual processing parameters on microstructural and mechanical identifiers. In this study, a high throughput multiscale characterization was performed to quantify impact of processing parameters, such as build height, scan velocity and column thickness, on size and morphology evolution of gamma grains (γ), gamma prime (γ') precipitates and carbides. Vickers microhardness testing was used to correlate variations in microstructural features with mechanical properties. Further, the effect of a two-step ageing (1050 ⁰C/2 hours/air cooling + 788 ⁰C/8 hours/air cooling) and a one-step ageing (800 ⁰C/4 hours/air cooling) post process heat treatment on microstructure and Vickers hardness was evaluated. A bimodal distribution of γ' precipitates was observed in both as-deposited and heat-treated states. Backscattered electron imaging performed using a scanning electron microscope (SEM) revealed a decrease in size of primary γ' ( 40%) along the build direction (BD) for the as-deposited state. Local variations in γ' size along BD were observed after heat treatments. Energy dispersive X-ray spectroscopy results revealed presence of discrete, blocky Ti, Mo rich MC type carbide (open full item for complete abstract)

Committee: Carolin Fink (Advisor); Gopal Viswanathan (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2022, Materials Science and Engineering

In the last 20 years, research in magnesium alloys has greatly expanded with demand for high-strength lightweight alloys in the transportation industry. Mg-RE (rare earth) alloys have been of particular interest due to the formation of two strengthening phase types: long period stacking order (LPSO) phases and β-series precipitates. This work focuses on the development of high-strength cast Mg-RE multicomponent alloys that combine LPSO and β-series phases using a CALPHAD (CALculation of PHAse Diagrams)-based design approach. This work began by using CALPHAD modeling to study the effects of maximizing the LPSO phase fractions. Experimental samples demonstrated there was a slight increase in mechanical properties with high LPSO volume fractions, but the properties were below those obtained through β' precipitation in the commercial alloy WE43 (Mg-4Y-3.4RE-0.7Zr, all in wt%). It was also found that the CALPHAD model was underpredicting the LPSO phase fractions by ~20 vol%. Improvements were made to the Pandat database to bring the predictions within ~5 vol% of experimental values. In the second stage of this work, small-angle scattering (SAS) was used to quantitatively explore the effects of micro-alloying in the Mg-Nd system on β-series precipitates. Two SAS techniques were used in addition to transmission electron microscopy (TEM) to study the effects of micro-alloying: small-angle neutron scattering (SANS) and small-angle x-ray scattering (SAXS). It was found SAXS was a better technique to quantify the change in precipitate size with micro-alloying and aging, but more understanding of the system is needed to extract phase fraction changes. In the final stage of this work, the LPSO and β-series strengthening mechanisms were combined in an attempt to produce an Mg-Y-Nd-Zn-Zr alloy with properties superior to WE43. Nd does not form any LPSO phase, so there is less competition between the phases during formation. CALPHAD modeling is used to tailor the phase fracti (open full item for complete abstract)

Committee: Alan Luo (Advisor); Steve Niezgoda (Committee Member); Jenifer Locke (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2021, Welding Engineering

Stress Relief Cracking (SRC) in low alloy steels was the core focus for this work. Stress relief cracking is an ongoing concern for thick-walled creep resistant steel welds during PWHT when high restraint and high residual stresses are present after welding. While much is already known about SRC, the persistence of its occurrences motivates continued research to further study this cracking phenomenon due to the desire to completely eliminate SRC occurrences during future fabrications. This body of research can be broken into three elements, SRC test development, analysis of the SRC mechanism and controlling factors, and modeling. The goal was to develop a test that can accurately recreate the SRC mechanism which would then be used to study SRC as it naturally occurs in weldments during PWHT. Grade 11 and Grade 22 Steel were the primary focus of this research. A Gleeble based SRC testing procedure was developed at The Ohio State University in order to carry out experimentation for this research. SRC occurs in highly restrained welds where high residual stresses are present after welding. Past research has shown stress can affect the precipitation kinetics in low alloy steels making the recreation of high residual stress crucial for replicating the microstructural evolution of susceptible materials during both heating and PWHT. The OSU SRC Test procedure loaded a dog bone to 90%YS at room temperature, then while heating to PWHT temperature at 200°C/hour, additional Gleeble stroke was added to counteract the compressive strain from thermal expansion with the goal of the sample reaching 90% of its elevated temperature YS upon reaching PWHT temperature. The Gleeble displacement was fixed upon reaching PWHT temperature to simulate high restraint and the sample was held for 8 hours. Digital image correlation was utilized for measuring strain across the surface. All results of testing showed the OSU SRC Test is accurately determining SRC susceptibility as well as accu (open full item for complete abstract)

Committee: Boian Alexandrov (Advisor); Avi Benatar (Advisor); Wei Zhang (Committee Member); Carolin Fink (Committee Member); Desmond Bourgeois (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2020, Materials Science and Engineering

The realization of advanced alloy compositions in service relies on a thorough understanding of metallurgical processing variables. Within this work, the gamma prime precipitation of an advanced powder metallurgy nickel-base superalloy during controlled cooling from supersolvus temperatures is compared to prior alloy generations using a complement of characterization and modeling approaches. The on-cooling precipitation of the alloy is studied and characterized to calibrate a multi-scale precipitation model. The proposed framework incorporates a computationally efficient addition to the mean-field modeling approach that increases its ability to model dynamic, multi-modal gamma prime burst events. The gamma prime size predicted by the model shows good agreement with experimental results. The precipitation calculation is applied to the element integration points of a continuum Finite Element heat conduction simulation, where the latent heat generated from the precipitation is accounted for. The results are compared to experimental findings and indicate potential use of the model for evaluating precipitation effects at multiple length scales. The lattice misfit evolution of two commercial PM nickel superalloys during cooling from supersolvus temperatures is also characterized, using in-situ synchrotron X-Ray Diffraction (XRD). The diffraction pattern deconvolution necessary for quantifying misfit was accomplished by combining observation of the superlattice peak intensities with thermodynamic modeling to quantify the intensity relationship between the overlapping phases. The misfit from the XRD measurements was compared to the Scanning Electron Microscopy observations of gamma prime particle shapes for a subset of the experimental conditions. The trend of measured misfit agreed with the microstructural characterization. Time-resolved observations of the on-cooling lattice parameter suggest that lower-temperature changes to the peak intensity characteristics coinc (open full item for complete abstract)

Committee: Michael Mills (Advisor); Wei Zhang (Advisor); Yunzhi Wang (Committee Member); Stephen Niezgoda (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science

Master of Science, The Ohio State University, 2020, Industrial and Systems Engineering

Additive manufacturing, or 3-D printing, is becoming a pervasive manufacturing technique due to its flexibility and reliability. The incremental printing of 3-D objects allows parts to be prepared with more flexibility and precision than older manufacturing techniques like casting, forging, etc. The opportunities with 3-D printing are endless and are already being used in the Department of Defense, medical field, and aeronautics to name a few. With the increased flexibility and ability to manufacture complex geometries, challenging process science, control, and scheduling issues arise. Additive manufactured parts are susceptible to defects throughout the manufacturing process, specifically during the pre-processing, printing and post-processing of the parts, and the development of internal residual stress in the parts is of particular focus in this work. In order to minimize the residual stress after builds, parts are placed in a furnace to initiate stress relaxation. However, this process is currently being accomplished in small batches due to the current limited volume of AM produced parts. As this technology scales, optimization of these post-processing steps will become vital for increasing throughput and enabling the appropriate scale-up of the technology. In anticipation of the scale-up of AM technologies, the objective of this thesis is to investigate an optimal schedule for the stress relaxation process in various scenarios and determine which of these scenarios is optimal. We introduce a physics-based ii scheduling optimization framework through nonlinear mixed integer programming for toggling parts' heating and cooling stages. We analyze different strategies to include modifying time steps a part is in and out of the furnace, introducing an insulated holding area, modifying the number of parts per batch, and changing our objective function. We will then compare the results to the legacy process that is used in order to determine what strategy is the m (open full item for complete abstract)

Committee: Michael Groeber (Advisor); Andrew Gillman (Advisor) Subjects: Operations Research

Master of Science (MS), Bowling Green State University, 2019, Biological Sciences

Understanding responses of food webs to climate change is vital, especially when those food webs influence important ecosystem services, like pollination, valued at over $3 billion globally. Historically the focus has been on single factors (e.g. temperature) and mechanisms (e.g. change in mortality). However, global climate change is predicted to alter temperature and moisture simultaneously. Additionally, thermal and hygric physiological performance and species interactions are both likely mechanisms underlying food web responses to changing climate. The current lack of a synergistic, mechanistic understanding of how food webs respond to key aspects of global climate change is a major research gap. Here we questioned how changes in temperature and moisture may alter food web composition through filtering of sensitive taxa (physiological limits) or by modifying consumption (trophic interactions). We placed bumblebees (Bombus impatiens) and tomato plants (Solanum lycopersicum) in 32 mesocosms within a greenhouse in Bowling Green, OH in July 2018. We explored differences in fruit set and tomato quality by excluding half of the flowers from buzz-pollination via bags. Additionally, all mesocosms were categorized in four abiotic treatments (cool/dry, cool/moist, hot/dry, hot/moist), and were paired based on predator presence (with or without Green Lynx spiders (Peucetia viridans)). We found that predatory spider body temperature was significantly higher when more moisture was available in the environment (SE=0.779, df=28.0, t-ratio=-3.661, p=0.005). Our findings also indicate that if predatory spiders are more hydrated, they change their behavior and expose themselves more to heat (χ2=4.028, df=1, p= 0.045). Furthermore, this behavioral change influences spider consumption of bumblebees. When more moisture was available in the environment, spiders ate significantly more bumblebees (χ2=8.924, df=1, p=0.003). However, there were no significant differences between the h (open full item for complete abstract)

Committee: Kevin McCluney Dr. (Advisor); Helen Michaels Dr. (Committee Member); Daniel Wiegmann Dr. (Committee Member) Subjects: Behavioral Sciences; Biology; Climate Change; Conservation; Ecology; Entomology

Master of Sciences (Engineering), Case Western Reserve University, 2018, Materials Science and Engineering

In this work, investigations on Inconel 718 cladded H13 and 4140 have been carried out using two different cladding methods: Direct Metal Deposition (DMD) and Laser Hot-Wire (LHW). Heat treatments were conducted to optimize mechanical properties using Vickers microhardness as the primary metric. Electron microscopy and X-Ray Diffraction were used to analyze cladding composition and microstructure. DMD Inconel on 4140 demonstrated severe iron depletion adjacent to the substrate. Hardness increases from 278 HV to 438 HV and 312 HV to 465 HV were achieved for DMD samples by high-temperature solutionizing and ageing for the 4140 and H13 substrate systems respectively. High-deposition power LHW cladding showed high cladding dilution by the substrate and a much lower as-cladded average hardness of 200 HV which was unresponsive to heat treatment. Low-deposition power LHW cladding displayed less dilution and higher as-cladded hardness of 304 HV. Results demonstrate feasibility for cladded die system improvement.

Committee: Matthew Willard (Advisor); James McGuffin-Cawley (Committee Member); John Lewandowski (Committee Member); Gerhard Welsch (Committee Member) Subjects: Materials Science

MS, University of Cincinnati, 2018, Engineering and Applied Science: Materials Science

The microstructure and stress states bestowed by the manufacturing process administer the reliability and performance of each component in its final application. Additive Manufacturing (AM) is the trending process among all the innovative methods to produce uniform distribution of microstructure and properties in the constituent parts in a cost-effective manner. However, most of the fusion based manufacturing techniques possess a drawback in the form of residual stresses developed during the processing stage. This demands for the development of more effective AM methods having the potential for near-net shape manufacturing of the parts with minimized residual stresses which has led to the inception of a novel solid-state AM process named “MELD”. This study investigated the microstructure and properties developed in the multi-layer Alloy 600 deposit on 304L stainless steel manufactured by MELD process. Unlike other fusion based AM processes, MELD showed a compressive residual stress (~ -380 MPa) on the surface of the deposited material. The average hardness of the deposit (~ 3.29 GPa) was comparable with that of Alloy 600 manufactured by other AM processes. Additionally, a localized increase in the hardness could be observed at the interfaces between two subsequent layers which was attributed to the grain refinement resulting from dynamic recrystallization in the interfacial areas during the MELD process. Large amount of carbide precipitates formed during the recrystallization at the interface restricted the grains size by pinning them together. High temperature in areas away from interface caused dissolution of carbides leading to grain coarsening. This trend of grains size and carbide precipitates was repeated in each of the deposited layers. The point and space group of the carbide precipitate was determined from TEM analysis. The deposit possessed very low dislocation density and hence low plasticity. Though, the distribution of sub-grains and low angle bounda (open full item for complete abstract)

Committee: Vijay Vasuedevan Ph.D. (Committee Chair); Ashley Pazy Puenta Ph.D. (Committee Member); Matthew Steiner Ph.D. (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2018, Food Science and Technology

Processors of American pickles utilize fermentation or direct acidification in conjunction with thermal processing as a part of their preservation step. Health conscious consumers are demanding for clean-labeled products that are minimally processed with reduced salt/sugar and free from synthetic preservatives. This has prompted the pickle manufactures to investigate clean food processing methods such as high pressure processing (HPP) and other minimally processed methods with reduced thermal impact. Our hypothesis is that by reducing thermal exposure, combined pressure-thermal treatment can help to better retain quality attributes of selected acidified vegetable pickles over 30 days storage at 25oC. The objective of this research were to evaluate the heat of compression of pickling liquid with various solute concentration as well as vegetables subjected to two different acidification pretreatment approaches (2) assess the quality changes of acidified vegetables treated by various pressure (600 MPa)-thermal (45-65oC) combinations with and without thermal blanching. First set of experiments investigated the heat of compression values of pickling solution with varying solute concentration as well as pickling vegetables subjected to two different pre-treatments. Subsequently samples were pressure treated in a pilot scale high-pressure processor at 600 MPa, 45° or 65°C for 5 min and stored at ambient temperature for 30 days. Quality analyses included texture, enzyme activity, color, pH and °Brix. Solute concentration, initial temperatures and vegetable pretreatments significantly influenced heat of compression values of pickling liquid and vegetables. At 25oC, heat of iii compression values of the pickling liquid varied as a function of varying solute concentration (p<0.05). On the other hand, thermal effect dominated over solute concentration at 60oC. Both methods of acidification (thermal blanching and overnight soaking) of vegetables influenced heat of compressio (open full item for complete abstract)

Committee: V.M. Balasubramaniam (Advisor); Rafael Jimenez-Flores (Committee Member); Lynn Knipe (Committee Member) Subjects: Engineering; Food Science

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

Third generation Al-Cu-Li alloys have improved localized corrosion resistance compared to previous generations and are attractive to the aerospace industry because of the mix of low density and good mechanical properties. Al-Cu-Li alloy AA2099 (Al 2.7Cu 1.8Li 0.6Zn 0.3Mg 0.3Mn 0.08Zr) is a newer precipitation-strengthened alloy with a cleaner microstructure that contributes to increased corrosion resistance. However, there is still a susceptibility for intergranular and inter-subgranular (IGC/IsGC). Because localized corrosion associated with coarse constituent particles is diminished due to alloy cleanliness, intergranular forms of attack are a larger factor in the corrosion profile of this alloy. The susceptibility to localized corrosion in AA2099 was characterized based on the attack morphology after exposure to various NaCl aqueous solutions. Alloy samples were subjected to a series of artificial heat treatments conducted at temperatures ranging from 120°C to 180°C for times ranging from 12 to 168 hours, corresponding to time and temperature ranges that are commensurate with commercial practice. The resulting microstructures were analyzed using scanning transmission electron microscopy (TEM), electron back-scattering, and diffraction methods, which characterized the precipitates formed during artificial aging. The formation of the strengthening phase T1 (Al2CuLi) was of particular interest due to its reported anodic behavior relative to the alloy matrix. This particle is prone to corrosion attack and plays a significant role in the evolution of localized corrosion mode and morphology depending on its location within the alloy. The results from the exposure experiments provided a map for the various heat treatments to identify when IsGC susceptibility will occur. Results showed that AA2099 went through several attack categories as samples were aged to under-aged (UA), peak-aged (PA), and over-aged (OA) conditions. The morphology in the cross section progre (open full item for complete abstract)

Committee: Rudolph Buchheit (Advisor) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2018, Welding Engineering

Subsea high pressure equipment used in production of oil and gas is routinely clad with nickel base alloys for corrosion protection. In the equipment with partial clad for sealing purpose, dissimilar metal interfaces are possibly exposed to the production fluids containing H2S. After cladding, a high hardness heat affected zone (HAZ) is produced in the base metal adjacent to the fusion boundary and is possibly susceptible to hydrogen assisted cracking (HAC) and sulfide stress cracking (SSC). National Association of Corrosion Engineers (NACE) standard MR0175/International Standard Organization (ISO) 15156 requires that HAZ hardness should be less than 22 HRC or 250 VHN. Postweld heat treatment (PWHT) is applied to reduce the HAZ hardness to meet this requirement. However, PWHT causes the carbon to diffuse from the base metal to the weld metal and pile up in a narrow region adjacent to the fusion boundary, possibly causing interface embrittlement. Also, prolonged PWHT can overtemper the base metal and impair its strength. Therefore, the optimal PWHT conditions need to be determined, which reduce the HAZ hardness to meet the industry standard, do not harm base metal strength, and do not increase the HAC and SSC susceptibility near or at the fusion boundary. In this work, nickel base Alloy 625 overlays on F22 (2.25Cr-1Mo) steel and AISI 8630 steel, or F22/625 and 8630/625 dissimilar metal welds (DMWs), were studied. A wide range of PWHT conditions indicated by Hollomon-Jaffe Parameter (HJP) was investigated to determine an optimal balance between HAZ softening and interface embrittlement. Vickers hardness testing revealed that the CGHAZ hardness decreases with the HJP increase due to martensite decomposition. There is a secondary hardening effect in F22 CGHAZ. The hardness of the planar growth zone (PGZ) of the interface and the weld metal increases with HJP, and the PGZ hardness increases at a higher rate than the weld metal. Nanoindentation and optical microsc (open full item for complete abstract)

Committee: John Lippold (Advisor); Boian Alexandrov (Committee Member); David Phillips (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

The development of new magnesium alloys with improved mechanical properties is important for lightweighting applications, since the current high pressure die cast (HPDC) magnesium alloys, i.e. AM50/60 (Mg-5/6wt.%Al-0.2wt.%Mn) and AZ91 (Mg-9wt.%Al-1wt.%Zn), have limited mechanical properties. Two magnesium alloy systems, Mg-Al-Sn (AT) and Mg-Al-Sn-Si (ATS), were investigated for potential automotive applications. A CALPHAD (CALculation of PHAse Diagrams) approach was used in the development of AT and ATS alloys and to aid in the design of heat treatment schedules. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and transmission electron microscopy (TEM) techniques were used to characterize the microstructure of the alloys in the as-cast and heat treated conditions. Mechanical testing was performed on cast specimens, as well as samples cut from thin-wall HPDC components to compare the strength and ductility of these alloys to currently used magnesium alloys. To expand the applications of HPDC components in the transportation industries, further development and optimization of the process is needed. The development of super vacuum die casting (SVDC) process for aluminum and magnesium thin-wall castings were explored using process simulation and experimental validation. Two experimental dies, i.e., a test specimen die and a fluidity die, were designed to evaluate the castability of several new aluminum alloys and optimize process parameters for these alloys. The process conditions were successfully validated in industrial castings such as an automotive door inner and a side impact beam.

Committee: Alan Luo (Advisor); Michael Mills (Committee Member); Glenn Daehn (Committee Member); Gary Kennedy (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Toledo, 2017, Mechanical Engineering

Magnesium (Mg) alloys have shown biodegradable properties that make them appealing for various biomedical applications. Mg corrodes gradually in the body and it has low density and modulus of elasticity, close to that of the bone. However, the fast rate of degradation and low strength are the main challenges that hinder the use of Mg alloys for bone fixation applications. This dissertation provides a comprehensive review of the literature on the most promising Mg alloys and possible techniques to improve their mechanical and corrosion properties. The main goal of this research is to develop bioresorbable Mg-based fixation hardware with adequate strength and acceptable degradation rate using nontoxic alloying elements. To this end, finite element analysis, design of experiments, and novel post-fabrication techniques (heat treatment and coating) were combined towards patient-specific biodegradable fixation hardware. As the initial step, various Mg-Zn-Ca-based alloys, as the most biocompatible alloys, were designed and fabricated. Heat treatment, as a favorable post-fabrication process for parts produced in their final shape, was investigated to understanding the effect of heat treatment on the corrosion behavior, microstructural characteristics, and mechanical properties of Mg-Zn-Ca-based alloys. Heat treatment was found to be a practical approach to significantly reduce the corrosion rate and to enhance the corrosion behavior of these alloys. Aging Mg-Zn-Ca-based alloys that contain low Zn contents (between 1.2-2 wt.%) and a small amount of Mn (0.5 wt.%) at 200 °C for 2-5 hours was found to result in the best mechanical and corrosion properties. Despite the enhanced corrosion properties of the heat-treated alloys, biocompatible coatings are essential to protect the device during the healing period of bone, during which the implant is under maximum loads. Such coating should enable delaying the degradation of Mg-based fixation hardware to maintain the mechanical integ (open full item for complete abstract)

Committee: Mohammad Elahinia (Committee Chair); Arunan Nadarajah (Committee Member); Efstratios Nikolaidis (Committee Member); Sarit Bhaduri (Committee Member); Matthew Franchetti (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Metallurgy

Doctor of Philosophy, The Ohio State University, 2015, Comparative and Veterinary Medicine

Human norovirus (HuNoV), hepatitis A virus (HAV), and rotavirus (RV), are responsible for the majority of foodborne illnesses. Seafood, particularly bivalve shellfish, is one of the major high risk foods for enteric viruses contamination. Therefore, there is an urgent need to develop effective thermal and non-thermal processing technologies to eliminate virus hazards in seafood. This study aims to determine the bioaccumulation patterns of human enteric viruses in shellfish tissues, to determine whether heat or high pressure processing (HPP) are capable of effectively inactivating enteric viruses in shellfish, and to determine whether viruses can develop resistance to processing technologies. Oysters (Grassostrea gigas) were cultivated in seawater artificially contaminated with HuNoV surrogates (Tulane virus, TV; murine norovirus, MNV-1), HAV, or RV at level of 1 × 10^4 PFU/ml, or 1 × 10^4 RNA copies/ml of a HuNoV GII.4 strain. Oysters were harvested after 24, 48, and 72 h post-inoculation, and the presence of viruses was determined in gills, digestive glands, and muscles by plaque assay or real time PCR (RT-qPCR). It was found that caliciviruses and HAV were localized in the stomach at a high level within the first 24 h, while RV was detected in the highest level in the gills. Next we determined the thermal stability of each of the viruses. It was found that Decimal reduction time (D-values) of TV, MNV-1, HAV, and RV ranged from 0.13 to 1.81 min and 1.26 to 7.29 s at 62 and 72°C, respectively. At 80°C the time to first log10 reduction (TFL-value) ranged between 0.46 and 32 s in cell culture medium, and ranged between 0.61 to 19.99 min in oysters. In terms of thermal resistance the four viruses can be ranked as the following: HAV>RV>TV>MNV-1. This study also compared the baro-sensitivity of seven RV strains (G1: Wa, Ku, and K8, G2: S2, G3: SA-11 and YO, and G4:ST3) following HPP. It was found that RV strains showed varying responses to HPP based on the initial temp (open full item for complete abstract)

Committee: Jianrong Li (Advisor); Hua Wang (Committee Member); Melvin Pascall (Committee Member); Gireesh Rajashekara (Committee Member) Subjects: Food Science; Microbiology; Veterinary Services; Virology

Master of Science, University of Toledo, 2015, Mechanical Engineering

In recent years, shape memory alloys (SMAs) have entered a wide range of engineering applications in fields such as aerospace and medical applications. Nickel-titanium (NiTi) is the most commonly used SMAs due to its excellent functional characteristics (shape memory effect and superelasticity behavior). These properties are based on a solid-solid phase transformation between martensite and austenite. Beside these two characteristics, low stiffness, biocompatibility and corrosion properties of NiTi make it an attractive candidate for biomedical applications (e.g., bone plates, bone screws, and vascular stents). It is well know that manufacturing and processing of NiTi is very challenging. The functional properties of NiTi are significantly affected by the impurity level and due to the high titanium content, NiTi are highly reactive. Therefore, high temperature processed parts through methods such as melting and casting which result in increased impurity levels have inadequate structural and functional properties. Furthermore, high ductility and elasticity of NiTi, adhesion, work hardening and spring back effects make machining quite challenging. These unfavorable effects for machining cause significant tool wear along with decreasing the quality of work piece. Recently, additive manufacturing (AM) has gained significant attention for manufacturing NiTi. Since AM can create a part directly from CAD data, it is predicted that AM can overcome most of the manufacturing difficulties. This technique provides the possibility of fabricating highly complex parts, which cannot be processed by any other methods. Curved holes, designed porosity, and lattice like structures are some examples of mentioned complex parts. This work investigates manufacturing superelastic NiTi by selective laser melting (SLM) technique (using PXM by Phenix/3D Systems). An extended experimental study is conducted on the effect of subsequent heat treatments with different aging conditions on phase (open full item for complete abstract)

Committee: Mohammad Elahinia (Advisor); Mehdi Pourazady (Committee Member); Matthew Franchetti (Committee Member) Subjects: Mechanical Engineering