Master of Science, The Ohio State University, 2024, Welding Engineering

Ultrasonic vibration has widely been studied for potential in the metal forming industry for its ability to temporarily soften the material. The lack of understanding of the underlying mechanisms of ultrasonic softening and difficulty in scaling to industrial applications has limited its use. To better understand the fundamentals to the softening mechanism, ultrasonic-assisted (UA) micro-tensile tests of low-carbon steel, aluminum alloy 2219 varying grain size, and titanium grades 2 & 5 are conducted in this study. The ultrasonic vibration is oriented along the tensile axis, and the ultrasonic amplitude is uniform in micro-dogbone specimen. Acoustic softening is observed, increasing with ultrasonic amplitude for all materials. Further investigation on the unique residual effect after ultrasonic treatment based on the microstructure is conducted. Low-carbon steel exhibited residual softening increasing with ultrasonic amplitude. EBSD analysis was conducted on the steel samples strained to 10% strain to explain the reduction of strain hardening during UA and residual softening after UA. Two ultrasonic amplitude levels were compared along with a control NoUA case. Higher LAGB fractions were observed with increasing ultrasonic amplitude, attributed to enhanced dislocation motion resulting in dipole annihilation and subgrain formation. Lower amplitudes assisted in lattice rotation with minor change in the microstructure while higher amplitudes resulted in significant intragranular deformation. Aluminum alloy 2219 was friction stir processed to achieve a refined microstructure and compared to a Al2219-T4 temper with a larger grain size. The resultant reduction of flow stress from ultrasound with varying grain size was similar, however, residual hardening was observed in the T4 temper, while no residual effect was observed in the refined microstructure. Also, the ultimate tensile stress and elongation improved after ultrasonic treatment in the T4-temper. With the (open full item for complete abstract)

Committee: Xun Liu (Advisor); Avraham Benatar (Committee Member) Subjects: Materials Science; Mechanical 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

Doctor of Philosophy, The Ohio State University, 2023, Welding Engineering

Duplex stainless steels (DSS) are extensively used in heavy industry, such as Oil and gas, pulp and paper, and chemical, due to their remarkable corrosion resistance, yield strength, and toughness. The most corrosion-resistant DSS subgroups, super duplex stainless steels (SDSS) with Pitting Resistance Equivalent numbers (PREn) of 40-48, and the hyper duplex stainless steels (HDSS) with a PREn over 48, are highly alloyed. Additions of Cr and Mo provide better PREn but also promote intermetallic phases such as the chi and sigma phases. These intermetallics form when the material is exposed to temperatures between 600oC – 1100oC. It is known that even small volumetric fractions of the sigma phase severely reduce the material's corrosion resistance and mechanical performance. A dedicated study on sigma phase formation kinetics was developed to control sigma phase presence in these specific alloys. A field studied but not yet completely connected between scientific research and industrial applications. Fundamental aspects of sigma phase kinetics were analyzed, computationally modeled, and experimentally validated. As a result of these efforts, the interface area per unit of volume was revealed as a critical microstructure factor for the sigma phase kinetics. The resultant model's efficacy was further evaluated by building GTAW cladded mockups, and investigation into this material's mechanical and corrosion performance further expanded on the impacts of the sigma phase. A Gleeble® system was used to develop experimental time temperature transformation (TTT) maps on SDSS and HDSS filler metals for sigma phase precipitation kinetics. Classical nucleation theory was then implemented on the CALPHAD-based kinetics model. In this model, the interfacial energy and nucleation sites were identified as the kinetics parameters to adjust the model based on experimental data. The sigma phase kinetics continuous cooling transformation CCT curves were calculated using the additiv (open full item for complete abstract)

Committee: Antonio Ramirez (Advisor); Stephen Niezgoda (Committee Member); Carolin Fink (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering

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, Welding Engineering

The increasing demand for reducing carbon footprint has prompted the research and development of high strength alloys for lightweight applications. Replacing the conventional alloys with higher strength-to-weight ones can significantly decrease the weight of automobile components and increase fuel efficiency. However, the high strength of these materials presents additional challenges in the field of forming. High strength increases tool and die wear. Higher capacity machines are required in forming, which can be costly. In addition, the high strength increases spring back which makes it challenging to maintain accuracy in geometry. One promising solution is to temporarily soften the material during forming with the application of ultrasonic vibration. It was found that the flow stress of material decreased significantly when ultrasonic vibration was applied during deformation. Since its discovery in the 1950s, the ultrasonic softening effect has been studied extensively and various metal forming processes with ultrasonic assistance (UA) have been developed. However, literature reports inconsistent results on ultrasonic softening, and the underlying mechanism of this effect remains unclear. One potential reason for the insistent results in the literature is related to the artifacts in experimental setups. In this research, a novel ultrasonically assisted micro-tensile testing system was developed. The specimen size is designed to be more than an order of magnitude smaller than that of ultrasonic wavelength. This ensures that the distribution of vibration amplitude along the specimen gauge length is uniform. Using this technique, it was found that the flow stress of pure copper drops by around 10% with 20 kHz, 1.3 μm amplitude ultrasonic vibration. In situ infrared thermography was performed and the results showed that the minor increase in temperature could not account for the significant reduction in flow stress. Electron backscatter diffraction (EBSD) chara (open full item for complete abstract)

Committee: Xun Liu (Advisor); Alper Yilmaz (Committee Member); Avraham Benatar (Committee Member); Stephen Niezgoda (Committee Member) Subjects: Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2019, Materials Science and Engineering

Processing of martensitic steels requires a thermally driven phase transformation into the austenite phase field, where rapid cooling initiates the diffusionless transformation into martensite. The resultant microstructural constituent is a hard, brittle phase that requires subsequent heat treatment to soften the material for optimized mechanical properties. Although the transformation microstructure has the largest influence on these mechanical properties, the prior austenite microstructure has been shown to significantly affect the final product material in the form of ductile to brittle fracture occurrence, classification of creep and cavitation sites, increasing martensite packet and block sizes resulting in Hall-Petch effects, and temper embrittlement. Therefore, reconstruction of the prior austenite phase field can help optimize both the processing of a sample steel or binary ferrous alloy and predicative examinations on the material. However, analysis of the austenite to martensite transformation is hindered by the large volume of noise associated with the transformation. This can be attributed to the scale of the transformation, which results in a single prior austenite grain producing up to 24 martensitic variants; the plasticity associated with the massive formation of martensite; variations in the orientation relationship across variable compositions and morphologies; errors associated with the EBSD-indexing of the transformation microstructure; and annealing twins forming across the prior austenite microstructure. Due to the inherent noise associated with the transformation, modern reconstruction algorithms using point-to-point or flood-fill algorithms struggle to produce accurate and consistent reconstructions of the austenite microstructure. We therefore propose a probabilistic approach to austenite reconstruction in steels and ferrous alloys based on the graph cutting algorithm. This technique can be applied to a number of inverse problems in mate (open full item for complete abstract)

Committee: Stephen Niezgoda PhD (Advisor); Eric Payton PhD (Committee Member); Antonio Ramirez PhD (Committee Member); Yunzhi Wang PhD (Committee Member); Nicholas Brunelli PhD (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2019, Materials Science and Engineering

Thermoelectric materials have drawn wide attention for decades because of their ability of converting between electricity and heat, making them one of the attractive solutions to the world-wide energy and environment challenges. A 2014 Nature article reported SnSe to exhibit an unprecedented thermoelectric performance at 600-700 °C. Oxidation and sublimation are of significant concern at such temperatures. The first part of this study investigates the oxidation behavior of SnSe between 600 °C and 700 °C in atmospheric air by monitoring its weight change. The oxidized samples are then characterized using optical microscopy, SEM, EDS, and powder XRD. Constituents of oxidation and resultant microstructure after oxidation are examined. Severity of oxidation and sublimation are discussed and a suggestion for mitigation is provided. SnSe's ultrahigh ZT is attributed to its extra low thermal conductivity property, but there has been a significant discrepancy of its thermal conductivity values between experimental measurements and computational observations, as well as among experimental values reported by various groups. The second part of this study employed a high-throughput thermal conductivity measurement approach which is capable of measuring orientation-dependent thermal conductivities accurately at a micrometer scale. By integrating time-domain thermoreflectance (TDTR) with electron backscatter diffraction (EBSD) orientation measurement, a list of orientation-dependent thermal conductivities is obtained from polycrystalline SnSe. Three principal thermal conductivities, which were only attainable on single crystals previously, are obtained. This approach demonstrates a novel methodology to acquire principal thermal conductivities reliably without the necessity of growing single crystals. A comparison with experimentally measured values reported in the literature including the original Nature data is presented. The last part of this study aims to understand la (open full item for complete abstract)

Committee: Ji-Cheng Zhao (Advisor); Wolfgang Windl (Committee Member); Glenn Daehn (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 (MS), Ohio University, 2018, Mechanical Engineering (Engineering and Technology)

The purpose of this thesis was to investigate the plastic anisotropic mechanical properties of drawn and annealed copper tubing through mechanical testing and texture analysis. Three standard tube diameters were considered to analyze the effect of increasing amounts of prior cold work induced by drawing. Samples were also examined in a heat-treated state to simulate a brazing thermal cycle, which effectively anneals the material. Tensile tests were performed on specimens from each diameter and condition (as drawn and annealed), and in the axial (drawing direction) and transverse (perpendicular to the drawing direction) orientations. This was done to quantify the anisotropic stress-strain response. The stress-strain response was then modeled using the Voce constitutive equation in combination with the Hill and Hosford anisotropic yield criteria for orthotropic symmetry. The microstructure was characterized using optical light microscopy, micro-hardness testing, and Electron Backscatter Diffraction (EBSD). The axial specimens consistently exhibited a higher flow stress in both the as-drawn and annealed conditions when compared to the transverse specimens. Transverse specimens exhibited higher tensile ductility (elongation before fracture) than axial specimens. Plastic strain ratios were calculated for the axial and transverse orientations to experimentally quantify plastic anisotropy. Plastic strain ratios were found to increase towards 1.0 with prior cold-work in both the as-drawn and annealed states. A Voce type constitutive equation was fit to the stress-strain data with a high degree of precision. The transverse plastic flow stress was predicted using the axial state of stress and plastic strain ratios with the Hill and Hosford anisotropic yield criteria. Both yield criteria overestimated the transverse stress state with Hill's yield criterion providing more accurate predictions. Light microscopy and EBSD of the as-drawn condition revealed clear grain distortions (open full item for complete abstract)

Committee: Frank Kraft PhD (Advisor); Timothy Cyders PhD (Committee Member); Alireza Sarvestani PhD (Committee Member); David Drabold PhD (Committee Member) Subjects: Materials Science; Mechanical Engineering; Metallurgy

Doctor of Philosophy, The Ohio State University, 2017, Materials Science and Engineering

High entropy alloys (HEAs) are a relatively new class of materials that have garnered significant interest over the last decade due to their intriguing balance of properties including high strength, toughness, and corrosion resistance. In contrast to conventional alloy systems, HEAs are based on four or more principal elements with near equimolar concentrations and tend to have simple microstructures due to the preferential formation of solid solution phases. HEAs appear to offer new pathways to lightweighting in structural applications, new alloys for elevated temperature components, and new magnetic materials, but more thorough characterization studies are needed to assess the viability of the recently developed multicomponent materials. One such HEA, AlMo0.5NbTa0.5TiZr, was selected to be the basis for this characterization study in part due to its strength at elevated temperatures (s0.2 = 1600 MPa at T = 800 ºC) and low density compared with commercially available Ni-based superalloys. The refractory element containing HEA composition was developed in order to balance the high temperature strength of the refractory elements with the desirable properties achieved by the high entropy alloying design approach for potential use in aerospace thermal protection and structural applications. Ingots of AlMo0.5NbTa0.5TiZr were cast by vacuum arc melting followed by hot isostatic pressing (HIP) and homogenization at 1400 ºC for 24 hrs with a furnace cool of 10 ºC/min. The resulting microstructure was characterized at multiple length scales using x-ray diffraction (XRD), scanning transmission electron microscopy (SEM), conventional and scanning transmission electron microscopy (TEM and STEM), and x-ray energy dispersive spectroscopy (XEDS). The microstructure was found to consist of a periodic, coherent two phase mixture, where a disordered bcc phase is aligned orthogonally in an ordered B2 phase. Through microstructural evolution heat treatment stud (open full item for complete abstract)

Committee: Hamish Fraser (Advisor); Michael Mills (Committee Member); Yunzhi Wang (Committee Member); William Brantley (Committee Member) Subjects: Materials Science

Master of Science, University of Toledo, 2014, Mechanical Engineering

Driven by the consideration of reducing fuel consumption, rapidly growing automobile industries are becoming increasingly attracted to weight reduction techniques. Due to their distinctive strength-to-weight ratio and ductility, aluminum alloys are widely accepted as vehicle body materials by global auto makers. But there are still barriers to be overcome, such as the difficulty in welding these materials and the high consumption rate of electrodes. The present investigation is about using a new joining technique for joining aluminum alloy AA5754 called Friction-Stir Riveting, developed at the University of Toledo, which combines the two previously well-developed techniques of FSW and SPR. In this process, a joint is formed by spinning and pressing a steel rivet into two layers of aluminum sheets. As the aluminum was not melted, adverse metallurgical changes in welding can be avoided. Tensile-shear tests were conducted, showing the peak load, displacement and energy of the joint with different processing parameters such as spindle speed, feed rate and feed depth. After this, Design of Experiments method was used analyzing a two-level, three-factor, and three-replicate experiment, trying to find out the best combination of processing parameters resulting in a good joining quality. In this study, microstructure has been examined employing the SEM, DSC and EBSD techniques, investigating on the plastic strain, grain size, grain orientation, and grain boundary characteristics of a riveted joint. TMAZ was shown having the largest amount of deformation and the smallest grain size, and both the TMAZ and HAZ are proven to have undergone a dynamic recrystallization making the finished FSR a heat stable structure.

Committee: Hongyan Zhang (Advisor) Subjects: Mechanical Engineering

Master of Sciences (Engineering), Case Western Reserve University, 2014, Materials Science and Engineering

Fracture behavior of Zr-based bulk metallic glasses (BMG) and metallic glass matrix composites (BMGMC), was investigated while varying testing temperature, loading condition and strain rate. Samples were tested in tension, compression, three-point bending and Charpy impact in order to determine the effects of changes in strain rate and test temperature on the tensile strength, compressive strength, ductility, fracture toughness and impact toughness. An increase in temperature was found to have a similar effect as decreasing strain rate. At similar temperatures, displacement-controlled tensile tests caused severe necking to failure after significant ductility, while load-controlled conditions caused samples to draw into long, thin wires, a morphology that was not observed in BMGMC samples. Microstructural evolution of dendrites in deformed BMGMC samples was characterized using electron backscatter diffraction (EBSD) to determine change in crystallographic orientation with progressing deformation. Less dendrite area was indexable as deformation progressed, and the operative deformation mechanism was theorized to be dislocation motion.

Committee: Jennifer Carter Dr. (Advisor); John Lewandowski Dr. (Advisor) Subjects: Materials Science

Master of Science, The Ohio State University, 2012, Mechanical Engineering

Micromechanical crystal plasticity finite element simulations of the response of synthetic titanium microstructures are carried out with the goal of quantifying the effect of microstructure on mechanical properties. Two separate materials are studied: (1) an alpha-beta Ti-6Al-4V material and (2) a highly-textured, rolled alpha Ti-3Al-2.5V sheet material. Performing accurate finite element analyses begins with accurate image-based characterization of the morphological and crystallographic features of the materials at the microstructural scale. Then, statistically equivalent representative 3D microstructures are built and meshes are generated for crystal plasticity based finite element method (CPFEM) analysis. For the Ti-3Al-2.5V material, experimental results from the displacement controlled mechanical testing of dog bone shaped, rolled specimens are used for the calibration of elastic parameters as well as anisotropic crystal plasticity parameters. The inspection of micrographs of the rolled material showed elongated grain shapes which led to the updating of the crystal plasticity model to include grain aspect ratio dependence on the Hall-Petch size effect--an update of a previous size effect model which assumed spherical grains. Model validation is achieved by comparing load controlled experimental results with simulated creep results. For the Ti-6Al-4V material, the robust and validated analysis tool is used to perform sensitivity analyses and a quantitative understanding of how individual microstructural parameters affect the mechanical response properties of the alloy is developed. Functional dependencies are proposed that directly connect the metal's microstructural features to creep response, yield strength response, and tensile response.

Committee: Somnath Ghosh Dr. (Advisor); June Lee Dr. (Committee Member); Reji John Dr. (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy, The Ohio State University, 2009, Materials Science and Engineering

The effect of alloying on the microstructure of ferritic weld metal produced with a self-shielded flux cored arc welding process (FCAW-S) has been studied. The welding electrode has a flux core that is intentionally alloyed with strong deoxidizers and denitriding elements such as aluminum, titanium and zirconium in addition to austenite formers such as manganese and nickel. This results in formation of microstructure consisting of carbide free bainite, retained austenite and twinned martensite. The work focuses on characterization of the microstructures and the precipitates formed during solidification and the allotropic phase transformation of the weld metal. Aluminum, manganese and nickel have significant solubility in iron while aluminum, titanium and zirconium have very strong affinity for nitrogen and oxygen. The effect of these alloying elements on the phase transformation and precipitation of oxides and nitrides have been studied with various characterization techniques. In-situ X-ray synchrotron diffraction has been used to characterize the solidification path and the effect of heating and cooling rates on microstructure evolution. Scanning Transmission Electron Microscopy (STEM) in conjunction with Energy Dispersive Spectroscopy (EDS) and Electron energy loss spectroscopy (EELS) was used to study the effect of micro-alloying additions on inclusion evolution. The formation of core-shell structure of oxide/nitride is identified as being key to improvement in toughness of the weld metal. Electron Back Scattered Diffraction (EBSD) in combination with Orientation Imaging Microscopy (OIM) and Transmission electron microscopy (TEM) has been employed to study the effect of alloying on austenite to ferrite transformation modes. The prevention of twinned martensite has been identified to be key to improving ductility for achieving high strength weld metal.

Committee: Michael Mills Dr (Advisor); Sudarasanam Babu Dr (Committee Member); Hamish Fraser Dr (Committee Member); Marie Quintana P.E (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2009, Materials Science and Engineering

In recent years, friction stir processing has emerged as a solid state metalworking technique capable of substantial microstructure refinement in aluminum and nickel-aluminum-bronze alloys. The purpose of the present study is to determine the feasibility of friction stir processing and assess its effect on the microstructure and mechanical properties of the most widely used alpha + beta titanium alloy, Ti-6Al-4V. Depending on processing parameters, including tool travel speed, rotation rate and geometry, the peak temperature in the stir zone was either above or below the beta transus. The resulting microstructures consisted of either ~1 micron equiaxed α grains, ~25 micron prior beta grains containing a colony alpha + beta microstructure or a combination of 1 micron equiaxed alpha and fine, acicular alpha + beta. The changes in microstructure were characterized with scanning and transmission electron microscopy and electron backscatter diffraction. The texture in the stir zone was nearly random for all processing conditions, however, several components of ideal simple shear textures were observed in both the hexagonal close packed alpha and the body centered cubic beta phases which provided insight into the operative grain refinement mechanisms. Due to the relatively small volume of material affected by friction stir processing, conventionally sized test specimens were unable to be machined from the stir zone. Thus, the mechanical properties were investigated using micropillar compression and microtensile specimens. The effect of friction stir processing on crack initiation resistance was assessed using high cycle fatigue tests conducted in four-point bend which put only the stir zone in maximum tension. The results indicated that at constant stress amplitude, there was greater than an order of magnitude increase in fatigue life after friction stir processing. In addition, the fatigue strength of the investment cast material was improved between 20 pct. and 60 pct. (open full item for complete abstract)

Committee: James Williams PhD (Advisor); Mary Juhas PhD (Advisor); Hamish Fraser PhD (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

MS, Kent State University, 2010, College of Arts and Sciences / Department of Earth Sciences

In the Western Tatra Mountains, the Variscan-age (~340 Ma) exhumed shear zone, reveals high-grade metamorphic rocks thrust over medium-grade metamorphic rocks, creating an unusual macroscopic rock geometry known as an inverted metamorphic sequence. Polyphase petrographic fabrics record the formation of the inverted metamorphic sequence, making it ideal for characterizing mid-crustal deformation mechanisms of large-scale tectonic processes. A combination of microstructural (optical petrography) and microanalytical (monazite EMPA, Titanium thermometry, Electron backscatter diffraction-EBSD fabric analysis) techniques reveal the dynamic processes involved in the evolution of this major crustal-scale discontinuity. The timing of the Early Variscan continent-continent collision was measured by U/Pb monazite dating at c. 370 Ma in the mica schists, with titanium-in-zircon temperatures of ~ 880 °C in the migmatite. These data reflect the peak metamorphic conditions of Early Variscan deformation. During or following exhumation of the high-grade rocks into the mid-crust, titanium-in-quartz data suggests the newly formed inverted metamorphics coexisted at temperatures of approximately 540 °C. The age of Variscan SE thrusting (~ 340 Ma) and its kinematic indicators are lacking in the mica schists. Instead, additional monazite ages from mica schists correlate to younger (c. 315 Ma) plutonism/uplift? and microstructural and analytical results reflect kinematics in a E-W orientation. Collectively, data on the textures, temperatures, and timing within the Tatra tectonic zone do not support the ‘hot iron' model of inverted metamorphic formation. Rather, simultaneous or closely related exhumation of the high-grade metamorphics with orogen parallel extension.

Committee: Daniel Holm (Advisor); David Scneider (Committee Member); Donald Palmer (Committee Member) Subjects: Geological; Geology