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  • 1. Okeyemi, Moyosore Design and Characterization of Ternary and Quaternary Eutectic Aluminum Alloys with Minor Additions of Iron, Nickel, and Cobalt

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

    Aluminum alloys have been heavily studied through research and extensively used in the manufacturing industry for decades. To enhance its properties, aluminum has been alloyed with several elements. This study focuses on the design and characterization of ternary and quaternary Al-rich alloys with minor additions of iron, nickel, and cobalt. In this study, aluminum alloys Al-2Fe-1Co, Al-2Ni-1Co, and Al-2Fe-2Ni-1Co (all compositions in weight percent) were investigated with a focus on the microstructural evolution and changes in hardness with respect to composition and aging. Computational analyses of the alloys were first carried out using Thermo-Calc, a software package based on the Calculation of Phase Diagrams (CALPHAD) methodology, to predict the phase equilibria in these systems. Subsequently, experimental studies were performed to verify predictions from computational analysis. First, pure aluminum, iron, nickel, and cobalt were measured to a sum of 30 g for each of the alloy compositions under consideration. The weighed elemental mixtures were homogeneously arc melted, using the vacuum arc melting (VAM) technique. The three as-cast aluminum alloys were then cut into samples of 25 pieces each. One as-cast piece from each alloy was mounted, polished and examined. First the microhardness tests were performed using a Vickers microhardness tester, and then the microstructural analysis was conducted using a scanning electron microscope, equipped with a back-scattered electron detector and an energy dispersive X-ray spectrometer, and an X-ray diffractometer. The remaining samples were aged by heat treating at 300 and 400?C each and held for 1 hour, 2 hours, 4 hours, 8 hours, 16 hours, 24 hours (1 day), 2 days, 4 days, 8 days, 16 days, 30 days, and 60 days respectively. The microstructure, hardness values, and thermal stability were then examined. The graphs were plotted to compare the hardness values with respect to aging thereby predicting thermal sta (open full item for complete abstract)
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    Committee: Dinc Erdeniz Ph.D. (Committee Chair); Matthew Steiner Ph.D. (Committee Member); Eric Payton Ph.D. (Committee Member) Subjects: Materials Science
  • 2. Mukhopadhyay, Semanti Development of High-Performance Ni-Fe-based Superalloys for Land-Based Industrial Gas Turbine Wheels

    Doctor of Philosophy, The Ohio State University, 2023, Materials Science and Engineering

    Background: A land-based Industrial gas turbine (9HA) lies at the heart of two world records for efficient power generation. Based on thermodynamic principles, the efficiency of gas turbines is dictated by their operating temperatures. Thus, the drive for more efficient power generation ultimately revolves around increasing the operating temperature of gas turbine engines. Specifically, developing a more efficient powerplant requires a gas turbine wheel operating at or above 1200°F (649°C). However, because of the massive size of such turbine wheels (average reported diameters are about 40''), no current superalloy can meet the above temperature goals. In fact, because of its large size, maintaining microstructural stability during the thermomechanical processing of gas turbine wheels is a herculean task. The Unknown: However, most polycrystalline superalloys, including the current state-of-the-art wheel material (Alloy 706), exhibit a hierarchy of microstructures spanning multiple length scales. In that case, microstructural optimization reliant on intragranular precipitate phases alone may not achieve the desired high-temperature performance. Objectives and Findings: The present research focused on optimizing the microstructure of polycrystalline superalloys through concurrent multi-scale structure-property correlation studies. Specifically, I looked at three aspects of the hierarchical nature of the microstructure observed in any typical polycrystalline superalloy: (1) intragranular precipitate distribution, (2) precipitation and consequent precipitate-free zones near annealing twin boundaries, and (3) secondary precipitate evolution on high angle grain boundaries. Our results indicate that unless alloy development strategies utilize a simultaneous optimization approach for these three aspects, achieving the desired high performance in Ni-Fe-based superalloys is difficult. Results from several advanced characterization experiments using various in-si (open full item for complete abstract)
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    Committee: Michael J. Mills (Advisor) Subjects: Materials Science
  • 3. Dunn, Anna Effect of Build Geometry and Build Parameters on Microstructure, Fatigue Life, and Tensile Properties of Additively Manufactured Alloy 718

    Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2022, Materials Science and Engineering

    Additive Manufacturing (AM), particularly laser powder bed fusion, is being studied for use in critical component applications. Tensile and fatigue testing shows differences when built using different laser powers. However, when fabricated in an as-printed geometry, the gauge sections of the two specimens are different and experience different thermal behavior. This work explores microhardness, microstructure size, Niobium segregation, and porosity from samples made with varying laser power and different build geometry sizes representative of the gauge sections in the tensile and fatigue bars. Results show that microhardness varies spatially across the sample. Smaller diameter metallographic coupons (fatigue diameter) have a coarser microstructure and lower microhardness than the larger diameter (tensile diameter) when built using the same parameters. Therefore, the fatigue and tensile properties are not comparing the same material structure. Understanding the effect of build geometry on microstructure provides insight towards consistency in AM mechanical properties testing strategies.
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    Committee: Henry D. Young Ph.D. (Committee Co-Chair); Joy Gockel Ph.D. (Committee Co-Chair); Onome Scott-Emuakpor Ph.D. (Committee Member) Subjects: Engineering; Materials Science
  • 4. Davidson, Laura Microstructural Characterization of LENSTM Ti-6Al-4V: Investigating the Effects of Process Variables Across Multiple Deposit Geometries

    Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2018, Materials Science and Engineering

    Laser based additive manufacturing of Ti-6Al-4V components is under consideration for aerospace applications. The mechanical properties of the finished components depend on their microstructure. Process mapping compares process variables such as heat source power, heat source travel speed, material feed rate, part preheat temperature and feature geometry to process outcomes such as microstructure, melt pool geometry and residual stresses. In this work, the microstructure of two-dimensional pads, multilayer pads, thin walls, and structural components at the steady state location was observed. A method for measuring β grain widths that allows for the calculation of standard deviations, confidence intervals, and variances in grain size was developed. This represents an improvement over the commonly used line-intercept method. The method was used to compare variability of β grain widths across different part geometries. It was found that thin wall parts have the highest β width variability and that the width of the β grains varies more towards the top of multi-layered samples than towards the bottom. Experimental results for α and β grain size across multiple deposit geometries are presented that offer new insight into the effect of process variables on microstructure. β grain widths are also compared for different deposit geometries with the same power, velocity, and feed rate. Single layer pad geometries were found to have the smallest β grain widths, multi-layer pads had larger β grain widths, and thin wall samples had the largest β grain widths. Trends in α width with Vickers hardness were also considered in the context of thermal gradient measurements. Hardness maps were created for the structural component samples. Optical microscopy was used to observe a layering effect in structural component samples. It was found that light and dark bands had different Vickers microhardness values.
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    Committee: Nathan Klingbeil Ph.D. (Advisor); Joy Gockel Ph.D. (Committee Member); Raghavan Srinivasan Ph.D. (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Metallurgy
  • 5. Patel, Rishikumar Investigating the Mechanical Behavior of Conventionally Processed High Strength Aluminum Alloy 2024

    Master of Science in Engineering, University of Akron, 2018, Mechanical Engineering

    In this thesis document, the results and interpretations of an experimental study aimed at investigating and rationalizing the mechanical behavior of a conventionally processed high strength aluminum alloy is presented and discussed. The aluminum alloy chosen for this study was the high strength Al-Cu-Mg alloy, designated as 2024 by the Aluminum Association of America (Washington, D.C., USA). In this study, a few mechanical tests, to include: tension, compression, hardness, shear and cyclic stress-controlled fatigue, were conducted in synergism with microstructural characterization and macroscopic observation and record of the nature of fracture with the objective of establishing the role of alloy microstructure in governing the macroscopic mechanical response and fracture behavior of the chosen aluminum alloy. The mechanical tests were conducted in accordance with procedures detailed in the standards of ASTM. The test specimens for each test were precision machined from the as provided wrought alloy stock. For the cyclic fatigue tests, the presence of a notch, conforming to specifications detailed in ASTM Standard, on cyclic fatigue life is presented. The test results are presented and briefly discussed with specific reference to nature of loading and microstructural influences.
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    Committee: Tirumalai Srivatsan Dr. (Advisor); Anil Patnaik Dr. (Committee Member); Craig Menzemer Dr. (Committee Member) Subjects: Engineering; Materials Science; Metallurgy
  • 6. Loughnane, Gregory A Framework for Uncertainty Quantification in Microstructural Characterization with Application to Additive Manufacturing of Ti-6Al-4V

    Doctor of Philosophy (PhD), Wright State University, 2015, Engineering PhD

    The sampling of three dimensional (3D) mesoscale microstructural data is typically prescribed using simple rules, likely resulting in data under- or oversampling depending on the measurement(s) of interest. The first part of this work investigates one approach for determining a minimally sufficient sampling scheme for 3D microstructural data, using computer-generated phantoms of polycrystalline grain microstructures. Sources of error that are observed experimentally are modeled using phantoms, in order to determine the effect that errors have on the microstructural statistic(s)-of-interest. Minimally-sufficient sampling schemes are then established based on a required accuracy in the microstructural statistic(s). The characterization error modeling framework is subsequently demonstrated on experimentally-derived statistics from high resolution 3D serial sectioning data, in order to inform future experiments on the same material. The second part of this work lends the aforementioned approach to the additive manufacturing (AM) of Ti-6Al-4V. Statistical analysis and virtual modeling tools developed herein are used to analyze alpha and beta phase microstructures in two thin-walled Ti-6Al-4V samples. Ultimately, this research aims to provide a virtual modeling framework for analyzing uncertainty in microstructural characterization, and to produce an offering of novel solutions for addressing current issues associated with rapid qualification methods for AM of Ti-6Al-4V components.
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    Committee: Nathan Klingbeil Ph.D. (Advisor); Ramana Grandhi Ph.D. (Committee Member); Raghu Srinivasan Ph.D., P.E. (Committee Member); Michael Uchic Ph.D. (Committee Member); Jaimie Tiley Ph.D., P.E. (Committee Member); Peter Collins Ph.D. (Committee Member) Subjects: Aerospace Materials; Materials Science; Mechanical Engineering