Master of Science, The Ohio State University, 2023, Materials Science and Engineering

Ti-10V-2Fe-3Al (Ti-1023) is a near beta titanium alloy. It is commonly used in airframes and landing gear due to its high fatigue life, high strength, and deep hardenability. Titanium alloy components for aerospace applications can be produced using additive manufacturing (AM), however, as-deposited Ti alloys typically form columnar grains parallel to the build direction resulting in anisotropic properties. Previous research has shown that the addition of beta eutectoid stabilizers to Ti alloys can promote an equiaxed grain structure in AM depositions by increasing the freezing range. In this research, the effect of adding Fe, a beta eutectoid stabilizer, to Ti-1023 was studied to determine its influence on the freezing range, grain morphology and alpha-lath structure. ThermoCalc was used to predict the freezing range of Ti-1023 with Fe additions of up to 3 wt.%. The freezing range increased from 79°C for Ti-1023 to 149°C for Ti-1053 (3 wt% Fe addition). Samples were produced by vacuum arc melting to determine the effect of Fe on the grain morphology. The aspect ratio was similar for all compositions, however, the average grain size decreased with increasing Fe additions. Heat treatments were performed on the alloys and compared to other Ti alloys with a similar molybdenum equivalency. It was determined that the alpha-lath thickness can be modified by varying the heating rate to the aging temperature.

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

Coke drums are large pressure vessels used in the oil refining process, which generate lightweight oil products and solid cokes as a byproduct from the heavy residual oil. Coke drums are critical units in the delayed coking process and often undergo severe thermo-mechanical loadings that cause plastic deformation in the vessels. The accumulative damage in coke drums over operation cycles leads to low-cycle fatigue failure that significantly reduces the lifetime of coke drums. Many factors can contribute to the low-cycle fatigue damage in coke drums, including design, fabrication, operation, and repair. One of the inherent reasons is the thermal and mechanical incompatibility between the base metal and weld metal, as low-cycle fatigue damages are frequently observed adjacent to the weld seams. The structural integrity is significantly compromised at a bulging or cracking region, so coke drum repair is required before continuing the operation. Welding repair has been widely adopted in industry to restore the structural integrity of damaged regions. However, the repaired regions are also susceptible to subsequent failures due to welding defects and mechanical incompatibility. A careful selection of filler metal and the welding process is critical to improve the efficacy of welding repair. To address the issue of selecting the optimal filler metal and welding process for coke drum repair, a study regarding coke drum welding repair was initiated in the Manufacturing & Materials Joining Innovation Center (MA2JIC) at OSU in the year of 2016. In Phase-I, a novel isothermal low-cycle fatigue (ILCF) testing approach was developed using the Gleeble® thermo-mechanical simulator, and a wide range of filler metals and welding processes were evaluated using this technique. The project entered Phase II in the year 2019. The Phase-II study continues Phase-I efforts on filler metal selection based on low-cycle fatigue evaluation and expands the materials selection scope to coke drum (open full item for complete abstract)

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

Recent increases in computational power have led to growing enthusiasm about the volume of data that can be collected and analyzed for many applications. However, the amount of data some physical/virtual systems generate is so great that an increased reliance on mathematical, statistical, and algorithmic based approaches to analyze and make decisions from the data is required. Application of these computational tools can lead to sharper decision making and vast amounts of knowledge discovered. The abstraction of the scientific decision-making process has led many researchers to consider observing systems with more tunable experimental parameters. This makes traditional experimentation, which is based on human researchers conducting the experiment and using their intuition to drive the next set of experiments, intractable for these applications. Autonomous experimentation (AE) systems, which are also a byproduct of the computational explosion, are able to address this issue and have found use across the fields of biology, chemistry, and materials science. AE systems are typically capable of conducting certain types of experiments with lower and more reliable turnaround times as opposed to their human counterparts. The automated execution of experiments naturally leads one to think about how those experiments can be parallelized and otherwise completed faster due to the lack of human presence in the experimentation environment. Therefore, AE systems are considered when designing many high-throughput experimentation (HTE) efforts. This thesis presents an overview of the current state-of-the-art for AE systems in Chapter 1, a framework developed to increase the independence of AE systems from human assistance in Chapter 2, and a machine-learning (ML) data processing pipeline that automates the image post-processing phase of the analysis of backscattered-electron scanning electron microscope images in Chapter 3.

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

Adequate feedability is essential for GMAW processes to ensure efficiency. The feedability of a wire refers to the wire's ability to feed continuously through the contact tip. While there are several known causes of feedability difficulties when using cored welding wires, there are many variables that have yet to be explored thoroughly. Three factors are investigated in this research to determine their effects on feedability of cored wires: fill percentage, baking time, and baking temperature. A set of metal-cored arc welding wires were created with various fill percentages, baking times, and baking temperatures. Tension testing, microhardness testing, microstructural characterization, and feedability testing were performed on all wires. The tension testing and microhardness testing showed that the baking cycles do slightly affect these properties for the wires. The feedability testing did not show any significant differences amongst the wires dependent upon the fill percentage or baking conditions.

Master of Science, The Ohio State University, 2022, Welding Engineering

For many years, the defense industry has made large investments into making their armored combat vehicles as light as possible without compromising the security of the operators. These heavy vehicles are less agile and more expensive to operate and transport. Friction Stir Welding (FSW) offers a lightweight solution that promotes the weight reduction of these armored vehicles. Traditional arc welding processes create issues that FSW eliminates. As a solid-state process, FSW utilizes low peak temperatures during the welding process which results in superior mechanical performance due to the reduction of the heat affected zone (HAZ) and the dynamic recrystallization that occurs within the stir zone while simultaneously eliminating the potential for hot cracking and hydrogen induced cracking. The overarching goal of this work is to create welds that exceed the capabilities of current arc welding processes utilized in the armor industry. To achieve this goal, this body of work explores the utilization of various in-process thermal management techniques to improve production time and mechanical performance on High Hard Armor (HHA) Steel. This work also investigates the residual stresses present following FSW of Rolled Homogenous Armor (RHA) steel while also looking into the ballistic strength of friction stir welded RHA joints. The in-process induction heating system allowed for the welding speed to be increased by 50%. When this heating system was paired with an ancillary cooling system, the resulting process produced a non-uniform stir zone with various points of high hardness and a larger heat affected zone. Induction assisted + ancillary cooling FSW produced similar toughness values when compared to conventional FSW in all regions of the weld. Residual stresses were successfully measured utilizing neutron diffraction and align with previous research where in the transverse and normal directions high tensile residual stresses were seen in the advancing side and in the (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2022, Welding Engineering

Otherwise ductile metals can experience catastrophic brittle failure in the presence of liquid metals. Although this phenomenon was first noted in the early 1900s, it has gained recent attention as the cause of failure in novel advanced high strength steels during welding. With the right combination of stress, temperature, and microstructure liquid metal can percolate through the grain boundaries of the solid substrate and reduce ductility to near zero. Although many mechanisms for embrittlement have been put forth suggesting brittle failure, reduction in surface energy, dislocation emission due to liquid metal adsorption, and dissolution, no consensus has been reached. The effects of test temperature and hold time are explored for both zinc and copper embrittlement of type 304L stainless steel through the use of hot tensile testing. Copper embrittlement peaks slightly above the melting temperature of copper (1085°C), while zinc embrittlement is most severe at 800°C. Holding the samples at the testing temperature before applying strain allowed the zinc plated samples to regain ductility, but only had slight effects on copper embrittlement. The reasons for these trends in embrittlement are explored in reference to the pseudo-binary phase diagrams between steel and zinc and copper. iv Characterization of zinc-steel interactions via electron microscopy revealed the presence of an α ferrite layer which forms as the zinc diffuses into the solid steel, which causes nickel to be ejected into the remaining liquid. At high enough concentrations of nickel the liquid layer isothermally solidifies as γ Zn (Ni). Thermo-Calc is also used to perform diffusion simulations of the zinc-steel interface both to the bulk and at a grain boundary. The simulations provide a chain of events which lead to the formation of the characterized structures. The results gleaned during characterization in combination with the diffusion simulations are then used to formulate a mechanism for embr (open full item for complete abstract)

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)

Doctor of Philosophy, The Ohio State University, 2022, Welding Engineering

Ductility-dip cracking (DDC) in face-centered cubic (FCC) alloys, such as nickel-based alloys and 300-series stainless steels, is a challenge faced by nuclear power generation. Aging reactors need to be repaired via multipass weld overlays to extend their lifetime. DDC often occurs in the first few layers of these overlays, and the nuclear industry has low flaw tolerance, making DDC subject to costly repair and rework. The prevailing theory describing DDC is based on observations of grain boundary (GB) sliding, microvoid formation, and the effect of GB tortuosity. This work aims to quantify the effect welding process parameters and welding generated stresses have on the formation of DDC and to provide clear avenues for productive future research. The main project objectives include the development of methodology, based on combining physical experiments and computational modeling, for prediction of DDC in multipass welds of austenitic alloys that is applicable for materials selection and process optimization. An additional study on the DDC fracture surface was conducted due to findings from the experimental component. Research began with the development of a Gleeble-based experimental procedure that evaluates a material's susceptibility to elevated temperature embrittlement. The procedure is called simulated strain ratcheting (SSR), and preliminary testing led to the use of the imposed mechanical energy (IME), defined as the integral of experienced stress vs. strain, as a parameter for quantification of thermo-mechanical loading in Gleeble tests and FEA models of multipass welds. This experimental procedure was used to successfully generate DDC in various nickel-based alloys and 310 stainless steel. Fracture surfaces generated from this testing were found to exhibit thermal faceting (TF), which warranted further study. Samples which contained high amounts of DDC, or those which experienced fracture, also generally experience higher IME than those which showed no s (open full item for complete abstract)

Master of Science in Mechanical Engineering (MSME), Wright State University, 2022, Mechanical Engineering

Refractory metal alloys in the tungsten molybdenum rhenium ternary system were additively manufactured using laser power bed fusion. Four ternary alloys with varying concentrations of tungsten, molybdenum, and rhenium were manufactured and manufactured again with an addition of 1 wt% hafnium carbide. Samples were heat treated to heal cracks, reduce porosity, and reduce inhomogeneity. Material microstructure was characterized before and after heat treatment using microscopy, energy dispersive x-ray spectroscopy, and electron backscatter diffraction mapping. Mechanical testing was conducted on both three-point bend specimens and compression specimens, resulting in maximum bending strengths of 677.86 MPa, and maximum compression 0.2% yield strengths of 583.88 MPa for the strongest composition. The ternary alloy samples exhibited less porosity, less cracking, more refined grains, and higher strengths. The hafnium carbide doped samples exhibited more cracking and porosity, larger grains, and lower overall strengths.

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

The process of laser impact welding utilizes impact welding and laser-driven flyers to form solid-state, metallurgical welds between similar or dissimilar metallic flyers and targets. With chemically augmented laser impact welding, stronger and thicker metal flyers and targets can be welded together. Using a high-powered laser, a laser pulse is shot through a transparent tamping layer onto a translucent layer of chemical liquid and the bare surface of a metallic flyer. The energy from the laser pulse detonates the chemical augment and the pressure created from the explosion is confined by the tamping layer. This pressure is directed towards the flyer that is then driven to velocities in the hundreds of meters per second within 20 microseconds. Under the correct conditions, high speed and acceptable impact angle between the flyer and target, jetting will occur. The jet cleans the surface of the flyer and target of oxides, and the two surfaces will form a solid-state, metallurgical bond. Using a chemical augment, thicker, stronger flyers and targets can be welded compared to unaugmented laser impact welding. With the chemical augment, a 3J, 8.1ns laser pulse can weld a 0.5mm Al2024-T3 flyer to a 0.5mm Al2024-T3 target. To explore the capabilities of chemically augmented laser impact welding, two chemical augments were used as candidates for the process. Various tamping materials and thicknesses were also investigated along with variance in the laser spot diameter. The velocities of flyers were measured using Photon Doppler Velocimetry and a thicker tamping layer produced higher velocities and larger deformations than thinner tamping layers did with the same parameters. The strength of the welds between 0.5mm Al2024-T3 flyers and targets were also measured using a tensile test. Over two-thirds of the welded samples failed by nugget pullout during these tensile tests, validating the strength of the welds formed. Micrographs of a welded sample were also collected to o (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2022, Welding Engineering

Dissimilar material welding has grown in popularity in the lightweight design of biomedical, automotive, and aerospace products. However, welding of two or more different materials presents difficulties due to their notable mismatch in chemical, physical and mechanical properties. Some traditional joining methods are undesirable due to the formation of intermetallic compounds and thermally induced defects. These defects make the dissimilar welds unable to reliably serve in actual applications. Vaporizing Foil Actuator Welding (VFAW), an impact welding method, can minimize the abovementioned defects and join various dissimilar metals in solid state with reliable properties. This dissertation focuses on developing VFAW to join three metal pairs including Ti/stainless steel (SS), NiTi/SS, and NiTi/brass alloy. The process, microstructure, and properties of these dissimilar impact welds were explored through advanced techniques and compared with traditional welding methods. This work also introduces a new additive manufacturing method based on impact welding, called Ballistic Additive Manufacturing (BAM). The potential applications and overall long term vision of BAM were demonstrated. The results show that VFAW was effective in joining Ti and stainless steel. Ti/SS impact welds have reproducible macro- and micro-structure and show spatial heterogeneities at large and small length scales. Simulation shows that strength and failure modes are not affected adversely by the size of the central unbonded zone. Since mufflers in automobile could encounter thermal exposure ranging from 300 to 800 °C, a Nb interlayer was introduced to improve the thermal resistance. Both types of bonds give base metal failure in lap shear tests in as-welded condition. Guidelines for the production, properties and applications of these classes of welds are provided. High strength and fatigue resistant impact welds were produced between a NiTi shape memory alloy and dissimilar metals including (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2022, Welding Engineering

Lightweight structures are receiving continuous attention for improving fuel efficiency and reducing carbon emissions. This closely relies on utilization of advanced lightweight and multi-material structures. Joining is considered as the backbone of any manufactured assemblies and it becomes more challenging when it comes to join dissimilar materials. Resistance spot welding (RSW) is widely used in automotive industry based on its high level of productivity and degree of automation. However, RSW welds are prone to various defects such as solidification cracks, porosities, residual stresses, and brittle intermetallics that significantly deteriorate weld quality. On the other hand, power ultrasonics involves the utilization of high intensity acoustic waves to change materials and processes. In this research, a hybrid joining process known as ultrasonic resistance welding (URW) is developed, which integrates high-power ultrasonic vibrations into conventional RSW process. The weldability of galvanized transformation induced plasticity (TRIP-780) steel is investigated via URW process. Ultrasonic resistance welds showed nugget pullout failure mode and more ductility compared with conventional resistance spot welds. Optical and scanning electron microscopic analysis revealed the refined microstructure in the fusion zone and heat affected zone of ultrasonic resistance welds. Coalesced bainite is present in the fusion zone of conventional resistance spot welds while possible tempered martensite and feathery bainite is observed in ultrasonic resistance welds, which accounts for their higher ductile behavior. Moreover, URW of aluminum alloy AA6061-T6 at various conditions was studied and compared with the results from RSW. Lap shear tensile tests of URW welds showed significantly improved mechanical properties, including higher strength, better ductility and higher amount of energy absorbed prior to failure compared with RSW welds. Optical micrographs of the weld cross (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2022, Mechanical Engineering

Ultrasonic additive manufacturing (UAM) is an additive manufacturing technology which combines ultrasonic metal welding, CNC machining, and mechanized foil layering to create large gapless near net-shape metallic parts in solid state. Its integration with subtractive processes enables the creation of complex design features such as heat exchangers. The low formation temperature of the UAM process allows the integration of temperature-sensitive components, smart materials, cooling channels, organic polymers, and electronics into metal matrices. UAM is currently limited to niche applications, as resource-intensive trials are required to evaluate the feasibility of joining new material combinations due to a lack of process models in the literature with predictive ability to establish process-property relationships. The key thrusts of this research are to characterize the energy flow in the UAM process, investigate the role of cold working and friction on UAM bond strength, and develop an energy-based model for process-property relationships of UAM builds. Analytical and finite element (FE) models are used to describe the state of stress under plastic deformation in UAM. An empirical model is developed between the estimated energy of plastic deformation, a driver of bond quality in UAM, and the measured strength of the weld interface in shear. In-situ measurements are conducted using a Doppler velocimetry to monitor the in-situ vibration dynamics of the foil during UAM and to characterize energy losses associated with friction. Each objective is accompanied by analytical, finite element, or experimental findings to aid and supplement the effort.

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

This dissertation presents a thorough study of the microstructure evolution of alloys and welds subjected to different processing conditions. The microstructure of alloys and welds are strongly influenced by processing conditions which influences the materials mechanical properties and performance. A new technique has been developed to quantify the spatial variation of grain sizes, grain shapes, and grain boundary curvatures in the fusion zone (FZ) and heat affected zone (HAZ) of welds. Very limited past work has been done to quantify many of these grain microstructure properties characterized from this technique. Trends between each microstructural feature has been captured between welds subjected to different welding parameters and post weld processing. Accruing knowledge of the microstructural trends with processing conditions has proven to be advantageous in developing correlations with various mechanical properties and advancing weld engineering. The microstructure evolution of gas tungsten arc molybdenum welds subjected to multiple weld processing conditions has been evaluated with the developed technique. Varying the heat input, welding speed, and welding technique caused noticeable to drastic changes in the FZ and HAZ grain microstructure which also influenced the materials mechanical properties. The microstructure evolution of DOP-26 GTA welds subjected to different levels of thermal exposures has also been evaluated with the developed technique. Iridium alloys are primary used in space applications and the thermal exposures simulated typical operation conditions and launch failure scenarios. Annealing causes significant changes to many grain properties in the FZ of these welds which was correlated to changes in mechanical properties. Other techniques including SEM and EBSD has been done to capture the precipitate distribution and grain texture in the weld answering questions posed from the microstructure evaluation results. Alloy design and deve (open full item for complete abstract)

Master of Science, The Ohio State University, 2021, Welding Engineering

Ferromagnetic shape memory alloys (FSMAs) have the ability to revert back to original shapes and properties after significant deformation. When in single crystalline form, these alloys produce up to 10% reversible magnetic field induced strain (MFIS) which can be beneficial in actuators, sensors, and self-assembly. Advanced manufacturing techniques such as laser-based additive manufacturing enables the fabrication of complex parts, but creates complex microstructures that are characteristic for non-functional alloys. Thus, there is a critical need to establish a fundamental understanding of how non-equilibrium processing and complex thermal cycling affect microstructural evolution and functional properties in ferromagnetic shape memory alloys. The overall goal of this work is to correlate the effect of rapid solidification to microstructure and mechanical and magnetic properties in Ni-Mn-Ga Heusler alloys. In order to develop processing-microstructure-property relations, setup and optimization of various rapid solidification techniques was conducted, including levitation-drop melting, electrode arc melting, and laser beam melting. Determination of cooling rates before solidification for the different techniques was done using thermocouple, pyrometer and infrared camera measurements, finite element thermal analysis, and measurements of secondary dendrite arm spacing on solidified samples. Characterization of rapidly solidified Ni2MnGa alloy (and two off-stoichiometric compositions) was performed in terms of solidification microstructure, segregation behavior, phase transformation temperature and magnetic and mechanical properties as a function of cooling rate. Light optical and scanning electron microscopy, electron dispersive spectroscopy, and X-ray diffraction, differential scanning calorimetry, vibration sample magnetometry, and micro-hardness testing were performed. Results were compared to microstructure and properties in samples from laser-metal depositi (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2021, Materials Science and Engineering

Crystal plasticity modeling was used to understand the deformation process of FCC metals and alloys. Firstly, we investigated the issue of cube texture development during static recrystallization of FCC metals, which has been vigorously debated over the last 70 years. A Full-field elasto-viscoplastic fast-Fourier transform (EVP-FFT)based crystal plasticity solver coupled with dislocation density based constitutive model was employed to understand the deformation process in copper under plane strain compression. Simulation results revealed that the grains with initially cube orientation retained a small fraction of the cube component in the deformed state, whereas, some of the grains with initially non-cube orientations developed the cube component during the deformation. For strain up to 0.46, non-cube grains which are within 10-20 deg from the ideal cube orientation showed the highest affinity to develop the cube component during deformation. However, the cube component developed during the deformation was unstable and rotated away from the cube orientation with further deformation. With increasing strain up to 1.38, some of the grains with higher angular deviation from the ideal cube orientation also developed the cube component. No particular axis preference was observed for the non-cube grains, rather, the evolution of the cube component becomes dynamic at larger strain. Rotation of the non-cube grains towards the cube component is mainly driven by the local relaxation of the imposed boundary conditions. Significant changes in lattice rotation and slip activity were observed with different relaxed constraints. Best correlation was found for the e13 strain component and the development of cube component. Analysis of the disorientation angle and the dislocation density difference with the neighboring locations showed that the cube component developed during the deformation can play a significant role during nucleation. (open full item for complete abstract)

Master of Science, The Ohio State University, 2021, Welding Engineering

The objective of this study was to evaluate the feasibility of Inline Coherent Imaging Technology (ICIT), a real-time quality monitoring technology, for Hybrid Laser Arc Welding (HLAW) of ship panel butt joints. The ICIT system offers monitoring in the pre-weld (gap and mismatch), in-weld (root tracking and subsurface defect formation) and, post-weld (bead face geometric inspection) positions. To determine the ICIT sensor's flaw detection capabilities, quality scenario tests (QSTs) were designed to evaluate potential sources of discontinuities and understand their impact on the welding process. The QSTs were designed to create discontinuities such as porosity, undercut, underfill, lack of fusion, and lack of penetration. HLAW process parameters were also varied to develop an optimized and “sound” base-line weld condition using a 6kW laser. A large part of the investigation assessed autogenous partial and full penetration welds during laser keyhole mode welding to allow focused evaluation of the ICIT system. These welds were performed on two different joint configurations that were made from two different thicknesses of AH36 structural ship steel. Tests focused on keyhole depth (KHD) tracking accuracy at varying powers and reference plane positions (RPP)s. Field of view (FOV) shifting and multi-factor monitoring were evaluated to understand their effects on the ICIT system's flaw detection capabilities. Tests were also carried out to determine the effects of adverse tracking and laser conditions on ICIT sensor accuracy. Additional welds were performed to study the geometric compensation feature and whether the sensor has applicability beyond laser keyhole welding. The QST matrix provided a range of discontinuities for analysis and is representative of conditions in naval shipyards. The ICIT sensor system was able to track the root, seam, and bead shape of a partial penetration weld with high accuracy. Full penetration KHD was difficult to track accurately and co (open full item for complete abstract)

Master of Science, The Ohio State University, 2021, Welding Engineering

Grade 92 is a creep-strength enhanced ferritic (CSEF) steel widely used in the power generation industry. This steel shows a clear reduction in the cross-weld creep performance resulting in Type IV failure in the heat affected zone (HAZ). To study the creep behavior of the susceptible HAZ region responsible for reduction in cross-weld creep behavior, phase transformation analysis and microstructural characterization techniques are being utilized as part of an overall effort to develop a standardized procedure for creating representative and relevant synthetic HAZ microstructures and samples. Simulated and real weld HAZ microstructures are characterized using optical and electron microscopy techniques. Simulated Grade 92 HAZ samples were prepared using a Gleeble™ 3800 Thermomechanical simulator. Heating rates for the HAZ simulations represented furnace heating and commonly used arc welding processes for component fabrication. Peak temperatures range from 880°C to 1250°C, representative of the partially transformed zone (PTZ) and completely transformed zone (CTZ), respectively. All samples were prepared using standard techniques, etched with Vilella's reagent for optical microscopy, analyzed using SEM imaging, EBSD, and carbon replica extraction in the TEM for carbide analysis. Simulated samples were then compared to bead-on-plate samples created using representative heat inputs. Dilatometry results from Gleeble™ HAZ simulations confirmed Ac1 and Ac3 transformation temperatures for each heating rate used in this study. Simulated samples were then created in the CTZ well above the Ac3 temperature, PTZ between the Ac1 and Ac3 temperatures, and PTZ above the Ac3 temperature. Bead on plate tests were conducted on 1” Grade 92 plates using 20, 35, and 50 kJ/in heat inputs to represent SMAW, SAW, and GTAW processes. BOP tests were cut and measured for thermocouple placement for thermal history acquisition. Previous studies found that increasing the heating rate for the (open full item for complete abstract)

Master of Science, The Ohio State University, 2021, Welding Engineering

Large-scale additive manufacturing (AM) capabilities is offered through the use of pulse gas metal arc directed energy deposition (P-GMA DED). This process incorporates a commercial robotic cell and gas metal arc welding apparatus to generate components additively layer by layer. The advantages of this platform include lower costs and higher deposition rates when compared to other DED processes, positioning this technology for widespread industrial adoption. To enable the digital manufacturing of a component from a computer-aided design (CAD) file, computer-aided manufacturing (CAM) solutions must generate required robot path and welding parameter commands as programs. These instructions are highly dependent on the feature and application requirements as well as material used. To this end, scalable and robot-agnostic computer-aided robotics (CAR) software is required to automate the programming for deposition. This work establishes the use of Autodesk PowerMill Ultimate software as a CAM/CAR solution for arc-based DED processes across robot manufacturers. An 8-axis OTC Daihen P-GMA robot DED welding system was converted into a DED system by modeling the robot cell (i.e. the digital twin) and coding a post-processor that compiles the PowerMill build simulation solution into the “physical” robot build plan program. P-GMA DED welding parameters were developed to produce a wide range of features and components using aluminum-magnesium alloy ER5183 filler wire material. This alloy is widely used in shipbuilding and large vehicle structures based on its good strength and weldability where large-scale DED can reduce cost and schedule. Systematic parameter development techniques were applied and developed to determine parameters for single-pass per layer “walls” and multi-pass per layer “block” features. Builds and features of increasing complexity were evaluated using different wall and block parameters. Walls and block parameter were systematically modified (open full item for complete abstract)

Master of Arts (MA), Ohio University, 2021, Art History (Fine Arts)

The ‘damasquinado' is a beautiful and technical artform that is derived from one of the oldest metalworking styles in the world, dating back to ancient times, and resulting in a variety of wonderful art objects that show the evolution of the metalworking technique and design style. I will be analyzing some pieces that span this timeline of the ‘damasquinado', defining the term itself, that will show the effects of the tourist art market on the artform, and the relationships that form therein, that has helped to keep the artform relevant in contemporary Spain.