Master of Sciences (Engineering), Case Western Reserve University, 2015, Materials Science and Engineering

In this study, a number of established additive manufacturing processes were evaluated for their suitability repairing high-pressure die cast tooling. The processes included in this study are laser hot wire (LHW), electron beam freeform fabrication (EBF3), gas metal arc welding (GMAW), Laser Engineered Net Shaping (LENS®), and direct metal deposition (DMD). To determine each process' suitability, blocks of maraging 250 steel were deposited on H-13 base metal. The results show that the maraging deposits are capable of providing good strength (>160 ksi), toughness (>15 ft-lbs), and hardness (45 HRC) for die tooling applications, but care must be taken to limit the occurrence of defects, particularly porosity. Of the processes tested, the LHW, DMD, and LENS® processes had the best balance of deposit properties. However, additional work will be required to optimize the processing parameters for each process.

Committee: David Schwam (Advisor); John Lewandowski (Committee Member); Gerhard Welsch (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Master of Science in Engineering, Youngstown State University, 2024, Department of Civil/Environmental and Chemical Engineering

A longitudinal study in corrosion was performed on tensile-elongation dog-bones, created using 3D-printed stainless steel. The effects of exposure to an acidic environment were investigated regarding mass-loss, tensile and yield strength, modulus of elasticity, profilometry of pits and defects, and microscopy of fracture-sites. The SS316L specimens were manufactured using different print-directions, specifically overlapping unidirectional or rotated bidirectional for each layer by an additive manufacturing unit, the Mazak VC-500/5X AM HWD. The novel aspect of this research is focusing on the differences that the path the hot-wire, direct energy deposition, print-head has on its corrosion characteristics, as opposed to only focusing on the printing-parameters. The goal was to determine what printing-directions and methods were best for resisting corrosion. The research outlines the process of preparing samples for controlled weight-loss in HCl as well as the methods used to measure the mechanical properties. This allows for the results to be repeated if desired. Upon thoroughly reviewing the data and drawing connections where applicable, it was determined within the test samples that unidirectional print-directions yielded better mass-loss and mechanical attributes than bidirectional printing. It was found that some print directions, namely 90°, which is perpendicular to the printing door, performed notably better than other directions such as 0° or 45°.

Committee: Holly Martin PhD (Advisor); Pedro Cortes PhD (Committee Member); Bharat Yelamanchi PhD (Committee Member) Subjects: Chemical Engineering; Chemistry; Engineering; Experiments; Materials Science

Doctor of Philosophy in Materials Science and Engineering, Youngstown State University, 2023, Materials Science

This work discusses the relevance of Metal Additive Manufacturing (MAM) and focuses on one method: Direct Energy Deposition (DED). Different types of DED processes are discussed, including their main parameters and issues. A general procedure to simulate DED processes is presented and founded on the finite element analysis (FEA) workflow. Based on this, two initial case studies are analyzed, which were selected from the literature and reproduced via a commercially available FEA software. Their results provided evidence of the feasibility of the software in simulating a DED process. Two experiments were carried out, called single bead and rectangular prism, for the purpose of this research. These were built with a hot wire and laser DED system, where experimental thermal data was obtained. Geometric information was obtained later via a 3D scan. Limitations of the equipment used as well as observed defects in the material deposition are discussed based on the experimental data. FEA models were developed to duplicate the experiments, which included a detailed geometry of the single bead. Two modifications to the bead geometry are presented and evaluated, where it was concluded that a semicircular bead approximation provides better results than if a rectangular one is assumed. This led to the definition of a thermal and structural equivalent model of the single bead, which was the basis for the numerical work of the rectangular prism. The results obtained for the latter show good agreement with the thermal results, although differences in the structural results are perceptible.

Committee: Kyosung Choo PhD (Advisor); Pedro Cortes PhD (Committee Member); Timothy Wagner PhD (Committee Member); Jae Joong Ryu PhD (Committee Member); Holly Martin PhD (Committee Member) Subjects: Experiments; Materials Science; Mechanical Engineering; Mechanics

Doctor of Philosophy (PhD), Ohio University, 2019, Physics and Astronomy (Arts and Sciences)

Quantum confinement of charge carriers in semiconductor nanostructures have garnered considerable attention in the past few decades. With new materials being discovered and advanced growth techniques allowing them to be engineered into nanoscale devices with atomic precision, the localization of charge carriers is becoming easier to control. The focus of this dissertation is to highlight the employed growth techniques and the characterization of the device structures studied in our lab.In the first project of the dissertation we examined the temporal dynamics of the Optically Generated Electric Field (OGEF) within a CQD device. We demonstrated the potential of using the interdot transition as a sensitive probe to measure electric fields by using photovoltaic band flattening in a Schottky diode structure. A modulated high energy laser was used to create the OGEF leading to photovoltaic band flattening. A CW laser with energy required to create the interdot transition was used to monitor the electric field in the device and characterize the temporal behavior of the field to determine rise time and decay time as well as to show how they depend on different variables.In the Second project we report on monolayer TMD metal semiconductor metal photodetectors produced using a CVD process. The photodetectors showed maximum responsivity of up to 15 A/W. The response time of the devices is found to be on the order of 1 µs, an order of magnitude faster than previous reports. The main project in this dissertation involved using the CVD growth technique employed in developing TMD devices to create deterministic single photon emitters (SPEs) by carrying out the growth on etched substrates. While we have seen successful growth with TMDs growing over perturbations, SPEs are yet to be found. However, in the process of developing these devices we were able to address several challenges in our technique.As highlighted in previous work in the group while the growth technique employed do (open full item for complete abstract)

Committee: Eric Stinaff Ph.D. (Advisor); Sergio Ulloa Ph.D. (Committee Member); David Tees Ph.D. (Committee Member); Wojciech Jadwisienczak Ph.D. (Committee Member) Subjects: Condensed Matter Physics; Physics; Solid State Physics