Master of Sciences (Engineering), Case Western Reserve University, 2024, Materials Science and Engineering

In this work, in-situ alloying of a dispersion strengthened copper alloy made via laser powder bed fusion (LPBF) and the effect of hot isostatic pressing on the materials properties were examined. Dispersion strengthened copper alloys such as GRCop-42 that contain 7 vol% of Cr2Nb are used in high temperature applications such as rocket engines. This work examines the effects of HIP post processing on an in-situ alloyed dispersion strengthened Cu alloy. Elemental powders of Cu, Cr and Nb were mixed and used to print two different builds with different print settings that were characterized in the as-deposited and HIP conditions. Microstructure characterization included porosity measurements, metallography, EBSD, SEM, and EDS to examine the effectiveness of in-situ alloying to create Cr2Nb during AM as well as details of the dispersoids, grain morphology, and texture in the as-built and HIPed condition. Mechanical properties including tension, fatigue, and creep properties of the as-built and HIPed material were also determined. Uniaxial tension testing at 25˚ C, 400˚ C, and 600˚ C was conducted and Four-point bend fatigue at a load ratio, R = 0.1, was conducted on material to create S-N plots. Vacuum creep testing at 500˚ C, 650˚ C, and 800˚ C was also conducted on HIPed material, and all fracture surfaces were examined in the SEM. Results from characterization of the in-situ alloyed Cu alloy were compared to literature values for dispersion strengthened copper alloys. In summary, in-situ alloying of the dispersion strengthened copper alloy was demonstrated but improved printing parameters will be needed to produce fully dense materials with complete conversion of Cr2Nb. The effectiveness of HIP was dependent upon the degree of interconnected porosity in the as-deposited material.

Committee: John Lewandowski (Committee Chair); David Ellis (Committee Member); James McGuffin-Cawley (Committee Member); Sunniva Collins (Committee Member) Subjects: Aerospace Materials; Materials Science

Master of Computing and Information Systems, Youngstown State University, 2023, Department of Computer Science and Information Systems

Additive Manufacturing (AM), particularly LASER Powder Bed Fusion (LPBF), has gained prominence for its flexibility and precision in handling complex metal structures. However, optimizing L-PBF for intricate designs involves analyzing over 130 process parameters, leading to prolonged duration and increased costs. This thesis proposes a novel approach by harnessing statistical and machine learning algorithms to predict manufacturability issues before the printing process. By performing a comparative analysis of the intended design with the machine produced result, the study introduces two machine learning and one artificial neural network (ANN) algorithm to forecast the printability of new designs accurately. This innovative method aims to reduce or eliminate the need for iterative printing, reducing productivity costs and optimizing the LPBF additive manufacturing process.

Committee: Alina Lazar PhD (Advisor); John R. Sullins PhD (Committee Member); Hunter Taylor PhD (Committee Member) Subjects: Computer Engineering; Computer Science; Engineering; Information Science; Information Systems; Information Technology; Materials Science; Mechanical Engineering

Master of Science (MS), Ohio University, 2022, Mechanical Engineering (Engineering and Technology)

Laser Powder Bed Fusion (L-PBF) is a branch of metal additive manufacturing technologies which has become increasingly more popular due to the geometric freedoms and strategic design methods which it allows. L-PBF produces metallic components to near net shape within a single process step while simultaneously allowing for the creation of complex geometries and internal structures which are not readily produced by other manufacturing techniques. Not without issues, L-PBF produces materials with preferential directions of growth in the underlying material microstructure as well as undesirable phase content in many cases. While techniques exist to change microstructure of L-PBF materials, many rely on post-processing or in situ control over the flow of heat. This thesis documents the development and analysis of a novel technique separate from previous methods which allows for in situ modification of grain structure produced in LPBF without the need of complex modification of the machine. Ultrasonic vibrations are introduced to the build process as an added parameter, hypothesizing that in situ ultrasonic cavitation will reduce grain size and modify the formation of secondary phases in a way that is beneficial to the as-manufactured material properties.

Committee: Brian Wisner (Advisor) Subjects: Mechanical Engineering

Doctor of Philosophy (PhD), Wright State University, 2021, Engineering PhD

In the pursuit of optimum performance, materials engineering seeks to design the microstructure and thus the properties of a material through the control of the material composition and processing. Functionally graded materials (FGM) are designed to incorporate location-specific material properties through compositional changes within the part. Moving toward location-specific design of material properties requires the ability to produce material gradients in three dimensions which can be accomplished through the use of additive manufacturing (AM). This research examines the composition-process-structure-property relationship of early iteration titanium (Ti) and tantalum (Ta) graded alloys built in a novel laser powder bed fusion (LPBF) process through the characterization of vertical and horizontal graded orientations. Ultimate tensile strength, fractography, and Vicker's microhardness (HV) are used to evaluate the mechanical properties and materials characterization includes X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The binary Ti-Ta alloy system is of great interest to many fields of engineering including biomedical and aerospace because of the unique thermal and mechanical properties it possesses. This work discovered that the concentration of Ta required to promote full beta phase stabilization in Ti is 25% greater than what has been previously reported when used in LPBF. Understanding of AM processing effects includes influences from both the thermal behavior and machine processing strategy which impacts composition location control and influences phase evolution. Elemental segregation occurs due to incomplete mixing in the melt pool and remelting at the horizontal interfaces. It is also established that the interfaces are structurally sound, but phase transformations and resulting microstructures differed between the vertically and horizontally gra (open full item for complete abstract)

Committee: Joy E. Gockel Ph.D. (Advisor); Raghavan Srinivasan Ph.D. (Committee Member); Henry D. Young Ph.D. (Committee Member); Todd Butler Ph.D. (Committee Member) Subjects: Engineering; Materials Science

Master of Science (MS), Wright State University, 2021, Computer Science

The additive manufacturing (AM) field is striving to identify anomalies in laser powder bed fusion (LPBF) using multi-sensor in-process monitoring paired with machine learning (ML). In-process monitoring can reveal the presence of anomalies but creating a ML classifier requires labeled data. The present work approaches this problem by printing hundreds of Inconel-718 coupons with different processing parameters to capture a wide range of process monitoring imagery with multiple sensor types. Afterwards, the process monitoring images are encoded into feature vectors and clustered to isolate groups in each sensor modality. Four texture representations were learned by training two convolutional neural network texture classifiers on two general texture datasets for clustering comparison. The results demonstrate unsupervised texture-driven clustering can isolate roughness categories and process anomalies in each sensor modality. These groups can be labeled by a field expert and potentially be used for defect characterization in process monitoring.

Committee: Tanvi Banerjee Ph.D. (Advisor); Thomas Wischgoll Ph.D. (Committee Member); John Middendorf Ph.D. (Committee Member) Subjects: Computer Science; Materials Science

Master of Science, University of Toledo, 2021, Industrial Engineering

In this project, the processing-structure-property-performance correlation of a newly developed high-strength TiB2 reinforced aluminum-copper alloy, i.e., Al-Cu-Mg-Ag-TiB2 (A205), in the laser powder-bed fusion and casting conditions are investigated. This research work aims at assessing the mentioned correlation between the as-fabricated and the heat-treated materials. The studied A205 alloy is indeed characterized as a heat-treatable aluminum alloy. Therefore, the effects of different post-fabrication heat-treatment processes, including (i) solution treatment (520℃ for 2 h) and (ii) over-aging and stabilizing treatment (T7), are also assessed. To this end, depth-sensing indentation testing and extensive structural analyses, including optical, scanning electron, and transmission-electron microcopies, as well as texture assessment through electron backscattered diffraction, are conducted to evaluate the stated relationship in the additive manufacturing (AM) and casting conditions. Detailed microstructural analyses confirm the presence of fine equiaxed grains, with grain size less than 1 µm, in the as-built condition with enhanced mechanical properties compared with the cast counter material where the grains are in the range of 46 µm in size. This would offer a new compositional window for the lightweight, high-strength AM material categories for various applications, including automotive and aerospace industries. Besides, our findings demonstrate the importance of controlling the precipitates through the post-fabrication heat treatment processes. The post-fabrication solution heat-treatment and T7 aging significantly altered the microstructure and mechanical properties of the materials. In particular, the T7 treatment highly enhanced the mechanical properties of the materials, both at AM and casting conditions. The present project also investigates ambient (room) temperature indentation creep of AM and cast Al-Cu-Mg-Ag-TiB2 alloy at as-fabricated and T7 heat-tre (open full item for complete abstract)

Committee: Meysam Haghshenas (Committee Chair); Mohammad Elahinia (Committee Member); Anju Gupta (Committee Member); Behrang Poorganji (Committee Member) Subjects: Materials Science

MS, University of Cincinnati, 2021, Engineering and Applied Science: Materials Science

The Inconel 625 nickel-based superalloy is commonly used in aerospace and petrochemical industries for its excellent mechanical and corrosion properties in high temperature environments. In this study, a plate of Inconel 625 additively manufactured by a laser powder bed fusion process was subjected to microstructural characterization and mechanical testing post and prior to heat treatments. While this is a solid solution strengthened alloy, it also gains considerable strengthening through heat treatments by means of precipitating the favorable ?” secondary phase. However, during exposure to high temperatures, the precipitation regime for such a phase can coexist along with unfavorable phases; most notably, ? and other TCP phases. It is thus important to know the limits of such exposures and as well as the interrelationship between these phases. An aging heat treatment process between 600 ?C – 700 ?C can help study this material in its most important and frequently operated temperatures and can also help obtain a state with most beneficial mechanical properties. LPBF alloys, however, are subjected to rapid solidification during manufacturing and can possess considerably high amounts of residual stresses which can alter both, the microstructure and the mechanical properties. This requires a comparison study with similarly treated wrought counterpart material in order to assess the material's feasibility for additive manufacturing. By characterizing the material using SEM, TEM and XRD, it was seen that the as-LPBF material possessed an epitaxial microstructure with a high concentration of dislocation cells, and which is seen as a major factor in enhancing its mechanical properties at room temperatures to be comparable to the heat-treated wrought alloy. With further aging heat treatments, by following a solution treatment and without one, it was seen that the material performed considerably better without recrystallization of its LPBF microstructure in room temperatu (open full item for complete abstract)

Committee: Vijay Vasudevan Ph.D. (Committee Chair); Yao Fu Ph.D. (Committee Member); Ashley Paz y Puente Ph.D. (Committee Member) Subjects: Materials Science

Master of Science, University of Toledo, 2021, Mechanical Engineering

NiTi Shape memory alloys (SMAs) have recently gained increased interest due to their unique features such as super elasticity and shape memory effect. There is an ongoing research effort on practical Additive Manufacturing (AM) processing to arrive at optimized AM process parameters to develop functional NiTi devices with minimal post-processing. Laser Powder Bed Fusion (LPBF) is a promising free-form AM method for fabricating this material. It is well established that LPBF AM can be used to tailor the properties of NiTi SMAs by adjusting various process parameters. Modeling approaches are cost and time-effective tools to expedite the study of process parameters optimization for AM fabricated parts. Since the LPBF process deals with ii thermal cycling over the material, thermal modeling of the LPBF process is an essential step of the process and material optimization. That is why it is essential to have a comprehensive thermal understanding of the phenomena using a thermal model to open the door for NiTi optimization. More specifically, melt pool geometry is an essential thermal parameter that affects the resulting material properties. In this thesis, a thermal model has been developed to predict the melt pool size during the LPBF of NiTi. Macroscale physics has been selected for the modeling framework utilizing COMSOL Multiphysics® to develop a thermal model for LPBF melt pool size of NiTi alloy. The Two main stages that are considered to model the melt pool are 1) thermal/melt pool modeling of single laser pass on a NiTi substrate and 2) thermal/melt pool modeling of single layer pass over a single layer of NiTi powder with a thickness of 30μm spread on a NiTi substrate. The model was calibrated in the first stage of modeling the thermal process over the substrate. Through matching the experimental and modeling results, the thermal properties were calculated. These properties were then used to calculate powder thermal properties in the second stage of simulat (open full item for complete abstract)

Committee: Mohammad Elahinia Dr. (Committee Chair); Meysam Haghshenas Dr. (Committee Member); Ala Qattawi Dr. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2020, Engineering and Applied Science: Mechanical Engineering

Metal additive manufacturing (AM) has a variety of applications ranging from gas turbine engines to biomedical implants. By not being constrained to subtractive manufacturing limitations, additive manufacturing gives engineers greater design freedom than conventional manufacturing methods. Of particular interest has been Laser-Powder Bed Fusion (L-PBF), as it enables printing fine features with up to 99.9% dense material. One issue that has hindered the adoption of additively produced metal parts is that supports are typically required to anchor the printed part to the build plate as to resist warping caused by residual stress accumulation, as well as to prevent shifting due to lateral forces generated by the powder recoater. Additionally, the supports provide a path for heat conduction to allow the area of the part being printed to cool. However, the presence of supports increases the labor and cost of the manufacturing process once the parts are removed from the printer by requiring post-processing steps to be added including an extra thermal treatment, cutting of the part from the build plate, and removal of the supports. With recent advancements to the L-PBF process and printer technology, supports are no longer required for certain parts such that the parts are being supported solely by the powder bed itself, which is more commonly referred to as free-floating. One advancement is that the newest generation of machines have a non-contact recoater, thus eliminating lateral forces being applied to the part. An additional criteria is that the part being printed must initiate from a single point to avoid deformation due to residual stresses. Beyond the single point initiation, however, the geometrical constraints prior to process breakdown are not well understood. The common shapes generated when printing free-floating parts are cones, tetrahedrons and pentahedrons. Therefore, these standard geometries with varying overhang angles and filet radii were chosen to (open full item for complete abstract)

Committee: Ashley Paz y Puente Ph.D. (Committee Chair); Jing Shi Ph.D. (Committee Member); Sarah Watzman Ph.D. (Committee Member) Subjects: Engineering

Master of Science in Engineering, Youngstown State University, 2019, Department of Mechanical, Industrial and Manufacturing Engineering

Additive manufacturing is one of the more recent advances in manufacturing technology. Additive manufacturing processes allow for the creation of parts in a layer-by-layer fashion. There are several materials that can be used in additive manufacturing processes including metal, ceramic, and polymers which each presenting their own challenges. This work focuses on metal based additive manufacturing parts made out of AlSi10Mg using a process called laser powder bed fusion. Laser powder bed fusion is one of the three major metal additive manufacturing processes with the other two being multi-pass welding and direct energy deposition. One of many challenges that occur with the laser power bed fusion process is minimizing the residual stresses and distortion that are present in the part during and after the build. During the early days of additive manufacturing that was mostly done through a trial-and-error process where multiple version of a part would be printed until a desired outcome was achieved, and this was often very expensive, and time consuming. There has been plenty of research in developing simulation models in order to predict the distortions and stresses that developed during the additive manufacturing process. These simulations allowed engineers to optimize parts before they were printed, and thus reduce the number of wasted prints. This work demonstrates and validates use of a software package call Autodesk Netfabb Simulation in order to find the optimal orientation of a complex part. The optimal orientation was selected for three categories: distortion, stress, and printability. Optimal orientations were selected from a selection of 23 orientations that were simulated. To validate the simulations, two test parts along with three of the aforementioned orientations were printed and measured using 3D scanning while still the build plate. The result of this was that the optimal orientation was different for each of three criteria meaning it is up to the part (open full item for complete abstract)

Committee: Jason Walker PhD (Advisor); Brett Conner PhD (Committee Member); Virgil Solomon PhD (Committee Member) Subjects: Engineering; Mechanical Engineering; Metallurgy