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

The work in this dissertation is focused on the development of new manufacturing technologies at the early stage. Two concepts are developed in the category of Impact Welding and two in the category of Metamorphic Manufacturing. Under the Impact Welding category two different welding processes are studied, the Vaporizing Foil Actuator Welding and the Augmented Laser Impact Welding processes. Both of these processes were demonstrated to produce impact welds between traditionally unweldable aircraft aluminum alloys which performed as well or better than comparable riveted joints without the need for the drilling of holes or removal of surface coatings. Additionally, basic engineering guidelines are established for the design of foils for the Vaporizing Foil Actuator Welding process and basic performance metrics are established for the Augmented Laser Impact Welding technique. Two new data analysis techniques were developed for the Augmented Laser Impact Welding process which were validated by the use of high-speed videography. Models of the impact conditions for both of these impact welding techniques were established. For the Augmented Laser Impact Welding process, a technique for accurately measuring the welding velocity during an impact event is developed and validated. Metamorphic Manufacturing refers to the agile use of deformation to create shapes and modify microstructure. In this area two concepts were developed where metallic components are transformed from one shape into a second more desirable and useful form. A device and process for bending medical fixation plates to match patient skeletal anatomy is developed. The method can make arbitrary controlled shapes and may save time in the operating room for reconstruction surgeries. The second concept is an approach for Robotic Blacksmithing, a process for incrementally transforming a malleable material into useful shapes by deformation. This concept was initially developed on a purpose-built desktop robotic (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Antonio Ramirez (Committee Member); Boyd Panton (Committee Member); Enam Chowdhury (Committee Member) Subjects: Materials Science; Medicine; Robotics

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)

Committee: Glenn Daehn (Advisor); Boyd Panton (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

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

Collision welding or impact welding is a solid-state welding technique which enables unique materials joining opportunities. The high velocities and short timescales of the welding process lead to extreme peak collision pressures, high strain rates, low heat inputs, steep thermal gradients, and narrow thermo-mechanically affected zones (TMAZ). These features can be advantageous in the joining of traditionally unweldable materials such as 2XXX or 7XXX series aluminum alloys, and for the joining of dissimilar metals which would form unwanted phases under traditional fusion welding. However, these same features can also make impact welding challenging to control and characterize. Analytic process limits have been developed to calculate limiting flyer velocities and impact angles for welding success as functions of the weld member properties based on the physical mechanisms that enable joining. The maximum impact velocity for a weld is determined by a dynamic solidification cracking mechanism: reflected dynamic tensile stresses arrive to the nascent weld interface prior to full interface cohesion, which is mediated by the presence of interfacial melting. However, current analytic models for the upper limit of the collision welding window were developed for autogenous welds, which develop symmetric stress conditions at impact. In this thesis, we develop alternative formulations to the analytical upper limit of the welding window which better support dissimilar welding. Shock-informed calculation of the asymmetric stress and thermal partitioning between dissimilar weld members is achieved through the application of modified Rankine-Hugoniot relations. We compare the application of the shock-informed upper limit to the existing upper limits in the context of historical data. The shock upper limit is further validated experimentally through the use of The Ohio State University Impulse Manufacturing Laboratory's (IML) Laser Impact Welding (LIW) and Vaporizing Foil Actu (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Wei Zhang (Advisor); Eric Seiber (Committee Member); Boyd Panton (Committee Member); Avraham Benatar (Committee Member); Kevin Doherty (Committee Member) Subjects: Materials Science; Mechanics

Doctor of Philosophy, The Ohio State University, 2020, Materials Science and Engineering

Driven by the need for global carbon footprint reduction, the automotive industries are increasingly focusing on lightweighting of vehicles. Use of multi-material combinations for body-in-white applications is one of the practical ways of accomplishing the broader goal of lightweighting. Over the past decade, the vehicular structure has seen progressive replacement of the more conventional low-carbon mild steels with a variety of advanced and ultrahigh-strength steels including Dual Phase (DP), high-strength low-alloy (HSLA) and boron, and also extensive integration of light metals, such as Al alloys. Development of strong, repeatable and dependable joints is crucial for the effective implementation of these multi-material combinations. Direct welding of disparate Al-steel combination is difficult to impossible through conventional fusion welding routes. Mechanical fastening and clinching techniques provide alternatives to fusion welding, however, there are stack-up feasibility limitations and addition of an externally exposed joining element adds weight and negates the larger goal of lightweighting as well as increases the susceptibility of the joint to galvanic corrosion. Solid-state welding technologies are good substitutes to fusion welding and mechanical fastening and clinching techniques and are currently being employed on a small scale in industries. Here, Vaporizing Foil Actuator Welding (VFAW), a variant of solid-state impact welding technique is being utilized to produce similar and dissimilar joints with materials relevant to the automotive industries. VFAW, a high-speed impact welding technique utilizes the very high pressures generated due to the rapid vaporization of a foil actuator to cause the impact of metal sheets to form nominally solid-state joints with little to no presence of heat affected zone, providing the process the ability to join a wide array of similar and dissimilar material pairs. The present study applies an adaptation of the V (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Antonio Ramirez (Committee Member); Boyd Panton (Committee Member) Subjects: Engineering; Experiments; Materials Science; Metallurgy

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

High-temperature metallic materials such as nickel-based and titanium alloys are attractive as skin structures for aerospace vehicles. They can allow significant performance improvement and mass reduction in aircraft. However, there are substantial challenges in welding and forming them affordably for service. This project examines the use of impulse-based methods, as enabled by the vaporizing foil actuator method, for the impact welding and precise shaping of alloys Ni - 718, Ni - 625, Ni - 230, and Ti 6242. The mechanical properties and weld microstructure of four similar and Six dissimilar VFA spot welding combinations are presented and analyzed. Microhardness measurements showed the absence of a heat affected zone (HAZ). The dissimilar Ni - Ni joints and Ni - Ti joints exhibited high loads to failure in lap-shear tests and show great potential for applications involving transition joints, repair welding, medical devices, and more. The VFA method is cheap, safe, fast, durable, and marks the advancement in the solid-state joining of dissimilar nickel and titanium systems. Nickel alloys typically exhibit low springback during quasi-static forming processes. However, the large amounts of strain hardening that occurs during these operations often requires a second annealing stress relief operation. Titanium alloys are commonly known to exhibit high springback levels due to the high strength to stiffness ratios of titanium alloys. Sheet metals components are usually shaped by hot or superplastic forming. This process is expensive and has long lead-times. This work examines an athermal process to relax or remove the residual stresses and elastic strains in sheet metals. All the materials explored, especially titanium showed significant improvements in shape conformance when processed through the VFA method. Recent shock-based calibration studies have provided some insight into the previously unconfirmed mechanism of springback relief. The driving hypothesis f (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Stephen Niezgoda (Committee Member); Xun Liu (Committee Member) Subjects: Engineering; Materials Science

Master of Science, The Ohio State University, 2019, Materials Science and Engineering

Laser impact welding is a relatively new technology that combines the existing technologies of impact welding and laser-driven flyers to create solid state welds between a thin metallic flyer and a target. A high power laser pulse is fired through a transparent confinement layer and onto an ablative layer that is directly attached to the flyer. This ablative layer absorbs the laser energy and is vaporized creating a plasma that is in turn confined by the transparent confinement layer directing the pressure into the flyer. This drives the flyer to velocities of hundreds to thousands of meters per second in under a microsecond. When the flyer impacts the target if the velocity is high enough and the angle between the two is sufficient, the two surfaces of the materials will be cleaned of their oxides, which in turn allows for a solid-state metallurgical bond to be made between the flyer and target. By controlling the laser parameters, much thicker flyers than previously reported can be welded. Using a 24J 65ns pulse, a 305µm 3003Al flyer was welded to 6061-T6Al. These welds were extremely strong and failed through the 3003Al flyer in all cases when peeled. To further push laser impact welding towards a scalable industrial process, liquid backing layers such as water and glycerin solution were studied for their effect on flyer impact velocity. Impact velocity was measured using Photon Doppler Velocimetry and it was determined that while both are suitable for welding, water would be the preferred backing in an industrial application due to its ease of use and low cost. Potential applications of laser impact welding, such as beverage can manufacturing, are also outlined and discussed.

Committee: Glenn Daehn (Advisor); Xun Liu (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

Impact welding is a method for joining similar and dissimilar metals by a high-speed collision. In this study, a novel impact welding technology, Vaporizing Foil Actuator Welding (VFAW), is used to investigate the process-structure-property relationship of impact welding and expand its applications. VFAW has been shown to successfully weld aluminum alloy plates of over 6 mm thickness to steel in a laboratory environment. Mechanical testing results show that the joint lap shear strength is equivalent or superior to the shear strength of the base materials. A significant portion of this work contributes to understanding of process parameter effects on the weld interface morphology. The typical wave-like interface found in impact welds regularly shows a distinctive wavelength and amplitude, and is believed to indicate a high joint strength by possible mechanical interlocking as well as metallurgical bonding. The determining factors of the wave size and shape are investigated by manipulating process parameters such as material thicknesses and collision angle. From both experimental and numerical observations, the interfacial wavelength is found to be positively correlated with both material thicknesses and collision angle, but the correlation seems to weaken when the target thickness exceeds two times the flyer thickness. The relationships are validated by robust numerical simulations using Arbitrary Lagrangian-Eulerian (ALE) and Smooth Particle Hydrodynamics (SPH) methods, performed by the project collaborators. The relationships are explained in terms of propagation and interference of shock waves at the interface. Metallurgical characteristics of the weld interface are also studied using several advanced microscopy techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD), X-ray micro-computed tomography (µ-CT), energy-dispersive X-ray spectroscopy (EDXS), and nano-diffraction. (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Michael Mills (Committee Member); Stephen Niezgoda (Committee Member); Brad Kinsey (Committee Member) Subjects: Automotive Materials; Experiments; Materials Science; Mechanical Engineering; Metallurgy

Doctor of Philosophy, The Ohio State University, 2016, Materials Science and Engineering

The continual push for vehicle weight reduction has called for the incorporation of non-conventional automotive alloys, such as advanced high-strength steels, aluminum alloys, and even magnesium alloys and titanium alloys. The advent of these new alloys calls for new joining technologies. Resistance Spot Welding and Arc Welding have served the automotive industry well in joining steel components. However, because these are fusion-based processes involving high heat, they are not suitable for joining combinations of dissimilar metals or high-performance alloys. Thus the search continues for a technique capable of joining the said metals effectively, economically, and flexibly. The work featured in this dissertation aims to explore and develop Vaporizing Foil Actuator Welding (VFAW) as a promising technique for dissimilar-metal joining. VFAW is a form of solid-state impact welding that was developed in the Ohio State University in 2011. In this work, some 20 dissimilar-metal combinations of industrially relevant structural alloys were screened for weldability by VFAW. Successful welds were obtained for some 10 combinations, many of which were Al/Fe pairs, which are a most popular material pair for automotive weight reduction. Various aspects of VFAW were explored according to the axiom of Materials Science: process, microstructure, and property. First, the VFAW process was characterized by grooved target plates and photonic Doppler velocimetry (PDV). The former characterized the angle of impact and the latter, the speed of impact, where the speed and angle of impact are the critical process parameters of impact welding. Using these tools, optimal welding parameters were obtained for select material pairs. Second, the microstructure of the weld was studied by metallography. The best weld bonds were associated with continuous direct metal-metal interfaces with little or no voids or intermediate phases such as intermetallic compounds (IMCs). In addition, impact wel (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Michael Mills (Committee Member); Stephen Niezgoda (Committee Member) Subjects: Engineering; Materials Science