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

The period of niobium refractory alloy development in the 1950s-1970s was significant in metallurgical history because of its unique ability to operate at high temperatures (1200+ °C). Marred by high costs and lack of processability through traditional industrial techniques, novel alloy development diminished, leaving behind a limited catalog of alloys and production methods. There is now a resurging interest in niobium alloys. However, the empirical metallurgy principles relied on for the development of the alloys in earlier research are no longer sufficient. Their exploration of alternative processing techniques such as metal powder consolidation was limited, at best. This work investigates hot isostatic pressing (HIP) of C103 (Nb-10Hf-1Ti wt%) and WC3009 (Nb-30Hf-9W wt%) powders into near net shapes. Subsequent isothermal heat treatments were conducted to better understand recrystallization behavior during HIP processing. This effort was performed to identify key alloy attributes that drive processability through HIP such that higher strength niobium alloys can be utilized. Dilute binary niobium alloys (Nb-1[Ti, Zr, Hf] at%) were fabricated and analyzed to elucidate variances in solute strengthening potency. Room-temperature mechanical tensile tests and nanoindentation were conducted to compare the relative strengths of alloys and to generate a deformed microstructure. Advanced SEM characterization of HIP-processed, pre-, and post-deformation structures was accomplished using electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI). The results shown in this study show that HIP processing of powder niobium alloys is a viable method to produce near-net shapes. Furthermore, the fact that alloys such as WC3009 can be consolidated indicates that this process is not limited to historically fabricable alloys like C103; It can also be applied to high-performance alloy systems that were previously thought impossible to use. The micr (open full item for complete abstract)

Committee: Hamish Fraser PhD (Advisor); Joerg Jinschek PhD (Committee Member); Steven Niezgoda PhD (Committee Member) Subjects: Materials Science; Metallurgy

Master of Science, The Ohio State University, 1980, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1987, Graduate School

Committee: Not Provided (Other) Subjects:

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

Refractory complex concentrated alloys (RCCAs) are known for their high-temperature mechanical properties, but less attention has been given to their low-temperature thermophysical behavior. High-throughput calculation of phase diagrams (CALPHAD) was used to study the body centered cubic (BCC) phase dominance within the Nbx(MoTi2V4)100-x alloy system by adding Niobium (Nb) at atomic concentrations of x=9%,23%,and 37%, and two additional alloys where vanadium (V) is substituted with hafnium (Hf) and zirconium (Zr) to form Hf10Mo24Nb38Ti28 and Mo24Nb38Ti28Zr10 alloys. Alloys were tested to see the effect of Nb content on the superconducting transition temperature (TC) and the effect of substituting V with Hf or Zr on TC. This approach tests the common assumption of the correlation between VEC with TC, to clarify the role of composition relative to VEC. Button specimens were cast via vacuum arc melting and were measured for electrical resistivity at different temperatures using a Quantum Design DynaCool system. X-ray diffraction (XRD) was used to confirm the formation of the phases predicted by CALPHAD. Five out of the six alloy samples exhibited superconductivity, with some anomalies observed and addressed in this study. These results are compared to literature to enhance understanding of the results.

Committee: Eric Payton Ph.D. (Committee Chair); Matthew Steiner Ph.D. (Committee Member); Sarah Watzman Ph.D. (Committee Member) Subjects: Materials Science

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

Refractory high entropy alloys (RHEAs) have received significant attention for their remarkable strength at very high temperatures. However, even for ductile compositions, conventional thermomechanical processing remains extremely challenging due to the very same elevated temperature strength properties that make this family of alloys interesting for extreme environmental applications. Many researchers have proposed additive manufacturing as a potential solution for fabrication of components as a possible route for taking advantage of RHEA properties. This research thesis investigates screening metrics through which the additive manufacturability of RHEAs can be assessed and their hot crack susceptibility. Crack susceptibility criteria are calculated using parameters derived from a calculation of phase diagrams (CALPHAD) approach, using commercially available databases. Solidification predictions are used to predict possible phases, alloy compositions, and freezing ranges for a database of alloys published in the literature. It is found that different castability metrics can differ substantially from one another. The computational predictions are then assessed using laser glazing at two laser powers and eight laser scan speeds for arc-melted alloy pairs at opposite extremes of the solidification crack susceptibility and castability metrics. Cracking susceptibility differences and melt pool behavior are quantified and compared for key alloy pairs, and the correlation between crack propagation and microstructure are analyzed using scanning electron microscopy, and energy dispersive spectroscopy. An assessment of prospects for additive manufacturing processability prediction for refractory high entropy alloys will be presented, along with observations relevant to alloy design strategies for solidification crack tolerant complex compositions of refractory alloys.

Committee: Eric Payton Ph.D. (Committee Chair); Matthew Steiner Ph.D. (Committee Member); Ashley Paz y Puente Ph.D. (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 1971, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1971, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1966, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1969, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1970, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2024, Welding Engineering

As Additively Manufactured (AM) refractory alloys are developed for extreme temperature environments, new methodologies evaluating their fitness for service must be developed. AM processes alter the properties and behavior versus wrought counterparts, and as much of the refractory alloy development ended decades ago, the adaptation of AM to refractory alloys introduces new challenges. Because refractory alloys are desirable for their high strengths at very high temperatures, they must be tested at these temperatures. A Gleeble 3800 thermomechanical simulator was modified and used to evaluate mechanical properties and oxidation of AM refractory alloys at their expected service temperatures, ranging from room temperature to thousands of degrees Celsius. Both the fixturing and sample's geometry for this new test were designed considering the joule heating utilized by the testing system as well as the potential risk of damaging standard components inside the test chamber. Oxidation during testing was manipulated by controlling the vacuum in the chamber and utilizing argon backfills. AM C103, TZM, and tungsten samples were built based on the designs created for this research and were tensile tested up to ultra-high temperatures. Mechanical properties were evaluated with the measurement of ultimate tensile strengths (UTS), yield strengths (YS), elongation, and strain-hardening coefficient as a function of temperature. C103 was the highest performing material, with an average UTS of ~650 MPa and over 25% elongation at room temperature. Strength at 500 °C - 1000°C showed similar behavior, but the strength from 1200 °C -1400 °C rapidly declined, and YS and UTS values were identical. Fractography analysis of the fracture surface indicated ductile fracture for the C103, while brittle fracture was observed in TZM and tungsten. Electron Backscatter Diffraction (EBSD) maps and pole figures of the C103 samples enabled the evaluation of the microstructures at the transition section (open full item for complete abstract)

Committee: Boian Alexandrov (Committee Member); Antonio Ramirez (Advisor) Subjects: Engineering; Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Welding Engineering

Improved die materials and repair procedures are needed to improve costs in high pressure die casting. Conventioanl die materials center around hot work tool steels which make up the bulk of high pressure die casting dies, but these materials accumulate damage rapidly in aggressive environments. Refractory based alloys provide superior die casting performance, but processing difficulties and high cost limit applications to small die regions / inserts. Direct cladding of die steels with refractory alloys has historically been limited by intermetallic formation and a lack of wire consumables for high deposition rate automated processes. A new refractory based tungsten heavy alloy known as Anviloy Wire was recently developed for use as a die hardfacing consumable, but welding metallurgy and die casting performance were unknown. To implement Anviloy wire cladding technology, this study investigated the arc weldability of Anviloy wire clads, the effect of H13 tool steel dilution on clad microstructure and thermal stability, feasibility of temperbead repair of H13 dies, effect of molten aluminum exposure on clad surface microstructure, and the effect of rapid solidification on Anviloy wire clad microstructure. Arc weldability was investigated using hot wire gas tungsten arc welding (HW-GTAW), pulsed gas metal arc welding (GMAW-P), and reciprocating wire feed gas metal arc welding (RWF-GMAW) processes using bead on plate experiments where weld quality and dilution minimization were optimized. A cladding procedure was developed to prepare an Anviloy wire clad H13 shot block for in-plant trial service evaluation using RWF-GMAW based on high weld quality and low dilution. Effect of clad dilution levels on microstructure and thermal stability was analyzed using arc-crucible melted samples aged isothermally at 600 and 725°C. Experiments involving static immersion of Anviloy wire calds and H13 in molten A380 aluminum were undertaken to better understand chemical soldering mechan (open full item for complete abstract)

Committee: Dennis Harwig (Advisor); Boian Alexandrov (Committee Member); Antonio Ramirez (Committee Member) Subjects: Materials Science

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.

Committee: Nathan Klingbeil Ph.D. (Advisor); Daniel Young Ph.D. (Committee Member); Ryan Kemnitz Ph.D. (Committee Member) Subjects: Materials Science; Mechanical Engineering; Metallurgy

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 in Materials Science and Engineering (MSMSE), Wright State University, 2021, Materials Science and Engineering

A metallic network has been embedded in a silicon carbide fiber– silicon carbide (SiC) matrix ceramic composite (CMC) in order to combine the functional properties of the metal and the structural properties of the CMC. The processing of the composite involves iterative pre-ceramic polymer infiltration and heating to temperatures at 1100°C. The metallic structure embedded in the CMC must retain its unique properties during processing and cannot convert to a silicide or carbide resulting from diffusion of Si and C species from the SiC matrix. To gain an understanding of the diffusion process, a fully processed CMC with tungsten, tantalum, and molybdenum wires will be heated at various temperatures for the same duration. The diffusion zone will be measured and then kinetics equations will be applied to determine the failure kinetics. Understanding the diffusion kinetics and phases formed at higher temperature can provide a processing path which avoids metal degradation.

Committee: Hong Huang Ph.D. (Advisor); Joy Gockel Ph.D. (Committee Member); Zlatomir Apostolov Ph.D. (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2020, Welding Engineering

High pressure die casting is used to quickly and repeatably manufacture high volumes of aluminum parts with good surface finish. Thermal fatigue cracking (heat checking) from thousands of thermal cycles, local soldering of aluminum part features to the surface, and buildup of lubricant residue leads to damage of die surfaces. Manual repair of hot work tool steel (HWTS) dies using arc welding is burdensome, involving high preheats and post weld heat treatment (PWHT) to restore HWTS properties. Improved automated repair procedures and materials are necessary to reduce die casting costs. This effort focused on developing automated arc welding repair procedures, characterizing clad deposit microstructure, evaluating tempering effects in the H13 heat affected zone (HAZ), and cladding shot block dies for in-plant trials using an experimental Anviloy (W-27.5Ni-12.5Fe) alloy wire on H13 HWTS dies. Mechanized hot wire gas tungsten arc welding (HW-GTAW) procedures were developed to produce low dilution single and double layer deposits. The minimum weld dilution with HW-GTAW required to produce sound clads was 18%. HW-GTAW trials showed that consistent, sound Anviloy wire clads could be deposited onto H13 using arc welding. Robotic gas metal arc welding pulse (GMAW-P) procedures were developed for conformal cladding the shot block. The robotic GMAW-P system provided better accessibility to accommodate shot block features. Both a DC+ and DC- advanced waveform were evaluated, but only the DC- waveform resulted in stable and sound deposition of Anviloy wire consumable. The die block's complex shape mandated the use of sub-optimal torch angles when cladding in the 2G position. Work angle oscillation was used to improve bead shape in these adverse torch positions. A weld stop procedure was developed to improve conformal cladding complex shapes. The developed two layer cladding procedure minimized number of weld passes and amount of deposited material needed to create a 10mm clad l (open full item for complete abstract)

Committee: Dennis Harwig (Advisor); Boyd Panton (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Master of Sciences, Case Western Reserve University, 2019, Biomedical Engineering

Low-frequency audio-visual stimulation has been shown to effectively reduce seizures in two animal models of medically refractory epilepsy. As such, low-frequency sensory stimulation (LFSS) may result in decreased epileptogenic activity in patients with MRE. A clinical trial was used to study the effect of LFSS in 6 patients with MRE. Each patient received both LFSS and control stimulation from a non-invasive audio-visual device for 20 minutes. Spike rates were then compared between stimulation, pre-stim, and post-stim periods. Globally, LFSS increased spike rates compared to baseline (116.126% increase, p = 0.005). For analysis of spikes originating from leads within the hypothesized epileptogenic zone, LFSS decreased spike rates compared to baseline (-41.567%, p < 0.001) and controls stimulation did not (-28.365%, p = 0.089). Therefore, LFSS decreases spike frequency in the EZ, indicating likely therapeutic effects with longer stimulation times, a study of which is needed in order to draw definitive conclusions.

Committee: Dominique Durand Ph.D. (Advisor); Colin Drummond Ph.D. (Committee Member); Richard Burgess M.D. Ph.D. (Committee Member); Dileep Nair M.D. (Advisor); Jorge Gonzalez-Martinez M.D. Ph.D. (Committee Co-Chair) Subjects: Biomedical Engineering; Biomedical Research; Engineering; Health Care; Medicine; Neurology; Neurosciences; Surgery

Doctor of Philosophy (Ph.D.), Bowling Green State University, 2018, Communication Disorders

In addition to motor deficits, it is widely accepted that individuals with Parkinson Disease (PD) experience impairments in cognitive functions including central processing (e.g., Wichmann & DeLong, 2013). Previous research has found that the psychological refractory period (PRP) paradigm is a useful method to examine response time delays attributed to limitations in central processing capacity (e.g., Pashler, 1990). This paradigm allows for the study of an individual's ability to perform two tasks as they increasingly overlap in time. The current study used the psychological refractory period paradigm to examine the effects of cognitive complexity and response modality in two overlapping tasks in 8 individuals with PD compared to 11 individuals without PD. Specifically, the study aimed to determine how the central process of decision-making affects response times in three different experimental conditions with increasing cognitive complexity (no choice, choice, and overlapping choice conditions) and how vocal versus manual responses are affected by these conditions. Results revealed no significant group (PD vs. Controls) differences for simple reaction or 2-choice response time. Additionally, task overlap did not affect groups differently. A significant task by group interaction was found with participants with PD having significantly longer response times compared to controls only in the more complex task with 3 response options. Overall, results revealed significantly longer response times in PD only in the more complex task but no difference in how task overlap affected groups. These results suggest that delays in response time in PD are related to more central decision or response selection processes in response tasks and not to motor execution. Furthermore, results suggest that there is no slowing of central processes due to task overlap in PD relative to control participants.

Committee: Alexander Goberman (Advisor); Ronald Scherer (Committee Member); Howard Casey Cromwell (Committee Member); Jason Whitfield (Committee Member); Andrea Cripps (Committee Member) Subjects: Speech Therapy

Doctor of Philosophy, The Ohio State University, 2017, Materials Science and Engineering

High entropy alloys (HEAs) are a relatively new class of materials that have garnered significant interest over the last decade due to their intriguing balance of properties including high strength, toughness, and corrosion resistance. In contrast to conventional alloy systems, HEAs are based on four or more principal elements with near equimolar concentrations and tend to have simple microstructures due to the preferential formation of solid solution phases. HEAs appear to offer new pathways to lightweighting in structural applications, new alloys for elevated temperature components, and new magnetic materials, but more thorough characterization studies are needed to assess the viability of the recently developed multicomponent materials. One such HEA, AlMo0.5NbTa0.5TiZr, was selected to be the basis for this characterization study in part due to its strength at elevated temperatures (s0.2 = 1600 MPa at T = 800 ºC) and low density compared with commercially available Ni-based superalloys. The refractory element containing HEA composition was developed in order to balance the high temperature strength of the refractory elements with the desirable properties achieved by the high entropy alloying design approach for potential use in aerospace thermal protection and structural applications. Ingots of AlMo0.5NbTa0.5TiZr were cast by vacuum arc melting followed by hot isostatic pressing (HIP) and homogenization at 1400 ºC for 24 hrs with a furnace cool of 10 ºC/min. The resulting microstructure was characterized at multiple length scales using x-ray diffraction (XRD), scanning transmission electron microscopy (SEM), conventional and scanning transmission electron microscopy (TEM and STEM), and x-ray energy dispersive spectroscopy (XEDS). The microstructure was found to consist of a periodic, coherent two phase mixture, where a disordered bcc phase is aligned orthogonally in an ordered B2 phase. Through microstructural evolution heat treatment stud (open full item for complete abstract)

Committee: Hamish Fraser (Advisor); Michael Mills (Committee Member); Yunzhi Wang (Committee Member); William Brantley (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 1985, Graduate School

Committee: Not Provided (Other) Subjects: Engineering