Doctor of Philosophy, Case Western Reserve University, 1994, Materials Science and Engineering

In situ processing techniques were used to incorporate elongated primary niobium (Nb p) and secondary niobium (Nb s) phases in a brittle niobium silicide (Nb5Si3) intermetallic matrix. The presence of these phases increased the fracture resistance of the composite by the ductile-phase toughening mechanism Resistance-curve behavior and peak toughnesses of 28 Mpasurdm at 380 μm crack extension were determined in slow displacement rate tests monitored in real-time. Bridging and deformation of Nb p ligaments between the crack faces in the Nb5Si3, and plasticity in a process zone ahead of the crack tips, provided for the increased fracture resistance. The properties were compared to previously developed fracture models. The work of rupture (χ) of the ligaments were determined to be 1.6 and constrained flow stresses were predicted to be about six times the uniaxial tensile yield stress (ς y). Even under these high constraints, the Nb p ligaments plastically deformed and exhibited dimpled fracture. Experiments were performed over a range of strain rates at 298 K and 77 K to increase the yield stresses of the body-centered cubic Nb p ligaments and increase propensity for cleavage fracture behavior . On each fracture surface created at 298 K, the Nb p phases exhibited a consistent, smoothly varying fracture behavior with respect to the specimen dimensions. The increasing frequency of cleavage fracture was found to be related to global strain rates experienced by the samples, induced through the motion of the loading point in the notched three point bend test. The higher strain rates augmented yield stresses and subsequently produced a transition in fracture mode. The toughness values determined from experiments spanning six orders magnitude in loading rate at 298 K and 77 K, exhibited little change, even in situations when the majority of Nb p phases failed by cleavage. Although χ-values were calculated to drop to fractions of the slow, 298 K value, the constancy of the toug (open full item for complete abstract)

Committee: John Lewandowski (Advisor) Subjects: Engineering, Materials Science

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

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1965, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1964, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1960, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy (Ph.D.), University of Dayton, 2023, Electrical Engineering

Doping of metal oxide semiconductors with other metal oxides or metal ions is an effective way to improve the sensing performance of gas sensors. In this dissertation, In-doped SnO2 thin film is used in different gas sensing platforms, such as surface acoustic wave (SAW) transducers and impedance spectroscopy, for the detection of volatile organic vapors at room temperature. The properties of the piezoelectric materials play a critical role in determining the sensing response of the SAW based gas sensors. Recently, various ferroelectric materials have been used as piezoelectric materials in the manufacturing of SAW based gas sensors. Among them, Ba0.6Sr0.4TiO3 (BST) has emerged as a potential candidate due to its high acoustic velocity and electromechanical coupling coefficient. In the development of gas sensors, noble metals are extensively used as electrode or transducer materials. However, noble metals are expensive and scarce. On the basis of their favorable electrical conductivity, 2D metallic transition-metal dichalcogenides (VTe2, NbTe2, and TaTe2) are emerging as promising candidates for use in 2D electronic devices. In this dissertation, the design, fabrication, and validation of BST-based SAW and NbTe2- based impedance spectroscopy sensor platforms with the In-doped SnO2 sensing film were demonstrated. Different deposition and photolithography techniques were applied to fabricate the sensors. The morphology, structural, elemental compositions, and electrical properties of the as-deposited samples were characterized by HRSEM, XRD, EDS, and the four-point probe sheet resistance method. The samples exhibited excellent film adhesion. Furthermore, the sensing performances of the SAW and impedance spectroscopy-based gas sensors towards ethanol and humidity were evaluated at room temperature. The SAW sensors exhibited a significant negative frequency shift, which can be attributed to the mass and electric loading effects o (open full item for complete abstract)

Committee: Guru Subramanyam (Advisor) Subjects: Electrical Engineering; Materials Science; Nanotechnology

Master of Science in Engineering, Youngstown State University, 2023, Department of Mechanical, Industrial and Manufacturing Engineering

This thesis presents a comparative analysis of the dissimilar laser welding of Ti6Al4V and Ni-Ti with two different interlayers, namely vanadium and niobium, using a continuous fiber laser welding machine. This study attempts to solve the problem associated with dissimilar welding of the Ni-Ti and Ti6Al4V with the use of interlayers specimen. The objective of this study is to improve the welding strength between Ni-Ti and Ti6Al4V in comparison to previous research and to investigate the effect of interlayer composition on the quality of the weld joint. The welding process was performed using identical laser power, welding speed, and focal position, and the quality of the weld joint was evaluated through scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) analysis, hardness testing, and tensile testing. The welding was successfully performed using both interlayers. The tensile strength of the welded samples with niobium interlayer was found to be 100 MPa greater than that of the samples with vanadium interlayer. Scanning electron microscopy images showed that the fracture occurred at the welding region interface between the Ni-Ti-interlayer in both cases due to the dendritic structure, which caused the region to be more brittle. Furthermore, the hardness of the Ni-Ti-interlayer interface was higher, resulting in brittle fracture at the same interface in both cases during tensile testing. The findings suggest that the use of niobium interlayer produces a higher quality weld joint with improved mechanical properties under the same laser welding parameters compared to the vanadium interlayer. These results are significant for designing the laser welding process and selecting the appropriate interlayer for specific applications. Further research can be conducted to optimize the laser welding parameters and explore the impact of different interlayer thicknesses on the welding behavior.

Committee: Jae Joong Ryu PhD (Advisor); Virgil Solomon PhD (Committee Member); Kyosung Choo PhD (Committee Member) Subjects: Materials Science; Mechanical Engineering; Morphology

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

MS, University of Cincinnati, 2019, Engineering and Applied Science: Electrical Engineering

Resistive RAM has high scalability with fast switching speed, low operating voltage making it one of the promising emerging nonvolatile memory technologies. Interfacial layer between the electrode and metal-oxide interface in a Resistive RAM (ReRAM) could either enhance or deteriorate the switching performance of the device. In this study, we investigate the role of Aluminum (Al) as an interfacial layer under the top electrode (TE) layer in a Niobium Oxide (Nb2O5) based ReRAM. We compare the Current-Voltage (I-V), Capacitance-Voltage (C-V) characteristics and endurance effects of the Nb2O5 based ReRAM with an Al interfacial layer below the Tungsten (W) TE and a control sample without the Al interfacial layer to contrast the performance of each type. Additionally, we connect the tested device behavior with the enthalpy, entropy, and Gibb's free energy of Aluminum and Tungsten which are the metal electrode materials to illustrate that aluminum is an inefficient interfacial layer in the niobium oxide ReRAM.

Committee: Rashmi Jha Ph.D. (Committee Chair); Wen-Ben Jone Ph.D. (Committee Member); Carla Purdy Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2017, Physics

Classical interatomic potentials are an important bridge between nano-scale and meso-scale properties of materials, and facilitate an understanding of deformation and phase transitions at the atomistic level. This work presents the development of two semi-empirical interatomic potentials, one for the body-centered cubic metal tungsten and another for multi-phase titanium-niobium alloys. Accurate density functional theory calculations constitute large databases of forces, stresses and energies to which the empirical models are fit using an evolutionary algorithm. Accuracy of the potentials is verified by comparison with experiment and first-principles calculations for numerous structural, elastic and thermal properties. The models are used to investigate structural phase transitions under high pressure, in the case of tungsten, and chemical disorder, in the case of titanium-niobium. The presented models provide improved descriptions of these technologically important metals over existing classical potentials.

Committee: John Wilkins (Advisor); Maryam Ghazisaeidi (Committee Member); Richard Kass (Committee Member); Fengyuan Yang (Committee Member) Subjects: Condensed Matter Physics; Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 1981, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1964, Graduate School

Committee: Not Provided (Other) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1954, Graduate School

Committee: Not Provided (Other) Subjects: Physics

MS, University of Cincinnati, 2015, Engineering and Applied Science: Materials Science

Transparent conducting oxide (TCO) films fabricated by pulsed laser deposition (PLD) is the industrial standard for transparent electrodes in a variety of applications from smart phones to photovoltaics. The most common material used for TCOs is indium oxide doped with tin at about 8% (ITO). The problem of chemical vapor deposition (CVD) or PLD deposited ITO is cost and safety hazards. A lower cost fabrication method coupled with a lower cost and safer material could have market advantage for TCOs. This thesis investigates an alternative fabrication method using a new oxide. Flame spray pyrolysis (FSP) is used to fabricate the TCO thin films using niobium doped titania (TNO) by decomposition of titanium tetra-isopropoxide with dopant quantities of niobium (IV) 2- ethlyhexanoate. Two coating methods have been explored in order to improve the uniformity of the thin films: dip coating and flame coating. In this thesis, structural, optical, and electrical properties of a series Nb doped titania films are presented. Comparison is made between pristine TiO2 and TNO films in order to understand the role of Nb as a dopant. Substitution of Ti atoms by Nb atoms in the TiO2 lattice, increases the anatase content and suppresses the formation of the rutile phase. Conductivity is improved significantly. For 20 % Nb doping in the films annealed in N2, the conductivity is 980 S/cm. This is better than TNO films doped on glass synthesized by pulsed laser deposition. The results indicate that the introduction of Nb generates carrier electrons in the conduction band. The results show that doped TNO films made by flame spray pyrolysis are promising alternatives for current ITO films.

Committee: Gregory Beaucage Ph.D. (Committee Chair); Jude Iroh Ph.D. (Committee Member); Vesselin Shanov Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2014, Nuclear Engineering

Precise knowledge of prompt γ-ray intensities following neutron capture is critical for elemental and isotopic analyses, homeland security, modeling nuclear reactors, etc. A recently-developed database of prompt γ-ray production cross sections and nuclear structure information in the form of a decay scheme, called the Evaluated Gamma-ray Activation File (EGAF), is under revision. Statistical model calculations are useful for checking the consistency of the decay scheme, providing insight on its completeness and accuracy. Furthermore, these statistical model calculations are necessary to estimate the contribution of continuum γ-rays, which cannot be experimentally resolved due to the high density of excited states in medium- and heavy-mass nuclei. Decay-scheme improvements in EGAF lead to improvements to other databases (Evaluated Nuclear Structure Data File, Reference Input Parameter Library) that are ultimately used in nuclear-reaction models for generating the Evaluated Nuclear Data File (ENDF). In this work, gamma-ray transitions following neutron capture in 93Nb have been studied at the cold-neutron beam facility at the Budapest Research Reactor. Measurements have been performed using a coaxial HPGe detector with Compton suppression. Partial γ-ray production capture cross sections at a neutron velocity of 2200 m/s have been deduced relative to that of the 255.9-keV transition after cold-neutron capture by 93Nb. With the measurement of a niobium chloride target, this partial cross section was internally standardized to the cross section of the 1951-keV transition after cold-neutron capture by 35Cl. The resulting (0.1377 ± 0.0018) barn (b) partial cross section produced a calibration factor that was 23% lower than previously measured for the EGAF database. The thermal-neutron capture cross sections were deduced for the 93Nb(n,γ)94mNb and 93Nb(n,γ)94gNb reactions by summing the experimentally-measured partial γ-ray production cross sections associated with t (open full item for complete abstract)

Committee: Lei Cao PhD (Advisor); Tunc Aldemir PhD (Committee Member); Thomas Blue PhD (Committee Member); Shamsuzzoha Basunia PhD (Committee Member) Subjects: Nuclear Engineering

PhD, University of Cincinnati, 2003, Arts and Sciences : Physics

In this dissertation, measurements on two different niobium (Nb) based systems, namely superconductor-normal-metal-superconductor (SNS) Josephson junction arrays (JJA), and thin Nb films with nanoscale size magnetic dot arrays, are presented. Without high frequency (rf) signals at nearly zero magnetic field, these measurements show similarities for the two systems. These similarities are explained by proposing that very close to the critical temperature (Tc) of the Nb film sample, the stray magnetic field of the dots reduces the superconductivity in the film to make it a perconductor-weaker-superconductor-superconductor (SS'S) JJA. With rf signals, their dc-voltage-current characteristics (VI's) show the appearance of constant voltage steps known as Shapiro steps. For SNS-JJA, the dependence of the width of the steps (Delta-I-n) on the amplitude of the rf current (Irf) is Bessel-function-like. The maximum width of the first step ([Delta-I-1]MAX) was found to increase as a function of rf frequency (frf) reaching a maximum for frf~1.8 times the array's Josephson frequency (fc). This maximum was maintained for frf>4.9fc. Also, in JJA with missing junctions, [Delta-I-n]MAX was smaller, disappearing for frf~fc. For Nb films near Tc, no Bessel-function-like oscillations were observed for Delta-I-n. Also, Delta-I-0 (or critical current, Ic) showed a maximum for Irf different from 0, contrary to what was found in SNS-JJA, falling to zero for higher Irf. This enhancement of Ic with Irf was attributed to non-equilibrium superconductivity mechanisms near Tc. Observation of higher order steps (n=1,2,3,etc) became evident only from the dynamic resistance (dV/dI)vs.V plots (where a step corresponds to a minima for this curve). The first step was most evident for Irf values that made Delta-I-0=0. At these values, V1 (the voltage that corresponded to the first minimum in the dV/dIvs.V curve) satisfied the Josephson relation V1=N(h/2e)frf, where N is the number of “junctions” in the (open full item for complete abstract)

Committee: Dr. David B. Mast (Advisor) Subjects:

Master of Science, The Ohio State University, 2012, Materials Science and Engineering

Pure Niobium is the material used to make Superconducting Radio Frequency (SRF) cavities. These cavities need to be free from surface defects like pits, bumps and protrusions to achieve the best performance. Electropolishing is commonly used as a final process to give a good surface finish to the niobium surface. The standard electrolyte used for electropolishing niobium is a 1:9 ratio of HF (48%) and H2SO4 (96%) respectively. The mechanism of electropolishing is not fully understood and also the best electropolishing parameters need to be determined. Acid concentration, stirring, temperature and amount of material removed are the parameters expected to affect the surface finish. Their effect is studied using electrochemical polarization measurement, galvanostatic and potentiostatic techniques. The electro-dissolution occurring needs to be under mass transport control for the phenomenon of electropolishing to occur. This is characterized by the presence of a current density plateau in the niobium polarization curves. However Galvanostatic experimental result analysis points to other interfering transport processes as well. Results based on microscopy, surface profile measurement and current transient measurements for different electrode configurations indicate the presence of natural convection as one of the reason which could be causing deviation from a perfect semi infinite linear diffusion model.

Committee: Gerald S. Frankel ScD (Advisor); Michael Sumption PhD (Committee Member); Rudolph Buchheit PhD (Committee Member) Subjects: Materials Science

Master of Science, The Ohio State University, 2010, Materials Science and Engineering

In the present work multifilamentary Tube type and distributed barrier Rod-in-Tube (RIT) type Nb3Sn composites were studied in detail. Tube type composites consisting of subelements of Nb-7.5 wt% Ta alloys with simple Cu/Sn binary metal inserts were studied in an attempt to enhance the performance boundaries of these conductors. We focused on correlating the composition and morphology of the intermetallic A15 to the transport and magnetic properties for varying heat treatments. In particular, lower temperature HTs were studied, specifically 625°C and 635°C as a function of time. The extent of A15 formation, the ratio of the coarse/fine grain areas, and the amount of untransformed 6:5 phase were then observed as a function of time –temperature. A15 stoichiometry was investigated and compared for two different Nb3Sn strand designs, specifically Tube type and high performance RIT type strands. Transport measurements were performed on both categories of conductors for various conditions. The objective of the study was to investigate the limits of tube type conductor performance and to compare this to that of RIT conductors. Specifically, the Sn stoichiometry and A15 grain size for RIT and Tube type conductors were compared and to correlated with the transport properties of the two strand types. Tube type conductors were compared to RIT conductors, each after the application of single step and two-step HTs with plateaus ranging from 615°C to 675°C for various times. The influence of strand geometry and reaction route was related to the resulting A15 stoichiometries. Fractography was performed to investigate the effect of a two-step reaction on the morphology, the ratio of coarse/fine grain area and grain size of fine grain A15. The effect of Ti doping on superconducting properties of RIT type Nb3Sn strands was also studied.

Committee: Micheal Sumption Dr. (Advisor); John Morral Dr. (Advisor); Katharine Flores Dr. (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2008, Materials Science and Engineering

With current high temperature structural materials such as nickel based superalloys being pushed to the limits of suitable operating conditions, there comes a need for replacement materials with even higher temperature capabilities. Niobium silicon based systems have been shown to have superior density normalized strength at elevated temperatures when compared to currently used alloys. The drawbacks associated with the niobium silicon system are due to catastrophic oxidation behavior at elevated temperatures. Alloying addition have been shown to increase the oxidation resistance near suitable levels, but also decrease the high temperature strength and increases creep rates when compared to the binary alloy system.The microstructure of the material is similar to metal matrix composites in which high melting temperature silicides are dispersed in a niobium based matrix phase. The silicides produce high temperature strength while the niobium based matrix increases the room temperature properties such as fracture toughness. The bulk of the research has been conducted on directionally solidified material which has a coarse microstructure due to the slow cooling rates associated with the processing condition. The current research uses a powder metallurgy process termed Laser Engineered Net Shaping, or LENS, to produce material with a significantly refined microstructure due to fast cooling rates associated with the laser process. Several compositions of alloys were examined and the ideal processing parameters were determined for each alloy. The resulting microstructures show a refinement of the microstructure as expected with a fine scale distribution of Nb5Si3 and Nb3Si dispersed in a niobium based matrix phase. The high temperature oxidation behavior of the LENS deposited alloys was comparable to alloys produced using other techniques. A non protective oxide scale formed on samples exposed for only 0.5 hours but was not protective and showed large amounts of spallation (open full item for complete abstract)

Committee: Michael Mills PhD (Advisor); Hamish Fraser PhD (Committee Member); James Williams PhD (Committee Member); Sabine Jeschonnek PhD (Committee Member) Subjects: Materials Science

Master of Sciences (Engineering), Case Western Reserve University, 2009, Materials Science and Engineering

Niobium based In Situ composites are desired for high temperature structural materials for aerospace applications in order to gain a better understanding of the mechanical properties is desired. The microstructure and mechanical properties of several Niobium based In Situ composites were analyzed. The microstructure was analyzed using SEM and optical microscopy. The materials consisted of a niobium solid solution matrix and a large volume fraction (~45-55%) of hexagonal silicide particles and smaller Laves phase particles. Mechanical properties were evaluated at both room temperature and elevated temperature at 550°C. The main purpose of the present research was to characterize the room temperature and high temperature fatigue crack growth behavior. The fatigue threshold, Paris slope, and overload toughness obtained during fatigue was determined through direct current potential drop method (DCPD) at room temperature and elevated temperature (550°C). It was observed that the majority of alloys had fatigue threshold of 5-8 MPa√m at room temperature and elevated temperature. The majority of alloys tested had room temperature notch toughness, room temperature toughness obtained during fatigue overload and elevated temperature toughness acquired during fatigue overload of 10-20 MPa√m. It was also observed that testing at high temperature (550°C) in air produced time dependent crack growth behavior in some compositions. The toughness and hardness was also determined at room temperature. The fatigue crack path was quantified at different delta K levels after reaching threshold at room temperature and high temperature. Several extrinsic toughening mechanisms were observed to occur in the composites. The toughening mechanisms and crack path behavior were qualitatively and quantitatively evaluated. Preferential crack growth was observed to occur in the silicide particles while largely avoiding the Laves particles.

Committee: John Lewandowski Phd (Committee Chair); David Scwam Phd (Committee Member); Gary Michal PhD (Committee Member) Subjects: Materials Science