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- Title
- Process-Dependent Microstructure And Severe Plastic Deformation In SiCp Reinforced Aluminum Metal Matrix Composites.
- Creator
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Uribe Restrepo, Catalina, Sohn, Yongho, Coffey, Kevin, Orlovskaya, Nina, University of Central Florida
- Abstract / Description
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Discontinuously reinforced MMCs with optimized microstructure are sought after for exceptional high strain rate behavior. The microstructure evolution of a stir-cast A359 aluminum composite reinforced with 30 vol.% SiCp after isothermal anneal, successive hot-rolling, and high strain rate deformation has been investigated. Quantitative microstructural analysis was carried out for the as-cast, annealed (470(&)deg;C, 538(&)deg;C and 570(&)deg;C) and successively hot rolled specimens (64, 75, 88...
Show moreDiscontinuously reinforced MMCs with optimized microstructure are sought after for exceptional high strain rate behavior. The microstructure evolution of a stir-cast A359 aluminum composite reinforced with 30 vol.% SiCp after isothermal anneal, successive hot-rolling, and high strain rate deformation has been investigated. Quantitative microstructural analysis was carried out for the as-cast, annealed (470(&)deg;C, 538(&)deg;C and 570(&)deg;C) and successively hot rolled specimens (64, 75, 88, and 96% rolling reductions). Selected composites were also examined after high strain rate deformation. X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy were employed for microstructural characterization. The strength and ductility of the A359 Al alloys, and the composite, were greatly influenced by the brittle eutectic silicon phase and its morphology. Lamellar eutectic silicon spheroidized with isothermal anneal and successive hot rolling with a corresponding decrease in hardness. The hot rolling process also considerably decreased the SiC particle size (approximately 20% after 96% reduction) by breaking-up the hard SiC particles. However, this break-up of particles increased the homogeneity of SiCp size distribution. Successive hot rolling also healed voids due to solidification shrinkage, incomplete infiltration of molten Al and defects originating from fractured particles. Four selected specimens of composites were examined after high strain rate deformation. Fractography and metallographic analysis for the craters, voids, and relevant regions affected by the high velocity impact were carried out. The deposition of impact residuals was frequently observed on the exposed fracture surfaces. These residuals were typically observed as (")molten-and-solidified(") as a consequence of excessive heat generated during and after the damage. Particularly in regions of entry and exit of impact, intermixing of residuals and composite constituents were observed, demonstrating that the Al matrix of the composite also had melted.In all samples examined, cracks were observed to propagate through the eutectic Si network while a small number of broken reinforcement particles were observed. A slight variation in failure mechanisms was observed (e.g., radial, fragmentation, petalling) corresponding to the variation in ductility against high strain rate deformation. In selected specimens, parallel sub-cracks at the exit were observed at 45(&)deg; and 30(&)deg;. These sub-cracks were again filled with intermixed constituents from projectile residuals and composites. This observation suggests that the melting of composite constituents that leads to intermixing occured after the crack propagation and other damage.
Show less - Date Issued
- 2011
- Identifier
- CFE0004172, ucf:49056
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004172
- Title
- ZrB2-SiC BASED ULTRA HIGH TEMPERATURE CERAMIC COMPOSITES: MECHANICAL PERFORMANCE AND MEASUREMENT AND DESIGN OF THERMAL RESIDUAL STRESSES FOR HYPERSONIC VEHICLE APPLICATIONS.
- Creator
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Stadelmann, Richard, Orlovskaya, Nina, Kumar, Ranganathan, Raghavan, Seetha, University of Central Florida
- Abstract / Description
-
Ultra-high temperature ceramics (UHTCs), such as ZrB2-based ceramic composites, have been identified as next generation candidate materials for leading edges and nose cones in hypersonic air breathing vehicles. Mechanical performance of ceramic composites play an important role in the ultra-high temperature applications, therefore SiC is added to ZrB2 as a strengthening phase to enhance its mechanical performance. The high melting temperatures of both ZrB2 and SiC, as well as the ability of...
Show moreUltra-high temperature ceramics (UHTCs), such as ZrB2-based ceramic composites, have been identified as next generation candidate materials for leading edges and nose cones in hypersonic air breathing vehicles. Mechanical performance of ceramic composites play an important role in the ultra-high temperature applications, therefore SiC is added to ZrB2 as a strengthening phase to enhance its mechanical performance. The high melting temperatures of both ZrB2 and SiC, as well as the ability of SiC to form SiO2 refractory oxide layers upon oxidation make ZrB2-SiC ceramics very suitable for aerospace applications. Thermal residual stresses appearing during processing are unavoidable in sintered ZrB2-SiC ceramic composites. Residual microstresses appear at the microstructural level (intergranular microstresses) or at the crystal structure level (intragranular microstresses). These microstresses are of enormous importance for the failure mechanisms in ZrB2-SiC ceramics, such as ratio of the trans- and intergranular fracture; crack branching or bridging, microcracking, subcritical crack growth and others, as they govern crack propagation(-)induced energy dissipation and affect the toughness and strength of the ceramic material. Therefore, understanding the evolution of residual stress state in processed ZrB2-SiC ceramic composites and accurate measurements of these stresses are of high priority. In the present research the ZrB2-17vol%SiC, ZrB2-32vol%SiC, and ZrB2-45vol%SiC ultra-high temperature particulate ceramic composites were sintered using both Hot Pressing (HP) and Spark Plasma Sintering (SPS) techniques. The mechanical performance of the ZrB2-SiC composites was investigated using 3- and 4-point bending techniques for measurements of instantaneous fracture strength and fracture toughness. Resonant Ultrasound Spectroscopy was used for measurement of Young's, shear, and bulk moduli as well as Poisson's ratio of the composites. The distribution of thermal residual stresses and the effect of the applied external load on their re-distribution was studied using micro-Raman spectroscopy. Piezospectroscopic coefficients were determined for all compositions of ZrB2-SiC ceramic under study and their experimentally obtained values were compared with the piezospectroscopic coefficients both published in the literature and calculated using theoretical approach. Finally, the novel ZrB2-IrB2-SiC ceramic composites were also produced using Spark Plasma Sintering (SPS), where IrB2 powder was synthesized using mechanochemical route. It is expected that the IrB2 additive phase might contribute to the improved overall oxidation resistance of ZrB2 based ultra-high temperature ceramic composites.
Show less - Date Issued
- 2015
- Identifier
- CFE0006008, ucf:51004
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006008
- Title
- INVESTIGATION OF REACTIVELY SPUTTERED SILICON CARBON BORON NITRIDE (SICBN) THIN FILMS FOR HIGH TEMPERATURE APPLICATIONS.
- Creator
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Vijayakumar, Arun, Sundaram, Kalpathy, University of Central Florida
- Abstract / Description
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The increasing demand for efficient energy systems in the last decade has brought about the development of advanced sensor systems that utilize advance detection methods to help in preventive maintenance of these essential systems. These usually are needed in hard to access environments where conditions are extreme and unfit for human interaction. Thin film based sensors deposited directly on the surfaces exposed to harsh environments can serve as ideal means of measuring the temperature of...
Show moreThe increasing demand for efficient energy systems in the last decade has brought about the development of advanced sensor systems that utilize advance detection methods to help in preventive maintenance of these essential systems. These usually are needed in hard to access environments where conditions are extreme and unfit for human interaction. Thin film based sensors deposited directly on the surfaces exposed to harsh environments can serve as ideal means of measuring the temperature of the component during operation. They provide the basic advantage of proximity to the surface and hence accurate measurement of the surface temperature. The low mass size ratio provides the additional advantage of least interference to system operation. The four elements consisting of Si, C, B, and N can be used to form binary, ternary and quaternary compounds like carbides, nitrides, which are chemically and thermally stable with extreme hardness, thermal conductivity and can be doped n- and p-type. Hence these compounds can be potential candidates for high temperature applications. This research is focused on studying sputtering as a candidate to obtain thin SiCBN films. The deposition and characterization of amorphous thin films of silicon boron carbon nitride (SiCBN) is reported. The SiCBN thin films were deposited in a radio frequency (rf) magnetron sputtering system using reactive co-sputtering of silicon carbide (SiC) and boron nitride (BN) targets. Films of different compositions were deposited by varying the ratios of argon and nitrogen gas in the sputtering ambient. Investigation of the oxidation kinetics of these materials was performed to study high temperature compatibility of the material. Surface characterization of the deposited films was performed using X-ray photoelectron spectroscopy and optical profilometry. Studies reveal that the chemical state of the films is highly sensitive to nitrogen flow ratios during sputtering. Surface analysis shows that smooth and uniform SiCBN films can be produced using this technique. Carbon and nitrogen content in the films seem to be sensitive to annealing temperatures. However depth profile studies reveal certain stoichiometric compositions to be stable after high temperature anneal up to 900ºC. Electrical and optical characteristics are also investigated with interesting results. Finally a metal semiconductor metal structure based optoelectronic device is demonstrated with excellent performance improvement over standard silicon based devices under higher temperature conditions.
Show less - Date Issued
- 2007
- Identifier
- CFE0001914, ucf:47490
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001914
- Title
- Mechanical Properties and Thermal Residual Stresses of ZrB2-SiC Ceramic Composites for Hypersonic Vehicle Applications.
- Creator
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Stadelmann, Richard, Orlovskaya, Nina, Kumar, Ranganathan, Raghavan, Seetha, University of Central Florida
- Abstract / Description
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Ultra High Temperature Ceramic (UHTC) ZrB2- 10, 20, 30wt%SiC composites are of high interest for use in hypersonic air-breathing vehicles. In this work, ZrB2- 10, 20, 30wt%SiC UHTC composites were produced by the Spark Plasma Sintering (SPS) technique. After sintering, almost dense ceramics with ~ 5-8% porosity were produced. Their mechanical properties, such as Young's, shear, and bulk moduli, along with Poisson's ratio, 4-point bending strength, and single edge V-notched beam (SEVNB)...
Show moreUltra High Temperature Ceramic (UHTC) ZrB2- 10, 20, 30wt%SiC composites are of high interest for use in hypersonic air-breathing vehicles. In this work, ZrB2- 10, 20, 30wt%SiC UHTC composites were produced by the Spark Plasma Sintering (SPS) technique. After sintering, almost dense ceramics with ~ 5-8% porosity were produced. Their mechanical properties, such as Young's, shear, and bulk moduli, along with Poisson's ratio, 4-point bending strength, and single edge V-notched beam (SEVNB) fracture toughness were measured. In addition, in-situ bending experiments under a Raman microscope were performed to determine the piezo-spectroscopic coefficients of SiC Raman active peaks for calculation of thermal residual stresses. The results show that these materials are possible candidates for hypersonic air-breathing vehicles due to their high Young's modulus, ability to withstand high temperatures, and relatively low densities.
Show less - Date Issued
- 2013
- Identifier
- CFE0005060, ucf:49945
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005060
- Title
- Design and Characterization of High Temperature Packaging for Wide-Bandgap Semiconductor Devices.
- Creator
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Grummel, Brian, Shen, Zheng, Sundaram, Kalpathy, Yuan, Jiann-Shiun, University of Central Florida
- Abstract / Description
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Advances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor...
Show moreAdvances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor device packaging with high reliability at high temperatures is necessary. Transient liquid phase (TLP) die-attach has shown in literature to be a promising bonding technique for this packaging need. In this work TLP has been comprehensively investigated and characterized to assess its viability for high-temperature power electronics applications. The reliability and durability of TLP die-attach was extensively investigated utilizing electrical resistivity measurement as an indicator of material diffusion in gold-indium TLP samples. Criteria of ensuring diffusive stability were also developed. Samples were fabricated by material deposition on glass substrates with variant Au(-)In compositions but identical barrier layers. They were stressed with thermal cycling to simulate their operating conditions then characterized and compared. Excess indium content in the die-attach was shown to have poor reliability due to material diffusion through barrier layers while samples containing suitable indium content proved reliable throughout the thermal cycling process. This was confirmed by electrical resistivity measurement, EDS, FIB, and SEM characterization. Thermal and mechanical characterization of TLP die-attached samples was also performed to gain a newfound understanding of the relationship between TLP design parameters and die-attach properties. Samples with a SiC diode chip TLP bonded to a copper metalized silicon nitride substrate were made using several different values of fabrication parameters such as gold and indium thickness, Au(-)In ratio, and bonding pressure. The TLP bonds were then characterized for die-attach voiding, shear strength, and thermal impedance. It was found that TLP die-attach offers high average shear force strength of 22.0 kgf and a low average thermal impedance of 0.35 K/W from the device junction to the substrate. The influence of various fabrication parameters on the bond characteristics were also compared, providing information necessary for implementing TLP die-attach into power electronic modules for high-temperature applications. The outcome of the investigation on TLP bonding techniques was incorporated into a new power module design utilizing TLP bonding. A full half-bridge inverter power module for low-power space applications has been designed and analyzed with extensive finite element thermo-mechanical modeling. In summary, TLP die-attach has investigated to confirm its reliability and to understand how to design effective TLP bonds, this information has been used to design a new high-temperature power electronic module.
Show less - Date Issued
- 2012
- Identifier
- CFE0004499, ucf:49276
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004499
- Title
- DESIGN AND DEVELOPMENT OF HETEROGENOUS COMBUSTION SYSTEMS FOR LEAN BURN APPLICATIONS.
- Creator
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Terracciano, Anthony, Orlovskaya, Nina, Vasu Sumathi, Subith, Chow, Louis, Kassab, Alain, University of Central Florida
- Abstract / Description
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Combustion with a high surface area continuous solid immersed within the flame, referred to as combustion in porous media, is an innovative approach to combustion as the solid within the flame acts as an internal regenerator distributing heat from the combustion byproducts to the upstream reactants. By including the solid structure, radiative energy extraction becomes viable, while the solid enables a vast extension of flammability limits compared to conventional flames, while offering...
Show moreCombustion with a high surface area continuous solid immersed within the flame, referred to as combustion in porous media, is an innovative approach to combustion as the solid within the flame acts as an internal regenerator distributing heat from the combustion byproducts to the upstream reactants. By including the solid structure, radiative energy extraction becomes viable, while the solid enables a vast extension of flammability limits compared to conventional flames, while offering dramatically reduced emissions of NOx and CO, and dramatically increased burning velocities. Efforts documented within are used for the development of a streamlined set of design principles, and characterization of the flame's behavior when operating under such conditions, to aid in the development of future combustors for lean burn applications in open flow systems. Principles described herein were developed from a combination of experimental work and reactor network modeling using CHEMKIN-PRO. Experimental work consisted of a parametric analysis of operating conditions pertaining to reactant flow, combustion chamber geometric considerations and the viability of liquid fuel applications. Experimental behavior observed, when utilizing gaseous fuels, was then used to validate model outputs through comparing thermal outputs of both systems. Specific details pertaining to a streamlined chemical mechanism to be used in simulations, included within the appendix, and characterization of surface area of the porous solid are also discussed. Beyond modeling the experimental system, considerations are also undertaken to examine the applicability of exhaust gas recirculation and staged combustion as a means of controlling the thermal and environmental output of porous combustion systems. This work was supported by ACS PRF #51768-ND10 and NSF IIP 1343454.
Show less - Date Issued
- 2014
- Identifier
- CFE0005269, ucf:50549
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005269