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Title: System for metal coated fiber fabrication.
Creator: Zhang, Da, Amezcua Correa, Rodrigo, Schulzgen, Axel, Shah, Lawrence, University of Central Florida
Abstract / Description: For many specific applications, such as sensors, aerospace, chemical industry, deep-well oil-field industry, metal-coated fiber shows strong abilities to satisfy people's requirement. With in-line coating technology, we are able to coat Aluminum on the fibers.Using electromagnetic induction, we can easily heat an electrically conducting thing such as a metal with the eddy current. This process is defined as Induction heating. And we will melt the Aluminum by this induction heating during...
Show moreFor many specific applications, such as sensors, aerospace, chemical industry, deep-well oil-field industry, metal-coated fiber shows strong abilities to satisfy people's requirement. With in-line coating technology, we are able to coat Aluminum on the fibers.Using electromagnetic induction, we can easily heat an electrically conducting thing such as a metal with the eddy current. This process is defined as Induction heating. And we will melt the Aluminum by this induction heating during drawing the fibers on the tower. Introduce the fiber tower system. The drawing process of in-line technology is formed of the following steps: Position, Melting, Forming into fibers, Checking the diameter, Revising, Protective coatings. We will follow these to make the Aluminum coating fiber.With the help of the software which is 123D Design, I have four 3D model of the coating systems. Show the details of the all the coating systems such as the shape and the length of coated-fiber we can get.Talk about the photonic lantern which is the first project that I took part in when I joined the group. Show the mode profiles of our 6 to 1 lantern.
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Date Issued: 2017
Identifier: CFE0006677, ucf:51251
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006677

Title: DEVELOPMENT OF TITANIUM NITRIDE/MOLYBDENUM DISULPHIDE COMPOSITE TRIBOLOGICAL COATINGS FOR CRYOCOOLERS.
Creator: Pai, Anil, Dhere, Neelkanth, University of Central Florida
Abstract / Description: Hydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a...
Show moreHydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a cryogenic propellant. Efficient storage and transfer of liquid hydrogen is essential for reducing the launch costs. A Two Stage Reverse Turbo Brayton Cycle (RTBC) CryoCooler is being developed at University of Central Florida. The cryocooler will be used for storage and transport of hydrogen in spaceport and space vehicle application. One part in development of the cryocooler is to reduce the friction and wear between mating parts thus increasing its efficiency. Tribological coatings having extremely high hardness, ultra-low coefficient of friction, and high durability at temperatures lower than 60 K are being developed to reduce friction and wear between the mating parts of the cryocooler thus improving its efficiency. Nitrides of high-melting-point metals (e.g. TiN, ZrN) and diamond-like-carbon (DLC) are potential candidates for cryogenic applications as these coatings have shown good friction behavior and wear resistance at cryogenic temperatures. These coatings are known to have coefficient of friction less than 0.1 at room temperature. However, cryogenic environment leads to increase in the coefficient of friction. It is expected that a composite consisting of a base layer of a hard coating covered with layer having an ultra-low coefficient of friction would provide better performance. Extremely hard and extremely low friction coatings of titanium nitride, molybdenum disulphide, TiN/MoS2 bilayer coatings, DLC and DLC/MoS2 bilayer coatings have been chosen for this application. TiN film was deposited by reactive DC magnetron sputtering system from a titanium target and MoS2 film was deposited by RF magnetron sputtering using a MoS2 target. Microwave assisted chemical vapor deposition (MWCVD) technique was used for preparation of DLC coatings. These composite coatings contain a solid lubricating phase and a hard ceramic matrix phase as distinctly segregated phases. These are envisioned as having the desired combination of lubricity and structural integrity. Extremely hard coatings of TiN and DLC were chosen to provide good wear resistance and MoS2 was chosen as the lubricating phase as it provides excellent solid lubricating properties due to its lamellar crystal structure. This thesis presents preparation; characterization (SEM and XRD), microhardness and tribological measurements carried out on TiN and TiN/MoS2 coatings on aluminum and glass substrate at room temperature. It also presents initial development in preparation of DLC coatings.
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Date Issued: 2004
Identifier: CFE0000326, ucf:46305
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000326

Title: PLASMA PROCESSING FOR RETENTION OF NANOSTRUCTURES.
Creator: Venkatachalapathy, Viswanathan, Seal, Sudipta, University of Central Florida
Abstract / Description: Plasma spray processing is a technique that is used extensively in thermal barrier coatings on gas and steam turbine components, biomedical implants and automotive components. Many processing parameters are involved to achieve a coating with certain functionality. The coating could be required to function as thermal barrier, wear resistant, corrosion resistant or a high temperature oxidation resistant coating. Various parameters, such as, nozzle and electrode design, powder feeding system,...
Show morePlasma spray processing is a technique that is used extensively in thermal barrier coatings on gas and steam turbine components, biomedical implants and automotive components. Many processing parameters are involved to achieve a coating with certain functionality. The coating could be required to function as thermal barrier, wear resistant, corrosion resistant or a high temperature oxidation resistant coating. Various parameters, such as, nozzle and electrode design, powder feeding system, spray distances, substrate temperature and roughness, plasma gas flow rates and others can greatly alter the coating quality and resulting performance. Feedstock (powder or solution precursor) composition and morphology are some of the important variables, which can affect the high end coating applications. The amount of heat a plasma plume has to offer to the particles being processed as a coating depends primarily on the dissociation of the atoms of gaseous mixtures being used to create the plasma and the residence time required for the particle to stay in the flame. The parameters that are conducive for nanostructured retention could be found out if the residence time of the particles in the flame and the available heat in the plume for various gas combinations could be predicted. If the feedstock is a liquid precursor instead of a powder feedstock, the heat that has to be offered by the plasma could be increased by suitable gas combination to achieve a good quality coating. Very little information is available with regard to the selection of process parameters and processing of nano materials feedstock to develop nanostructured coatings using plasma spray. In this study, it has been demonstrated that nano ceramics or ceramic composites either in the form of coatings or bulk free form near net components could be processed using DC plasma spray. For powder feedstock, analytical heat transfer calculations could predict the particle states for a given set of parameters by way of heat input from the plasma to the particles. The parameter selection is rendered easier by means of such calculations. Alumina nano ceramic particles are processed as a coating. During Spray drying, a process of consolidation of nano alumina particles to spherical agglomerates, parameter optimization for complete removal of moisture has been achieved. The parameters are tested for alumina nanoparticles with a plasma torch for the veracity of calculations. The amount of heat transfer from the surface of the agglomerates to the core has been quantified as a function of velocity of particles. Since preparation of nanostructured feedstock for plasma spray is expensive and cumbersome, alternative solution precursor route for direct pyrolysis of precursor to coating has been studied in case of nanocrystalline rare earth oxides. Thus, it has also been shown by this research that nanostructured coatings could be either from a powder feedstock or a solution precursor feedstock. MoSi2-Si3N4, Ni-Al2O3, W-HfC nano ceramic composite systems have been processed as a bulk free form nanocomposite with 60-70% retained nanostructures. The importance of selection of substrates, roughness and the substrate temperature for development of free form bulk components has been highlighted. The improvement in mechanical and high temperature properties associated with having such nanostructured coatings or bulk nanocomposites are revealed. These nanostructured coatings are known for their low thermal conductivity, high wear resistance and can be potentially used as steam and gas turbines coatings for improved thermal efficiency. In summary, bulk nanocomposite through plasma spray processing is a viable alternative to conventional processes such as sintering, HIP for high fracture toughness and hardness applications.
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Date Issued: 2007
Identifier: CFE0001680, ucf:47203
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001680

Title: Synthesis and Characterization of Antimicrobial Non-Color Forming Silica-Silver Nanocomposite.
Creator: Bazata, Joshua, Santra, Swadeshmukul, Moore, Sean, Jewett, Travis, University of Central Florida
Abstract / Description: Silver has been utilized for its antimicrobial properties for thousands of years in a variety of fields, extending the shelf life of food and water, rendering eating utensils sanitary, and more recently in biomedical applications such as silver based antiseptic creams. While effective as an antimicrobial agent at very low concentrations ((&)#181;g/mL), silver imparts a strong color to objects it is incorporated into, due to its high plasmonic efficiency. The goal of this study was to...
Show moreSilver has been utilized for its antimicrobial properties for thousands of years in a variety of fields, extending the shelf life of food and water, rendering eating utensils sanitary, and more recently in biomedical applications such as silver based antiseptic creams. While effective as an antimicrobial agent at very low concentrations ((&)#181;g/mL), silver imparts a strong color to objects it is incorporated into, due to its high plasmonic efficiency. The goal of this study was to determine if incorporating silver nanoparticles into a silica matrix could reduce or eliminate the plasmonic signal, while retaining the antimicrobial effects of the silver nanoparticles.Citrate capped silver nanoparticles (AgNP) were synthesized using a borohydride reduction method as outlined by Zheng et. al., and incorporated into silica nanoparticles using a method adapted from Fleger et. al. To test the antimicrobial efficacy of these synthesized silica coated silver nanoparticles (SiAgNP), minimum inhibitory concentration testing at three time points, 1, 4, and 8 hours, was carried out against E. coli and S. aureus using broth microdilution and Alamar Blue as an indicator of microbial growth. Efficacy was judged against uncoated AgNP and aqueous silver nitrate (AgNO3) solutions at equivalent Ag concentrations. Silica nanoparticles (SiNP) were utilized as a negative control. Further antimicrobial characterization using a bacterial viability assay revealed a time dependent killing trend in the SiAgNP, suggesting a controlled release of Ag+ from within the silica matrix. Efficacy of the SiAgNP was determined to fall between the most effective antimicrobial form of silver tested, AgNO3, and least effective, AgNP. However, the SiAgNP material exhibited no visible plasmon peak when UV-Visible spectrophotometric readings were taken, as well as remaining colorless when coated onto a ceramic substrate. Zeta potential revealed a high degree of colloidal stability of the SiAgNP. TEM imaging studies were carried out, verifying the presence of Ag within and on the silica nanoparticles, as well as the crystalline structure of the uncoated AgNP. It was determined that coating AgNP synthesized through borohydride reduction with silica through a St(&)#246;ber synthesis mechanism yields a material with enhanced antimicrobial effects compared to AgNP, but with no detectable plasmon signal, effectively producing a non-color forming silver based antimicrobial.
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Date Issued: 2015
Identifier: CFE0006208, ucf:51097
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006208

Title: Synthesis, Processing and Characterization of Polymer Derived Ceramic Nanocomposite Coating Reinforced with Carbon Nanotube Preforms.
Creator: Yang, Hongjiang, Gou, Jihua, Xu, Yunjun, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: Ceramics have a number of applications as coating material due to their high hardness, wear and corrosion resistance, and the ability to withstand high temperatures. Critical to the success of these materials is the effective heat transfer through a material to allow for heat diffusion or effective cooling, which is often limited by the low thermal conductivity of many ceramic materials. To meet the challenge of improving the thermal conductivity of ceramics without lowering their performance...
Show moreCeramics have a number of applications as coating material due to their high hardness, wear and corrosion resistance, and the ability to withstand high temperatures. Critical to the success of these materials is the effective heat transfer through a material to allow for heat diffusion or effective cooling, which is often limited by the low thermal conductivity of many ceramic materials. To meet the challenge of improving the thermal conductivity of ceramics without lowering their performance envelope, carbon nanotubes were selected to improve the mechanical properties and thermal dispersion ability due to its excellent mechanical properties and high thermal conductivity in axial direction. However, the enhancements are far lower than expectation resulting from limited carbon nanotube content in ceramic matrix composites and the lack of alignment. These problems can be overcome if ceramic coatings are reinforced by carbon nanotubes with good dispersion and alignment. In this study, the well-dispersed and aligned carbon nanotubes preforms were achieved in the form of vertically aligned carbon nanotubes (VACNTs) and Buckypaper. Polymer derived ceramic (PDC) was selected as the matrix to fabricate carbon nanotube reinforced ceramic nanocomposites through resin curing and pyrolysis. The SEM images indicates the alignment of carbon nanotubes in the PDC nanocomposites. The mechanical and thermal properties of the PDC nanocomposites were characterized through Vickers hardness measurement and Thermogravimetric Analysis. The ideal anisotropic properties of nanocomposites were confirmed by estimating the electrical conductivity in two orthogonal directions.
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Date Issued: 2014
Identifier: CFE0005446, ucf:50385
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005446

Title: NONDESTRUCTIVE EVALUATION OF THERMAL BARRIER COATINGS WITH THERMAL WAVE IMAGING AND PHOTOSTIMULATED LUMINESCENCE SPECTROSCOPY.
Creator: Franke, Barbara, Sohn, Yong-ho, University of Central Florida
Abstract / Description: Gas Turbine manufacturers strive for increased operating temperatures of gas turbine engines to improve efficiency and performance. One method of increasing the temperature beyond material limits is by applying thermal barrier coatings (TBCs) to hot section components. TBCs provide a thermal gradient between the hot gases and metallic substrate, and allow an increase in turbine inlet temperatures of 100-150ºC. However, spallation of TBCs can cause catastrophic failure of turbine engines...
Show moreGas Turbine manufacturers strive for increased operating temperatures of gas turbine engines to improve efficiency and performance. One method of increasing the temperature beyond material limits is by applying thermal barrier coatings (TBCs) to hot section components. TBCs provide a thermal gradient between the hot gases and metallic substrate, and allow an increase in turbine inlet temperatures of 100-150ºC. However, spallation of TBCs can cause catastrophic failure of turbine engines by incipient melting of the substrate. To prevent such an occurrence, non-destructive evaluation (NDE) techniques are critical for quality control, health monitoring, and life assessment of TBCs. Two techniques in development for this purpose are thermal wave imaging (TWI) and photostimulated luminescence (PL) spectroscopy. TWI is a promising NDE technique with the ability to detect integrity and thickness of TBCs. In this study, TWI was employed as an NDE technique to examine as-coated TBCs with varying thicknesses, and thermally-cycled TBCs for initiation and progression of subcritical-subsurface damage as a function of thermal cycling. TWI and thermal response amplitude were correlated to the microstructural characteristics and damage progression of TBCs based on phenomenological expressions of thermal diffusion. The TBC specimens examined consisted of air plasma sprayed ZrO2 - 7wt.% Y2O3 on NiCoCrAlY bond coats with Haynes 230 superalloy substrate. As-coated specimens of varying thicknesses were evaluated by TWI to examine its applicability as a thickness measurement tool. It was found that heat dissipation through the TBC following pulsed excitation by xenon flash lamps initially followed the 1-D law of conduction and deviated from it as a function of thickness and time. The deviation resulted from quick dissipation of heat into the conductive metallic substrate. Therefore, with calibration, TWI can be used as a tool for YSZ thickness measurements of APS TBCs in the as-coated condition for quality control measures. Specimens of uniform thickness were evaluated as a function of thermal cyclic oxidation for subcritical-subsurface damage detection. Thermal cycling was carried out in air with 30-minute heat-up, 10-hour dwell at 1150°C, 30-minute air-quench and 1-hour hold at room temperature. During thermal cycling, TBC specimens were evaluated non-destructively by TWI at room temperature every 10 to 20 thermal cycles, and selected specimens were removed from thermal cycling for microstructural analysis by scanning electron microscopy (SEM). Higher thermal response amplitude associated with disrupted heat transfer was observed where localized spallation at or near the YSZ/TGO interface occurred. The health of the TBC was monitored by a rise in thermal response amplitude which may indicate a coalescence of microcracks to a detectable level. PL has been developed to measure stress, and detect subsurface damage and polymorphic transformation within the thermally grown oxide (TGO) of TBCs. PL was employed in this study as an NDE technique for TBCs to correlate subsurface damage as a function of thermal cyclic oxidation. The TBCs consisted of ZrO2 – 7 wt.% Y2O3 applied by electron beam physical vapor deposition with an as-coated (Ni,Pt)Al bond coat on a CMSX-4 superalloy substrate. Specimens were thermally cycled with a 10 minute ramp to a peak temperature of 1121°C, 40 minute hold at peak temperature, and 10 minute forced air quench. The TBCs were periodically removed from thermal cycling for NDE using PL until failure. Two specimens were removed from thermal oxidation after 10% and 70% of the average lifetime for microstructural analysis by SEM. During initial thermal cycling, metastable phases and polymorphic transformations of the Al2O3 scale were examined by PL. The polymorphic transformation from a metastable phase to equilibrium a-Al2O3 was detected. Since metastable phases are thought to be detrimental to coating lifetime, detection of these phases by PL can be used as a quality control tool. Nearing end-of-life, relief of the TGO from the compressive residual stress arising from thermal expansion mismatch was detected with PL and confirmed with microstructural analysis that revealed damage initiation (e.g. microcracking within the TGO scale parallel to the interfaces.) Rise in luminescence near the R-line frequency for polycrystalline a-Al2O3 without any residual stress (i.e. n = 14402 cm-1 and n = 14432 cm-1) corresponded to regions where cracked TGO was adhered to YSZ and not exposed to compressive stresses from thermal expansion mismatch upon cooling.
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Date Issued: 2005
Identifier: CFE0000717, ucf:46613
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000717

Title: CORRELATING MICROSTRUCTURAL DEVELOPMENT AND FAILURE MECHANISMS TO PHOTOSTIMULATED LUMINESCENCE SPECTROSCOPY AND ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY IN THERMAL BARRIER COATINGS.
Creator: Jayaraj, Balaji, Sohn, Yongho, University of Central Florida
Abstract / Description: Thermal barrier coatings (TBCs) are widely used for thermal protection of hot section components in turbines for propulsion and power generation. Applications of TBCs based on a clearer understanding of failure mechanisms can help increase the performance and life-cycle cost of advanced gas turbine engines. Development and refinement of robust non-destructive evaluation techniques can also enhance the reliability, availability and maintainability of hot section components in gas turbines...
Show moreThermal barrier coatings (TBCs) are widely used for thermal protection of hot section components in turbines for propulsion and power generation. Applications of TBCs based on a clearer understanding of failure mechanisms can help increase the performance and life-cycle cost of advanced gas turbine engines. Development and refinement of robust non-destructive evaluation techniques can also enhance the reliability, availability and maintainability of hot section components in gas turbines engines. In this work, degradation of TBCs was non-destructively examined by photostimulated luminescence spectroscopy (PSLS) and electrochemical impedance spectroscopy (EIS) as a function of furnace thermal cycling carried out in air with 10-minute heat-up, 0.67, 9.6 and 49.6 -hour dwell duration at 1121°C (2050°F), and 10-minute forced-air quench. TBCs examined in this study consisted of either electron beam physical vapor deposited and air plasma sprayed yttria-stabilized zirconia (YSZ) on a variety of bond coat / superalloy substrates including bond coats of NiCoCrAlY and (Ni,Pt)Al, and superalloys of CMSX-4, Rene'N5, Haynes 230 and MAR-M-509. Detailed microstructural characterization by scanning electron microscopy and energy dispersive spectroscopy was carried out to document the degradation and failure characteristics of TBC failure, and correlate results of PSLS and EIS. Mechanisms of microstructural damage initiation and progression varied as a function of TBC architecture and thermal cycling dwell time, and included undulation of the interface between the thermally grown oxide (TGO) and bond coats, internal oxidation of the bond coats, and formation of Ni/Co-rich TGO. These microstructural observations were correlated to the evolution in compressive residual stress in the TGO scale determined by PSLS shift. Correlations include stress-relief and corresponding luminescence shift towards stress-free luminescence associated with subcritical cracking of the TGO scale and stress-relaxation associated with gradual shift in the luminescence towards stress-free luminescence is related to the undulation of TGO/bondcoat interface (e.g., rumpling and ratcheting). Microstructural changes in TBCs such as YSZ sintering, TGO growth, and subcritical damages within the YSZ and TGO scale were also correlated to the changes in electrochemical resistance and capacitance of the YSZ and TGO, respectively. With thermal exposure the YSZ/TGO resistance and capacitance increased and decreased as result of sintering and TGO growth. With progressive thermal cycling damages in the TGO was related to the TGO capacitance showing a continuous increase and at failure TGO capacitance abruptly increased with the exposure of bondcoat. Further correlations among the microstructural development, PSLS and EIS are documented and discussed, particularly as a function of dwell time used during furnace thermal cycling test, with due respect for changes in failure characteristics and mechanisms for various types of TBCs.
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Date Issued: 2011
Identifier: CFE0003635, ucf:48882
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003635

Title: ENVIRONMENTAL DEGRADATION OF OXIDATION RESISTANT AND THERMAL BARRIER COATINGS FOR FUEL-FLEXIBLE GAS TURBINE APPLICATIONS.
Creator: Mohan, Prabhakar, Sohn, Yongho, University of Central Florida
Abstract / Description: The development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature...
Show moreThe development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature protective coatings, one critical challenge that received greater attention in recent years is their resistance to high-temperature degradation due to corrosive deposits arising from fuel impurities and CMAS (calcium-magnesium-alumino-silicate) sand deposits from air ingestion. The presence of vanadium, sulfur, phosphorus, sodium and calcium impurities in alternative fuels warrants a clear understanding of high-temperature materials degradation for the development of fuel-flexible gas turbine engines. Degradation due to CMAS is a critical problem for gas turbine components operating in a dust-laden environment. In this study, high-temperature degradation due to aggressive deposits such as V2O5, P2O5, Na2SO4, NaVO3, CaSO4 and a laboratory-synthesized CMAS sand for free-standing air plasma sprayed (APS) yttria stabilized zirconia (YSZ), the topcoat of the TBC system, and APS CoNiCrAlY, the bond coat of the TBC system or a stand-alone ORC, is examined. Phase transformations and microstructural development were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. This study demonstrated that the V2O5 melt degrades the APS YSZ through the formation of ZrV2O7 and YVO4 at temperatures below 747Ã‚Â°C and above 747Ã‚Â°C, respectively. Formation of YVO4 leads to the depletion of the Y2O3 stabilizer and the deleterious transformation of the YSZ to the monoclinic ZrO2 phase. The investigation on the YSZ degradation by Na2SO4 and a Na2SO4 + V2O5 mixture (50-50 mol. %) demonstrated that Na2SO4 itself did not degrade the YSZ, however, in the presence of V2O5, Na2SO4 formed vanadates such as NaVO3 that degraded the YSZ through YVO4 formation at temperature as low as 700Ã‚Â°C. The APS YSZ was found to react with the P2O5 melt by forming ZrP2O7 at all temperatures. This interaction led to the depletion of ZrO2 in the YSZ (i.e., enrichment of Y2O3 in tÃ‚Â'-YSZ) and promoted the formation of the fluorite-cubic ZrO2 phase. Above 1250Ã‚Â°C, CMAS deposits were observed to readily infiltrate and significantly dissolve the YSZ coating via thermochemical interactions. Upon cooling, zirconia reprecipitated with a spherical morphology and a composition that depended on the local melt chemistry. The molten CMAS attack destabilized the YSZ through the detrimental phase transformation (tÃ‚Â' -> t -> f + m). Free standing APS CoNiCrAlY was also prone to degradation by corrosive molten deposits. The V2O5 melt degraded the APS CoNiCrAlY through various reactions involving acidic dissolution of the protective oxide scale, which yielded substitutional-solid solution vanadates such as (Co,Ni)3(VO4)2 and (Cr,Al)VO4. The molten P2O5, on the other hand, was found to consume the bond coat constituents significantly via reactions that formed both Ni/Co rich phosphates and Cr/Al rich phosphates. Sulfate deposits such as Na2SO4, when tested in encapsulation, damaged the CoNiCrAlY by Type I acidic fluxing hot corrosion mechanisms at 1000Ã‚Â°C that resulted in accelerated oxidation and sulfidation. The formation of a protective continuous Al2O3 oxide scale by preoxidation treatment significantly delayed the hot corrosion of CoNiCrAlY by sulfates. However, CoNiCrAlY in both as-sprayed and preoxidized condition suffered a significant damage by CaSO4 deposits via a basic fluxing mechanism that yielded CaCrO4 and CaAl2O4. The CMAS melt also dissolved the protective Al2O3 oxide scale developed on CoNiCrAlY by forming anorthite platelets and spinel oxides. Based on the detailed investigation on degradation of the APS YSZ and CoNiCrAlY by various corrosive deposits, an experimental attempt was carried out to mitigate the melt-induced deposit attack. Experimental results from this study demonstrate, for the first time, that an oxide overlay produced by electrophoretic deposition (EPD) can effectively perform as an environmental barrier overlay for APS TBCs. The EPD protective overlay has a uniform and easily-controllable thickness, uniformly distributed closed pores and tailored chemistry. The EPD Al2O3 and MgO overlays were successful in protecting the APS YSZ TBCs against CMAS attack and hot corrosion attack (e.g., sulfate and vanadate), respectively. Furnace thermal cyclic oxidation testing of overlay-modified TBCs on bond-coated superalloy also demonstrated the good adhesive durability of the EPD Al2O3 overlay.
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Date Issued: 2010
Identifier: CFE0003099, ucf:48315
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003099

Title: EVOLUTION OF MICROSTRUCTURE AND RESIDUAL STRESS IN DISC-SHAPE EB-PVD THERMAL BARRIER COATINGS AND TEMPERATURE PROFILE OF HIGH PRESSURE TURBINE BLADE.
Creator: Mukherjee, Sriparna, Sohn, Yongho, University of Central Florida
Abstract / Description: A detailed understanding of failure mechanisms in thermal barrier coatings (TBCs) can help develop reliable and durable TBCs for advanced gas turbine engines. One of the characteristics of failure in electron beam physical vapor deposited (EB-PVD) TBCs is the development of instability, named rumpling, at the interface between (Ni, Pt)Al bond coat and thermally grown oxide (TGO). In this study, thermal cycling at 1100[degrees]C with 1 hr dwell time was carried out on 25.4mm disc specimens of...
Show moreA detailed understanding of failure mechanisms in thermal barrier coatings (TBCs) can help develop reliable and durable TBCs for advanced gas turbine engines. One of the characteristics of failure in electron beam physical vapor deposited (EB-PVD) TBCs is the development of instability, named rumpling, at the interface between (Ni, Pt)Al bond coat and thermally grown oxide (TGO). In this study, thermal cycling at 1100[degrees]C with 1 hr dwell time was carried out on 25.4mm disc specimens of TBCs that consisted of EB-PVD coated ZrO2-7wt.%Y2O3, (Pt,Ni)Al bond coat, and CMSX-4 Ni-based superalloy. At specific fraction of lifetime,TBCs were examined by electron microscopy and photostimulated luminescence (PL). Changes in the average compressive residual stress of the TGO determined by PL and the magnitude of rumpling, determined by tortuosity from quantitative microstructural analyses, were examined with respect to the furnace thermal cyclic lifetime and microstructural evolution of TBCs. The combination of elastic strain energy within the TGO and interfacial energy at the interface between the TGO and the bond coat was defined as the TGO energy, and its variation with cyclic oxidation time was found to remain approximately constant ~135J/m2 during thermal cycling from 10% to 80% thermal cyclic lifetime. Parametric study at ~135J/m2 was performed and variation in residual stress with rumpling for different oxide scale thicknesses was examined. This study showed that the contribution of rumpling in residual stress relaxation decreased with an increase in TGO thickness. High pressure turbine blades serviced for 2843 hours and in the as coated form were also examined using electron microscopy and photostimulated luminescence. The difference in residual stress values obtained using PL on the suction and pressure sides of as-coated turbine blade were discussed. The presence of a thick layer of deposit on the serviced blade gave signals from stress free alpha-Al2O3 in the deposit, not from the TGO. The TGO growth constant data from the disc-shape TBCs, thermally cycled at 1100[degrees]C, and studies by other authors at different temperatures but on similar EB-PVD coated TBCs with (Pt, Ni)Al bond coat and CMSX-4 Ni- based superalloy were used to determine the temperature profile at the YSZ/bond coat interface. The interfacial temperature profiles of the serviced blade and the YSZ thickness profile were compared to document the variable temperature exposure at the leading edge, trailing edge, suction and the pressure side.
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Date Issued: 2011
Identifier: CFE0003927, ucf:48700
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003927

Title: Nanocomposite Coating Mechanics via Piezospectroscopy.
Creator: Freihofer, Gregory, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, Schulzgen, Axel, University of Central Florida
Abstract / Description: Coatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of...
Show moreCoatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of nanocomposites and their coatings has been applied to give material property measurements, providing an understanding of particle reinforced composite behavior.Understanding the nanoparticle-coating-substrate mechanics is essential to interpreting the spectral shifts for stress sensing of structures. In the past, methods to experimentally measure the mechanics of these embedded nano inclusions have been limited, and much of the design of these composites depend on computational modeling and bulk response from mechanical testing. The PS properties of Chromium doped alumina allow for embedded inclusion mechanics to be revisited with unique experimental setups that probe the particles state of stress under applied load to the composite. These experimental investigations of particle mechanics will be compared to the Eshelby theory and its derivative theories in addition to the nanocomposite coating mechanics. This work discovers that simple nanoparticle load transfer theories are adequate for predicting PS properties in an intermediate volume fraction range. With fundamentals of PS nanocomposites established, the approach was applied to selected experiments to prove its validity. In general it was observed that the elastic modulus values calculated from the PS response were similar to that observed from macroscale strain measurements such as a strain gage. When simple damage models were applied to monitor the elastic modulus, it was observed that the rate of decay for the elastic modulus was much higher for the PS measurements than for the strain gage.A novel experiment including high resolution PS maps with secondary strain maps from digital image correlation is reviewed on an open hole tension, composite coupon. The two complementary measurements allow for a unique PS response for every location around the hole with a spatial resolution of 400 microns. Progression of intermediate damage mechanisms was observed before digital image correlation indicated them. Using the PS nanocomposite model, elastic modulus values were calculated. Introducing an elastic degradation model with some plastic deformation allows for estimation of material properties during the progression of failure.This work is part of a continuing effort to understand the mechanics of a stress sensing PS coating. The mechanics were then applied to various experimental data that provided elastic property calculations with high resolution. The significance is in the experimental capture of stress transfer in particulate composites. These findings pave the way for the development of high resolution stress-sensing coatings.
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Date Issued: 2014
Identifier: CFE0005614, ucf:50223
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005614

Title: EFFECTS OF BOND COAT SURFACE PREPARATION ON THERMAL CYCLING LIFETIME AND FAILURE CHARACTERISTICS OF THERMAL BARRIER COATINGS.
Creator: Liu, Jing, Sohn, Yong-ho, University of Central Florida
Abstract / Description: Thermal barrier coatings (TBCs) have been widely used in gas turbine engines to protect the underlying metal from high operating temperature so as to improve the durability of the components and enhance the engine efficiency. However, since the TBCs always operate in a demanding high-temperature environment of aircraft and industrial gas-turbine engines, a better understanding of this complex system is required to improve the durability and reliability.The objective of this study is to...
Show moreThermal barrier coatings (TBCs) have been widely used in gas turbine engines to protect the underlying metal from high operating temperature so as to improve the durability of the components and enhance the engine efficiency. However, since the TBCs always operate in a demanding high-temperature environment of aircraft and industrial gas-turbine engines, a better understanding of this complex system is required to improve the durability and reliability.The objective of this study is to investigate the effects of surface modification for the NiCoCrAlY bond coats on the thermal cycling lifetime and failure characteristics of TBCs. Parameters of modification for the bond coats included as-sprayed, barrel-finished, hand-polished and pre-oxidation heat treatment at 1100 C in =10-8 atm up to 4 hours, carried out prior to the electron beam physical vapor deposition (EB-PVD) of ZrO2-7wt% Y2O3 (7YSZ) ceramic topcoat. The resulting characteristics of the bond coat and the thermally grown oxide (TGO) scale were initially documented by surface roughness, phase constituents of the TGO scale, and residual stress of the TGO scale. The thermal cycling test consisted of 10-minute heat-up to 1121 C, 40-minute hold at 1121 C, and 10-minute forced air-quench. As-coated and thermally-cycled TBCs were characterized by optical profilometry (OPM), photo-stimulated luminescence spectroscopy (PSLS), optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and scanning/transmission electron microscopy (TEM/STEM) equipped with high angle annular dark field (HAADF) and X-ray energy dispersive spectroscopy (XEDS). TBC specimens for TEM/STEM analysis were prepared by focused ion beam (FIB) in-situ lift-out (INLO) technique.Superior thermal cycling lifetime was observed for TBCs with as-sprayed bond coats regardless of pre-oxidation heat treatment, and TBCs with hand-polished bond coats only after pre-oxidation heat treatment. With pre-oxidation heat treatment, relative photostimulated luminescence intensity of the equilibrium ¦Á-Al2O3 increased. Thus, the improvement in TBC lifetime can be correlated with an increase in the amount of ¦Á-Al2O3 in the TGO scale, given a specific surface modification/roughness. The lifetime improvement due to pre-oxidation was particularly significant to TBCs with smooth hand-polished bond coats and negligible for TBCs with rough as-sprayed bond coats.Spallation-fracture paths depended on the lifetime of TBCs. Premature spallation of TBCs occurred at the interface between the YSZ and TGO. Longer durability can be achieved by restricting the fracture paths to the TGO/bond coat interface. Small particulate phase observed through the TGO scale was identified as Y2O3 (cubic) by diffraction analysis on TEM. While small addition of Y in the NiCoCrAlY bond coat helps the adhesion of the TGO scale, excessive alloying can lead to deleterious effects.
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Date Issued: 2004
Identifier: CFE0000097, ucf:46083
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000097

Title: MECHANISMS OF LIFETIME IMPROVEMENT IN THERMAL BARRIER COATINGS WITH HF AND/OR Y MODIFICATION OF CMSX-4 SUPERALLOY SUBSTRATES.
Creator: Liu, Jing, Sohn, Yong ho, University of Central Florida
Abstract / Description: In modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime...
Show moreIn modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime of TBCs was measured using a furnace thermal cycle test that consisted of 10-minute heat-up, 50-minute dwell at 1135C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over 3200 cycles with appropriated Hf- and/or Y alloying of CMSX-4 superalloys. This significant improvement in TBC lifetime is the highest reported lifetime in literature with similar testing parameters. Beneficial role of reactive element (RE) on the durability of TBCS were systematically investigated in this study. Photostimulated luminescence spectroscopy (PL) was employed to non-destructively measure the residual stress within the TGO scale as a function of thermal cycling. Extensive microstructural analysis with emphasis on the YSZ/TGO interface, TGO scale, TGO/bond coat interface was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning electron microscopy (STEM) as a funcion of thermal cycling including after the spallation failure. Focused ion beam in-situ lift-out (FIB-INLO) technique was employed to prepare site-specific TEM specimens. X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) were also employed for phase identification and interfacial chemical analysis. While undulation of TGO/bond coat interface (e.g., rumpling and ratcheting) was observed to be the main mechanism of degradation for the TBCs on baseline CMSX-4, the same interface remained relatively flat (e.g., suppressed rumpling and ratcheting) for durable TBCs on Hf- and/or Y-modified CMSX-4. The fracture paths changed from the YSZ/TGO interface to the TGO/bond coat interface when rumpling was suppressed. The geometrical incompatibility between the undulated TGO and EB-PVD YSZ lead to the failure at the YSZ/TGO interface for TBCs with baseline CMSX-4. The magnitude of copressive residual stress within the TGO scale measured by PL gradually decreased as a function of thermal cycling for TBCs with baseline CMSX-4 superalloy substrates. This gradual decrease corrsponds well to the undulation of the TGO scale that may lead to relaxation of the compressive residual stress within the TGO scale. For TBCs with Hf- and/or Y-modified CMSX-4 superalloy substrates, the magnitude of compressive residual stress within the TGO scale remained relatively constant throughout the thermal cycling, although PL corresponding to the stress-relief caused by localized cracks at the TGO/bond coat interface and within the TGO scale was observed frequently starting 50% of lifetime. A slightly smaller parabolic growth constant and grain size of the TGO scale was observed for TBCs with Hf- and/or Y- modified CMSX-4. Small monoclinic HfO2 precipitates were observed to decorate grain boundaries and the triple pointes within the alpha-Al2O3 scale for TBCs with Hf- and/or Y-modified CMSX-4 substrates. Segregation of Hf/Hf4+ at the TGO/bond coat interfaces was also observed for TBCs with Hf- and/or Y-modified CMSX-4 superalloys substrates. Adherent and pore-free YSZ/TGO interface was observed for TBCs with Hf- and/or Y-modified CMSX-4, while a significant amount of decohesion at the YSZ/TGO interface was observed for TBCs with baseline CMSX-4. The beta-NiAl(B2) phase in the (Ni,Pt)Al bond coat was observed to partially transform into gama prime-Ni3Al (L12) phase due to depletion of Al in the bond coat during oxidation. More importantly, the remaining beta-NiAl phase transformed into L10 martensitic phase upon cooling even though there was no significant difference in these phase transformations for all TBCs. Results from these microstructural observations are documented to elucidate mechanisms that suppress the rumpling of the TGO/bond coat interface, which is responsible for superior performance of EB-PVD TBCs with (Ni,Pt)Al bond coat and Hf- and/or Y-modified CMXS-4 superalloy.
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Date Issued: 2007
Identifier: CFE0001872, ucf:47382
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001872

Title: MULTIPLE SCATTERING OF LIGHT IN INHOMOGENEOUS MEDIA AND APPLICATIONS.
Creator: Mujat, Claudia, Dogariu, Aristide, University of Central Florida
Abstract / Description: Light scattering-based techniques are being developed for non-invasive diagnostics of inhomogeneous media in various fields, such as medicine, biology, and material characterization. However, as most media of interest are highly scattering and have a complex structure, it is difficult to obtain a full analytical solution of the scattering problem without introducing approximations and assumptions about the properties of the system under consideration. Moreover, most of the previous studies...
Show moreLight scattering-based techniques are being developed for non-invasive diagnostics of inhomogeneous media in various fields, such as medicine, biology, and material characterization. However, as most media of interest are highly scattering and have a complex structure, it is difficult to obtain a full analytical solution of the scattering problem without introducing approximations and assumptions about the properties of the system under consideration. Moreover, most of the previous studies deal with idealized scattering situations, rarely encountered in practice. This dissertation provides new analytical, numerical, and experimental solutions to describe subtle effects introduced by the properties of the light sources, and by the boundaries, absorption and morphology of the investigated media. A novel Monte Carlo simulation was developed to describe the statistics of partially coherent beams after propagation through inhomogeneous media. The Monte Carlo approach also enabled us to study the influence of the refractive index contrast on the diffusive processes, to discern between different effects of absorption in multiple scattering, and to support experimental results on inhomogeneous media with complex morphology. A detailed description of chromatic effects in scattering was used to develop new models that explain the spectral dependence of the detected signal in applications such as imaging and diffuse reflectance measurements. The quantitative and non-invasive characterization of inhomogeneous media with complex structures, such as porous membranes, diffusive coatings, and incipient lesions in natural teeth was then demonstrated.
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Date Issued: 2004
Identifier: CFE0000048, ucf:46143
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000048

Title: Analysis of residual stress and damage mechanisms of thermal barrier coatings deposited via PS-PVD and EB-PVD.
Creator: Rossmann, Linda, Raghavan, Seetha, Sohn, Yongho, Vaidyanathan, Raj, Ghosh, Ranajay, University of Central Florida
Abstract / Description: Thermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of...
Show moreThermal barrier coatings (TBCs) are critical to gas turbine engines, as they protect the components in the hot section from the extreme temperatures of operation. The current industry standard method of applying TBCs for turbine blades in jet engines is electron-beam physical vapor deposition (EB-PVD), which results in a columnar structure that is valued for its high degree of strain tolerance. An emerging deposition method is plasma-spray physical vapor deposition (PS-PVD), capable of producing a variety of customizable microstructures as well as non-line-of-sight deposition, which allows more complex geometries to be coated, or even multiple parts at once. The pseudo-columnar microstructure that can be produced with PS-PVD is a possible alternative to EB-PVD. However, before PS-PVD can be used to its full potential, its mechanical properties and behavior must be understood. This work contributes to this understanding by characterizing PS-PVD TBCs that have been thermally cycled to simulate multiple lifetimes (0, 300, and 600 thermal cycles). Residual stress in the thermally grown oxide (TGO) layer is characterized by photoluminescence piezospectroscopy as TGO residual stress is correlated with the lifetime of the coating. Residual stress in the top coat is characterized by Raman spectroscopy, because this stress drives cracking in the top coat that can lead to failure. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) are performed to observe microstructural and phase evolution to provide context and possible explanations for the stress results. In addition, EB-PVD samples of the same thermal cycling history are characterized in the same way so that PS-PVD can be benchmarked against the industry standard. The compressive residual stress in the TGO in both coatings was relieved with thermal cycling due to the TGO lengthening as well as microcracking. The PS-PVD samples had slightly lower TGO stress than the EB-PVD, which is attributed to the greater extent of cracking within the TGO, whereas cracking in the EB-PVD samples was at the TGO/topcoat interface. The PS-PVD cycled samples had significant cracking within the topcoat near the TGO due to both greater porosity than EB-PVD samples and regions of unmelted particles that provide little resistance to cracking. The greater convolution of the TGO in the PS-PVD samples results in greater out-of-plane tensile stresses that cause crack initiation, as well as diverts cracks away from the difficult-to-follow interface. The TGO stress results agree with existing literature and extend the thermal cycling beyond what has previously been reported for PS-PVD coatings, revealing a trend of stress relief and stress values similar to that of EB-PVD coatings in this study and in the literature. Residual stress in the topcoat for both coating types became increasingly compressive with thermal cycling, indicating loss of strain tolerance by sintering. The trend of the YSZ stress for both coating types to become more compressive with cycling and with depth agrees with the literature, and the thermal cycling is longer than has been previously reported for PS-PVD. The two coating types had quite different microstructures and crack modes as well as different as-deposited residual stresses, but after thermal cycling had similar stresses in both the TGO and top coat. No samples experienced spallation. These results indicate that, while PS-PVD coatings have different properties and behavior from EB-PVD coatings, they had comparable levels of damage to EB-PVD coatings of the same lifetime and are a viable alternative to EB-PVD. Further tuning of the processing parameters may result in PS-PVD coatings with even more similar behavior to EB-PVD coatings.
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Date Issued: 2019
Identifier: CFE0007717, ucf:52429
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007717

Title: NON-DESTRUCTIVE MICROSTRUCTURAL EVALUATION OF YTTRIA STABILIZED ZIRCONIA, NICKEL ALUMINIDES AND THERMAL BARRIER COATINGS USING ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY.
Creator: Vishweswaraiah, Srinivas, Sohn, Yongho, University of Central Florida
Abstract / Description: There has been an urge for increasing the efficiency in advanced gas turbine engines. To fulfill these needs the inlet gas temperatures should be increased in the gas turbine engines, thermal barrier coatings (TBCs) have gained significant applications in increasing the gas inlet temperatures. Insulating characteristics of ceramic TBCs allow the operation at up to 150~250 ˚C higher gas temperatures. Because of the severe turbine engine operating conditions that include high...
Show moreThere has been an urge for increasing the efficiency in advanced gas turbine engines. To fulfill these needs the inlet gas temperatures should be increased in the gas turbine engines, thermal barrier coatings (TBCs) have gained significant applications in increasing the gas inlet temperatures. Insulating characteristics of ceramic TBCs allow the operation at up to 150~250 ˚C higher gas temperatures. Because of the severe turbine engine operating conditions that include high temperature, steep temperature gradient, thermal cycling, oxidation and hot-corrosion, TBCs can fail by spallation at the interface between the metal and ceramic. The lack of understanding in failure mechanisms and their prediction warrant a development of non-destructive evaluation technique that can monitor the quality and degradation of TBCs. In addition, the development of NDE technique must be based on a robust correlation to the characteristics of TBC failure.The objective of this study is to develop electrochemical impedance spectroscopy (EIS) as a Non-destructive evaluation (NDE) technology for application to TBCs. To have a better understanding of the multilayer TBCs using EIS they were divided into individual layers and EIS were performed on them. The individual layers included polycrystalline ZrO2-7~8 wt.%Y2O3 (YSZ) (topcoat) of two different densities were subjected to sintering by varying the sintering temperature and holding time for three different thickness and hot extruded NiAl alloy buttons which were subjected to isothermal oxidation with varying temperature and time. NiAl is as similar to the available commercial bondcoats used in TBCs. Then degradation monitoring with electrolyte penetration was carried out on electron beam physical vapor deposited (EB-PVD) TBCs as a function of isothermal exposure. Quality control for air plasma sprayed TBCs were carried out as a function of density, thickness and microstructure. Dense vertically cracked TBCs were tested as a function of vertical crack density and thickness.Electrochemical impedance response was acquired from all specimens at room temperature and analyzed with an AC equivalent circuit based on the impedance response as well as multi-layered structure and micro-constituents of specimens. Physical and microstructural features of these specimens were also examined by optical and electron microscopy. The EIS measurement was carried out in a three-electrode system using a standard Flat Cell (K0235) from Princeton Applied Research and IM6e BAS ZAHNER frequency response analyzer. The electrolyte employed in this investigation was 0.01M (molar) potassium Ferri/Ferro Cyanide {(K3Fe(CN)6/K4Fe(CN)6•3H2O)}.The thickness and density were directly related to the resistance and capacitance of the polycrystalline YSZ with varying thickness and open pores. As the effective thickness of the YSZ increased with sintering time and temperature, the resistance of the YSZ (RYSZ) increased proportionally. The variation in capacitance of YSZ (CYSZ) with respect to the change in porosity/density and thickness was clearly detected by EIS. The samples with high porosity (less dense) exhibited large capacitance, CYSZ, compared to those with less porosity (high density), given similar thickness. Cracking in the YSZ monoliths resulted in decrease of resistance and increase in capacitance and this was related to the electrolyte penetration.Growth and spallation of TGO scale on NiAl alloys during isothermal oxidation at various temperatures and holding time was also correlated with resistance and capacitance of the TGO scale. With an increase in the TGO thickness, the resistance of the TGO (RTGO) increased and capacitance of the TGO (CTGO) decreased. This trend in the resistance and capacitance of the TGO changed after prolonged heat treatment. This is because of the spallation of the TGO scale from the metal surface. The parabolic growth of TGO
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Date Issued: 2004
Identifier: CFE0000041, ucf:52855
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000041

Title: Fatigue Lifetime Approximation based on Quantitative Microstructural Analysis for Air Plasma Sprayed Thermal Barrier Coatings.
Creator: Bargraser, Carmen, Sohn, Yongho, An, Linan, Heinrich, Helge, University of Central Florida
Abstract / Description: The durability of thermal barrier coatings (TBCs) affects the life of the hot section engine components on which they are applied. Fatigue is the general failure mechanism for such components and is responsible for most unexpected failures; therefore it is desirable to develop lifetime approximation models to ensure reliability and durability.In this study, we first examined the microstructural degradation of air plasma sprayed ZrO2-8wt.%Y2O3 TBCs with a low-pressure plasma sprayed CoNiCrAlY...
Show moreThe durability of thermal barrier coatings (TBCs) affects the life of the hot section engine components on which they are applied. Fatigue is the general failure mechanism for such components and is responsible for most unexpected failures; therefore it is desirable to develop lifetime approximation models to ensure reliability and durability.In this study, we first examined the microstructural degradation of air plasma sprayed ZrO2-8wt.%Y2O3 TBCs with a low-pressure plasma sprayed CoNiCrAlY bond coat on an IN 738LC superalloy substrate. The durability of TBCs were assessed through furnace thermal cyclic tests carried out in air at 1100(&)deg;C with a 1-, 10-, and 50-hour dwell period, preceded by a 10-minute heat-up and followed by a 10-minute forced-air-quench. Failure mechanisms of the TBCs were thoroughly investigated through materials characterization techniques including: X-Ray Diffraction, Scanning Electron Microscopy, and Energy Dispersive X-Ray Spectroscopy.Quantitative microstructural analyses were then carried out to document the growth of the thermally grown oxide (TGO) scale, the depletion of the Al-rich ?-NiAl phase in the bond coat, and the population and growth of micro-cracks near the YSZ/bond coat interface. Trends in the TGO growth and the ?-phase depletion in the bond coat followed those of diffusion-controlled processes(-)parabolic growth of the TGO and exponential depletion of the ?-phase. Formation and propagation of cracks within the YSZ resulted in complete spallation of the YSZ topcoat from the bond-coated superalloy substrate.Evolution in these microstructural features was correlated to the lifetime of TBCs, which showed cracking within the YSZ to be the cause of failure; thus a lifetime approximation model was developed, via modification of Paris Law, based on the experimental data. The model predicted the TBC lifetime within 10% of the experimental lifetime.
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Date Issued: 2011
Identifier: CFE0004087, ucf:49145
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004087

Title: Rare Earth Oxide Coating with Controlled Chemistry Using Thermal Spray.
Creator: Singh, Virendra, Seal, Sudipta, Coffey, Kevin, Raghavan, Seetha, Heinrich, Helge, Zhai, Lei, University of Central Florida
Abstract / Description: Cerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent...
Show moreCerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent consolidation, specially using thermal spray.This dissertation aims to develop a scientific understanding towards the development of pure and doped ceria- based coating for a variety of technological applications, from SOFC applications to corrosion resistant coating. Atmospheric plasma spray (APS) and solution precursor plasma spray (SPPS) techniques for the fabrication of nano ceria coating were investigated. For feedstock powder preparation, a spray drying technique was used for the agglomeration of cerium oxide nano particles to achieve high density coating. Deposition efficiencies and coating porosity as a function of processing parameters were analyzed and optimized using a statistical design of experiment model. The coating deposition efficiency was dependent on the plasma temperature and vaporization pressure of the ceria nanoparticles. However, low standoff distance and high carrier gas flow rate were responsible for the improved density upto 86 (&)#177;3%.An alternative novel SPPS technique was studied for a thin film of cerium oxide deposition from various cerium salt precursors in doped and undoped conditions. The SPPS process allows controlling the chemistry of coating at a molecular level. The deposition mechanism by single scan experiments and the effect of various factors on coating microstructure evolution were studied in terms of splats formation. It was found that the precursor salt (nitrate of cerium) with lower thermal decomposition temperatures was suitable for a high density coating. The high concentration and low spray distance significantly improve the splat morphology and reduced porosity (upto 20%). The feasibility of the trivalent cations (Sm 3+ and Gd 3+) doping into cerium oxide lattice in high temperature plasma was discussed and experimentally studied. XRD analysis revealed the nano crystalline characteristic of the coating and lattice expansion due to doping. The extensive transmission electron microscopy, Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric were conducted to evaluate the precursors, and coating microstructure.Due to facial switching between Ce4+ and Ce3+ oxidation state, the cerium oxide surface becomes catalytically active. Thus, the APS ceria coatings were investigated for their applicability under extreme environmental conditions (high pressure and temperature). The air plasma sprayed coated 17-4PH steel was subjected to high pressure (10 Kpsi) and temperature (300 oF) corrosive environment. The coated steel showed continuous improvement in the corrosion resistance at 3.5 wt% NaCl at ambient temperature for three months study whereas, high pressure did not reveal a significant role in the corrosion process, and however, one needs to do further research. The ceria coated steel also revealed the improvement in corrosion protection (by 4 times) compared to the bare steel at low pH, 300 oF and 4000 Psi environment. This study projects the importance of cerium oxide coatings, their fabrication, optimization and applications.
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Date Issued: 2012
Identifier: CFE0004230, ucf:49023
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004230

Title: experimental and numerical investigations on bond durability of cfrp strengthened concrete members subjected to environmental exposure.
Creator: Al-Jelawy, Haider, Mackie, Kevin, Gou, Jihua, Chopra, Manoj, University of Central Florida
Abstract / Description: Fiber reinforced polymer (FRP) composites have become an attractive alternative to conventional methods for external-strengthening of civil infrastructure, particularly as applied to flexural strengthening of reinforced concrete (RC) members. However, durability of the bond between FRP composite and concrete has shown degradation under some aggressive environments. Although numerous studies have been conducted on concrete members strengthened with FRP composites, most of those studies have...
Show moreFiber reinforced polymer (FRP) composites have become an attractive alternative to conventional methods for external-strengthening of civil infrastructure, particularly as applied to flexural strengthening of reinforced concrete (RC) members. However, durability of the bond between FRP composite and concrete has shown degradation under some aggressive environments. Although numerous studies have been conducted on concrete members strengthened with FRP composites, most of those studies have focused on the degradation of FRP material itself, relatively few on bond behavior under repeated mechanical and environmental loading.This thesis investigates bond durability under accelerated environmental conditioning of two FRP systems commonly employed in civil infrastructure strengthening: epoxy and polyurethane systems. Five environments were considered under three different conditioning durations (3 months, 6 months, and 1 year). For each conditioning environment and duration (including controls), the following were laboratory tested: concrete cylinders, FRP tensile coupons, and FRP-strengthened concrete flexural members. Numerical investigations were performed using MSC MARC finite element software package to support the outcomes of durability experimental tests. Precise numerical studies need an accurate model for the bond between FRP and concrete, a linear brittle model is proposed in this work that is calibrated based on nonlinear regression of existing experimental lap shear data.Results of tensile tests on FRP coupons indicate that both epoxy and polyurethane FRP systems do not degrade significantly under environmental exposure. However, flexural tests on the FRP strengthened concrete beams indicate that bond between FRP and concrete shows significant degradation, especially for aqueous exposure. Moreover, a protective coating suppresses the measured degradation. Also, experimental load-displacement curves for control beams show excellent agreement with numerical load-displacement curves obtained using the proposed bond model. Finally, a bond-slip model is predicted for concrete leachate conditioned beams by matching load-displacement curves for those beams with numerical load-displacement curves.
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Date Issued: 2013
Identifier: CFE0004971, ucf:49589
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004971

Title: FABRICATION OF FUNCTIONAL NANOSTRUCTURES USING POLYELECTROLYTE NANOCOMPOSITES AND REDUCED GRAPHENE OXIDE ASSEMBLIES.
Creator: Chunder, Anindarupa, Zhai, Lei, University of Central Florida
Abstract / Description: A wide variety of nanomaterials ranging from polymer assemblies to organic and inorganic nanostructures (particles, wires, rods etc) have been actively pursued in recent years for various applications. The synthesis route of these nanomaterials had been driven through two fundamental approaches - Ã‚Â'Top downÃ‚Â' and Ã‚Â'Bottom upÃ‚Â'. The key aspect of their application remained in the ability to make the...
Show moreA wide variety of nanomaterials ranging from polymer assemblies to organic and inorganic nanostructures (particles, wires, rods etc) have been actively pursued in recent years for various applications. The synthesis route of these nanomaterials had been driven through two fundamental approaches - Ã‚Â'Top downÃ‚Â' and Ã‚Â'Bottom upÃ‚Â'. The key aspect of their application remained in the ability to make the nanomaterials suitable for targeted location by manipulating their structure and functionalizing with active target groups. Functional nanomaterials like polyelectrolyte based multilayered thin films, nanofibres and graphene based composite materials are highlighted in the current research. Multilayer thin films were fabricated by conventional dip coating and newly developed spray coating techniques. Spray coating technique has an advantage of being applied for large scale production as compared to the dip coating technique. Conformal hydrophobic/hydrophilic and superhydrophobic/hydrophilic thermal switchable surfaces were fabricated with multilayer films of poly(allylaminehydrochloride) (PAH) and silica nanoparticles by the dip coating technique, followed by the functionalization with thermosensitive polymer-poly(N-isopropylacrylamide)(PNIPAAM) and perfluorosilane. The thermally switchable superhydrophobic/ hydrophilic polymer patch was integrated in a microfluidic channel to act as a stop valve. At 70 degree centigrade, the valve was superhydrophobic and stopped the water flow (close status) while at room temperature, the patch became hydrophilic, and allowed the flow (open status). Spray-coated multilayered film of poly(allylaminehydrochloride) (PAH) and silica nanoparticles was fabricated on polycarbonate substrate as an anti-reflection (AR) coating. The adhesion between the substrate and the coating was enhanced by treating the polycarbonate surface with aminopropyltrimethoxylsilane (APTS) and sol-gel. The coating was finally made abrasion-resistant with a further sol-gel treatment on top of AR coating, which formed a hard thin scratch-resistant film on the coating. The resultant AR coating could reduce the reflection from 5 to 0.3% on plastic. Besides multilayered films, the fabrication of polyelectrolyte based electrospun nanofibers was also explored. Ultrathin nanofibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylaminehydrochloride) (PAH) were fabricated using the electrospinning technique and methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. The fiber was also loaded with a real life anti-depressant drug (2,3-tertbutyl-4-methoxyphenol) and fiber surface was made superhydrophobic. The drug loaded superhydrophobic nanofiber mat was immersed under water, phosphate buffer saline and surfactant solutions in three separated experiments. The rate of release of durg was monitored from the fiber surface as a result of wetting with different solutions. Time dependent wetting of the superhydrophobic surface and consequently the release of drug was studied with different concentrations of surfactant solutions. The results provided important information about the underwater superhydrophobicity and retention time of drug in the nanofibers. The nanostructured polymers like nanowires, nanoribbons and nanorods had several other applications too, based on their structure. Different self-assembled structures of semiconducting polymers showed improved properties based on their architectures. Poly(3-hexylthiophene) (P3HT) supramolecular structures were fabricated on P3HT-dispersed reduced graphene oxide (RGO) nanosheets. P3HT was used to disperse RGO in hot anisole/N, N-dimethylformamide solvents, and the polymer formed nanowires on RGO surfaces through a RGO induced crystallization process. The Raman spectroscopy confirmed the interaction between P3HT and RGO, which allowed the manipulation of the composite's electrical properties. Such a bottom-up approach provided interesting information about graphene-based composites and inspired to study the interaction between RGO and the molecular semiconductor-tetrasulphonate salt of copper phthalocyanine (TSCuPc) for nanometer-scale electronics. The reduction of graphene oxide in presence of TSCuPc produced a highly stabilized aqueous composite ink with monodispersed graphene sheets. To demonstrate the potential application of the donor (TSCuPc)Ã‚Â–acceptor (graphene) composite, the RGO/TSCuPc suspension was successfully incorporated in a thin film device and the optoelectronic property was measured. The conductivity (dark current) of the composite film decreased compared to that of pure graphene due to the donor molecule incorporation, but the photoconductivity and photoresponsivity increased to an appreciable extent. The property of the composite film overall improved with thermal annealing and optimum loading of TSCuPc molecules.
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Date Issued: 2010
Identifier: CFE0003292, ucf:48509
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003292

Title: Graphene Oxide Reinforcement in Plasma Sprayed Nickel-5%Aluminum Coatings.
Creator: Ward, David, Seal, Sudipta, Vaidyanathan, Raj, Heinrich, Helge, Zhai, Lei, University of Central Florida
Abstract / Description: Metallic plasma sprayed coatings are widely used in the aerospace industry for repair on worn engine components. However, the inherent defects in these coatings limit the variety of repairs and reduce the service life of the repaired parts. A potential solution to overcome this problem is to mix small amounts of inexpensive graphene oxide in the powder feedstock. The incredible strength to weight ratio of graphene oxide makes it a viable additive to improve mechanical properties of metallic...
Show moreMetallic plasma sprayed coatings are widely used in the aerospace industry for repair on worn engine components. However, the inherent defects in these coatings limit the variety of repairs and reduce the service life of the repaired parts. A potential solution to overcome this problem is to mix small amounts of inexpensive graphene oxide in the powder feedstock. The incredible strength to weight ratio of graphene oxide makes it a viable additive to improve mechanical properties of metallic plasma sprayed coatings. The powder system chosen for this research is Nickel-5Aluminum since it is a common coating for such repairs. The greatest challenge was retaining graphene oxide, which combusts at 400(&)deg;C, while melting the Nickel above 1450(&)deg;C using a high temperature plasma plume. Graphene oxide was successfully retained in the coatings using either of two configurations: (1) Injecting the graphene oxide powder via solution suspension separately from the metal powder, or (2) Installing a shroud on the front of the plasma gun and backfilling with Argon to inhibit combustion. The uniquely designed solution suspension configuration resulted in a higher deposition efficiency of graphene oxide while the inert shroud configuration had a more homogeneous distribution and retention of graphene oxide in the coatings. The best overall coating was achieved using the inert shroud configuration using a powder mixture containing 2% weight Edge Functionalized Graphene Oxide. Vickers microhardness increased 46% and tensile adhesion strength increased 26% over control samples. This is possible due to the mechanisms of dislocation strengthening and stress transfer previously reported in graphene oxide reinforced Aluminum composites formed by flake powder metallurgy. It was also observed that the energy released by the combustion of graphene oxide helps to uniformly melt the Nickel particles and improve the coating microstructure, allowing for more forgiving spray parameters. The methods developed and results attained in this research open opportunities for graphene oxide to be added as inexpensive reinforcements to other metallic compositions for widespread use in metal matrix composite manufacturing.
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Date Issued: 2014
Identifier: CFE0005901, ucf:50857
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005901

Thermal Barrier Coatings (3)	+ -
residual stress (3)	+ -
thermal barrier coatings (3)	+ -
Coatings (2)	+ -
Plasma Spray (2)	+ -

TBC (2)	+ -
bond coat (2)	+ -
coating (2)	+ -
composite (2)	+ -
electrospray (2)	+ -
lifetime (2)	+ -
nanoparticle (2)	+ -
stress (2)	+ -
synchrotron (2)	+ -
thermal barrier coating (2)	+ -
thermally grown oxide (2)	+ -
x-ray diffraction (2)	+ -
(Pt (1)	+ -
304 stainless steel (1)	+ -
AM (1)	+ -
ANSYS (1)	+ -
Alumina (1)	+ -
Anti-reflective Coating (1)	+ -
Antimicrobial (1)	+ -
Buckypaper (1)	+ -
CEB (1)	+ -
CNC Micro-Machining (1)	+ -
Calcium-Magnesium-Alumina-Silicate (CMAS) (1)	+ -
Ceria (1)	+ -
Cerium Oxide (1)	+ -

ETD Collection (28)	+ -
Honors Collection (2)	+ -

University of Central Florida (30)	+ -
Sohn, Yongho (7)	+ -
Raghavan, Seetha (6)	+ -
Gordon, Ali (3)	+ -
Gou, Jihua (3)	+ -

Heinrich, Helge (3)	+ -
Seal, Sudipta (3)	+ -
Vaidyanathan, Raj (3)	+ -
Zhai, Lei (3)	+ -
Bai, Yuanli (2)	+ -
Ghosh, Ranajay (2)	+ -
Liu, Jing (2)	+ -
Schulzgen, Axel (2)	+ -
Sohn, Yong-ho (2)	+ -
Al-Jelawy, Haider (1)	+ -
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An, Linan (1)	+ -
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Coffey, Kevin (1)	+ -
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Del Barco, Enrique (1)	+ -
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