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- Title
- CORRELATING MICROSTRUCTURAL DEVELOPMENT AND FAILURE MECHANISMS TO PHOTOSTIMULATED LUMINESCENCE SPECTROSCOPY AND ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY IN THERMAL BARRIER COATINGS.
- Creator
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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.
Show less - Date Issued
- 2011
- Identifier
- CFE0003635, ucf:48882
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003635
- Title
- 2008 EMISSIONS INVENTORY OF CENTRAL FLORIDA.
- Creator
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Ross, Jessica, Cooper, Dr. C. David, University of Central Florida
- Abstract / Description
-
An emissions inventory of VOCs, NOx, and CO2 was conducted for three central Florida counties Orange, Seminole, and Osceola (OSO) for calendar year 2008. The inventory utilized three programs: MOBILE6, NONROAD2005, and EDMS (Emissions and Dispersion Modeling System) to model on-road mobile, non-road mobile, and airport emissions, respectively. Remaining point and area source data was estimated from the Florida Department of Environmental Protection (FDEP) and the U.S. Environmental...
Show moreAn emissions inventory of VOCs, NOx, and CO2 was conducted for three central Florida counties Orange, Seminole, and Osceola (OSO) for calendar year 2008. The inventory utilized three programs: MOBILE6, NONROAD2005, and EDMS (Emissions and Dispersion Modeling System) to model on-road mobile, non-road mobile, and airport emissions, respectively. Remaining point and area source data was estimated from the Florida Department of Environmental Protection (FDEP) and the U.S. Environmental Protection Agency's (U.S. EPA) 2008 emissions inventory. The previous OSO emissions inventory was done in 2002 and in the six years between inventories, there have been changes in population, commerce, and pollution control technology in central Florida which have affected the region's emissions. It is important to model VOC and NOx emissions to determine from where the largest proportions are coming. VOCs and NOx are ozone precursors, and in the presence of heat and sunlight, they react to form ozone (O3). Ozone is regulated by the U.S. Environmental Protection Agency through the FDEP. The current standard is 75 parts per billion (ppb) and Orange County's average is 71 ppb. A new standard (which will likely be about 65 ppb) is being developed and is scheduled to be announced by July 2011. If OSO goes into non-attainment, it will need to prepare a contingency plan for how to reduce emissions to submit to the FDEP for approval. The 2008 inventory determined that approximately 71,300 tons of VOCs and 59,000 tons of NOx were emitted that year. The majority of VOCs came from on-road mobile sources (33%) and area sources (43%), while the majority of NOx came from on-road mobile sources (64%) and non-road mobile sources (17%). Other major sources of VOCs included gasoline powered non-road mobile equipment (lawn and garden equipment), consumer solvents, cooking, and gasoline distribution. With the numbers that could be determined for CO2 emissions, on-road mobile and point sources were responsible for 93%. Of the point source CO2 emissions, almost all of it (87%) came from one large coal-fired power plant in Orange County.
Show less - Date Issued
- 2011
- Identifier
- CFE0003703, ucf:48834
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003703
