PhD, University of Cincinnati, 2018, Engineering and Applied Science: Aerospace Engineering

The thermal barrier coating is applied to the surfaces of the metal components of the gas turbine hot section, for example, a combustor liner, vanes, and rotating turbine blades. The coating contributes to increasing the operating temperature by providing a heat shield between the hot gas and the metallic substrate of the gas turbine engines. As well as increasing the service life of the gas turbine engine, the specific fuel consumption can also be improved with the increased overall pressure ratio. In particular, 6-9% wt. Yttria partially stabilized zirconia (7YSZ) ceramic coating has been widely used because of its excellent hardness, good erosion resistance, low thermal conductivity, and thermal expansion coefficient similar to Nickel based super-alloys. However, the experimental erosion resistance study of TBC by solid particle impact has not been extensively carried out within the operating range of the gas turbine. Through presented study, a preliminary design was conducted for the development of a new advanced high-temperature capable erosion test facility. The optimized length of the accelerating tunnel and design parameters were obtained using the combination of analytical and computational analysis. The performance of developed erosion test facility was validated with the predicted data and compared with the existing legacy erosion tunnel at the University of Cincinnati. This dissertation presents an experimental investigation of the effects of microstructures of topcoat of air plasma sprayed 7 wt\% YSZ thermal barrier coatings (APS 7YSZ TBCs) on erosion resistance at high temperature. A combination of air plasma sprayed YSZ TBCs with three different microstructures (porosities of 12.9 +- 0.5%, 19.5 +- 1.2%, and 3.7 +- 0.7%) was tested in the advanced high-temperature erosion test facility under gas turbine operating temperatures. Experiments were conducted to investigate erosion of TBCs over a range of temperatures between 537C and 980C, gas veloc (open full item for complete abstract)

Committee: Awatef Hamed Ph.D. (Committee Chair); San-Mou Jeng Ph.D. (Committee Member); Jongguen Lee Ph.D. (Committee Member); Robert W. Bruce Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science in Engineering (MSEgr), Wright State University, 2013, Materials Science and Engineering

The use of thermal barrier coatings (TBCs) has been an important factor in the efficiency improvements of jet engines due to their ability to withstand the extreme environments within the engine. With this improved resistance, TBCs have also become more difficult to remove without damaging the substrate. Mound Laser & Photonics Center, Inc. (MLPC) has developed an innovative, laser based technique to spall this coating. The intention of this work was to investigate and better understand the removal mechanism. Through experimentation and analysis (such as high speed video, Scanning Electron Microscopy and Energy Dispersive Spectroscopy, semi-logarithmic analysis, and a numerical thermal model) information supportive of a two stage thermal and rapid vaporization based mechanism has been obtained. The method and analysis presented in this work helps to expand the understanding of thermal and rapid vaporization spallation techniques as well as guide MLPC in optimization of their process.

Committee: Daniel Young Ph.D. (Advisor); Scott Thomas Ph.D. (Committee Member); Raghavan Srinivasan Ph.D. (Committee Member); Ahsan Mian Ph.D. (Committee Member) Subjects: Aerospace Materials; Engineering; Materials Science

MS, University of Cincinnati, 2012, Engineering and Applied Science: Aerospace Engineering

Thermal Barrier Coatings (TBC) have been developed for modern highly loaded turbines to allow their operation at higher temperatures than allowed by substrate blade material. TBC health is critical to blade life and to maintaining the high power output and efficiency achieved with the increased turbine inlet temperatures. However unlike blade material alloys, knowledge of thermal barriers' deterioration as a result of impacts by suspended particles in the flow field is very limited. The purpose of this study was to gain better knowledge of turbine blades thermal barrier coatings intensity and pattern of erosion by ingested particles in rotary wing engines. A commercial Computation Fluid Dynamics code, CFX, was used to perform two-phase flow simulations to supply flow and particle trajectory data. The suspended particles tend to deviate from the 3D flow path due to their higher inertia. User Defined Functions (UDF) were developed for restitution coefficients and erosion rate of thermal barrier coated surface based on previous experimentally based empirical models. The UDF was verified to correctly calculate restitution coefficients and erosion rates in a simulated high temperature erosion tunnel. The models were implemented in ANSYS CFX code which was used to predict the blade surface erosion rates for a gas turbine Auxiliary Power Unit (APU) used in currently operating rotary aircraft. Results are presented for the erosion rates of turbine blade thermal barrier coatings with uniform 36 micron alumina particle ingestion and for non-uniform particle ingestion concentrated in the 5% of the span near the annulus walls. Results for both cases are compared to those obtained from numerical simulations using fixed restitution default models at the blade surface impacts.

Committee: Awatef Hamed PhD (Committee Chair); Shaaban Abdallah PhD (Committee Member); Mark Turner ScD (Committee Member) Subjects: Aerospace Materials

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

Higher performance and durability requirements of gas-turbine engines will require a new generation of thermal barrier coatings (TBCs). This is particularly true of engines operated at higher temperatures, where TBCs are subjected to attack by CaO-MgO-Al2O3-SiO2 (CMAS) glassy deposits. In this work, a new approach for mitigating CMAS attack on TBCs is introduced, where up to 20 mol% Al2O3 and 5 mol% TiO2 in the form of a solid solution is incorporated into Y2O3-stabilized ZrO2 (YSZ) TBCs. The fabrication of such TBCs with engineered chemistries is made possible by the solution-precursor plasma spray (SPPS) process, which is uniquely suited for depositing coatings of metastable ceramics with extended solid-solubilities. In the current work, the TBC serves as a reservoir of Al and Ti solutes, which are incorporated into the molten CMAS glass that is in contact with the TBC. An accumulation of Al concentration in the CMAS glass as it penetrates the TBC shifts the glass composition from the difficult-to-crystallize psuedowollastonite field to the easy-to-crystallize anorthite field. The incorporation of Ti in the glass promotes crystallization of the CMAS glass by serving as a nucleating agent. This combined effect results in the near-complete crystallization of the leading edge of the CMAS front into anorthite, essentially arresting the front. Both of these phenomena will help crystallize the CMAS glass, making it immobile and ineffective in penetrating the TBC. It is shown that incorporation of both Al and Ti in the CMAS glass is essential for this approach to be effective. In this dissertation, results from characterization and testing of these new TBCs are presented, together with a discussion of mechanisms responsible for CMAS-attack mitigation. The penetration of CMAS causes a loss of strain tolerance of the coating. Delamination maps are used to demonstrate the combined effects of CMAS penetration, temperature gradient and cooling inhomogeneity on the coating. Ev (open full item for complete abstract)

Committee: Nitin Padture PhD (Advisor); Glenn Daehn PhD (Committee Member); Sheikh Akbar PhD (Committee Member); Linda Weavers PhD (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2005, Mechanical Engineering

To more fully understand microstructural evolution and the development of damage in thermal barrier coating (TBC) systems, thermocyclic experiments were conducted on TBC specimens with and without top coats. The degradation of a PtAl (platinum modified aluminide) bond coat and a CMSX superalloy substrate were investigated for cyclic and quasi-isothermal heating to 1200 °C. To accelerate the oxidation of the specimens, the thermally grown oxide (TGO) was removed at 10 hour intervals. Scanning electron microscopy (SEM) and instrumented indentation were employed to investigate microstructural evolution and material property changes of the bond coat. The microstructural evolution of a PtAl bond coat is strongly affected by the type of thermal exposure and the presence of TGO. The differences between cyclic and quasi-isothermal heating indicate that stresses associated with cooling and heating significantly alter microstructural evolution. Damage to TBC specimens with EB-PVD (electron beam physical vapor deposition) processed YSZ (yttria stabilized zirconia) top coats, PtAl bond coats, and Rene N5 superalloy substrates was assessed during thermal cycling to 1200 °C. Acoustic emission (AE) techniques were used to temporally identify damage to the TBC. For automated, continuous, and high temperature AE detection, a custom made experimental setup with either a nickel-chrome alloy wire wave guide or an alumina wave guide was used. It was found that there are four distinct regions of AE activity during the life of a TBC. Throughout the cooling cycles, images of the top coat were collected with darkfield-type lighting. These images showed how undulations developed in the top coat. In addition, digital image correlation (DIC) was used to identify regions with interfacial damage. Finally, the images were used to analyze the spallation of the top coat. Cycling of an additional specimen was interrupted periodically for analysis with profilometry and SEM. The profilometry and SEM i (open full item for complete abstract)

Committee: Mark Walter (Advisor) Subjects:

Master of Science (MS), Ohio University, 2008, Electrical Engineering (Engineering and Technology)

Tail biting circular trellis block codes (TBC)2 used along with iterative Maximum A-Posteriori (MAP) decoders achieve performance very close to the Shannon limit. A Low Density Parity Check (LDPC) code using a Sum Product Algorithm (SPA) decoder is also known to achieve comparable performance. In this work the performance of (TBC)2 encoder used with an SPA decoder is presented. The goal of this research is to compare the performance of (TBC)2 encoder with different iterative decoders.In order to use the SPA for decoding, a parity check (H) matrix representation of the (TBC)2 is developed. It is shown that for small block lengths this H matrix achieves comparable performance. For larger block sizes the H matrix representation of the (TBC)2 encoder is found non-optimal for SPA decoding and the performance of the code is degraded.

Committee: Jeffrey Dill PhD (Advisor); Razvan Bunescu PhD (Committee Member); Douglas Lawrence PhD (Committee Member); Dinh Van Huynh PhD (Committee Member) Subjects: Electrical Engineering