Type
Text
Type
Thesis
Advisor
Gouma, Perena | Gentleman, Molly M | Venkatesh, T.A..
Date
2015-12-01
Keywords
Materials Science | Ceramic, ferroelastic, Raman Spectroscopy, Thermal Barrier Coating
Department
Department of Materials Science and Engineering
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/76156
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
The lifetime and efficiency of turbine engines for applications such as aerospace and power generation rely on the use of thermal barrier coatings (TBC). The TBC provides a thermal barrier between the metallic turbine engine components and the high temperature gas produced by the turbines combustion. They prevent oxidation as well as thermo-mechanical damage of the underlying metallic components. 7-8 weight-% yttria stabilized zirconia (7-8YSZ) is the industry standard material for thermal barrier coatings due to its high melting temperature, high toughness, low thermal conductivity, and high coefficient of thermal expansion which similar to that of the underlying metallic engine components. Although 7-8YSZ has proven to be the best choice for TBC’s, erosion damage caused by particles ingested into the engine and the potential for phase decomposition after long-term high temperature exposure has the potential to cause damage and eventual failure of even these coatings. Engineering new tougher materials to replace 7-8 YSZ can address both of these issues. There are two main mechanisms that are capable of increasing the toughness in zirconia-based ceramics, ferroelasticity and phase transformation toughening. Ferroelasticity is a phenomenon that allows the material to change its orientation through the process of twinning resulting in a shear strain in a mechanical load is applied. The ability for material unlike ferroelastic toughening, trans-formation toughening requires a volume constraint applied by the transformation from a metastable to stable phase in the zirconia system. Stabilizer poor compositions of stabilized zirconia exhibit a stable tetragonal phase a high temperature and stable monoclinic phase at low temperature. When cooled, the stabilizer- poor composition crosses over a transformation temperature (t0) that causes a martensitic transformation from tetragonal phase to monoclinic phase. This phase transformation is accompanied with volume expansion that can cause cracking in a porous material, but in dense mate-rials this expansion can lead to compressive stresses that toughen the material. In general, x-ray diffraction and TEM have been the primary method for studying the phase decomposition and toughening mechanisms in thermal barrier materials and systems. In this study, Raman Spectroscopy has been used explored as a method for exploring the ferroelastic toughening mechanism in both bulk and coated thermal barrier materials. Additionally is was explored as a method for exploring phase stability of these systems. | The lifetime and efficiency of turbine engines for applications such as aerospace and power generation rely on the use of thermal barrier coatings (TBC). The TBC provides a thermal barrier between the metallic turbine engine components and the high temperature gas produced by the turbines combustion. They prevent oxidation as well as thermo-mechanical damage of the underlying metallic components. 7-8 weight-% yttria stabilized zirconia (7-8YSZ) is the industry standard material for thermal barrier coatings due to its high melting temperature, high toughness, low thermal conductivity, and high coefficient of thermal expansion which similar to that of the underlying metallic engine components. Although 7-8YSZ has proven to be the best choice for TBC’s, erosion damage caused by particles ingested into the engine and the potential for phase decomposition after long-term high temperature exposure has the potential to cause damage and eventual failure of even these coatings. Engineering new tougher materials to replace 7-8 YSZ can address both of these issues. There are two main mechanisms that are capable of increasing the toughness in zirconia-based ceramics, ferroelasticity and phase transformation toughening. Ferroelasticity is a phenomenon that allows the material to change its orientation through the process of twinning resulting in a shear strain in a mechanical load is applied. The ability for material unlike ferroelastic toughening, trans-formation toughening requires a volume constraint applied by the transformation from a metastable to stable phase in the zirconia system. Stabilizer poor compositions of stabilized zirconia exhibit a stable tetragonal phase a high temperature and stable monoclinic phase at low temperature. When cooled, the stabilizer- poor composition crosses over a transformation temperature (t0) that causes a martensitic transformation from tetragonal phase to monoclinic phase. This phase transformation is accompanied with volume expansion that can cause cracking in a porous material, but in dense mate-rials this expansion can lead to compressive stresses that toughen the material. In general, x-ray diffraction and TEM have been the primary method for studying the phase decomposition and toughening mechanisms in thermal barrier materials and systems. In this study, Raman Spectroscopy has been used explored as a method for exploring the ferroelastic toughening mechanism in both bulk and coated thermal barrier materials. Additionally is was explored as a method for exploring phase stability of these systems. | 69 pages
Recommended Citation
Schubert, Amanda Brooke, "Observation of Ferroelastic Toughening in Ceramic Oxides by Polarized Raman Spectroscopy" (2015). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 2099.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/2099