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High Temperature Mechanics of Aerospace Ceramic Composites Characterized via Synchrotron Radiation
Title
High Temperature Mechanics of Aerospace Ceramic Composites Characterized via Synchrotron Radiation.
Creator
Manero, Albert, Raghavan, Seetha, Kauffman, Jeffrey L., Gou, Jihua, University of Central Florida
Abstract / Description
This research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine...
Show moreThis research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine inlet temperatures exceeding 1100(&)deg;C; and ii) ceramic matrix composites that have shown capability and promise for hypersonic applications beyond 1300(&)deg;C. Understanding the mechanical and material properties of these materials as they evolve with temperature and load requires in-situ measurements under realistic representative environments, and from these measurements life expectancy and failure mechanisms can be more completely elucidated.In this work, TBCs representative of typical jet engine turbine blade coatings, comprised of a Yttria-stabilized zirconia top coat and NiCoCrAlY bond coat deposited on an IN 100 superalloy substrate were studied. Particular interest was given to the thermally grown oxide (TGO) that develops between the top layer and the bond coat that has a major influence on TBC durability. The oxide scale's development is linked to the typical failure mechanisms observed in application for aircraft engines, and the influence of internal cooling has been shown to vary the behavior and evolution over its lifetime. Tubular specimens coated via electron beam physical vapor deposition (EB-PVD) were investigated with hard synchrotron X-rays at Argonne National Laboratory's Advanced Photon Source, while subjected to realistic mechanical and thermal loading representative of the engine environment. A multi-variable investigation was conducted to determine the influence and magnitude of internal flow cooling, external applied force loading, and thermal exposure in cyclical application. The superposition of all these variables together creates variation spatially across in service turbine blades. Lattice strains for the axial and radial directions were resolved for the YSZ top coat layer and the internal thermally grown oxide scale. The findings revealed that during sufficiently high axial loading the strain condition for both the thermally grown oxide and top coat layers may be reversed in direction, and demonstrated how the internal flow and applied mechanical loading produce opposing effects while showing the magnitude of each variable. This reversal of the strain direction is known to contribute to the failure mechanics in the system. This discovery shows that with increased internal cooling to critical zones that experience higher mechanical loads, it is possible to tune the response of the system and prevent the reversal from compressive to tensile strains (in the axial direction). The impact of the results has the potential to be used in design for enhanced durability of the multi-layer coatings.Ceramic matrix composites are identified to comprise the next generation of turbine blades and high temperature parts. All oxide ceramic matrix composites were investigated for the influence of micro-structure variations and processing on the mechanics of the system. Isolation techniques of the all alumina composite by means of synchrotron diffraction and tomography presented a novel non-destructive method for evaluating the constituent's properties and evolution. The study successfully revealed how variations in grain size and elastic modulus result in a complex strain states. Further tomographical analysis identified system mechanics influenced by porosity and processing effects. CMCs with an yttria based environmental barrier coating were investigated for comparison to uncoated parts to further capture the in service condition, and revealed considerations for how to improve the durability of the inter-laminar strength of environmental barrier coatings interface. Together the research conducted has contributed to the high temperature aerospace materials' community, and the experimental work taken strides to provide validation and support future numerical simulation for developing better lifetime modeling. Resulting high temperature mechanics' information has the potential to enhance the design of aerospace components for substantial increases in durability. The outcomes from this work can be leveraged to continue advancing material characterization for aerospace material systems under complex and extreme environments.
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Date Issued
2016
Identifier
CFE0006836, ucf:51794
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006836
Nondestructive Analysis of Advanced Aerospace Materials via Spectroscopy and Synchrotron Radiation
Title
Nondestructive Analysis of Advanced Aerospace Materials via Spectroscopy and Synchrotron Radiation.
Creator
Manero, Albert, Raghavan, Seetha, Kauffman, Jeffrey, Gou, Jihua, University of Central Florida
Abstract / Description
Advanced aerospace materials require extensive testing and characterization to anticipate and ensure their integrity under hostile environments. Characterization methods utilizing synchrotron X-Ray diffraction and spectroscopy can decrease the time required to determine an emerging material's readiness for application through intrinsic information on the material response and failure mechanisms. In this study, thermal barrier coating samples applicable to turbine blades of jet engines were...
Show moreAdvanced aerospace materials require extensive testing and characterization to anticipate and ensure their integrity under hostile environments. Characterization methods utilizing synchrotron X-Ray diffraction and spectroscopy can decrease the time required to determine an emerging material's readiness for application through intrinsic information on the material response and failure mechanisms. In this study, thermal barrier coating samples applicable to turbine blades of jet engines were studied using Raman and Photoluminescence spectroscopy as well as Synchrotron X-ray diffraction while Kevlar based fiber composites applicable to ballistic resistant armor were studied using Raman spectroscopy to investigate the mechanical state and corresponding damage and failure mechanisms. Piezospectroscopic studies on the stress state of the thermally grown oxide (TGO) within the thermal barrier coatings, on a hollow cylindrical specimen, provided results that indicate variations within the TGO. Comparison of measured photo-luminescence spectra of the specimen before and after long duration thermal aging showcases the development of the system and the initiation of micro-damage. Raman spectroscopy performed on Kevlar ballistic composites with nano-scale additives, presented insight into the additives' role in load transfer and damage propagation through a comparison of the shift in optical spectra to that of the pristine fibers. The results presented herein utilize changes in the measured emission from these non-destructive testing techniques to link the phenomena with material response. Techniques to optimize imaging and spectral collection are addressed as well. The findings will advance the use of the techniques in the development of aerospace materials, providing a more complete understanding of land and aircraft turbine blade coatings, and fiber composite response to complex loading.
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Date Issued
2014
Identifier
CFE0005657, ucf:50195
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005657