Abstract

Calcium-magnesium-aluminosilicates (CMAS), such as sand or volcanic ash, are ingested by aircraft jet engines during operation. CMAS then becomes molten while traveling through the combustor of the engine before depositing onto turbine blades within the turbine section of the engine. The molten CMAS melt infiltrates and interacts with the high temperature ceramic coated turbine blades. This infiltration increases coating stiffness and promotes coating phase destabilization, encouraging micro-crack formation and increasing the risk of spallation. Thermomechanical effects from CMAS infiltration were mapped over time with confocal Raman spectroscopy. The residual stresses within infiltrated 7YSZ EB-PVD coatings were captured with microscale resolution. The results show an interplay between both the thermomechanical and thermochemical effects influencing the residual stress state of the coating. Thermomechanical mechanisms have a prominent role on the residual stress early on in a coating's CMAS exposure and after 1 h of infiltration, inducing tensile stresses within the coating up to 100 MPa on tetragonal ZrO2 Raman bands. Chemical mechanisms impart a greater influence on a much slower scale and after 10 h of infiltration, inducing compressive stresses within the coating up to 100 MPa. A monoclinic phase volume fraction of about 35% was observed to be a transitional point for thermochemical mechanisms overtaking thermomechanical mechanisms in dominating the residual stress of the coating. These results elucidate, in a non-destructive and non-invasive manner, changes within a coating's residual stress as a result of CMAS exposure and the subsequent CMAS infiltration over varying annealing times. The results aid in the efforts to monitor coating degradation during maintenance and towards implementing CMAS-mitigation strategies in not only 7YSZ EB-PVD coatings, but also as a reference for more novel coating compositions under development.

Notes

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Graduation Date

2022

Semester

Fall

Advisor

Raghavan, Seetha

Degree

Master of Science in Aerospace Engineering (M.S.A.E.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Aerospace Engineering; Thermofluid Aerodynamic Systems

Format

application/pdf

Identifier

CFE0009414; DP0027137

URL

https://purls.library.ucf.edu/go/DP0027137

Language

English

Release Date

December 2022

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

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