Document Type
Paper
Abstract
Thermal barrier coatings (TBCs) are used to protect metallic blades subjected to the extreme temperatures found within the turbine sections following the combustion chamber of jet engines. Yttria-stabilized zirconia (YSZ) is the standard high temperature ceramic material used for TBCs. One of the primary deposition methods of these TBCs on the metallic blades is electron-beam physical vapor deposition (EB-PVD), which gives YSZ a characteristic columnar, porous structure. This allows for a higher strain tolerance than that of other deposition methods; however, it also increases the susceptibility of the coating to molten sand and volcanic ash infiltration, referred to as calcium-magnesium-alumino-silicates (CMAS), which greatly reduces the lifetime of TBCs. A variety of techniques are used to analyze and quantify the damage to the coating; two of which will be discussed and compared in this paper. 3D confocal Raman spectroscopy and high-energy x-ray diffraction (XRD) measurements were acquired non-destructively from CMAS-infiltrated samples. The results were compared to show how the similarities and differences in the data collected can reveal a complete picture of the chemical degradation within the TBC due to CMAS. This includes the comparison of phase volume fractions found by each method. Both methods showed that higher temperatures and longer annealing times lead to a greater volume of the monoclinic phase, which is linked to the eventual failure of the coating. 3D confocal Raman provides local phase volume fractions, spatially resolved for the assessing the effects of infiltration on single columns. Meanwhile, XRD provides a more global quantification of phase volume fractions throughout the probed volume. This work highlights the complimentary nature of 3D confocal Raman and XRD for high accuracy determination of degradation mechanisms for improved lifetime predictions of TBCs.
Comparison of 3D confocal Raman and high energy X-ray diffraction for the measurement of molten sand infiltration in turbine blade coatings
Thermal barrier coatings (TBCs) are used to protect metallic blades subjected to the extreme temperatures found within the turbine sections following the combustion chamber of jet engines. Yttria-stabilized zirconia (YSZ) is the standard high temperature ceramic material used for TBCs. One of the primary deposition methods of these TBCs on the metallic blades is electron-beam physical vapor deposition (EB-PVD), which gives YSZ a characteristic columnar, porous structure. This allows for a higher strain tolerance than that of other deposition methods; however, it also increases the susceptibility of the coating to molten sand and volcanic ash infiltration, referred to as calcium-magnesium-alumino-silicates (CMAS), which greatly reduces the lifetime of TBCs. A variety of techniques are used to analyze and quantify the damage to the coating; two of which will be discussed and compared in this paper. 3D confocal Raman spectroscopy and high-energy x-ray diffraction (XRD) measurements were acquired non-destructively from CMAS-infiltrated samples. The results were compared to show how the similarities and differences in the data collected can reveal a complete picture of the chemical degradation within the TBC due to CMAS. This includes the comparison of phase volume fractions found by each method. Both methods showed that higher temperatures and longer annealing times lead to a greater volume of the monoclinic phase, which is linked to the eventual failure of the coating. 3D confocal Raman provides local phase volume fractions, spatially resolved for the assessing the effects of infiltration on single columns. Meanwhile, XRD provides a more global quantification of phase volume fractions throughout the probed volume. This work highlights the complimentary nature of 3D confocal Raman and XRD for high accuracy determination of degradation mechanisms for improved lifetime predictions of TBCs.
