Residual stress measurement of YB silicates by Raman Spectroscopy: First-principles and experimental studies
November 5-9, 2017
Components of next-generation gas turbines made from lightweight SiC-based ceramics need environmental barrier coatings (EBCs) to protect from water vapor at high temperature because Si-based ceramics vaporize in such environments. Yb silicates Yb2SiO5 and Yb2Si2O7 are promising EBC materials. In EBCs, residual stresses develop during thermal cycling due to mismatch between the thermal expansion coefficients of the silicate and the underlying ceramics, resulting in critical fatigue of the coating structure . Raman microscopy is one method for measuring stress distributions in coating materials and has the potential to be used for diagnosing EBCs. Its suitability for analyzing stress states of Yb silicates has been unknown.
In this study, we examine Raman spectra of Yb2SiO5, and Yb2Si2O7 under hydrostatic pressure based on first-principles calculations based on the density functional theory and we also examine the spectra of Yb2Si2O7 under uniaxial compressive stress in experiments using polycrystalline samples. When no external pressures applied, good agreement between calculated and experimental spectra is obtained as shown in Figure 1. The differences in the spectra between the silicates demonstrate the utility of using Raman microscopy to detect compositional changes in Yb-silicate coatings. From the calculations, lattice vibrations associated with a Raman peak are identified as exemplified by the characteristic mode of Si2O7 units in Yb2Si2O7 shown in figure 1(a).
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Takafumi Ogawa, Yoshihisa Tanaka, Hideki Kakisawa, Taishi Yokoi, and Satoshi Kitaoka, "Residual stress measurement of YB silicates by Raman Spectroscopy: First-principles and experimental studies" in "Advanced Ceramic Matrix Composites: Science and Technology of Materials, Design, Applications, Performance and Integration", Yutaka Kagawa, Tokyo University of Technology, Japan Dongming Zhu, NASA Glenn Research Center, USA Ram Darolia, GE Aviation (retired), USA Rishi Raj, University of Colorado, Boulder, USA Eds, ECI Symposium Series, (2017). https://dc.engconfintl.org/acmc/12