Residual stress measurement of YB silicates by Raman Spectroscopy: First-principles and experimental studies

Authors

Takafumi Ogawa, Japan Fine Ceramics CenterFollow
Yoshihisa Tanaka, National Institute of Materials Science
Hideki Kakisawa, National Institute of Materials Science
Taishi Yokoi, Japan Fine Ceramics Center
Satoshi Kitaoka, Japan Fine Ceramics Center

Conference Dates

November 5-9, 2017

Abstract

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 [1]. 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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Recommended Citation

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 "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