Microstructure control of multi-layered EBC prepared by dual electron beam PVD

Authors

Taishi Yokoi, Japan Fine Ceramics Center, JapanFollow
Norio Yamaguchi, Japan Fine Ceramics Center, Japan
Satoshi Kitaoka, Japan Fine Ceramics Center, Japan
Masasuke Takata, Japan Fine Ceramics Center, Japan

Conference Dates

November 5-9, 2017

Abstract

Environmental barrier coatings (EBCs) can play important roles in enabling SiC fiber reinforced SiC matrix composites (SiC/SiC) for application to advanced hot-section components in airplane engines. EBCs must exhibit superior environmental shielding durability and excellent volatilization resistance in the combustion environment containing water vapor. Therefore, a multilayered structure is applied when designing EBCs. Yb silicates are promising substances for EBC use. Volatilization resistance of Yb₂SiO₅ is superior to Yb₂Si₂O₇. Thermal expansion coefficient of Yb₂Si₂O₇ is closer to SiC/SiC composites than Yb₂SiO₅ and it exhibits a single phase up to about 1873 K. Mullite has higher oxygen shielding performance than Yb₂Si₂O₇. Thus, we design EBC which is composed of a bond layer, dense mullite oxygen shielding layer, compositional-gradient dense Yb silicate layer showing water vapor shielding function, and Yb₂SiO₅ layer with segmented structure. The function of the Yb₂SiO₅ layer is reduction of thermal stresses during thermal cycling. Such an environmental shielding capability depends greatly on both the compositions and microstructures of the layers. Therefore, the coating processes used to make the EBCs should allow precise control of these factors. While it is difficult to strictly control the compositions of such complex oxides using conventional plasma spray deposition techniques due to incongruent evaporation of raw powders, dual electron beam physical vapor deposition (EB-PVD) is a potential process for constructing the complex oxides layer with controlled compositions as well as microstructures. We recently reported that formation of Yb₂Si₂O₇ layer by dual EB-PVD [1]. In the present study, we investigated the in-situ formation of a dense mullite layer, compositional gradient layer from Yb₂Si₂O₇ to Yb₂SiO₅ with dense structure, and Yb₂SiO₅ layer with segmented structure via dual EB-PVD, simultaneously heating the substrate.

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Recommended Citation

Taishi Yokoi, Norio Yamaguchi, Satoshi Kitaoka, and Masasuke Takata, "Microstructure control of multi-layered EBC prepared by dual electron beam PVD" 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/10