Interfacial characteristics and microstructural evolution of ceramics exposed to high temperature sand laden combustion environments
November 5-9, 2017
Sand laden combustion environments are a current challenge plaguing ceramic thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) on metallic and emerging ceramic matrix composite (CMC) turbomachinery components. Exposure of thermal and environmental barrier coatings on ceramic matrix composites to environmental particulate laden deteriorates the ceramic structure via chemical reactions and infiltration into pore structures. The challenge of environmental particulates, collectively referred to as calcium-magnesium-aluminosilicate (CMAS), is expected to be exacerbated in future components that utilize ceramic matric composites (CMCs), since the higher operating temperatures will accelerate particulate melting, infiltration, and diffusion kinetics. This study first presents efforts at ARL to develop sandphobic coatings resistant to CMAS infiltration and deposition. The results of a recent full scale sand ingestion engine test used to evaluate several ARL layered and blended coating compositions are presented. The study also includes the evaluation of interactions of CMAS plasma sprayed environmental barrier coatings and HfO2-Si bond coats on SiC/SiC CMCs in rig simulated engine test conditions. The focus is on the microstructural evolution of the coatings and the interfacial characteristics between the TBCs and EBCs and CMAS. Interfaces between coating constituents are also of interest in order to tailor coatings with superior thermal, structural, and chemical characteristics. Controlled studies on YSZ-based ceramic compacts are also performed in order to gain a more fundamental understanding of the effect of porosity on infiltration kinetics, as well as the nature of interfaces and interfacial products wrought by CMAS infiltration into YSZ ceramic grain boundaries. These model studies on YSZ are conducted by immersing the ceramic compacts into AFRL-02 sand and exposing the system to temperatures of up to 1300 °C. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electron back scattered diffraction, and focused ion beam (milling and imaging) are utilized for microstructural and interfacial characterization of the CMAS reacted thermal and environmental barrier coating systems.
Dongming Zhu, Anindya Ghoshal, Andy Nieto, Michael J. Walock, Muthuvel Murugan, Blake Barnett, Marc Pepi, Jeffrey Swab, William Gamble, Mark Graybeal, Andrew Wright, Jian L uo, Christopher Rowe, Robert “Tyler” Pegg, and Kevin Kerner, "Interfacial characteristics and microstructural evolution of ceramics exposed to high temperature sand laden combustion environments" 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). http://dc.engconfintl.org/acmc/2