|About this Abstract
||Materials Science & Technology 2012
||Surface Protection for Enhanced Materials Performance: Science, Technology and Applications
||Thermochemical Considerations in the Design of Multilayered EBCs
||David L Poerschke, Jason Van Sluytman, Carlos G Levi
|On-Site Speaker (Planned)
||David L Poerschke
Environmental barrier coatings (EBCs) are applied to SiC-based ceramic matrix composites (CMCs) to prevent detrimental volatilization of the SiO<sub>2</sub> scale in combustion environments. Conventional EBC materials effectively suppress volatilization but are particularly susceptible to attack by molten silicate deposits (CMAS) due to their high SiO<sub>2</sub> content. Multilayered coatings comprising a rare earth hafnate topcoat applied to a rare earth silicate EBC can arguably improve the CMAS resistance and increase the allowable system operating temperature. Implementation of these concepts requires sound understanding of the thermodynamic compatibility between layers. The problem is illustrated with an investigation of the equilibrium relationships in the HfO<sub>2</sub>-Yb<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> system at a prospective operating temperature of 1500°C. Emphasis is placed on the compatibility between the silicates Yb<sub>2</sub>SiO<sub>5</sub> and Yb<sub>2</sub>Si<sub>2</sub>O<sub>7</sub> and topcoats based on HfO<sub>2</sub> based fluorite solid solution, as well as the δ-Yb<sub>4</sub>Hf<sub>3</sub>O<sub>12</sub> and H<sub>3</sub>-Yb<sub>6</sub>HfO<sub>11</sub> phases in light of moderate SiO<sub>2</sub> solubility identified for some HfO<sub>2</sub>-Yb<sub>2</sub>O<sub>3</sub> compositions.