Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing
Multilayer EBCs of alcohol and sol-based slurries containing (a) 45% SiO2-34% Y2O3-%Al2O3, (b) mullite/Gd2SiO5 (88/12wt.%) with and without B2O3 addition, (c) mullite/rare-earth silicates (94/6wt.%, (Gd2SiO5, Lu2SiO5, Er2SiO5, and HfSiO4)), and (d) only mullite, were applied on hot pressed Y2O3/Al2O3 doped Si3N4 substrates. Of the four major EBC systems studied, only mullite/Gd2SiO5 (88/12wt.%) EBCs sintered in air at 1400^oC for 3h showed good bonding with the substrate. In all other EBC systems studied, the Y2O3/Al2O3 additives present in Si3N4 reacted with silica and rare-earth silicates to form low melting point constituents during sintering causing bubble formation and/or de-bonding at the substrate/coating interface. Thermal cyclic resistance of silicon nitride coupons coated with mullite/Gd2SiO5 (88/12wt.%) EBC was investigated in a moisture containing environment (90% H2O-10% O2) for 100 cycles from 1350^oC to room temperature (1h hot and 15min cold). Moisture exposure resulted in accumulation of large pores in the coating, mostly aligned along the substrate/coating interface.
Ramasamy, Sivakumar; Tewari, Surendra N.; Lee, Kang N.; Bhatt, Ramakrishna T.; and Fox, Dennis S., "EBC Development for Hot-Pressed Y2O3/Al2O3 Doped Silicon Nitride Ceramics" (2010). Chemical & Biomedical Engineering Faculty Publications. 61.
Ramasamy, S., Tewari, S., Lee, K., Bhatt, R., , & Fox, D. (2010). EBC development for hot-pressed EBC development for hot-pressed Y2O3/Al2O3 doped silicon nitride ceramics doped silicon nitride ceramics. Materials Science & Engineering A, 527(21-22), 5492-5498. doi:10.1016/j.msea.2010.05.067
NOTICE: this is the author’s version of a work that was accepted for publication in Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, 527, 21-22, (August 20, 2010) DOI 10.1016/j.msea.2010.05.067