Kang N. Lee1,2,3, Dennis S. Fox1,2, Jeffrey I. Eldridge1,2, Dongming Zhu1,2,4, R. Craig Robinson2,5, Narottam P. Bansal1,2, Robert A. Miller2
1*Member, American Ceramic Society.
2NASA Glenn Research Center, Cleveland, Ohio 44135
3Senior Research Scientist from Cleveland State University, Cleveland, OH.
4Research Scientist from Army, Cleveland, OH.
5Research Engineer from QSS Group, Inc, Brookpark, OH.
Tóm tắt
Current state‐of‐the‐art environmental barrier coatings (EBCs) for Si‐based ceramics consist of three layers: a silicon bond coat, an intermediate mullite (3Al2O3·2SiO2) or mullite + BSAS ((1−x)BaO·xSrO·Al2O3·2SiO2, 0 ≤x≤ 1) layer, and a BSAS top coat. Areas of concern for long‐term durability are environmental durability, chemical compatibility, volatility, phase stability, and thermal conductivity. Variants of this family of EBC were applied onto monolithic SiC and melt‐infiltrated SiC/SiC composites. Reaction between BSAS and silica results in a low‐melting (∼1300°C) glass, which can cause the spallation of the EBC. At temperatures greater than ∼1400°C BSAS suffers significant recession via volatilization in water‐vapor‐containing atmospheres. Both reactions can be EBC life‐limiting factors. BSAS undergoes a very sluggish phase transformation (hexagonal celsian to monoclinic celsian), the implications of which are not fully understood at this point. Initial rapid increase in thermal conductivity at temperatures as low as 1300°C indicates the sintering of EBC.
