Upper Temperature Limit of Environmental Barrier Coatings Based on Mullite and BSAS

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-xBaO-xSrO-Al2O3-2SiO2) layer, and a BSAS top coat. Areas of concern for long-term durability are environmental durability, chemical compatibility, silica volatility, phase stability, and thermal conductivity. Variants of this family of EBCs were applied to monolithic SiC and melt infiltrated SiC/SiC composites. Reaction between BSAS and silica results in low melting (approx. 1300 C) glasses at T > 1400 C, which can cause the spallation of the EBC. At temperatures greater than 1400 C, the BSAS top coat also degrades by formation of a porous structure, and it suffers significant recession via silica volatilization in water vapor-containing atmospheres. All of these degradation mechanisms 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. There was evidence of rapid sintering at temperatures as low as 1300 C, as inferred from the sharp increase in thermal conductivity.

[1]  Kang N. Lee.  Current status of environmental barrier coatings for Si-Based ceramics , 2000 .

[2]  James L. Smialek,et al.  SiC Recession Caused by SiO2 Scale Volatility under Combustion Conditions: I, Experimental Results and Empirical Model , 1999 .

[3]  Kang N. Lee.  Key Durability Issues With Mullite-Based Environmental Barrier Coatings for Si-Based Ceramics , 1999 .

[4]  David Brewer,et al.  HSR/EPM combustor materials development program , 1999 .

[5]  Kang N. Lee.  Contamination Effects on Interfacial Porosity during Cyclic Oxidation of Mullite‐Coated Silicon Carbide , 1998 .

[6]  Robert Miller,et al.  Development and environmental durability of mullite and mullite/YSZ dual layer coatings for SiC and Si3N4 ceramics , 1996 .

[7]  N. Jacobson,et al.  New generation of plasma-sprayed mullite coatings on silicon carbide , 1995 .

[8]  N. Jacobson.  Corrosion of Silicon-Based Ceramics in Combustion Environments , 1993 .

[9]  J. Price,et al.  Ceramic Oxide-Coated Silicon Carbide for High Temperature Corrosive Environments , 1992 .

[10]  J. Federer.  Alumina base coatings for protection of SiC ceramics , 1990 .

[11]  K. More,et al.  Evaluating Environmental Barrier Coatings on Ceramic Matrix Composites After Engine and Laboratory Exposures , 2002 .

[12]  Nathan S. Jacobson,et al.  SiC and Si3N4 Recession Due to SiO2 Scale Volatility Under Combustor Conditions , 1999 .

[13]  R. E. Hann,et al.  Paralinear Oxidation of CVD SiC in Water Vapor , 1997 .