Accession Number : ADA627390


Title :   CMAS Degradation of Environmental Barrier Coatings: Mechanisms and Mitigation


Descriptive Note : Final rept. 1 Jan 2006-29 Jun 2013


Corporate Author : CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS


Personal Author(s) : Levi, Carlos G


Full Text : http://www.dtic.mil/get-tr-doc/pdf?AD=ADA627390


Report Date : 30 Sep 2013


Pagination or Media Count : 18


Abstract : The overarching objective of this program was to develop fundamental insight into the degradation mechanisms that may limit the durability of environmental barrier coatings (EBCs) when exposed to calcium-magnesium alumino-silicate (CMAS) melts. A corollary objective was to identify strategies to enhance the environmental robustness of the underlying CMC matrix in the event of spallation or cracking of the EBC. In addition to generating fundamental understanding, the program sought to identify science-based solutions to these problems, explore their implementation and evaluate their performance in a laboratory setting. The EBC materials of primary interest were the rare earth silicates, exemplified by Y2Si05 (YMS) and Y2Si207 (YDS). A model CMAS with composition Ca33Mg9Ali3Si45, used in previous ONR work, was selected for the majority of the studies. Substantial insight was gained from the studies of CMAS interactions with EBCs, which revealed that both BSAS and YMS experienced significant degradation when exposed to the model CMAS used in this study. YMS was found to perform better than BSAS in avoiding grain boundary penetration by CMAS and forming a nearly dense layer of apatite at the reaction front, but the rate of recession at 1300 C was still deemed to be inadequate for practical applications. The lessons learned in this project were subsequently used in a study of a multilayer concept based on Yb silicates and hafnates, through an AFOSR-STTR with DVTI and Rolls Royce.


Descriptors :   *BARRIER COATINGS , *CERAMIC MATRIX COMPOSITES , DEGRADATION , SILICATES , THERMOCHEMISTRY , THERMODYNAMICS


Subject Categories : Physical Chemistry
      Coatings, Colorants and Finishes
      Laminates and Composite Materials


Distribution Statement : APPROVED FOR PUBLIC RELEASE