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Intern: Robert Stuart, Mechanical Engineering, UC Santa Barbara Mentor: Kendra Grant Faculty Supervisor: Carlos Levi Department: Materials

CALCIUM-MAGNESIUM ALUMINO-SILICATE ATTACK ON ENVIRONMENTAL BARRIER COATINGS

Environmental barrier coatings (EBCs) have the intended use of protecting ceramic matrix composites (CMCs) in use in jet turbines from atmospheric water vapor. CMCs are advantageous for use in jet turbines because of their light weight and high operating temperatures. But without an EBC, CMCs interact with water vapor at high temperatures and pressures, causing sublimation. There is cause for concern that silicate particulate matter in the environment (CMAS) will melt onto the EBCs and cause delamination, compromising coating integrity. Initial results from experiments involving CMAS melts on two prospective EBCs (barium-strontium alumino-silicate, BSAS, and yittria silicate, Y₂SiO₅) have shown there has been significant chemical attack of CMAS on the EBC. These results have been found by use of scanning electron microscope (SEM) analysis as well as energy dispersive X-ray (EDX) analysis. A consistent composition of the particulate matter testing substance, CMAS, was investigated. The application of CMAS onto EBC samples has been revised from its original tape form into pellet form. Difficulties of sample EBC production were overcome by changing to alternate production methods. The initial results are expected to be fully verified in the near future but early analysis suggests that the results have been replicated.

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