CMAS Attack – A Serious Challenge for Environmental Barrier Coatings

Abstract

Advanced ceramic matrix composites (CMC) promise higher energy efficiency of turbine engines due to substantially higher operation temperatures. The synergistic effect of heat and water-rich exhaust gases, however, is strongly affecting CMC lifetime. Consequently, the development of new, environmental barrier coatings (EBC) minimizing thermochemical degradation of CMC components is a continuing R&D topic. State of the art turbine components, typically Ni-based superalloys with ZrO2 thermal barrier coatings (TBC) experience severe thermal-chemical degradation by ingested airborne inorganic particles commonly referred to as CMAS. In this context CMAS melt infiltration of TBC is a major reason for premature coating failure. Increasing turbine operation temperatures will aggravate the problem since all kinds of CMAS particles are expected to impinge on turbine components in fully molten, low viscous state. Therefore, new CMC components require EBC materials with much higher CMAS resistance than state-of the art TBC. A promising way to tackle CMAS melt-infiltration is the use of highly reactive EBC materials or alloying elements which can trigger rapid crystallization of CMAS melts, thus enabling the application of EBC-protected CMC also in demanding thermochemical environments. The presentation will give an overview on current developments and directions in this R&D field.