59408 - Predicting Ebc Temperature Limits for Industrial Gas Turbines 

To continue to increase the turbine inlet temperature and thereby increase the efficiency of land-based industrial gas turbines, it is likely that ceramic matrix composites (CMC) will be needed for hot section components to replace superalloys.  These SiC/SiC CMC components will require environmental barrier coatings to protect against the detrimental effect of water vapor and with durability greater than 25,000 h, significantly longer than current aero-engine applications.  The goal of the current project is to determine the maximum bond coating temperature for EBCs for land-based turbines, which may exceed the 1414°C melting point of the Si bond coating used in most current EBCs.  Thus, current ytterbium disilicate EBCs with a Si bond coating and next-generation EBCs without a Si bond coating are being evaluated in laboratory testing using 1-h cycles in air+90%H₂O.  For this initial work, coatings were deposited on CVD SiC coupons.  Reaction kinetics at 1250°, 1300°,1350°C and 1400°C (the latter only without Si bond coating) have been evaluated by measuring the thickness of the thermally grown silica scale after 100-1000 cycles.  For comparison, values for uncoated SiC and Si specimens in dry and wet environments were included as minimum and maximum values, respectively.  Various failure criteria are discussed with estimated maximum temperatures calculated based on these criteria.  This research was sponsored by the U. S. Department of Energy, Office of Fossil Energy, Advanced Turbine Program.