3100F T-EBC Stable Coatings for SiC CMCs

Developing a T-EBC coating capable of providing extended performance of sic CMCs in high temperature, water vapor gas turbine engine environments at 3100oF coupled with the need to resist degradation from external sand/ salt ingestion is a daunting challenge. Of all the numerous studies by NASA, universities, private sector companies and other Federal laboratories, rare earth zirconia and hafnia compositions appear to offer the best resistance to both the water vapor laded combustion environment of turbine engines and molten sand degradation. TA&T proposes to develop and demonstrate that rare earth multi-layer based EBcs' have the potential to minimize SiOH2 reactions and volatilization with Sic substrate, restrict or delay CMAS interaction with EBC system, including liquid phase infiltration, develop self-healing capability once CMAS reactions occur and enable the bulk of the EBC coating to retain strain tolerance and toughness at 3100oF. Several variants of experimental EBC compositions will be explored using magnetron sputtering to deposit different multilayer compositions on SiC CMCs. Thin alternating multilayers have the advantages of reduced columnar growth, lower residual stress and reduced thermal conductivity compared to single layer coatings. In addition, the interfaces tend to deflect cracks. XRD, SEM and EDS characterization of the compositions, microstructures of the sputtered coatings will be used on iterative basis to arrive at the desired coating deposition parameters and coating properties. The experimental coatings will be subjected to isothermal dry air, flowing air-steam at 50% relative humidity without and with CMAS at 3100oF. Post-test analysis of delamination, cracking, phase changes, chemical interactions will be used to determine and compare the effectiveness of the graded EBC compositions to protect the Sic CMC substrates.