Protective CMAS Coatings for SiC CMCs

Graded rare earth hafnia multilayer coatings with three different top layer compositions will be deposited on SiC CMC and alumina substrates, characterized by XRD, SEM and EDS, and subjected to flowing air-steam at 50% relative humidity without and with CMAS in both isothermal and thermal cycling conditions. Post test analyses include weight change, SEM microstructure characterization changes, XRD/EDS chemical changes to determine and compare the effectiveness of the graded EBC compositions to protect the SiC CMC substrates. DSC/TGA analysis will be used to compare thermal properties of AFRL-03 and synthetic CMAS and correlate with possible differences in CMAS reactions with graded rare earth hafnia multilayer coatings. Coated buttons and bars will be provided to ARL and Honeywell for independent tests in laboratory scale and burner rig combustion-CMAS environments.