Resistance of Ultra High Temperature Ceramics to Calcia-Magnesia-Alumina-Silicate (CMAS) Attack
[Technical Report, Master's Thesis]
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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New hypersonic vehicles will operate inside the atmosphere through flight and are now subjected to increase atmospheric particulates exposure primarily composed of Calcia-Magnesia-Alumina-Silicate CMAS and is known as CMAS attack. CMAS attack affects thermal and environmental barrier coatings and is an ongoing problem for gas turbine engines GTE. New materials are needed to withstand high temperatures while resisting CMAS attack. This thesis aims to characterize CMAS interaction with the two candidates for hypersonic applications hafnium and zirconium diboride. Both ceramics were mixed with CMAS and then placed in isothermal holds at 1000- 1600 deg C between 1-100 hours of exposure. The samples were then analyzed via transmissionscanning electron microscope TSEM, energy dispersive spectroscopy EDS, and x-ray diffraction XRD to identify new phases. At all temperatures and durations, both diborides oxidized and produced MO2MHfZr. For durations less than an hour regardless of temperature, both diborides reacted weakly or did not react with the CMAS. For all other durations and temperatures, the silicate in the CMAS reacted with MO2 and produced MSiO4 but then revert back into their oxide and SiO2 at 1600 deg C. Further studies will look at bulk pucks of MB2 for better characterization of CMAS infiltration on both diborides under hypersonic conditions using a rig burner.
- Research and Experimental Aircraft
- Coatings, Colorants and Finishes
- Inorganic Chemistry