Abstract
The resistance of ultra-high temperature ceramic (UHTC) borides to calcia-magnesia-alumina-silicate (CMAS) attack is evaluated for the first time. ZrB2 and HfB2 are reacted with 23 mol% of CMAS 1000 °C, 1300 °C and 1600 °C, respectively, for 1 h, 10 h and 100 h, respectively, in atmosphere. Interestingly, borides first oxidize before reacting with CMAS to form ZrSiO4 and HfSiO4, respectively, which peaks at 1300 °C. At 1600 °C, the reaction with CMAS to form HfSiO4 is greatly suppressed; moreover, ZrB2 exhibits only oxidation and no reaction with CMAS nor formation of ZrSiO4 or any other CMAS induced reaction product. This unusual inertness at temperatures above 1600 °C could enable new approaches to addressing the CMAS problem in thermal and environmental barrier coatings.
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