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Open AccessArticle

Crack Healing in Mullite-Based EBC during Thermal Shock Cycle

1
School of Mechanical Engineering, Kookmin University, Seoul 02707, Korea
2
Advanced Materials Research Division, Korea Atomic Energy Research Institute, Daejeon 34057, Korea
*
Author to whom correspondence should be addressed.
Coatings 2019, 9(9), 585; https://doi.org/10.3390/coatings9090585
Received: 9 August 2019 / Revised: 9 September 2019 / Accepted: 10 September 2019 / Published: 17 September 2019
(This article belongs to the Special Issue Environmental Barrier Coatings)
Crack healing phenomena were observed in mullite and mullite + Yb2SiO5 environmental barrier coating (EBC) materials during thermal shock cycles. Air plasma spray coating was used to deposit the EBC materials onto a Si bondcoat on a SiCf/SiC composite substrate. This study reveals that unidirectional vertical cracks (mud cracks) formed after several thermal shock cycles; however, the cracks were stable for 5000 thermal shock cycles at a maximum temperature of 1350 °C. Moreover, the crack densities decreased with an increasing number of thermal shock cycles. After 3000 thermal shock cycles, cracks were healed via melting of a phase containing SiO2 phase, which partially filled the gaps of the cracks and resulted in the precipitation of crystalline Al2O3 in the mullite. Post-indentation tests after thermal shock cycling indicated that the mullite-based EBC maintained its initial mechanical behavior compared to Y2SiO5. The indentation load–displacement tests revealed that, among the materials investigated in the present study, the mullite + Yb2SiO5 EBC demonstrated the best durability during repetitive thermal shocks. View Full-Text
Keywords: crack healing; environmental barrier coating; thermal shock; Hertzian indentations; mechanical behavior; CMC composite crack healing; environmental barrier coating; thermal shock; Hertzian indentations; mechanical behavior; CMC composite
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MDPI and ACS Style

Seo, H.-I.; Kim, D.; Lee, K.S. Crack Healing in Mullite-Based EBC during Thermal Shock Cycle. Coatings 2019, 9, 585.

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