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Open AccessArticle

Crack Initiation Criteria in EBC under Thermal Stress

1
Japan Fine Ceramics Center, Nagoya 456-8587, Japan
2
National Institute for Materials Science, Ibaraki 305-0047, Japan
3
Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan
4
Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo 101-0062, Japan
5
Faculty of Art and Regional Design, Saga University, Saga 840-8502, Japan
*
Author to whom correspondence should be addressed.
Coatings 2019, 9(11), 697; https://doi.org/10.3390/coatings9110697
Received: 12 September 2019 / Revised: 14 October 2019 / Accepted: 21 October 2019 / Published: 24 October 2019
(This article belongs to the Special Issue Environmental Barrier Coatings)
For design of multi-layered environmental barrier coatings (EBCs), it is essential to assure mechanical reliability against interface crack initiation and propagation induced by thermal stress owing to a misfit of the coefficients of thermal expansion between the coating layers and SiC/SiC substrate. We conducted finite element method (FEM) analyses to evaluate energy release rate (ERR) for interface cracks and performed experiment to obtain interface fracture toughness to assess mechanical reliability of an EBC with a function of thermal barrier (T/EBC; SiC/SiAlON/mullite/Yb-silicate gradient composition layer/Yb2SiO5 with porous segment structure) on an SiC/SiC substrate under thermal stress due to cooling in fabrication process. Our FEM analysis revealed that a thinner SiAlON layer and a thicker mullite layer are most suitable to reduce ERRs for crack initiation at the SiC/SiAlON, SiAlON/mullite and mullite/Yb2Si2O7 interfaces. Interface fracture tests of the T/EBC with layer thicknesses within the proposed range exhibited fracture at the SiC/SiAlON and SiAlON/mullite interfaces. We also estimated the approximate fracture toughness for the SiC/SiAlON and SiAlON/mullite interfaces and lower limit of fracture toughness for the mullite/Yb2Si2O7 interface. Comparison between ERR and fracture toughness indicates that the fabricated T/EBC possesses sufficient mechanical reliability against interface crack initiation and propagation. View Full-Text
Keywords: fabrication process; layer thickness design; interface crack initiation/propagation; fracture toughness; energy release rate; finite element method analysis fabrication process; layer thickness design; interface crack initiation/propagation; fracture toughness; energy release rate; finite element method analysis
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MDPI and ACS Style

Kawai, E.; Kakisawa, H.; Kubo, A.; Yamaguchi, N.; Yokoi, T.; Akatsu, T.; Kitaoka, S.; Umeno, Y. Crack Initiation Criteria in EBC under Thermal Stress. Coatings 2019, 9, 697. https://doi.org/10.3390/coatings9110697

AMA Style

Kawai E, Kakisawa H, Kubo A, Yamaguchi N, Yokoi T, Akatsu T, Kitaoka S, Umeno Y. Crack Initiation Criteria in EBC under Thermal Stress. Coatings. 2019; 9(11):697. https://doi.org/10.3390/coatings9110697

Chicago/Turabian Style

Kawai, Emi; Kakisawa, Hideki; Kubo, Atsushi; Yamaguchi, Norio; Yokoi, Taishi; Akatsu, Takashi; Kitaoka, Satoshi; Umeno, Yoshitaka. 2019. "Crack Initiation Criteria in EBC under Thermal Stress" Coatings 9, no. 11: 697. https://doi.org/10.3390/coatings9110697

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