Interaction of CMAS on thermal sprayed ytterbium disilicate environmental barrier coatings: A story of porosity

Tejero-Martin, Daniel; Romero, Acacio Rincon; Wellman, Richard G.; Hussain, Tanvir

Abstract

Molten calcium magnesium alumina-silicates (CMAS) represent a challenge for the current generation of rare earth silicates environmental barrier coatings (EBCs). Their interaction with ytterbium disilicate (Yb2Si2O7) free-standing coatings deposited using thermal spraying technique has been studied to further understand the reaction mechanisms. Three coatings, deposited with different porosity levels and thickness, representing traditional EBCs (<3% porosity and ∼350 μm thickness) and abradable coatings (∼20% porosity and 500–1000 μm thickness) were exposed to CMAS at 1350 °C. The results show that higher porosity levels facilitates CMAS infiltration in the first hour of exposure, in combination with infiltration through the inter-splat boundaries. Preferential dissolution of ytterbium monosilicate (Yb2SiO5) takes place, forming a 10–15 μm Ca2Yb8(SiO4)6O2 apatite layer as the reaction product, producing a network of fine porosity (<10 μm) as the inter-splat boundary material is consumed. After exposure for 48 h, CMAS has completely infiltrated all three coatings, with apatite crystals present across the coatings, up to a depth of ∼550 μm. Despite the extensive CMAS infiltration and apatite formation, no damage could be observed in any of the coatings, providing a promising first step for environmental barrier abradable coatings.

Citation

Tejero-Martin, D., Romero, A. R., Wellman, R. G., & Hussain, T. (2022). Interaction of CMAS on thermal sprayed ytterbium disilicate environmental barrier coatings: A story of porosity. Ceramics International, 48(6), 8286-8296. https://doi.org/10.1016/j.ceramint.2021.12.033

• Journal Article Type: Article
• Acceptance Date: Dec 4, 2021
• Online Publication Date: Dec 6, 2021
• Publication Date: Mar 15, 2022
• Deposit Date: Dec 16, 2021
• Publicly Available Date: Dec 16, 2021
• Journal: Ceramics International
• Print ISSN: 0272-8842
• Electronic ISSN: 1873-3956
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 48
• Issue: 6
• Pages: 8286-8296
• DOI: https://doi.org/10.1016/j.ceramint.2021.12.033
• Keywords: Materials Chemistry; Surfaces, Coatings and Films; Process Chemistry and Technology; Ceramics and Composites; Electronic, Optical and Magnetic Materials
• Public URL: https://nottingham-repository.worktribe.com/output/7020234
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0272884221038037