Calcium-magnesium-alumina-silicate (CMAS) delamination mechanisms in EB-PVD thermal barrier coatings

Xi CHEN

doi:10.1016/j.surfcoat.2004.12.029

Calcium-magnesium-alumina-silicate (CMAS) delamination mechanisms in EB-PVD thermal barrier coatings

Xi CHEN^*

^*Corresponding author for this work

Research output: Journal Publications › Journal Article (refereed) › peer-review

115 Citations (Scopus)

Abstract

Thermal barrier coatings (TBCs) comprise thermally insulating materials having sufficient thickness and durability that they can sustain an appreciable temperature difference between the load bearing alloy and the coating surface. TBC exhibit multiple failure modes. Among them, in-service erosion caused by the deposition of significant amount of calcium-magnesium-alumina-silicate (CMAS) at high temperature was found to be one of the most prevalent failure modes. The large thermal expansion mismatch between the CMAS and TBC and the extra strain energy stored in the CMAS layer can lead to delamination cracks between the TBC and bond coat (BC). In this study, the energy release rate and mode mixity of a propagating delamination crack are calculated by using the finite element analysis. The columnar microstructure of EB-PVD TBC is factored into the approach. The effects of CMAS layer thickness, mechanical and thermal properties are examined, and the steady-state energy release rates are compared with a theoretical model. Two failure mechanisms associated with CMAS deposition are analyzed: cracking within individual columns and spallation of a large TBC layer. It is believed that both mechanisms have contributed to the CMAS delamination failure. Failure criterions are derived which provide useful insights on how to improve the resistance of CMAS delamination.

Original language	English
Pages (from-to)	3418-3427
Number of pages	10
Journal	Surface and Coatings Technology
Volume	200
Issue number	11
Early online date	2 Mar 2005
DOIs	https://doi.org/10.1016/j.surfcoat.2004.12.029
Publication status	Published - 15 Mar 2006
Externally published	Yes

Bibliographical note

The author is grateful for helpful discussions with Professor Anthony G. Evans at the University of California at Santa Barbara, and Professor John W. Hutchinson at Harvard University. This work was supported in part by ONR 04-123219, and in part by NSF CMS-0407743.

Keywords

CMAS
Delamination
Energy release rate
Fracture toughness
Thermal barrier coating

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10.1016/j.surfcoat.2004.12.029

Cite this

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title = "Calcium-magnesium-alumina-silicate (CMAS) delamination mechanisms in EB-PVD thermal barrier coatings",

abstract = "Thermal barrier coatings (TBCs) comprise thermally insulating materials having sufficient thickness and durability that they can sustain an appreciable temperature difference between the load bearing alloy and the coating surface. TBC exhibit multiple failure modes. Among them, in-service erosion caused by the deposition of significant amount of calcium-magnesium-alumina-silicate (CMAS) at high temperature was found to be one of the most prevalent failure modes. The large thermal expansion mismatch between the CMAS and TBC and the extra strain energy stored in the CMAS layer can lead to delamination cracks between the TBC and bond coat (BC). In this study, the energy release rate and mode mixity of a propagating delamination crack are calculated by using the finite element analysis. The columnar microstructure of EB-PVD TBC is factored into the approach. The effects of CMAS layer thickness, mechanical and thermal properties are examined, and the steady-state energy release rates are compared with a theoretical model. Two failure mechanisms associated with CMAS deposition are analyzed: cracking within individual columns and spallation of a large TBC layer. It is believed that both mechanisms have contributed to the CMAS delamination failure. Failure criterions are derived which provide useful insights on how to improve the resistance of CMAS delamination.",

keywords = "CMAS, Delamination, Energy release rate, Fracture toughness, Thermal barrier coating",

author = "Xi CHEN",

note = "The author is grateful for helpful discussions with Professor Anthony G. Evans at the University of California at Santa Barbara, and Professor John W. Hutchinson at Harvard University. This work was supported in part by ONR 04-123219, and in part by NSF CMS-0407743.",

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AU - CHEN, Xi

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N2 - Thermal barrier coatings (TBCs) comprise thermally insulating materials having sufficient thickness and durability that they can sustain an appreciable temperature difference between the load bearing alloy and the coating surface. TBC exhibit multiple failure modes. Among them, in-service erosion caused by the deposition of significant amount of calcium-magnesium-alumina-silicate (CMAS) at high temperature was found to be one of the most prevalent failure modes. The large thermal expansion mismatch between the CMAS and TBC and the extra strain energy stored in the CMAS layer can lead to delamination cracks between the TBC and bond coat (BC). In this study, the energy release rate and mode mixity of a propagating delamination crack are calculated by using the finite element analysis. The columnar microstructure of EB-PVD TBC is factored into the approach. The effects of CMAS layer thickness, mechanical and thermal properties are examined, and the steady-state energy release rates are compared with a theoretical model. Two failure mechanisms associated with CMAS deposition are analyzed: cracking within individual columns and spallation of a large TBC layer. It is believed that both mechanisms have contributed to the CMAS delamination failure. Failure criterions are derived which provide useful insights on how to improve the resistance of CMAS delamination.

AB - Thermal barrier coatings (TBCs) comprise thermally insulating materials having sufficient thickness and durability that they can sustain an appreciable temperature difference between the load bearing alloy and the coating surface. TBC exhibit multiple failure modes. Among them, in-service erosion caused by the deposition of significant amount of calcium-magnesium-alumina-silicate (CMAS) at high temperature was found to be one of the most prevalent failure modes. The large thermal expansion mismatch between the CMAS and TBC and the extra strain energy stored in the CMAS layer can lead to delamination cracks between the TBC and bond coat (BC). In this study, the energy release rate and mode mixity of a propagating delamination crack are calculated by using the finite element analysis. The columnar microstructure of EB-PVD TBC is factored into the approach. The effects of CMAS layer thickness, mechanical and thermal properties are examined, and the steady-state energy release rates are compared with a theoretical model. Two failure mechanisms associated with CMAS deposition are analyzed: cracking within individual columns and spallation of a large TBC layer. It is believed that both mechanisms have contributed to the CMAS delamination failure. Failure criterions are derived which provide useful insights on how to improve the resistance of CMAS delamination.

KW - CMAS

KW - Delamination

KW - Energy release rate

KW - Fracture toughness

KW - Thermal barrier coating

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JF - Surface and Coatings Technology

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ER -

Calcium-magnesium-alumina-silicate (CMAS) delamination mechanisms in EB-PVD thermal barrier coatings

Abstract

Bibliographical note

Keywords

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