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A new spallation mechanism of thermal barrier coatings and a generalized mechanical model

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journal contribution
posted on 14.08.2019, 12:22 by Bo Yuan, Christopher Harvey, Rachel Thomson, Gary Critchlow, David Rickerby, Simon Wang
Multilayer thermal barrier coating (TBC) systems typically consist of three layers of materials: A thermal barrier top coat (TC), a thermally-grown oxide (TGO), and a bond coat (BC) in addition to the substrate. Local strain energy concentrations, called ‘pockets of energy concentration (PECs)’ in this work, often occur around the interface between the TGO and the BC. They have various causes, including local phase changes, and non-uniform creep and plastic relaxation. It is discovered that both PECs and buckling drive the spallation of a TBC in a new spallation mechanism. A PEC-based mechanical model is developed that describes, explains and predicts how blisters nucleate in a TBC under constant biaxial compressive residual stress, steadily and then unsteadily grow, and finally spall off. Two conditions are established for the occurrence of TBC spallation, which depend on the compressive residual strain energy density in the TC and the TGO, and the interface fracture toughness. Experimental validation of the model was performed using aircraft jet engine turbine blades with electron beam physical vapor deposition (EBPVD) TBCs. The predictions from the developed PEC-based mechanical model for the radii of spallation in the TBC are in a good agreement with experiment results.

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Materials

Published in

Composite Structures

Volume

227

Publisher

Elsevier

Version

AM (Accepted Manuscript)

Rights holder

© Elsevier Ltd.

Publisher statement

This paper was accepted for publication in the journal Composite Structures and the definitive published version is available at https://doi.org/10.1016/j.compstruct.2019.111314.

Acceptance date

14/08/2019

Publication date

2019-08-16

Copyright date

2019

ISSN

0263-8223

Language

en

Depositor

Dr Christopher Harvey

Article number

111314

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