Strength and Durability of Thermal Barrier Coatings

Objectives

        To identify the  predominant degradation mechanisms  that control the long term durability of thermal barrier coatings (TBCs).

Results


Electron beam- physical vapor deposited  (EB-PVD) TBC system. The topmost coating is of a ceramic (8 wt% Yittria stabilized ZrO2), the intermediate coating is of MCraly bond coat (NiCoCrAlY alloy) and the bottommost is the superalloy substrate (Rene N5). This TBC system is used in GE Aircraft Engines. In absence of the ceramic topcoat, the bond coat developes waviness upon thermal cycling i. e. it "rumples". Rumpling is one of the important mechanisms of TBC degradation. Our present work explains the characteristic wavelengths  observed in the rumpling process using a diffusion model. When the ceramic topcoat is present, the rumpling gives rise to interfacial cracks that lead to catastrophic TBC failures. 

Future Work

1) 2-D modeling of surface waviness via surface and volume diffusion, 2) Experimental determination of the role of bond coat diffusive processes in the failure of Thermal Barrier Coatings

Publications

1. Panat, R., Zhang, S., Hsia, K. J.,"Bond coat surface rumpling in thermal barrier coatings" Acta Materialia, 51, 239-249 (2003). [PDF]

2. Panat, R. and Hsia, K. J.,"Experimental investigation of the bond coat rumpling instability under isothermal and cyclic thermal histories in thermal barrier systems", Proceedings of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences, 460, 1959-1979 (2004). [PDF]

3. Panat, R., Hsia, K. J., and Oldham, J.,"Rumpling instability in thermal barrier systems under isothermal conditions in vacuum," accepted for pubication in the Philosophical Magazine. [PDF]

4. Panat, R., Hsia, K. J., and Cahill, D. G., "Evolution of surface waviness in thin films via volume and surface diffusion," submitted for publication. [PDF]
 

Sponsored by  Critical Research Initiative at UIUC

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