Failure mechanisms of thermal barrier coatings on MCrAlY-type bondcoats associated with the formation of the thermally grown oxide
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The effect of the thermally grown oxide (TGO) formation on the lifetime of the thermal barrier coatings (TBC) with MCrAlY-bondcoats (BC) is reviewed. A number of factors affecting the TGO-formation and TBC-failure are discussed including the coating microstructure, geometrical (coating roughness and thickness) and processing parameters. Under given testing conditions for a specific EB-PVD-TBC-system forming a flat, uniform alumina TGO a critical TGO-thickness for TBC-failure can be defined. This TGO-morphology is, however, not necessarily optimum for obtaining long TBC-lifetime, which can be extended by formation of TGO’s with an uneven TGO/BC interface. In contrast, APS-TBC-systems are prone to formation of intrinsically inhomogeneous TGO-morphologies. This is attributed to non-uniform depletion of Y and Al underneath rough MCrAlY-surfaces as well as due to the commonly observed repeated-cracking/re-growth of the TGO during temperature cycling. The latter phenomenon depends on the exposure temperature and the mechanical properties of the APS-TBC. In both types of TBC-systems the TGO-formation and TBC-lifetime appear to be very sensitive to the manufacturing parameters, such as vacuum quality during bondcoat spraying and temperature regime of the bondcoat vacuum heat-treatment.
KeywordsOxide Scale HVOF Bond Coat Thermal Barrier Coating Thermally Grown Oxide
The authors are grateful to the following colleagues in the Institute for Energy Research of the Forschungszentrum Jülich for assistance in the materials procurement and experimental work: R. Vassen, K·H. Rauwald, H. Cosler, E. Wessel, M. Subanovic, and J. Toscano. Part of the present work was funded by the German Research Foundation (Grant No. NA-615-1) and German federal ministry for economy and technology (Grant No. 0326888D).
- 4.Quadakkers WJ, Tyagi AK, Clemens D, Anton R, Singheiser L (1999) In: Hampikian JM, Dahotre NB (eds) Elevated temperature coatings: surface and technology III. The Minerals, Metals & Materials Society, pp 119–130Google Scholar
- 25.Massalski TB (1996) ASM binary alloy phase diagrams. ASM International, Materials Park, OHGoogle Scholar
- 28.Täck U (2004) The influence of cobalt and rhenium on the behaviour of MCrAlY coatings (PhD thesis) Tech. Univ. Freiberg 25:151, 169Google Scholar
- 30.Lechner C, Seume J (eds) (2003) Stationaere Gasturbinen. Springer-Verlag, Berlin Heidelberg, Germany, p 749Google Scholar
- 31.Jansson B, Schalin M, Selleby M, Sundaman B (1993) In: Bale CW, Irins GA (eds) Computer software in chemical and extractive metallurgy. Canadian Institute of Metals, Quebec, p 57Google Scholar
- 32.Saunders N (2000) Ni-DATA information. Thermotech Ltd., Surrey Technology Centre, Surrey, UKGoogle Scholar
- 39.Kofstad P (1988) High temperature corrosion. Elsevier, LondonGoogle Scholar
- 48.Davis JR (ed) (1997) Heat resistant materials, ASM specialty handbook. ASM International, Materials Park, OH, p 305Google Scholar