Influence of TGO Composition on the Thermal Shock Lifetime of Thermal Barrier Coatings with Cold-sprayed MCrAlY Bond Coa
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JTTEE5 19:168–177 DOI: 10.1007/s11666-009-9372-8 1059-9630/$19.00 ASM International
Influence of TGO Composition on the Thermal Shock Lifetime of Thermal Barrier Coatings with Cold-sprayed MCrAlY Bond Coat Yong Li, Chang-Jiu Li, Qiang Zhang, Guan-Jun Yang, and Cheng-Xin Li (Submitted April 22, 2009; in revised form July 16, 2009) NiCoCrAlTaY bond coat was deposited by cold spraying to assemble thermal barrier coatings (TBCs). The microstructure of the cold-sprayed bond coat was examined using scanning electron microscopy. TBCs consisting of cold-sprayed bond coat and plasma-sprayed YSZ were pretreated at different conditions to form different thermally grown oxides (TGOs) before thermal cycling test. The influence of the TGO composition on the thermal cyclic lifetime was quantitatively examined through the measurement of the coverage ratio of the mixed oxides on the bond coat surface. The results showed that the bond coat exhibited a dense oxidation-free microstructure, and TGOs in different morphologies and constituents were present after thermal cyclic test. The formation of TGOs was significantly influenced by pretreatment conditions. Two kinds of TGO were detected on the surface of bond coat after the spallation of YSZ coatings. One is the a-Al2O3-based TGO and the other is the mixed oxide. It was found that the thermal cyclic lifetime is inversely proportional to the coverage ratio of the mixed oxides formed at the bond coat/YSZ interface. The high coverage ratio of the mixed oxide on the interface leads to the early spalling of YSZ coating.
Keywords
cold spraying, bond coat, thermal barrier coatings (TBCs), thermally grown oxide (TGO)
1. Introduction Thermal barrier coatings (TBCs) are widely used in gas turbine for propulsion and power generation (Ref 1-4) due to its ability to reduce the surface temperature of superalloy blades and to prolong the lifetime of blades (Ref 4-6). Constituents in a TBC system include the superalloy substrate, superalloy bond coat, ceramic coating (which is typically yttria-stabilized zirconia, YSZ), and a thermally grown oxide (TGO) formed at the interface This article is an invited paper selected from presentations at the 2009 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Expanding Thermal Spray Performance to New Markets and Applications: Proceedings of the 2009 International Thermal Spray Conference, Las Vegas, Nevada, USA, May 4-7, 2009, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2009. Yong Li, Chang-Jiu Li, Qiang Zhang, Guan-Jun Yang, and Cheng-Xin Li, State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, XiÕan Jiaotong University, XiÕan, Shaanxi 710049, P.R. China. Contact e-mail: [email protected].
168—Volume 19(1-2) January 2010
between the bond coat and ceramic coating during high temperature operation (Ref 1, 6). Recent inve
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