Effects of phase constituents/microstructure of thermally grown oxide on the failure of EB-PVD thermal barrier coating with NiCoCrAlY bond coat

    Authors

    J. Liu; J. W. Byeon;Y. H. Sohn

    Comments

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    Abbreviated Journal Title

    Surf. Coat. Technol.

    Keywords

    thermal barrier coatings; surface modification; photoluminescence; thermally grown oxide; thermal cycling; OXIDATION BEHAVIOR; STRESS; ALUMINA; DURABILITY; SCALES; DEPOSITION; ENGINES; NICKEL; SYSTEM; ALLOYS; Materials Science, Coatings & Films; Physics, Applied

    Abstract

    A correlation among thermal cycling lifetime, bond coat surface preparation, phase constituents and microstructure of thermally grown oxide (TGO) was examined for electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) consisting of ZrO2-7 wt-% Y2O3 (YSZ) ceramic topcoat, NiCoCrAlY bond coats and CMSX-4 superalloy. Variation in the bond coat surface is characterized based on surface roughness modification and pre-oxidation (1100 degrees C at Po-2. of 10(-8) atm up to 4 h) carried out prior to YSZ deposition by EB-PVD. TBC specimens with pre-oxidized bond coats exhibited longer lifetimes Than those without pre-oxidation, especially for metallographically polished bond coats. Given a surface roughness of NiCoCrAlY bond coats, TBC lifetime was observed to increase with an increase in the amount of CL-AI,03 in the initial thermally grown oxide (TGO) scale, which was detected by photostimulated luminescence (PL). Using focused ion beam in-situ lift out technique (FIB-INLO), site-specific preparation of thermally cycled TBC specimens for transmission electron microscopy (TEM) was successfully carried out. In addition to the presence of alpha-Al2O3, a small particulate phase identified as cubic Y2O3 was observed within the TGO scale by electron diffraction analysis on TEM. (c) 2005 Elsevier B.V. All rights reserved.

    Journal Title

    Surface & Coatings Technology

    Volume

    200

    Issue/Number

    20-21

    Publication Date

    1-1-2006

    Document Type

    Article

    Language

    English

    First Page

    5869

    Last Page

    5876

    WOS Identifier

    WOS:000237367600029

    ISSN

    0257-8972

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