Effects of phase constituents/microstructure of thermally grown oxide on the failure of EB-PVD thermal barrier coating with NiCoCrAlY bond coat
Abbreviated Journal Title
Surf. Coat. Technol.
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
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.
Surface & Coatings Technology
"Effects of phase constituents/microstructure of thermally grown oxide on the failure of EB-PVD thermal barrier coating with NiCoCrAlY bond coat" (2006). Faculty Bibliography 2000s. 6369.