Failure of Gadolinium Zirconate and Yttria Stabilized Zirconia Thermal Barrier Coatings Subjected to High Temperature Calcia-Magnesia-Alumino-Silicate Attack

Abstract

Nowadays, the contribution of rare-earth oxide compounds is extensively investigated with the aim to improve the service life of gas turbine engine components protected by thermal barrier coatings (TBCs) against the environmental Calcia-Magnesia-Alumino-Silicate (CMAS) attack. Therefore, the TBCs consisting of a NiCrAlY bond coat, Yttria Stabilized Zirconia (YSZ) and/or mixture of YSZ and Gadolinium Zirconate (YSZ+GZ) interlayers, and a GZ top coat, which were all deposited by atmospheric plasma spraying onto the nickel-based superalloy substrates, are introduced in this contribution. The CMAS-attack resistance was evaluated using an indirect method. Firstly, the thin layer of CMAS prepared from colloidal solutions was deposited onto the top coat surface and, after drying, the samples were heat treated with the aim to glassified the CMAS. Secondly, the coated samples containing CMAS glass debris were subjected to rapid heating (up to 1200 °C) and enforced cooling cycles at the burner-rig test device and the failure of TBC was investigated. In all cases, the failure mechanism due to the CMAS attack was the top coat spallation. The functional graded TBC was found to be the most resistant system.