Optimized sol–gel thermal barrier coatings for long-term cyclic oxidation life

Abstract

New promising thermal barrier coatings (TBCs) processed by the sol–gel route are deposited onto NiPtAl bond coated superalloy substrates usingthe dip and/or spray coating technique. In this study, the optimization of the process, including an appropriate heat treatment prone to densifythe yttria-stabilized-zirconia (YSZ) top-coat and leading to the sintering and the development of a resulting crack network, is investigated. Inparticular, relevant information on internal strain evolution during the heat treatment are obtained using in situ synchrotron X-rays diffraction andconfirm a stabilization of the TBC through the occurrence of the micro-cracks that beneficially releases the in-plane sintering stress. Such TBCs aresubsequently reinforced using additional material brought within the cracks using sol–gel spray coating. The effect of various process parameters,such as the pre-oxidation of the bond-coat, on the sol gel TBCs consolidation and their cyclic oxidation resistance enhancement, is presented.Reinforced sol–gel TBCs are successfully oxidized up to more than one thousand 1 h-cycles at 1100◦C, without any detrimental spallation.