Abstract
Abstract : This program has been directed at determining the mechanisms by which oxidation causes failure of thermal barrier coatings (TBCs) and developing modified systems with improved resistance to Oxidation-induced failures. The thermal barrier coating was yttria stabilized zirconia (YSZ) deposited via electron beam vapor deposition (EBPVD). This TBC was deposited on both platinum aluminide and NiCoCrA1Y bond coats which in turn were deposited on superalloy substrates of Rare N5. The oxidation testing was performed at 1000 deg, 1100 deg and 1200 deg C in air using cyclic exposures. The approach consisted of initially examining state-of-the-art systems and based upon the results obtained to prepare modified TBCs. Emphasis was placed upon bond coat modifications. In the case of the NiCoCrA1Y bond coats it was found that defects in the as-processed coatings at the TBC-bond coat interface caused failures. Procedures to prevent the formation of such defects extended TBC lives. The lives of TBCs on platinum-aluminide bond coats were influenced by ratcheting of the bond coat at the bond coat-TBC interface. Polishing of bond coats prior to TBC deposition is proposed to inhibit ratcheting and extend TBC lives.
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