Influence of electron beam physical vapor deposited thermal barrier coating microstructure on thermal barrier coating system performance under cyclicoxidation conditions

The lifetimes of electron beam physical vapor deposited (EB-PVD) thermal ba rrier coating (TBC) systems with three different microstructures of the Y2O 3-stabilized ZrO2 (YSZ) ceramic top layer were investigated in 1 h thermal cycles at 1100 and 1150 degrees C in flowing oxygen. Single crystal alloys CMSX-4 and Rene N5 that had been coated with an EB-PVD NiCoCrA1Y bond coat were chosen as substrate materials. At 1150 degrees C all samples failed af ter 80-100 1 h cycles, predominantly at the bond coat-alumina interface aft er cooling down from test temperature. The alumina scale remained adherent to the YSZ after spallation. Despite the different YSZ microstructures, no clear tendency regarding differences in spallation behavior were observed a t 1150 degrees C. At 1100 degrees C the minimum lifetime was 750 1 h cycles for CMSX-4, whereas the first Rene N5 specimen failed after 1750 1 h cycle s. The longest TBC lifetime on CMSX-4 substrates was 1250 1 h cycles, a whe reas the respective Rene N5 specimens have not yet failed after 2300 1 h cy cles. The failure mode at 1100 degrees C was identical to that at 1150 degr ees C, i.e. the TBC spalled off the surface exposing bare metal after cooli ng. Even though not all specimens have failed to date, the available result s at 1100 degrees C suggested that both the substrate alloy chemistry and t he YSZ microstructure significantly affect the spallation resistance of the TBC. (C) 1999 Elsevier Science S.A. All rights reserved.