COMPRESSIVE FATIGUE OF A PLASMA-SPRAYED ZRO2-8WT-PERCENT-Y2O3 AND ZRO2-10WT-PERCENT-NICRALCOY TTBC

High cycle ( > 10(6) cycles) fatigue (HCF) behavior of thick thermal b arrier coatings (TTBC's) was examined for applied stresses near the co mpressive strength of the material. Test data were obtained on four co ating systems: two base materials in the unsealed and CrO2 dip sealed conditions. Free standing tubular specimens were evaluated. The data s how that compressive fatigue limits exist for the four coating systems at room temperature (RT) and sealing with CrO2 improves RT fatigue li fe. Test results also show the ratio of the peak cyclic stress, at 10( 5) cycles, to ultimate compressive strength (UCS) of the Yttria Stabil ized Zirconia (YSZ) tubular specimens approaches 0.90 at R = 0.6 (R = minimum/maximum compressive stress). Residual UCS increases were obser ved after fatigue run-outs at elevated temperatures (5 at 700 degrees C and 1 at 400 degrees C) for both YSZ and the cermet. Ratchetting wit h cyclic hardening was observed during fatigue with deformation occurr ing primarily in the initial portion of the high cycle fatigue life of the specimens.