2772 J. Kimmel et al. Journal of the European Ceramic Society 22(2002)2769-2775 Fig. 6.(a) Thermal diffusivity image of Hi-Nicalon/SiC-Si MI inner liner after the EBC application; (b) digital image of the liner after the after the 13.937-h field test. The low density (red) area in the thermal image corresponds to the ebc-spalled area after the test. loss occurred at the aft end edges and in the middle (from aft to forward)on both liners. The EBC loss in the middle of the liners occurred in areas where fuel injectors were located and, thus, were in the hottest L BSAS areas. It was hypothesized that the EBC loss was due to licon oxidation and volatilization of the silicon-based coating layers. At the aft end edges, it appeared that the top and intermediate layers had spalled off, while the Sio2 silicon layer remained intact. The coating spallation at the aft end edges is due to mechanical interference between the EBC and the metallic combustor that sup ports the liners. Clearly, there was a need to revisit the attachment scheme to minimize/eliminate the EB Fig. 7. Baseline micrograph of the EBC in the aft end of the inner spallation in future engine tests. The combustor design liner after the 13,937-h field test was modified to accomplish this, and the modified design is being used in the sixth field test at Texaco Localized oxidation, manifested by"pinholes,was observed on the outer liner(Fig. 4). The location of inholes correlated with a repeatable pattern of surface asperities from CFCC liner proces- sing steps. However, pinholes were also observed in some locations that did not correlate with processing The pinholes were of different depths, some of them 段念 Mullite+ BSAS extending up 1.5 mm(about half of the liner thickness At one location on the liner the localized oxidation was severe enough to form a pinhole through the wall 2. 2. Nondestructive evaluation of liners Fig 8. Baseline micrograph of the EBC in the aft end of the outer An infrared thermal diffusivity image technique and liner after the 13, 937-h field test an air-coupled ultrasonic method were used to examine the CfCC liners before and after the EBC application correlated with the eBC spalled area after the field test and after the conclusion of the field test. The non-(Fig 6). Thus, it appears that nde can be successfully destructive evaluation (NDE) was performed by ANL. used as a screening tool to select EBC liners for engine Thermal diffusivity images indicated low diffusivity use. 7 (debonding) of the EBC layers on several locations where EBC appeared to be intact to visual observation 23. Microstructural evaluation at the end of the test(Fig. 5). For the inner liner, NDE images after the EBC application showed a significant Representative microstructures of the eBC applied to area of low density, the area and geometry of which the aft end of the inner and outer liner after the 13, 937-hloss occurred at the aft end edges and in the middle (from aft to forward) on both liners. The EBC loss in the middle of the liners occurred in areas where fuel injectors were located and, thus, were in the hottest areas. It was hypothesized that the EBC loss was due to silicon oxidation and volatilization of the silicon-based coating layers. At the aft end edges, it appeared that the top and intermediate layers had spalled off, while the silicon layer remained intact. The coating spallation at the aft end edges is due to mechanical interference between the EBC and the metallic combustor that sup￾ports the liners. Clearly, there was a need to revisit the attachment scheme to minimize/eliminate the EBC spallation in future engine tests. The combustor design was modified to accomplish this, and the modified design is being used in the sixth field test at Texaco. Localized oxidation, manifested by ‘‘pinholes’’, was observed on the outer liner (Fig. 4). The location of many of these pinholes correlated with a repeatable pattern of surface asperities from CFCC liner proces￾sing steps. However, pinholes were also observed in some locations that did not correlate with processing. The pinholes were of different depths, some of them extending up 1.5 mm (about half of the liner thickness). At one location on the liner, the localized oxidation was severe enough to form a pinhole through the wall. 2.2. Nondestructive evaluation of liners An infrared thermal diffusivity image technique and an air-coupled ultrasonic method were used to examine the CFCC liners before and after the EBC application and after the conclusion of the field test. The non￾destructive evaluation (NDE) was performed by ANL. Thermal diffusivity images indicated low diffusivity (debonding) of the EBC layers on several locations where EBC appeared to be intact to visual observation at the end of the test (Fig. 5). For the inner liner, NDE images after the EBC application showed a significant area of low density, the area and geometry of which correlated with the EBC spalled area after the field test (Fig. 6). Thus, it appears that NDE can be successfully used as a screening tool to select EBC liners for engine use.7 2.3. Microstructural evaluation Representative microstructures of the EBC applied to the aft end of the inner and outer liner after the 13,937-h Fig. 6. (a) Thermal diffusivity image of Hi-Nicalon/SiC-Si MI inner liner after the EBC application; (b) digital image of the liner after the after the 13,937-h field test. The low density (red) area in the thermal image corresponds to the EBC-spalled area after the test. Fig. 7. Baseline micrograph of the EBC in the aft end of the inner liner after the 13,937-h field test. Fig. 8. Baseline micrograph of the EBC in the aft end of the outer liner after the 13,937-h field test. 2772 J. Kimmel et al. / Journal of the European Ceramic Society 22 (2002) 2769–2775