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Figure 15. Microphotographs of corrosion tested button specimens with; a) PVD YSZ, b) plasma sprayed YSZ, and c) plasma sprayed CSZ coatings. Specimen (a) was tested for 75 hours whereas specimens (b) and (c) were tested for 45 hours each. The YSZ specimens do not show ■ corrosion whereas the CSZ specimen has dark areas where salt and t corrosion products were found. ; Spallation was limited to the i specimen edges (of b and c), probably related to the settling of the molten salt (by gravity) at the bottom of the specimens.

Figure 17.SEM micrograph of the surface of a sputtered YSZ sealant layer on a PVD YSZ coated button specimen, corrosion tested for 45 hours; crystals are apparently yttrium vanadate, the surrounding depleted in Y. EDS found the grey crystals to be Y and V rich; possibly yttrium vanadate, the surrounding YSZ (white area) was found to be depleted of yttrium. The dark areas are remaining salt.

Figure 17.SEM micrograph of the surface of a sputtered YSZ sealant layer on a PVD YSZ coated button specimen, corrosion tested for 45 hours; crystals are apparently yttrium vanadate, the surrounding depleted in Y. EDS found the grey crystals to be Y and V rich; possibly yttrium vanadate, the surrounding YSZ (white area) was found to be depleted of yttrium. The dark areas are remaining salt.

Figure 19 SEM micrograph of the surface of a plasma sprayed CSZ coated button specimens, corrosion tested for 60 hours; white crystals (area A) show only Ce by EDAX, apparently crystals of free ceria; surrounding CSZ is severely depleted of ceria.

Figure 18. SEM micrograph of the surface of a plasma sprayed YSZ coated button specimen, corrosion tested for 45 hours; dark areas are residual salt containing small quantities of Y, probably leached as yttrium sulphate. Light areas are YSZ with marginal loss of Y.

Figure 19 SEM micrograph of the surface of a plasma sprayed CSZ coated button specimens, corrosion tested for 60 hours; white crystals (area A) show only Ce by EDAX, apparently crystals of free ceria; surrounding CSZ is severely depleted of ceria.

Figure 20. SEM micrograph of the surface of a PVD CSZ button specimen corrosion tested for 30 hours; EDAS shows that the crystals contain Ce and V, apparently cerium vanadate. Surface reaction with the salt is evident.
Figure 22. SEM micrograph of the cross section of PVD CSZ button specimen corrosion tested for 30 hours; white areas are apparently free of ceria.
Figure 21. SEM micrograph of the cross section of plasma sprayed CSZ coating tested with NaV03 deposit in 0.2%S0ii+0a for 30 hours at 1380°F; EDAX of the dark regions between the splats shows high levels of Ce and S, probably cerium sulphate; the surrounding coating is depleted of ceria.
Figure 23. Micrograph of the PVD NiCoCrAlY bond coat - PVD YSZ interface, after hot corrosion testing for 75 hours; a thin Al depletion zone is observed but no hot corrosion of the bond coat is evident.
Figure 24. Micrograph of plasma sprayed NiCrAlY bond coat - plasma sprayed YSZ interface, after corrosion testing for 45 hours; no hot corrosion attack of the bond coat is evident.

Figure 25. Micrograph of PBC22 + Codep bond coat - plasma sprayed CSZ interface, after corrosion testing for 45 hours; negligible hot corrosion attack of the bond coat is evident.

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