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Plasma Sprayed YSZ 60

Plasma Sprayed CSZ 60

Coating intact although extensive reaction with salt, crystals of yttrium vanadate at the surface slight spallation of ceramic at button edges

Some leaching of Y by the salt, slight attack of the bond coat

Slight spallation of ceramic at button edges, slight bond coat attack, surface reaction with salt, regions of free ceria at the surface, local regions of cerium sulphate.

crystals were detected by EDAX on the sputtered YSZ specimens; these are presumably yttrium vanadates. On the PVD and plasma sprayed YSZ specimens, no crystals of yttrium vanadate were found but some evidence of Y leaching into the salt was observed. The CSZ specimens had more varied reaction products with both cerium and vanadium rich crystals (cerium vanadate) and cerium rich crystals (free ceria) observed.

SEM of cross sections showed evidence of reaction products within the ceramic coatings in the plasma sprayed CSZ where Ce and S rich areas between splats were found (Figure 21). The areas surrounding these reaction products were zirconia depleted in ceria. Areas of free ceria were observed in the cross section of the PVD CSZ specimen (Figure 22). The other specimens did not have any evidence of reaction products or salts within the ceramic coating. Hot corrosion attack of the bond coats did not occur (Figure 23-25). Although some salt penetration had occurred within the plasma spray and PVD CSZ, it was restricted to the areas away from the metallic bond coat, thus preventing attack of the bond coat.

slow even under these severe conditions and that the ceramic coatings were successful in preventing salts from reaching the metallic bond coats. All specimens (except PVD CSZ) survived the tests with the ceramic coating essentially intact and the substrates unattacked. It is encouraging that PVD YSZ specimens survived 75 hours of corrosion testing with 5 salt applications (and 5 thermal cycles), with no bond coat attack and little ceramic surface attack. The more important tests are yet to come when burner rig testing of ceramic coated pin specimens will be performed. The longer test times and greater number of thermal cycles will be a much better test of the coatings' survivability.

These early hot corrosion results have provided some valuable direction for the remainder of this program. Although the reaction of CSZ with the vanadium containing salts is disappointing, these results do show that the reactions of all the ceramic coatings were relatively

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