Some observations on the morphology and structure of high temperature oxides formed on three superalloys as a result of the superficial application of Ce(SO4)(2)

The application of a Ce(SO4)(2) slurry to two Ni-based, and one Fe-based su peralloy is analyzed in terms of oxide morphology and microstructure develo ped after oxidation in air at 930 degreesC for 225 h. It was found that the alloy containing the greatest amount of Al suffered the most internal dama ge upon application of the Ce(SO4)(2) slurry as compared with the control c oupon. The oxide/alloy and oxide/gas interfaces were also more convoluted f or the Ni-based alloys with the Ce(SO4)(2) coating than the control coupons . From inspection of the metallographic cross-sections it is apparent that the Ce(SO4)(2) application rendered a thinner oxide on the two Ni-based all oys. Transmission electron microscope (TEM) of the microstructure revealed differences in oxide grain size for the three alloys. The greatest variatio n was seen in the structure of the oxide formed on Inconel 601 with Ce(SO4) (2) application. The grains were 10 times larger on average, and crater-lik e formations were noted. Considerable plastic deformation in the form of di slocation loops was also present. Precipitates were noted predominately in the oxide grains formed on Incoloy 800, and at grain boundaries for Inconel 601. (C) 2001 Published by Elsevier Science B.V. All rights reserved.