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 superalloy is analyzed in terms of oxide morphology and microstructure developed after oxidation in air at 930°C for 225 h. It was found that the alloy containing the greatest amount of Al suffered the most internal damage upon application of the Ce(SO4)2 slurry as compared with the control coupon. The oxide/alloy and oxide/gas interfaces were also more convoluted for 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 alloys. Transmission electron microscope (TEM) of the microstructure revealed differences in oxide grain size for the three alloys. The greatest variation 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-like formations were noted. Considerable plastic deformation in the form of dislocation loops was also present. Precipitates were noted predominately in the oxide grains formed on Incoloy 800, and at grain boundaries for Inconel 601.