Early Stages of High Temperature Cyclic Oxidation of an Electrodeposited Ceria Coating on Nickel Superalloys Under Water-drop Tests

Abstract

Ceria coatings having a well-defined cracks network were electrodeposited onto Ni-based Rene N5 superalloys. After a subsequent annealing under argon for promoting the formation of a stable alpha alumina scale at the ceria layer/substrate interface, the samples were isothermally oxidized at 1,100 °C for 50 h to thicken the oxide scale. They were then subjected to cyclic oxidation at 1,100 °C for 1-h cycles. 10 μL water drops were put down onto the surface of the samples during the cold stages to study the influence of water onto the mechanical integrity of the pre-oxidized system. The multi-cracked ceria microstructure exhibited a widening of the cracks as well as refinement of the oxide grains. However, no spallation was observed and the composition remained stable for both ceria and alumina. It was demonstrated that the crystallization of ceria into the CeO2 fluorite structure conferred to the coating chemical inertness towards water.