A dip process for thermal barrier coating on superalloys

A new cerium oxide thermal barrier coating for superalloys has been investigated. The coating is applied by hot dipping superalloy substrates into a molten bath of low melting point Ce-Ni alloy. Annealing and selective oxidation of cerium at low oxygen activities produce a duplex coating of a continuous outer layer of cerium oxide (CeO 2) and an inner composite CeO 2-substrate layer. The effects of coating composition and processing variables on the microstructure and integrity of the coating on nickel- and cobalt-base alloys were studied in detail. Isothermal and cyclic oxidation tests showed that coating spallation could occur and was associated with the oxidation of nickel and cobalt incorporated in the coating. A model for the formation of the CeO 2 barrier and the subscale region is proposed that explains the presence of unwanted nickel and cobalt.