Study of high temperature oxidation kinetics of Co–Al coating on superalloy

Abstract

Nanostructured Co–Al coating on Superni-718 substrate was deposited by dc/rf magnetron sputtering. The high temperature oxidation kinetics of Co–Al coating on superalloy substrate was studied after 100 h of cyclic oxidation in air environment at 700–900°C. FE-SEM/EDS, AFM and XRD were used to characterise the microstructure, surface morphology and phase constituents of as deposited and oxidised coatings. The results indicate that the Co–Al coated superalloy substrate has higher oxidation resistance at 900°C. The presence of β-CoAl intermetallic phase in the Co–Al coating, the formation of Al₂O₃ and spinel phases such as CoCr₂O₄ and CoAl₂O₄ in the oxide scale are considered to be the reasons for the higher oxidation resistance shown by the Co–Al coated superalloy substrate after 100 h of cyclic oxidation in air at 900°C. Further, the oxide scale formed on the coated sample exhibits good spallation resistance during cyclic oxidation test at 900°C.