High temperature oxidation behaviour of Cr/Co–Al coated superalloy

The high temperature oxidation behaviour of nanostructured Cr/Co–Al coatings on Superni-718 substrate, deposited by sputtering, has been investigated. Cyclic high temperature oxidation tests were conducted on bare and coated samples at 900°C for up to 100 cycles. The results showed that a dense scale formed on the coated samples during thermal cycling at the peak temperature of 900°C. The external scale exhibited good spallation resistance during cyclic oxidation testing. The improvement in oxide scale spallation resistance is believed to be the fine grained structure of the coating. The Cr/Co–Al coating on the superalloy substrate showed better performance of cyclic high temperature oxidation resistance due to its possession of β-CoAl phase as Al reservoir and the formation of Al₂O₃ and spinel phases, such as CoCr₂O₄ and CoAl₂O₄, in the scale.