Microstructural Characterization and Cyclic Hot Corrosion Behaviour of Sputtered Co-Al Nanostructured Coatings on Superalloy

Nanostructured Co-Al coatings on Superni-718 superalloy substrate were deposited by DC/RF magnetron sputtering in the present work. The microstructure and cyclic hot-corrosion behavior of nanostructured Co-Al coatings on Superni-718 superalloy were investigated in molten salt of 40 wt% Na(2)SO(4) + 60 wt% V(2)O(5) at 900 A degrees C. The results showed that a dense scale formed on the coated samples exposed to corrosive environment during thermal cycling. The spinel phases of CoCr(2)O(4), CoAl(2)O(4) and NiCr(2)O(4) were found in the corroded scale of the coatings, resulting in an effective inhibition of O and S diffusion. The sputtered Co-Al coatings exhibited high hot corrosion resistance due to the formation of beta-CoAl phases in the coating. The relevant corrosion mechanisms substantiating the role of coatings are discussed.