Corrosion resistance of NiCrAl coatings in the salt spray tests

NiCrAl coatings were prepared on Ni-based superalloy through Atmospheric Plasma Spray (ASP), and the corrosion resistance of the coatings under the conditions of salt spray test and high-temperature oxidation was investigated. From the Tafel polarization curve of NiCrAl coatings before and after the salt spray test, it is shown that the corrosion potential of NiCrAl coatings becomes smaller while the corrosion current density becomes larger, indicating that the corrosion resistance of NiCrAl coatings after the salt spray test is decreased obviously. SEM images show that after the salt spray test, the corrosion of surface of the NiCrAl coatings is serious resulting from the appearance of many cracks and the loose microstructure, so the coatings have no protective capability. EDX analyses reveal that corrosion products are Me_xO_yCl_z. After the thermal treatment at 1000°C for 15 h, the corrosion resistance of NiCrAl coatings is enhanced because of the formation of θ-Al₂O₃ film.