Blistering of MCrAlY-coatings in H2/H2O-atmospheres

The oxidation behavior of vacuum plasma sprayed, free-standing MCrAlY-coatings was studied in Ar–20%O2 and Ar–4%H2–2%H2O. During exposure in Ar–4%H2–2%H2O the coating formed large “blisters”. This phenomenon was attributed to H2-gas evolution within the coating, creating high pressures sufficient for coating plastic deformation as a result of atomic hydrogen recombination on coating defects. It is suggested that the hydrogen is produced at the scale/metal interface by reaction of H2O-vapor with yttrium and aluminium present in the coating.