The cyclic oxidation behavior of the single crystal TMS‐82+ superalloy in humidified air

The cyclic oxidation behavior of a single crystal Ni‐based superalloy TMS‐82+ was studied at 800 and 900 °C for 200 h in water vapor (air plus 15% H 2 O). Regardless of the exposure temperature, time‐dependence of the growth rate of the scale for the superalloy was fitted by a subparabolic relationship. The oxidation rate was enhanced with increase in exposure temperature, which was evidenced by a higher mass gain and thicker scale. The oxides on the specimen at 800 °C consisted of (Ni,Co)O, CrTaO 4 , AlTaO 4 , Cr 2 O 3 , and θ‐Al 2 O 3 , whereas for the specimen exposed at 900 °C, spinels of NiCr 2 O 4 and (Ni,Co)Al 2 O 4 as well as α‐Al 2 O 3 were observed. An innermost dense α‐Al 2 O 3 layer was responsible for a stable growth rate of the scale after the initial rapid oxidation.