Oxidation Behavior of a Single-Crystal Ni-base Superalloy in Air at 900, 1000 and 1100°C

Abstract

The oxidation behavior of a single-crystal (SC) Ni-base superalloy was studied over the temperature range from 1000–1150°C and analysed by TGA, XRD, EDAX, and SEM. The results indicated that the SC Ni-base superalloy exhibited parabolic oxidation kinetics, which were controlled by the growth of the inner α-Al2O3 layer. A mixed scale formed on the SC Ni-base superalloy after prolonged oxidation. The scale consisted of an outer layer of spinel, a sublayer of mainly α-Al2O3 with small amount of spinel adjoined by a very thin and even discontinuous layer of CrTaO4-rich oxide, and an inner α-Al2O3 layer. The inner α-Al2O3 layer provided good protection. No internal oxides or nitrides were observed below the inner α-Al2O3 layer after 1000 hr at 1000°C, and after 200 hr at 1100 and 1150°C.