Oxidation behavior and mechanism of a Ni-based single crystal superalloy with single alpha-Al2O3 film at 1000 degrees C

摘要

Detailed long-term of 2000 h oxidation behavior of a Ni-based single crystal superalloy was investigated at 1000 degrees C. In the first oxidation stage, alpha-Al2O3 formed immediately, and then the mass gain curve obeys the parabolic law, which corresponds to the growth of alpha-Al2O3 film. A single alpha-Al2O3 film kept on the surface of the specimen before 750 h oxidation. The oxidation is controlled by the inward diffusion of oxygen anions to react with Al cations at the oxide/metal interface. The shape of the exfoliation region of single alpha-Al2O3 film is closed to an annulus, in which the (Ni, Co)O layer formed due to depletion of Al. The three-layer oxide scale formed rapidly after 750 h oxidation. With the continue consumption of Al, a discontinuous inner alpha-Al2O3 layer formed, making oxide scale spall seriously and gain mass rapidly. The states of alpha-Al2O3 film, the controlled film, are different in dendrite core and interdendritic region. (C) 2017 Elsevier B.V. All rights reserved.