Cyclic Oxidation Kinetics and Oxide Scale Morphologies Developed on the IN600 Superalloy

Abstract

The oxidation behavior of the IN600 Ni–Cr–Fe superalloy was investigated in air at temperatures ranging from 750 to 950 °C, for up to 12 cycles. Oxidation kinetics and oxide scale morphologies were examined using weight gain measurements, SEM-EDS, and X-ray diffraction. The cyclic oxidation kinetic results suggested that the oxidation behavior of the IN600 alloy approximately followed a sub-parabolic rate and the scaling process was controlled by the formation of a chromia scale. At 850 °C, SEM-EDS observations indicated that the formed oxide scale was primarily composed of Cr2O3, and the internal oxidation of Cr and Ti occurred. At 950 °C, a fast initial stage with high weight gain was observed, followed by a steady-state stage with gradual weight gain. Additionally, a considerable change in the oxidation kinetic occurred. SEM-EDS observations and XRD results indicated that the external scale was relatively thick with a localized porous, preferential adherent, and a complex oxide scale was developed. This complex oxide scale consisted of an outermost thin layer composed of MnCr2O4–Cr2O3 mixed together with a small amount of isolated TiO2, an intermediate relatively thick layer, composed of Cr2O3, and an innermost discrete layer formed at the scale/alloy interface, which enriched by Ni/NiO mixed with Ti-, Al-, and Fe-oxides. Finally, only the Al alloying element was internally oxidized to form Al2O3 fingers, which create a discrete and narrow internal oxidation zone. Al oxide was observed as a dark area and primarily grows along the alloy grain boundaries in the vicinity of the inward chromia pegs.