The Effect of Zirconium on the Isothermal Oxidation of Nominal Ni ‐ 14Cr ‐ 24Al Alloys

Abstract

The isothermal oxidation of , typical γ/γ′+β alloys, was performed in still air at 1100°, 1150°, and 1200°C for times up to 200 hr. The zirconium content of the alloys varied from 0–0.63 atom percent (a/o). The oxidized surfaces were studied by optical microscopy, x‐ray diffraction, and scanning electron microscopy. The base alloy was an alumina former with the zirconium‐containing alloys also developing some . The addition of zirconium above 0.066 a/o increased the rate of weight gain relative to the base alloy. Due to oxide penetration, the weight gain increased with Zr content, however, the scale thickness did not increase. The Zr did increase the adherence of the oxide, particularly at 1200°C. The ΔW/A vs. time data fit the parabolic model of oxidation. The specific diffusion mechanism operative could not be identified by analysis of the calculated activation energies. Measurements of the scale lattice constants yielded the same values for all alloys.