Effect of Aluminizing on the Oxidation of Inconel 718 and Inconel 738LC Superalloys at 925-1050°C

Abstract

Abstract A study was undertaken to investigate and compare the high temperature oxidation behaviors of aluminized Inconel 718 and Inconel 738LC nickel-based superalloys. Bare and high activity chemical vapor deposition (CVD) aluminized Inconel 718 and Inconel 738LC samples were oxidized in air at 925, 1000 and 1050°C for 200 hours. Detailed cross-sectional examinations, elemental analyses, mass change measurements, and x-ray diffraction studies were performed. It was observed that the oxidation resistances of both Inconel 718 and 738LC alloys were significantly improved by the Al2O3 layer formed on the NiAl phase that was created on the surfaces of the samples during aluminizing. The beneficial effect of aluminizing was found to be more evident in the case of 738LC alloy samples which showed lower oxidation rates in all test temperatures. It is suggested that the higher aluminum content of the Inconel 738LC alloy, which is 3.43 wt.% vs. 0.49 wt.% in 718, slows down the diffusional flux of Al away from the NiAl phase to the substrate and hence it is the main reason for the superior oxidation resistance of this alloy.