High-Temperature Oxidation Behavior of Chemical Vapor Deposition Aluminide Coatings on Inconel 718 Superalloy
Understanding the high-temperature oxidation behavior of aluminide coatings on Inconel 718 superalloy is crucial for enhancing the high-temperature oxidation resistance of hot-end components in gas turbines and aeroengines.In this study,the aluminide coating was deposited on the surface of Inconel 718 superalloy by chemical vapor deposition(CVD),and isothermal oxidation tests were conducted on the Inconel 718 superalloy and the CVD aluminide coating at 950 ℃ under atmospheric environment.The high-temperature oxidation behavior of the CVD aluminide coating before and after oxidation,as well as the Inconel 718 superalloy was investigated by characterization methods such as scanning electron microscopy,X-ray diffraction,and energy-dispersive X-ray spectroscopy.The results show that the CVD aluminide coating deposited on the surface of Inconel 718 superalloy exhibits a rough surface and a bilayer structure.The outer layer is a Ni-and Al-rich β-NiAl layer with an average thickness of 14.1 μm.And the inner layer is an interdiffusion layer with an average thickness of 5.9 μm in which the σ phase rich in Fe and Cr elements and the Laves phase rich in Nb,Mo,and Fe elements coexist.After isothermal oxidation tests,the oxide scale formed on the surface of Inconel 718 superalloy is Cr2O3,while the oxide scale formed on the surface of CVD aluminide coating is α-Al2O3.The growth of Cr2O3 and α-Al2O3 follows the parabolic growth law.The growth rate constant of Cr2O3 of Inconel 718 superalloy is 0.86 μm·h-1/2,while the growth rate constant of α-Al2O3 of CVD aluminide coating is 0.15 μm·h-1/2.Inconel 718 superalloy experienced internal oxidation,while no internal oxidation was observed in the CVD aluminide coating.The presence of β-NiAl phase in the CVD aluminide coating is the fundamental cause of the difference in oxidation behavior between Inconel 718 superalloy and CVD aluminide coating.This study elucidates the mechanism of high-temperature oxidation resistance of Inconel 718 superalloy and CVD aluminide coatings,and provides technical support for the preparation and application of high oxidation resistance CVD aluminide coatings for Inconel 718 superalloy.
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