Influence of Pre-Oxidation on High Temperature Oxidation and Corrosion Behavior of Ni-Based Aluminide Coating in Na2SO4 Salt at 1050°C

Abstract

Aluminide coating is prepared on K438 Ni-based superalloy by pack cementation. The hot corrosion test of as-received and pre-oxidation aluminide coating in Na2SO4 salt are carried out at 1050°C. The coating morphologies, phase composition, and corrosion products are characterized by XRD, SEM, EDS, and TEM. The conclusion is that the pre-oxidation aluminide coating has excellent hot corrosion properties. After hot corrosion, the oxide scale of pre-oxidation aluminide coating is the thinnest and maintains good integrity. However, the oxide scale of as-received aluminide coating fluctuates greatly and there are corrosion cavities. CrS is formed in the alloy immediately below the oxide scale for the two coating systems.

Effect of Pre-Oxidation on High-Temperature Oxidation Behavior of Al-Si Coating on Nickel-Based Superalloy

“…In recent years, through studying the influence of pre-oxidation on the high-temperature oxidation and heat resistance corrosion properties of the coating, Yang [ 9 ] found that a Pt-Al-coated sample can form a continuous and dense Al 2 O 3 film after pre-oxidation treatment, which can effectively prevent molten salt from directly entering the material surface, and the pre-oxidized samples did not indicate internal oxidation or a vulcanization phenomenon. In the process of a hot corrosion experiment, the oxide film formed on the surface of the pre-oxidized Al-Si coating is thin and maintains good integrity, but the structure of the oxide film formed fluctuates greatly, indicating that the oxide film grows toward the inner layer of the coating during the process of oxidation dissolution [ 10 , 11 ]. Gao Bo et al [ 12 ] studied the influence of oxidation on the high-temperature oxidation and hot corrosion behavior of Co-Al-W-based superalloy and found that, when the alloy pre-oxidized at 950 °C under normal oxygen, partial pressure was oxidized at 1000 °C, the oxidation products fell off less, the oxidation mass gain was slowed down and the oxidation resistance of the alloy was improved.…”