Microstructure and oxidation behavior of Al+Si co-deposited coatings on nickel-based superalloys

• Published in: Surface & coatings technology Vol. 258; pp. 347 - 352
• Main Authors: Fu, C., Kong, W.K., Cao, G.H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.11.2014; Elsevier
• Subjects: Aluminum base alloys; Applied sciences; Coating; Coatings; Cross-disciplinary physics: materials science; rheology; Diffusion; Diffusion coating; Exact sciences and technology; Intermetallics; Materials science; Metals. Metallurgy; Microstructure; Nickel aluminides; Oxidation; Oxidation resistance; Physics; Production techniques; Protective coatings; Silicon; Superalloys; Surface treatment; Surface treatments; Oxidation; Coating; Superalloys; Diffusion; Microstructure; Nickel base alloys; Scattering; Surface treatments; Coatings
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2014.09.003

Diffusion coatings have been widely used to metallic protective coatings or bond coats in thermal barrier coatings (TBCs) to protect the aeronautical turbine blades from detrimental oxidation and hot corrosion. However, degradation of these coatings caused by oxidation or hot corrosion can be particularly severe and rapid in the operating environment of the turbine. We present an experiment to modify γ-Ni+γ′-Ni3Al coating by co-deposition of Al and Si in order to improve the performance of coatings. In this study, microstructure and oxidation behavior of Al and Si co-deposited diffusion coatings were investigated. These coatings were deposited by Pt electroplating followed by aluminization and siliconization using the pack cementation process. The composition (in wt.%) of the packs was 2Al–4NH4Cl–xSi–(94−x)Al2O3 with different Si contents (x=4, 6, 8 and 10) and the corresponding microstructure of the coatings was δ-Ni2Si. The isothermal oxidation tests at 1000°C in air indicated that the coating formed using the packs containing 10wt.% Si had optimal oxidation resistance. After oxidation, the microstructure of the coatings was that of Cr2NiO4+NiO or NiO+Al2O3. The mechanisms through which Si-rich coating forms and protects against oxidation are discussed. •High Si in the coatings promotes the formation of Al2O3.•The active Si atoms stimulate the transformation of γ′-Ni3Al into δ-Ni2Si+β-NiAl.•The mechanism of Si on the oxidation resistance of the coatings is confirmed.