The formation, microstructure and hot corrosion behaviour of slurry aluminide coating modified by Ni/Ni-Co electrodeposited layer on Ni-base superalloy

• Published in: Surface & coatings technology Vol. 402; p. 126283
• Main Authors: Masoumi Balashadehi, M., Nourpour, P., Sabour Rouh Aghdam, A., Allahyarzadeh, M.H., Heydarzadeh, A., Hamdi, M.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.11.2020; Elsevier BV
• Subjects: Alloying elements; Aluminide coating; Aluminum; Chemical composition; Chromium; Coated electrodes; Cobalt; Corrosion resistance; Corrosion tests; Diffusion coating; Electrodeposition; Hastelloy (trademark); Hastelloy-X; Hot corrosion; Intermetallic compounds; Microstructure; Molybdenum; Nickel aluminides; Nickel base alloys; Nickel compounds; Protective coatings; Slurries; Slurry; Sodium sulfate; Substrates; Superalloys; Electrodeposition; Aluminide coating; Hastelloy-X; Hot corrosion; Cobalt; Slurry
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126283

In this research, microstructure and hot corrosion behaviour of a modified aluminide coating were studied. The coating was formed via a two-step process, Ni/Ni-Co electrodeposition on Ni-base superalloy, Hastelloy-X, followed by slurry aluminising. The obtained coatings with 140 ± 5 μm thickness were characterised by an X-ray diffractometer (XRD) and scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscope (EDS) and elemental mapping before and after the corrosion tests. The results showed the β-NiAl for simple and pure Ni pre-plated, and the β-(Ni,Co)Al for NiCo pre-plated aluminised samples were formed definitely as a predominant phase. The initial electrodeposited layer performed as a Ni reservoir to reinforce aluminide formation. Besides, it reduced outward diffusion of alloying elements such as Cr, Fe, and Mo from substrate alloy as a diffusion retardant. Accordingly, the chemical composition of substrate alloy in pre-plated samples remained almost constant rather than its simple aluminised counterpart during the diffusion coating process. After the hot corrosion test carried out in the salt mixture of Na2SO4/NaCl environment, the results indicated that the presence of Co was beneficial and improved corrosion resistance of the obtained coating even in the Cl-containing salt mixture. [Display omitted] •The efficient technique of the electrodeposition was used as one of coating steps.•The deposited layer was performed as a diffusion retardant for alloying elements.•The corrosion resistance of coating was improved even in Cl-containing environment.