Development of a new slurry coating design for the surface protection of gas turbine components

• Published in: Surface & coatings technology Vol. 374; pp. 521 - 530
• Main Authors: Grégoire, Benjamin, Bonnet, Gilles, Pedraza, Fernando
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.09.2019; Elsevier BV; Elsevier
• Subjects: Aluminizing; Chemical and Process Engineering; Diffusion; Diffusion layers; Diffusion rate; Engineering Sciences; Exothermic reactions; Gas turbines; Intermetallic compounds; Intermetallic phases; Intermetallics; Microparticles; Nickel; Nickel aluminides; Nickel base alloys; Nickel compounds; Protective coatings; Slurries; Slurry coatings; Substrates; Superalloys; Intermetallics; Aluminizing; Slurry coatings; Superalloys; Diffusion
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2019.06.020

A new slurry coating design incorporating a first layer of Cr microparticles at the substrate surface and a surmounting second layer of Al microparticles to enrich the substrate with Al was investigated. The microstructure of the coating was tailored by adjusting the initial thicknesses of Cr and Al layers. The intermediate layer of Cr microparticles acted as a barrier to molten Al by forming Al-Cr intermetallic compounds thereby suppressing the highly exothermic reactions usually observed between molten Al and nickel-based materials. This also significantly decreased the inward diffusion rate of Al towards the substrate at 700 °C. Annealing at 1100 °C then promoted the outward diffusion of nickel atoms from the substrate and their combination with Al from the synthesized Al-Cr intermetallic phases compounds resulting in the direct formation of β-NiAl with expelled Cr. The mechanisms of formation of the diffusion layers and the influence of Cr on the aluminizing progress are discussed. •The Cr-free Al slurry composition results in high-activity aluminide coatings.•The Cr interlayer reacts with molten Al by forming AlxCry intermetallics.•The formation of AlxCry intermetallics decreases the Al activity.•The Cr/Al ratio of the coating system has a tremendous influence on the mechanisms of formation and on the final coating microstructure.•The appropriate slurry coating design can lead to the formation of low-activity Cr-modified aluminide coatings.