Processing and microstructure of NiRuAl diffusion barrier coating on Ni-based superalloy

Abstract

Thermal barrier coatings (TBCs), consisting of ceramic topcoat and metallic bond coat, are applied onto Ni-based superalloy hot components in turbine engines to protect the components from high temperature gas. Detrimental phases in the superalloy substrate such as topologically close-packed phase (TCP) and secondary reaction zone (SRZ), resulting from interdiffusion between the bond coat and the substrate, significantly deteriorate the desired mechanical properties of the superalloy substrate. In this paper, a NiRuAl coating was produced onto Ni-based superalloy to inhibit the interdiffusion between the coating and substrate. During the processing, a dense and continuous Ru film of around 4 μm thickness was first electrodeposited onto a K3 superalloy at 70°C using a current density of 1·2 A dm⁻². The NiRuAl coating was formed by pack aluminisation of the Ru coated specimen in argon atmosphere at 900°C. The coating shows a two-layered structure: the top layer NiAl and the bottom layer NiRuAl, with the potential functions of diffusion barrier and high temperature oxidation resistance.

Keywords:

• Coatings
• Ruthenium
• Diffusion
• Topologically close-packed phase
• Microstructure
• Electrodeposition