The potential application of Ru in aluminide coatings with reduced Al contents: A combined experimental and theoretical study

Abstract

Aluminide coatings are widely used on turbine blades due to their excellent oxidation resistance. However, the interdiffusion between these coatings and superalloy substrates can lead to a deterioration of mechanical properties in the coated alloys. In the present study, Ni-Al alloys (Ni-50Al, Ni-40Al, and Ni-30Al), both with and without the addition of 10 at. % Ru, are prepared and used to form diffusion couples with a single crystal superalloy SCA21. After a diffusion process at 1150 ℃ for 100 h, interdiffusion layers with the matrix of β-NiAl or γ ′-Ni3Al form at the diffusion couple interfaces. The formation of L12-ordered Ni3Al phases is found to impede elemental interdiffusion. Consequently, Ni-30Al/SCA21, which exhibits only Ni3Al-based interdiffusion layers, displays the lowest interdiffusion coefficients among the diffusion couples without Ru addition. Furthermore, first-principles studies reveal that the addition of Ru increases the formation energies of point defects and defect clusters involved in elemental interdiffusion in stoichiometric NiAl, Ni-rich NiAl, and Ni3Al phases, particularly when Ru occupies the Al site of Ni3Al phases at high temperatures. The remarkable diffusion barrier effects of Ru in Ni-30Al coatings have the potential to significantly enhance their performance and broaden their application prospects.

Keywords

• Nickel-based single crystal superalloys
• Nickel aluminides
• Platinum group
• Diffusion mechanism
• First-principles calculations