Abstract
Advanced Ni-base single crystal (SC) superalloys containing high concentrations of refractory elements prone to generate a diffusion layer called Secondary Reaction Zone (SRZ) beneath their bond coating during exposure at high temperatures. SRZ cause a reduction of the load bearing cross section and it is detrimental to the creep properties of thin-wall turbine airfoils. In this study, a new bond coat system “EQ coating” designed to be in thermodynamic equilibrium with the Ni-based superalloy substrate has been proposed. Two types of EQ coating systems based on γ and γ′ compositions on the tie line of the base alloy (TMS-82+ or TMS-173) were studied and compared with a conventional bond coat. Each coating system was diffusion coupled with the substrate material and subjected to isothermal exposure at 1100°C for 300 hours. The results have indicated minimal interdiffusion occurred between EQ coating systems and the substrate. The EQ coating based on γ′ composition possesses the most promising oxidation resistance.
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