AlCoCrNiMo high-entropy alloy as diffusion barrier between NiAlHf coating and Ni-based single crystal superalloy

To solve the issue of elemental interdiffusion between protective coating and superalloy substrate during high-temperature service, an AlCoCrNiMo high-entropy alloy (HEA) diffusion barrier was deposited by direct current magnetron sputtering between NiAlHf protective coating and Ni-based single crystal superalloy (René N5). The interdiffusion behavior and high-temperature oxidation resistance of the coating system were investigated via isothermal oxidation at 1373 K. After long-term oxidation at 1373 K, no interdiffusion zone (IDZ), secondary reaction zone (SRZ) and rod/needle-like topologically close-packed (TCP) precipitates were observed in the coating system with HEA diffusion barrier. Besides, the NiAlHf coating exhibited an improved oxidation resistance with the addition of HEA diffusion barrier. The results indicate that the HEA diffusion barrier can suppress the interdiffusion of alloying elements between substrate and coating effectively, which is attributed to the sluggish diffusion effect of HEA and the in-suit formed alumina layers at the substrate/HEA and HEA/NiAlHf interfaces during high-temperature oxidation. Moreover, it was found that the Co element in HEA layer also plays an important role in suppressing the formation of SRZ and TCP precipitates in the superalloy.