Effect of tantalum and Ni[sbnd]Ta barriers on inter-diffusion between nickel coating and GH3535 alloy at 700 °C

Abstract

Nickel-coated GH3535 alloy is suitable used for molten salt reactor at elevated temperature. However, coating failure caused by inter-diffusion is still problematic. In this study, tantalum and NiTa films were deposited as barriers between nickel coating and GH3535 alloy by magnetron sputtering, respectively. The diffusion behaviors of the coatings were investigated by micro-structure analysis and calculation of diffusion coefficient. The results indicate that a Ta barrier can inhibit the diffusion of Cr and Fe due to the formation of Ni3Ta phases, but Ni diffusion from the substrate to the barrier is promoted causing the formation of Kirkendall voids. However, a novel NiTa barrier exhibits excellent diffusion resistance for Cr, Fe, and Ni in the Ni/GH3535 system at 700 °C.