Oxidation and diffusion barrier behaviors of double-layer NiCoCrAlY coatings produced by plasma activated EB-PVD

A double-layer (DL) NiCoCrAlY coating was coated onto a Hf-containing Ni-based superalloy DZ125. The bottom layer produced by plasma activated electron beam-physical vapor deposition (PA EB-PVD) was featured by coarse-grained equiaxed microstructure, which is different from the columnar microstructure of the top layer produced by EB-PVD. Oxidation resistance of the DL coating and a conventional single-layer (SL) NiCoCrAlY coating produced by EB-PVD was investigated at 1373 K. The DL coating exhibited an improved oxidation resistance as compared with the SL coating. The bottom layer in the DL coating effectively inhibited outward diffusion of refractory elements, such as Hf and W from the superalloy substrate. Oxidation and diffusion barrier mechanisms of the DL coating were also discussed.