Electrodeposition of rhenium-base layer as a diffusion barrier between the NiCoCrAlY coating and a Ni-based superalloy

The main goal of this study was to evaluate the microstructure and capability of the diffusion barrier Re-base layer between the NiCoCrAlY coating and a Ni-based superalloy. To this end, a duplex coating system consisting of the Re-base layer and NiCoCrAlY coating were deposited by the electroplating method and High Velocity Oxygen Fuel (HVOF) spraying, respectively. The mechanism of the deposition process and the effect of deposition time and surface preparation and cleaning on the Faradaic Efficiency (FE), surface morphology, thickness and quality of the Re-base diffusion barrier were studied. Also, the inter-diffusion behaviour of the substrate- NiCoCrAlY coating with and without the diffusion barrier was investigated by isothermal oxidation at 1000 °C. The microstructural features and the diffusion barrier behaviour of the Re-base layer were evaluated by a Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS). Criteria related to the properties of diffusion barrier layer based on to increase the Faradaic efficiency and the rhenium content in the coating were evaluated. Isothermal oxidation test results showed that the diffusion barrier coating could inhibit the inter-diffusion of the elements of the superalloy substrate and significantly decrease the growth rate of the inner β-NiAl depletion zone.