Thermal Stability of a Rhenium-Based Diffusion Barrier Coating Layer on a Ni-Based Superalloy

Abstract

The thermal stability of coatings containing a Re-based diffusion barrier layer was investigated by surface and cross-sectional analysis methods. A Re-based barrier layer accompanied by an outer Ni-Cr-Al layer was prepared by electrolytic plating onto a Ni-based superalloy, followed by Cr-pack cementation in vacuum at 1523 K. Vacuum annealing was carried out at 1423 K for 25 h. Another type of coating specimen, with an additional Al reservoir layer on the Re-based barrier layer, was oxidized in air for 25 one-hour cycles at 1423 K. EDXRF, XRD, SEM, EDS and EPMA were used for analysis to evaluate the effects of the heat treatments. It was found that the barrier layer decomposed at high temperature when it was coated with a low-Al Ni-Cr-Al phase, but had good stability when it was adjacent to a high-Al Ni-Cr-Al phase.