Suppressing the formation of SRZ in a Ni-based single crystal superalloy by RuNiAl diffusion barrier

NiAl-based bond coats applied in thermal barrier coating (TBC) systems containing Ru and Pt have been studied in recent years. Interdiffusion between the coatings and the underlying superalloy substrates usually results in degradation of the mechanical properties of the substrates. In this paper, a NiAl/Ru coating was deposited onto a single crystal superalloy DD6 by electroplating and electron beam physical vapor deposition (EB-PVD). Interdiffusion behavior of the NiAl/Ru and NiAl coated specimens at 1100 °C was comparatively investigated. For the NiAl coated specimen, after 100 h vacuum annealing, beneath the coating there was a 50 μm thickness secondary reaction zone (SRZ) with some needle-like topologically closed packed (TCP) phases. However no SRZ was observed in the NiAl/Ru coated specimen. This may be attributed to the RuNiAl that acted as a diffusion barrier to prevent the inward diffusion of Al from the coating and the outward diffusion of refractory elements from the substrate, and hence suppressing the formation of TCP phases and SRZ in the superalloy.