Microstructure stability of γ′ + β Ni–Al coated single-crystal superalloy N5 annealed at 1100 °C

γ′ + β Binary-phase Ni–Al coatings were prepared on second-generation single-crystal superalloy René N5 (N5) substrates by electron beam physical vapor deposition. Inter-diffusion behavior between coatings and substrates at 1100 °C and its effects on microstructure stability of the substrates were investigated. A 3-μm-thick substrate diffusion zone (SDZ) layer forms beneath the coating/substrate interface after 5-h heat treatment. The SDZ layer is composed of γ′-Ni₃Al phases and needle-like precipitates growing along (100) 〈 110 〉 or (100) 〈 1 1 ¯ 0 〉 direction. After 100-h annealing, the thickness of the SDZ layer increases to ~17 μm, much lower than that of the single β-NiAl-coated substrate, while keeping single-crystal microstructure.