The microstructures of a single-crystal Ni-based superalloy (with 16Cr, 8.5Co, 6W, 4Al, 4Ti and 1wt%Ta) were observed by transmission electron microscopy, before and after thermo-mechanical fatigue. Both the dislocation configurations and the γ′ precipitate morphologies under in-phase testing were found to be clearly different from those seen under out-of-phase testing. After in-phase testing, dense hexagonal dislocation networks were found on the horizontal interfaces; with irregular dislocation networks on the vertical interfaces. With decreasing mechanical strain amplitude, rafting of the γ′ precipitates became more pronounced. Under out-of-phase testing, no dislocation networks were found at the γ/γ′ interfaces. Also, the γ′ precipitates were sheared by superlattice stacking faults, and were not clearly rafted.

Microstructures of a Single-Crystal Nickel-Base Superalloy after Thermo-Mechanical Fatigue. Y.C.Wang, S.X.Li, L.Zhou, S.H.Ai, F.Liu, H.Zhang, Z.G.Wang: Philosophical Magazine, 2004, 84[31], 3335-51