Mechanisms of creep deformation in nickel-base superalloy single crystals in the directional coarsening regime were studied in alloys with large variations in γ-γ′ lattice misfit and phase composition, achieved by Ru additions and variable levels of Cr and Co. Interfacial dislocation spacings established by long-term annealing experiments under no externally applied stress indicated that the experimental alloys had high-temperature lattice misfits ranging from near-zero to as large as −0.65%. Variation in misfit influences the stress-induced directional coarsening (rafting) behavior during creep deformation at 950C and 290MPa. In post-creep deformed material, the density of excess dislocations (defined as the dislocations beyond those necessary to relieve the lattice misfit) at the γ-γ′ interfaces varied with alloy composition, with the most creep-resistant alloy containing the highest excess interfacial dislocation density. In the directional coarsening creep regime, continued deformation required shearing of the γ′ rafts and was strongly influenced by the resistance of the precipitates to shearing as well as the interfacial dislocation structure. A preliminary model for creep in the rafting regime was developed.

Interfacial Dislocation Networks and Creep in Directional Coarsened Ru-Containing Nickel-Base Single-Crystal Superalloys. L.J.Carroll, Q.Feng, T.M.Pollock: Metallurgical and Materials Transactions A, 2008, 39[6], 1290-307