The creep behavior at 1123K, and the microstructure of non-deformed and creep-deformed monocrystalline specimens of Ni-based solid solution alloys having various orientations, was investigated. One of the alloys had the composition of the matrix of the CMSX-4 superalloy and contained a 10% volume fraction of γ'-phase precipitates. A method for estimating the stress-state of matrix channels in superalloys was presented. A correlation between shear stress and dislocation density was determined for the particle-free matrix alloy. For the dislocation densities found in the matrix channels of the superalloy, the Taylor relationship predicted a resolved shear stress of 85 to 150MPa in vertical channels and 240 to 380MPa in horizontal channels. The predicted stress levels were in good agreement with finite-element calculations. An intensive dislocation analysis was carried out in order to determine the glide systems of the dislocations. For all of the specimen orientations used, octahedral glide predominated and only a small amount of cube glide was observed. During primary creep, the deformation was due mainly to single octahedral glide while only few of the possible octahedral glide systems with high Schmid-factors (and no systems with low Schmid-factors) were activated. During secondary creep, all of the octahedral glide systems were activated; even those having a Schmid-factor which was close to zero. The fractional density of each glide system corresponded roughly to its Schmid-factor. Near-screw and 60º dislocations appeared to predominate in all of the specimens. The fraction of 60º dislocations increased with strain.

Orientation Dependent Creep Behavior and Dislocation Structure of Nickel Solid Solution Single Crystals. D.Siebörger, U.Glatzel: Key Engineering Materials, 2000, 171-174, 253-60