Dislocation reactions at γ/γ′-interfaces during shear creep deformation in the macroscopic crystallographic shear system (001)[110] of CMSX6 superalloy single crystals at 1025°C

Reactions between dislocations and between dislocations and gamma'-particles are studied in CMSX6 single crystals which were subjected to shear creep deformation in the macroscopic crystallographic shear system (001)[110] at T = 1025 degrees C and tau = 85 MPa, Experiments comprise high resolution shear creep testing and transmission electron microscopy. Emphasis is placed on the formation of dislocation networks and on rafting. The number of activated crystallographic glide systems increases during creep. A number of dislocation reactions which rationalise the features of the observed dislocation networks is identified. In secondary creep a (microscopic) slip system of type (001)[110] starts operating. Moreover experimental evidence for a new type of interaction between interface dislocations and the coarsening process of the gamma'-particles is provided. The explanation is based on three elements: (i) the stress fields of the interface dislocations result in local differences in chemical potential; (ii) the interface dislocations provide pipe diffusion paths from one gamma'-surface to another; (iii) dislocation climb directly and indirectly (tube/sandbox-analogon) contributes to this interaction. (C) 1998 Elsevier Science S.A. All rights reserved.