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

Abstract

Reactions between dislocations and between dislocations and γ′-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°C and τ=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 γ′-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 γ′-surface to another; (iii) dislocation climb directly and indirectly (tube/sandbox-analogon) contributes to this interaction.