Analysis of dislocation structures after double shear creep deformation of CMSX6-superalloy single crystals at temperatures above 1000 °C

Dislocation structures which form during pure shear creep deformation of the superalloy single crystal alloy CMSX6 at 1025 °C under a shear stress of 85 MPa were analysed using transmission electron microscopy. Two macroscopic crystallographic shear systems were studied: 111〈110〉 and 100〈010〉. At the minimum creep rate (observed at shear values of 0.02) the system 111<110> deforms by a factor of ten faster than the system 100〈010〉. This creep rate ratio could not be rationalised merely on the basis of an external resolved shear stress argument. Shear creep deformation was always associated with multiple slip and nucleation of dislocations was not difficult (absence of incubation periods for creep). A detailed study of dislocation networks around γ′-particles underlined the importance of 〈110〉111 glide and climb processes in the γ-channels in the formation of these networks. Microstructural parameters and processes which must be considered to fully account for the mechanism of creep in superalloy SX are outlined. Channel work hardening always preceded the cutting of γ′-particles which started at the minimum creep rate.