ANALYSIS OF DISLOCATION-STRUCTURES AFTER DOUBLE SHEAR CREEP DEFORMATION OF CMSX6-SUPERALLOY SINGLE-CRYSTALS AT TEMPERATURES ABOVE 1000-DEGREES-C

Dislocation structures which form during pure shear creep deformation of the superalloy single crystal alloy CMSX6 at 1025 degrees C under a shear stress of 85 MPa were analysed using transmission electron micr oscopy. 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 fast er than the system {100} on the basis of an external resolved shear st ress argument. Shear creep deformation was always associated with mult iple slip and nucleation of dislocations was not difficult (absence of incubation periods for creep). A detailed study of dislocation networ ks around gamma'-particles underlined the importance of [110]{111} gli de and climb processes in the gamma-channels in the formation of these networks. Microstructural parameters and processes which must be cons idered to fully account for the mechanism of creep in superalloy SX ar e outlined. Channel work hardening always preceded the cutting of gamm a'-particles which started at the minimum creep rate.