Dislocation reactions and microstructural instability during 1025 °C shear creep testing of superalloy single crystals

Double shear creep tests of the nickel-base superalloy CMSX6 were performed in the high-temperature/low-stress regime where short dislocation segments move through the narrow γ-channels in between the γ′-cuboids and create long dislocation segments near the surface of the γ′-particles. At the same time there is a change in shape of the γ′-particles (rafting). The double shear technique allows for loading selected glide systems with high Schmid factors. We investigated the microstructure after creep testing in the macroscopic crystallographic shear system (001) [110]. Formation and transformation of the dislocation networks are analyzed. This analysis yields an unambiguous determination of the activated glide systems. It is found that several glide systems with relatively high Schmid factors are not activated. Slip on cube glide planes was shown not to be important during primary creep.