AN INSITU STUDY OF CUBE GLIDE IN THE GAMMA'-PHASE OF A SUPERALLOY .1. THE CONTROLLING MECHANISM

An in situ study of the plastic deformation of single crystals of the gamma'-phase of a CMSX2 superalloy (L1(2) structure) has been performed between 120 and 1150 K, in order to analyse the role and the mechanisms of glide of superdislocations in {001} cube planes. Extensive cube glide and dislocation sources are observed from very low-temperatures (140 K) to high-temperatures (1150 K), for a tensile axis close to <110>. Glide on cube planes is controlled by a locking-unlocking mechanism acting on screw dislocations, in the whole temperature range. This mechanism is described in detail and compared with that presented earlier for prismatic glide in beryllium. It corresponds to a series of cross-slip events, on super partial dislocations which are alternately extended in one intersecting octahedral plane, and in the cube plane. On the other hand, non-screw dislocations interact with small clusters or solute atoms. The explanation for the activation of cube glide at very low-temperatures is given in part II of this study.