AN INSITU STUDY OF CUBE GLIDE IN THE GAMMA'-PHASE OF A SUPERALLOY .2. THE ANOMALOUS STRESS TEMPERATURE-DEPENDENCE

Local stress measurements are performed on single superdislocations gliding in cube planes, in single crystals of the gamma'-phase of a CMSX2 superalloy, between 140 and 1150 K. The question is the origin of the extensive cube glide observed at very low temperatures and analysed in part I of this study. In agreement with the analysis of several macroscopic experiments in different ordered nickel-based alloys, it is found that the critical resolved shear stress of cube glide slightly increases as the temperature is increased between 140 and about 600 K. This anomalous behaviour accounts for the activation of cube glide at low temperatures. It results from an increase in the recombination energy of superpartial dislocations extended in one of the two possible intersecting octahedral planes (decrease in the complex stacking-fault energy), as the temperature is increased. This explanation is similar to that proposed earlier for the strength anomaly in the prismatic planes of beryllium. It is concluded that this new process should be taken into account in the analysis of the mechanical properties of nickel-based ordered alloys and superalloys.