Experiments were performed on <111> slip in single crystals. Specimens having the [001] orientation were compressed at 4.2 to 100K, where <111> slip occurred without any interference from kinking. It was noted that the yield strength was independent of temperature between 4.2 and 45K, and decreased slowly with increasing temperature, between 45 and 100K. Cross-slip between {110} and {112} occurred over the entire temperature range, but was most frequent at 4.2K. Lattice-resolution transmission electron microscopic observations of <111> screw dislocations did not reveal any dissociation. Serrated flow occurred between 4.2 and 20K, and was not caused by the locking of dislocations by interstitial solute atoms. The activation volume was deduced to be 3b3. The observation of cross-slip at temperatures as low as 4.2K provided indirect experimental evidence for a highly compact core structure in <111> screw dislocations. The temperature-independent yield strength at low temperatures was explained in terms of thermally activated slip and quantum-mechanical tunnelling. Neither of these could satisfactorily explain the temperature independence and strain-rate sensitivity of the yield strength.

Characteristics of <111> Slip in a NiAl [001] Single Crystal. Y.Q.Sun: Philosophical Magazine A, 2000, 80[2], 447-65