Characteristics of 〈111〉 slip in a NiAl [001] single crystal

Abstract

This paper reports experiments on 〈111〉 slip in a NiAl single crystal. Specimens in the [001] orientation were compressed in the temperature range 4.2–100K in which 〈111〉 slip occurred without the interference of kinking. The yield strength was independent of temperature between 4.2 and 45 K and decreased slowly with increasing temperature between 45 and 100K. Cross-slip between {110} and {112} occurred over the entire temperature range investigated and was most frequent at 4.2 K. Lattice resolution transmission electron microscopy observations of 〈111〉 screw dislocations did not reveal any dissociation. Serrated flow occurred between 4.2 and 20 K and was not caused by the locking of dislocations by interstitial solute atoms. The activation volume was measured to be 3b ³. The observation of cross-slip at temperatures as low as 4.2 K provides indirect experimental evidence for a highly compact core structure of 〈111〉 screw dislocations. The temperature-independent yield strength at low temperatures was discussed in terms of both thermally activated slip and quantum-mechanical tunnelling, neither of which could explain satisfactorily the temperature independence and the strain-rate sensitivity of the yield strength.