Internal Friction in Plastically Deformed High-Purity NiAl Single Crystals

Abstract

High-purity stoichiometric NiAl single crystals have been prepared by crucible-free inductive zone melting and afterwards well annealed at temperatures below 1200 K. Internal friction measurements of torsionally deformed single crystals show two relaxation maxima at 500 and 800 K which anneal during the measurement. The first maximum can be assigned to the dislocation motion by kinkpair formation and the annealing to pinning of these dislocations by interstitial impurity atoms. The second maximum is attributed to the Snoek-Köster relaxation of dislocations in the presence of mobile interstitial impurity atoms and the annealing to the pinning of dislocations by vacancies. The kink-pair formation enthalpy in NiAl was estimated.