INTERNAL-FRICTION IN NIAL SINGLE-CRYSTALS

High-purity NiAl single crystals with a stoichiometric composition hav e been prepared by crucible-free inductive zone melting under an Ar at mosphere. The internal friction was investigated in the temperature ra nge from 300 to 1400 K utilizing a low-frequency subresonance torsion apparatus operating in forced vibrations. In undeformed NiAl single cr ystals the internal friction exhibits above 1000 K a strongly increasi ng and frequency-dependent damping up to Q(-1) = 0.3 at 1400 K. After plastic deformation a maximum at around 1250 K (0.1 Hz) is superimpose d on this high-temperature damping. The activation enthalpy for the hi gh-temperature increase was determined to be 2.65 +/- 0.2 eV and for t he superimposed maximum to be 2.9 +/- 0.2 eV. The results are discusse d in terms of the diffusion-controlled climb of dislocations by vacanc ies.