Mechanical spectroscopy of high-purity NiAl single crystals

High-purity stoichiometric NiAl single crystals have been prepared by crucible-free inductive zone melting under an Ar atmosphere. After a special annealing treatment at temperatures below 1200 K a residual resistivity ratio of better than 15 has been achieved. The crystals can be easily deformed in torsion already at room temperature. The dislocation mobility was investigated by internal-friction measurements in the temperature range 300 to 1000 K. After torsional deformation at room temperature relaxation maxima were observed at about 550 and 800 K. Their relaxation strength depends on the crystal orientation and the amplitude of the torsional vibrations. Both maxima anneal already during the measurement and vanish after annealing at 1000 K. After an additional deformation in torsion at room temperature the maxima appear again. The results are discussed in terms of dislocation relaxations and dislocation pinning.