Effect of quenching and subsequent neutron irradiation on grain boundary relaxation peak

The effects of quenching and subsequent neutron irradiation on the internal friction of annealed polycrystalline aluminium wires(specpure) have been investigated as the temperature is varied. Internal friction has been measured from observations of free torsional vibrations. The main observation is that the grain boundary internal friction peak in case of quenched and subsequently irradiated sample is depressed and shifted towards a lower temperature with respect to that for the annealed sample. An attempt has been made to explain this effect in terms of reorientation of impurity-trapped dump-bell interstitial-vacancy pairs and the consequent migration and segregation of the impurity atoms at the grain boundaries. The experimentally determined value of the activation energy for reorientation by rotation of these defect complexes is found to be (0.045 +- 0.005) eV. (author)