Observation of dislocation relaxation peaks in aluminum

To study the damping mechanism of dislocation relaxations in aluminum, internal friction of a high purity aluminum crystal was measured for the frequency of 50 kHz at the temperatures between 2 and 240 K. There were three temperature regions of dislocation peaks, i.e. the Bordoni relaxation (Bordoni peak around 180 K and Niblett-Wilks peak around 120 K), Lax-Filson peak around 35 K, and the 11 K peak. The change of the peak temperatures with slight deformation and annealing was checked in the light of the prediction of kink pair formation (KPF) mechanism. As a result, the 11 K peak shifted to 10 K with subsequent deformation and returned to 11 K with annealing. This agrees with the prediction of KPF mechanism. For the Bordoni relaxation, however, the Bordoni peak shifted to lower temperature and did not return to the original temperature through subsequent deformation and annealing, which cannot be explained by the KPF mechanism.