Origin of the high temperature internal friction peak introduced by twisting deformation in aluminium single crystals and bamboo crystals

The internal friction peak appeared around 310°C (l Hz) in single crystals and bamboo crystals of high-purity aluminium introduced by twisting deformation as previously reported has been further studied especially concerning its relaxation properties. This peak is thermally-activated having a very high relaxation strength up to 0.3 and a very high activation energy of about 2 eV. The fact that the peak disappears after rapid cooling of the specimen leads to the proposition that dislocation climb does not play a dominating role to the non-elastic motion of the dislocations giving rise to this peak. TEM observations show that the stable dislocation configuration in the twisted specimen after the 600°C anneal always consists of uniformly distributed dislocation networks. Subsequent tensile deformation destructs such dislocation networks and converts it into cell structures so that the twisting peak is suppressed. It is suggested that the dislocation slip enhanced by the non-conservative shift of the node of the dislocation network contributes dominately to the high relaxation strength of the twisting peak and the dislocation climb controls the relaxation time of the relaxation process.