THE INTERNAL FRICTION OF SINGLE CRYSTALS, BICRYSTALS AND POLYCRYSTALS OF PURE MAGNESIUM

The internal friction of magnesium single crystals, bicrystals and polycrystals has been studied between room temperature and 450 degrees C. There is no internal friction peak in the single crystals, but a prominent relaxation peak appears at around 160 degrees C in polycrystals. The activation energy of the peak is 1.0 eV, which is consistent with the grain boundary self-diffusion energy of Mg. Therefore, the peak in polycrystals can be attributed to grain boundary relaxation. For the three studied bicrystals, the grain boundary peak temperatures and activation energies are higher than that of polycrystals, while the peak heights are much lower. The difference between the internal friction peaks in bicrystals and polycrystals is possibly caused by the difference in the concentrations of segregated impurities in grain boundaries.