MECHANISM OF THE BAMBOO BOUNDARY INTERNAL-FRICTION PEAK

At the beginning of the 1980s, an internal friction peak situated belo w the optimum temperature of the grain boundary peak of fine-grained s pecimens (the Ke peak) was observed in high-purity aluminium consistin g of bamboo crystals. This discovery has given rise to much controvers y, and the opinion has been expressed that this peak is only the Ke pe ak shifted toward lower temperature, and is not a new peak. However, o ur systematic study shows that the behaviour of this peak is quite dif ferent from that of the Ke peak. Recently, the bamboo boundary interna l friction peak and the Ke peak were observed separately on one intern al friction curve in sheet specimens consisting of mixed grains. This shows that the bamboo boundary peak is a new peak. TEM observations sh owed that dislocation substructures exist near the bamboo boundaries. Accordingly, we propose that such substructures intersecting and inter acting with the bamboo boundaries are dragged along with the bamboo bo undary during the viscous sliding of the boundary, so that the sliding process is limited with the appearance of an internal friction peak. A four-parameter mechanical model is suggested for describing the rela xation behavior of the bamboo boundary peak. The mathematical formulat ions and the experimental conditions for the appearance of the bamboo boundary peak derived according to this model agree with experiments.