VARIATION OF THE GRAIN-BOUNDARY RELAXATION STRENGTH WITH TEMPERATURE FOR ALUMINUM BICRYSTALS

It is found recently that the relaxation strength of grain boundary re laxation in polycrystalline and bamboo crystalline aluminium drops wit h decreasing temperature and reaches an undetectable value at a temper ature T0 which is about 1/2T(m) where T(m) is the melting temperature of bulk specimens. The existence of such a temperature T0 is confirmed lately by measurements of micro-creep and internal friction (in force d vibration) for aluminium bicrystals. These results are in conformity with those obtained by molecular dynamics simulation. According to th e grain boundary model of disordered atom groups, the relaxation stren gth of the grain boundary relaxation varies with the number of disorde red groups existing in the grain boundary and the degree of disorder o f each group. Consequently the existence of a temperature T0 reflects a pronounced transition of the grain boundary structure from the CSL m odel to that of disordered atom groups.