Change of Acoustic Emission Characteristics during Temperature Induced Transition from Twinning to Dislocation Slip under Compression in Polycrystalline Sn

In this study, acoustic emission (AE) measurements on polycrystalline tin as a function of temperature at different driving rates under compression were carried out. It is shown that there is a definite difference between the acoustic emission characteristics belonging to twinning (low temperatures) as well as to dislocation slip (high temperatures). The stress averaged values of the exponents of the energy probability density functions decreased from epsilon = 1.45 +/- 0.05 (-60 degrees C) to epsilon = 1.20 +/- 0.15 (50 degrees C) at a driving rate of epsilon=0.15 s-1, and the total acoustic energy decreased by three orders of magnitude with increasing temperature. In addition, the exponent gamma in the scaling relation S-AE similar to D-AE(gamma) (S-AE is the area and D-AE is the duration) also shows similar temperature dependence (changing from gamma = 1.78 +/- 0.08 to gamma = 1.35 +/- 0.05), illustrating that the avalanche statistics belong to two different microscopic deformation mechanisms. The power law scaling relations were also analyzed, taking into account that the detected signal is always the convolution of the source signal and the transfer function of the system. It was obtained that approximate values of the power exponents can be obtained from the parts of the above functions, belonging to large values of parameters. At short duration times, the attenuation effect of the AE detection system dominates the time dependence, from which the characteristic attenuation time, tau(a), was determined as tau(a) approximately equal to 70 mu s.