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 = 1.45 ± 0.05 (−60 °C) to = 1.20 ± 0.15 (50 °C) at a driving rate of , and the total acoustic energy decreased by three orders of magnitude with increasing temperature. In addition, the exponent γ in the scaling relation SAE~DAEγ (SAE is the area and DAEis the duration) also shows similar temperature dependence (changing from γ = 1.78 ± 0.08 to γ = 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, τa, was determined as τa≅ 70 μs.
General form of the well known-relation between the critical stress, necessary to start/finish martensite/austenite formation, and the test temperature is simply and plausibly obtained from our local equilibrium model of phase transformation [1], and compared to the classical forms of the Clausius-Clapeyron relation. Although in general, first of all because of the stress and temperature dependence of the transformation strain, εtr, the above relations are not inevitably linear, in most of the cases linear functions were observed. Using the results of our experiments carried out on single crystalline Cu-11.5wt%Al-5.0wt%Ni samples for the strain stress hysteretic loops at constant temperatures [2], the slopes of these functions are analyzed on the basis of the relations obtained and it is shown that these are different due to different stress dependence of the elastic energy contributions.
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