Analysis of the low frequency damping observed at medium and high temperatures

Isothermal internal friction measurements performed versus frequency exhibit often a large damping rise at very low frequency (10−2 to 10−4 Hz). This increasing is found for experiments at very high temperature above 0.7TM, (TM=melting point) similarly to the so-called high temperature background obtained during measurements at fixed frequency and often described in the literature. In some cases, as for instance in cold work metals or metallic alloys, such low frequency background occurs at lower temperature (0.3 TM<T<0.7TM) and disappears after high temperature sample annealing. This exponential background depends on the sample microstructure and can be analysed with the Schoeck’ model. On the contrary, experiments performed at temperature close to the melting point or the liquidus temperature for metallic alloys exhibit a peak. The high temperature background measured for instance at 1 Hz, is only the lower part of a peak and does not correspond to an exponential increase. This fact explains why none of the different expressions proposed in the literature is able to describe properly the experimental high temperature background.