The internal friction peak observed during martensitic transformation in copper-zinc-aluminum (Cu-Zn-Al) alloys has been analyzed in terms of the Delorme's model. This analysis performed on specimens with different austenitic microstructures and thermomechanical treatments demonstrates that the transient part of the internal friction peak cannot be completely explained by the transformation rate. It rather depends on the microstructural properties of the martensitic phase and especially on the austenite-martensite interface density, which has been derived semi-quantitatively from the fractal geometry.
Local transformation studies, including partial temperature cycling programs (PTC) and isothermal measurements (T effect) in the hysteresis regime, show that internal stresses cause additional contributions to the measured internal friction. It has been found that the loss of damping when stopping the temperature change can easily be restored by small temperature variations.