Influence of thermal treatments on the mechanical properties and the martensitic transformation in Fe-Pd-Mn ferromagnetic shape memory alloy

The effects of high temperature thermal treatments on the hardening behaviour, the damping capacity and the martensitic transformation in Fe66.8Pd30.7Mn2.5 Ferromagnetic Shape Memory Alloy have been determined by mechanical spectroscopy. Annealing below 753 K, lead to a hardening of the alloy without a marked decrease in the damping capacity. In addition, they increase both the austenite finish transformation temperature and the intensity of the damping peak related to the martensitic transformation. This variation can be controlled by the small volume fraction precipitation of small α phase particles. In contrast, thermal treatments performed above 753 K lead to a further hardening of the alloy, but they decrease the austenitic finish transformation temperature and the intensity of the damping peak related to the martensitic transformation; as a consequence of the decomposition of the metastable γ phase into the α+γ1 stable phases. In addition, two new damping peaks related to the mobility of dislocations and grain boundaries have been discovered at around 700 K and 900 K, respectively.