Thermodynamics of thermally induced martensitic transformations in Cu–Al–Ni shape memory alloys Original Research Article

The dependence of martensitic transformation characteristics on the type (β′, γ′ or β′+γ′) of thermally induced martensite has been studied in Cu–Al–Ni shape memory alloys. The energy balance of the martensitic transformation (MT) has been analyzed for the three possible transformations by calorimetric measurements. When a single MT, β→β′ or β→γ′ is present, the dissipative term linked to the irreversible entropy Si has been evaluated. This term that accounts for the hysteresis is higher for the β→γ′ transformation than for the β→β′ one, according to the hysteresis behavior. On the other hand, during mixed β→γ′+β′ transformation, a higher irreversible entropy and a negative total exchanged heat have been measured. In order to explain this behavior, a modification of the energy balance, which takes into account the presence of plastic deformation when martensite coexistence occurs, has been proposed.