A new quantitative approach to the thermoelastic martensitic transformation: The density of elastic states

A thermodynamic study, based on high-sensitivity adiabatic calorimetry, of the martensitic transformation undergone by Cu–Al–Ni shape memory alloys is presented. From the specific heat data, the thermodynamic function values, and in particular the crystal free energy, as functions of temperature, have been obtained. These results have permitted a careful estimation of the phase transformation temperatures of each β3′ martensite plate as a function of its stored elastic energy. Within this frame, the distribution density of the elastic energy states in the martensitic phase is directly derived from the specific heat data. It also permits a simple analysis of the nucleation processes and gives a convincing explanation of the temperature memory effects.