Martensitic transformation in an inhomogeneous off-stoichiometric Ni–Mn–Ga alloy

Inhomogeneities in the Ni–Mn–Ga alloy cause local changes in the structure. At room temperature, due to the broad range of transition temperatures, the structure of the parent phase, the modulation, and the martensite can be simultaneously observed by transmission electron microscopy (TEM). The kinetic hysteresis curves of the martensitic transformation recalculated from differential scanning calorimetry results showed a continuous evolution of the transition in contrast to the curves of internal friction and elastic-modulus obtained by dynamic mechanical analysis (DMA). Two peaks of the internal friction and related elastic-modulus minima on the DMA curves could be explained by using TEM and X-ray diffraction results to be attributed to the 10M and 14M martensite formation.