The track evolution of ions with energies Ei > ~ 100 MeV results in various phase transformations in a martensite phase as e.g. crystal-liquid-glass-crystaltransitions, martensite transformations or compositional order-disorder transformations. They occur at length scales of ~10 nm from track centre and at time scale of up to 1 ns. In order to get more insight in these phenomena we perform molecular dynamics simulations of phase transformations in a model NiAl alloy. The advantage of the Ni-Al system is that the embedded atom potentials are known. We start with the study of the thermodynamics and kinetics of this model alloy. We observe a wide hysteresis on the temperature dependence of the free energy at cooling and heating of initially B2 ordered alloy with composition ranges from 60 to 65 at. % of Ni. A strong influence of cylindrical and spherical extended defects on the character of martensite phase transformations in this alloy is observed. In order to distinguish the structural changes during the phase transformations we use a new approach for the determination of local order parameter of the alloy undergoing structural rearrangements. This method is based on combination of Voronoy tessellations and the common-neighbor analysis. Also, the basis of an analysis of local chemical order changes is discussed. Such method has been applied for local order-disorder transformations modelled by MC simulations.

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