Assessing the nature of martensitic transformations in alloys from an ab initio perspective

Alberto Ferrari, ICAMS, Ruhr-Universität Bochum, Bochum, Germany
Davide Sangiovanni, IFM, Linköping University, Linköping, Sweden
Jutta Rogal, ICAMS, Ruhr-Universität Bochum, Bochum, Germany
Ralf Drautz, ICAMS, Ruhr-Universität Bochum, Bochum, Germany

The peculiarity of shape memory materials is to exhibit extremely reversible martensitic transformations (MTs) when temperature or stresses are applied. Modelling these materials from first principles is not trivial, since static calculations are usually not sufficient to explore the most important aspects of the MTs, such as the Ehrenfest order of the phase transitions, their temperature hysteresis and their free energy barrier. In this contribution, a fully ab initio strategy to characterize MTs in alloys is presented. The temperature dependent order parameters of a MT are calculated with ab initio molecular dynamics; then, the free energy of the MT, from which all the thermodynamic properties relevant for the MT can be derived, is modelled with a Landau-like polynomial expansion. This approach is applied to the high-temperature shape memory Ti-Ta alloy, for which exceptionally small values for the free energy barrier and temperature hysteresis are observed.

« back