Martensite-austenite transition and phonon dispersion curves ofFe1−xNixstudied by molecular-dynamics …

We have done molecular-dynamics simulations of ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}$ employing a semiempirical model. We present a phase diagram of the martensite-austenite transition temperatures as a function of the Ni concentration which is in good agreement with experimental observations. In addition to this we have calculated the phonon dispersion curves of Fe and Ni from the model. Results show that the vibrational properties of the metals are well reproduced by the embedded-atom-method potentials. Finally, we have derived the phonon dispersion relations of bcc ${\mathrm{Fe}}_{80}{\mathrm{Ni}}_{20}.$ We find rather low energies of the $[110]\ensuremath{-}{\mathrm{TA}}_{1}$ phonons with a strong temperature dependence which we attribute to instabilities of Ni in the bcc phase. We do not find any indications of a soft mode at the martensite-austenite transition in ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}.$