Computer simulations of martensitic transformations in NiAl alloys

Ni1-xAlx alloys in the concentration range 34% < x < 40% exhibit a martensitic transformation from an austenitic phase with bcc structure to a close-packed structured martensitic phase. Above the transformation temperature electron microscopy shows the occurrence of tweed like structures which are accompanied by a considerable softening of the phonon energies at q = 1/6[1 1 0] - TA(2). We have done molecular dynamics simulations employing a semi-empirical model which allows us to study the transformation on an atomistic length scale, Our results show that local distortions of the crystal lattice, which come from the atomic disorder of the alloys, are responsible for the occurrence of tweed phenomena. Copyright (C) 1998 Elsevier Science B.V.