Martensitic Ni-Ti was observed to transform to the austenitic phase due to defects introduced either by ion or electron irradiations at a temperature where the martensitic phase is normally stable. The phenomenon was studied by molecular dynamics simulation in the Ni-Al shape memory alloy system where theoretical model potentials are well established. The simulations show that defects reduce the martensitic phase transition (MPT) temperature, and the high temperature austenite phase is favored. In the Ni-Al system, the difference of phase transition temperatures with and without defects is about 100 K. (c) 2006 Elsevier B.V. All rights reserved.