ATOMISTIC INVESTIGATIONS OF THE THERMODYNAMICAL STABILITY AND MARTENSITIC NUCLEATION OF FE 80 NI 20 NANOPARTICLES K. KADAU * and P. ENTEL Theoretische Tieftemperaturphysik, Gerhard-Mercator-Universit¨at, 47048 Duisburg, Germany (Received ...) Abstract The study of the thermodynamical stability of Fe 80 Ni 20 nanopar- ticles in the framework of embedded-atom method and molecular- dynamics simulations shows evidence of large surface contributions to the free energy for particles with diameters up to 15 nm or more. The change of the free energy compared to its bulk value leads to a reduc- tion of the martensitic equilibrium temperature, M 0 , and can suppress martensitic transformations in small particles. In addition the forma- tion of martensite can be suppressed due to the lack of pre-existing nucleation sites necessary to overcome the energy barrier along the transformation path from austenite to martensite. Keywords: Fe–Ni nanoparticles, Martensitic transformation, Molecular-dynamics simulations 1. INTRODUCTION Early experimental investigations by Cech and Turnbull (1957) of Fe-Ni alloy powder showed a reduction of the martensitic transformation temperature, M s , or even the suppression of the transformation in particles of some 10 μm in diameter (Wayman and Bhadeshia, 1996; Delaey, 1991). They interpreted * Corresponding author, tel. +49-203-3792794, fax: +49-203-3793665, email: kai@thp.uni-duisburg.de 1