Authors: K. Kadau, P.S. Lomdahl, P. Entel, D. Kadau, M. Kreth, T.C. Germann, B.L. Holian, F. Westerhoff and D.E. Wolf
Affilation: Los Alamos National Laboratory, United States
Pages: 338 - 339
Keywords: molecular dynamics, sintered nanoparticles
Nano-crystalline metals, in which the size of grains is in the nanometer range, exhibit physical properties different from ordinary polycrystalline materials, thus these materials are of technological interest . One example is the increasing hardness with decreasing grain size due to dislocation immobilisation at the grain boundaries (Hall-Petch effect). However when decreasing the grain size below a critical value, sliding processes between the grains decrease the hardness which is called the reverse Hall-Petch effect [2, 3]. Another interesting aspect is the phase stability of a polymorphic material and structural phase transitions such as martensitic transformations in Fe-based alloys  in nano-crystalline materials. Here we report on the first molecular-dynamics simulations  in combination with contact-dynamics . We used the contact-dynamics method to determine the arrangement of a number of particles with a given size-distribution. Using this arrangement as the initial configuration of randomly oriented nano-particles and modeling the sintering-process on the atomic scale within the framework of molecular-dynamics simulations, where the atomic interactions were described by an embedded-atom method (EAM) potential specially designed to model the Fe-Ni alloy [8, 7] and Al . After a simulation time of some 100 ps a more or less dense polycrystal has formed, whereas the density depends on the temperature and pressure. Interesting physical properties of the formed nano-phase material such as the afore mentioned reverse Hall-Petch effect and martensitic transformations were studied and compared to single-crystals.
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