Study of Structural and Phase Transition of Nickel Metal

Annealing study of nickel metal in the temperature range 300–1000？K has been carried out using molecular dynamics (MD) simulations. The simulation is done for models containing 104 particles Ni at both crystalline and amorphous states. We obtain the change as a function of annealing time for the potential energy of system, pair radial distribution function (PRDF), and distribution of coordination number (DCN). The calculation shows that the aging slightly reduces the potential energy of system. This result evidences that the amorphous model undergoes different quasiequilibrated states during annealing. The crystalline model undergoes the slow relaxation which reduces the energy of system and eliminates structural defects in crystal lattices. 1. Introduction The structure and atomic mechanism of glass formation from liquid metal have been under intensive study from both experiment and computer simulation. By using different diffraction techniques as X-ray and neutron diffraction or turning electronic microscopic, experiment data has provided the important information of structural general arrangement of metals through the RDF and structure factor. Both functions have splitting second peak, which was usually thought to be related to the existence of local icosahedral in amorphous state [1–7]. Based on the MD simulation, Liu et al. [6] suggested that a laboratory or simulated metallic glass is generally a distorted metallic solid including a significant amount of icosahedral, each consisting of 13 atoms; that is, every atom in metallic glass has 12 atoms in its first-neighbor shell to form an icosahedral. On the other hand, Lopez suggested that the shoulder of RDF indicates the presence of two displaced atoms. At higher temperature this presence is washed out by thermal averaging [7]. However, the atomic mechanism of amorphous formation from liquid state is still not well understood. In addition, we found only few works concerning this problem. In addition, our understanding of the atomic mechanism in crystalline and liquid states is still limited. From MD simulation study, Solhjoo et al. showed that during solidification of aluminum, a crystalline and amorphous-like structure is formed depending on the cooling rate [8]. Ozgen and Duruk [9] showed that when the slow cooling process is applied continuously, not gradually, the systems firstly have a tendency of complex arrangement in cluster level at the glassy transition temperature, and, again, it returned to liquid state since they have an energetically unfavorable structure. Sarkar et al. revealed that