Molecular Dynamics Simulation of Nano-Sized Crystallization During Plastic Deformation in an Amorphous Metal
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MOLECULAR DYNAMICS SIMULATION OF NANO-SIZED CRYSTALLIZATION DURING PLASTIC DEFORMATION IN AN AMORPHOUS METAL R. TARUMI, A. OGURA, M. SHIMOJO, K. TAKASHIMA and Y. HIGO Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan ABSTRACT An NTP ensemble molecular dynamics simulation was carried out to investigate the mechanism of nano-sized crystallization during plastic deformation in an amorphous metal. The atomic system used in this study was Ni single component. The total number of Ni atoms was 1372. The Morse type inter-atomic potential was employed. An amorphous model was prepared by a quenching process from the liquid state. Pure shear stresses were applied to the amorphous model at a temperature of 50 K. At applied stresses of less than 2.4GPa, a linear relation between shear stress and shear strain was observed. However, at an applied shear stress of 2.8 GPa, the amorphous model started to deform significantly until shear strain reached to 0.78. During this deformation process, phase transformation from amorphous into crystalline structure (fcc) was observed. Furthermore, an orientation relationship between shear directions and crystalline phase was obtained, that is, two shear directions are parallel to a (111) of the fcc structure. This crystallographic orientation relationship agreed well with our experimental result of Ni-P amorphous alloy. Mechanisms of phase transformation from amorphous into crystalline structure were discussed. INTRODUCTION When a liquid metal is quenched below its melting temperature, it enters a super cooled state. If the cooling rate is so high as to suppress the nucleation and growth of crystalline phases, a solid-state metal which has a random atomic structure is obtained. This is called an amorphous metal. Amorphous metals are thermally non-equilibrium state, so that solid-state phase transformation from amorphous into nano-sized crystalline phase (crystallization) may occur not only by heat treatment but also by plastic deformation [1]. Many plastic deformation models of amorphous metal have been proposed [2-3], however these models cannot explain the mechanism of crystallization during plastic deformation. Molecular dynamics (MD) simulation is one of the most valuable tools to investigate the phenomena that are difficult to investigate experimentally. In the field of amorphous metal, several researchers have simulated the crystallization by thermal diffusion [4-5]. However, no MD simulation has been performed focused on crystallization by plastic deformation. The purpose of this study is to investigate the crystallization process during plastic deformation using a molecular dynamics simulation. Furthermore, the result of simulation was compared with our experimental result of Ni-P amorphous alloy to confirm its validity. CALCULATION METHOD Algorithm The atomic system used in this study was constructed from 1372 Ni atoms. B1.9.1
This
model was employed to compare with our experimental result of a Ni-P amorpho
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