Kinetic Calculation of L1 0 Ordered System Based on Phase Field Methodand Cluster Variation Method
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KINETIC CALCULATION OF L10 ORDERED SYSTEM BASED ON PHASE FIELD METHOD AND CLUSTER VARIATION METHOD M. Ohno and T. Mohri Division of Material Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628 Japan ABSTRACT During ordering process, anti-site ordering proceeds in atomistic scale and anti-phase domain structure evolves in microstructural scale. In order to describe both the processes, a hybridized calculation of the Phase Field Method(PFM) and Cluster Variation Method(CVM) is attempted. The main objective of the present study is focused on the time evolution of atomic configuration during L10 ordering processes below and above the spinodal ordering temperature and their resultant microstructures. In order to investigate the interplay between atomistic and microstructural processes, we conducted two types of calculations. One is for a homogeneous system without an anti-phase boundary and the other is for an inhomogeneous system in which microstructure is formed by anti-phase domains. For the homogeneous system, the relaxation curve of Long-Range-Order parameter(LRO) indicates a transient appearance of an L12-like atomic configuration below the spinodal ordering temperature. Such an L12–like state corresponds to a saddle point configuration in the CVM free energy surface. When the composition of an alloy is located near L10 + L12 phase field in the phase diagram, the L12–like phase becomes highly ordered state. For the inhomogeneous system, it is implied that the appearance of the L12-like phase affects the resultant microstructure by providing the nucleation sites for the L10 ordered phase. INTRODUCTION Various properties including physical, mechanical and thermal properties of an intermetallic alloy are critically influenced by both an atomic configuration within an ordered domain and a microstructure which consists of numerous ordered domains separated by anti-phase boundaries (APB). The formation of a microstructure during a non-equilibrium process is driven by atomic movements followed by the motion of APB. Hence, it is necessary to describe both the atomistic and APB processes simultaneously in order to investigate microstructural evolution of an intermetallic alloy. For the past several years, a great progress has been made in a theoretical study of the microstructural evolution process. In particular, the theoretical calculation using the Phase Field Method (PFM) has been successfully extended to a wide range of inhomogeneous phenomena[1, 2]. However, the atomistic information of the system is by no means derived by the conventional PFM. Recently, in order to circumvent such a deficiency of PFM and to describe the atomistic and microstructural evolution processes simultaneously, the PFM is hybridized with the Cluster Variation Method (CVM) which has been regarded as a most reliable theoretical tool to provide detailed information of atomic configuration[3, 4]. The hybridized calculation of the PFM and the CVM has been applied to B2-disorder and L10-disorder t
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