深過(guò)冷液態(tài)金屬Cu的熱物理性質(zhì)和原子分布

深過(guò)冷液態(tài)金屬Cu的熱物理性質(zhì)和原子分布Thermophysical properties and atom distribution of undercooled liquid Cu

采用分子動(dòng)力學(xué)方法結(jié)合修正的嵌入原子勢(shì)研究了液態(tài)Cu的熱物理性質(zhì)和原子分布規(guī)律，包括熔點(diǎn)、密度、比熱和自擴(kuò)散系數(shù)，溫度范圍為800~2400 K，最大過(guò)冷度達(dá)到556 K。發(fā)現(xiàn)液態(tài)Cu的焓隨溫度呈線性關(guān)系變化，自擴(kuò)散系數(shù)隨溫度呈指數(shù)關(guān)系變化，而比熱則幾乎不隨過(guò)冷度的變化而變化。采用雙體分布函數(shù)研究了液態(tài)Cu的原子分布規(guī)律，發(fā)現(xiàn)液態(tài)體系原子短程有序度隨溫度升高而降低，短程有序結(jié)構(gòu)僅保持在3~4個(gè)原子間距范圍內(nèi)，且隨間距增大而展現(xiàn)出無(wú)序特征。

Due to the limitation of experiments, it is difficult to obtain thermophysical properties of metastable undercooled liquid mental. Thus theory prediction is becoming an expected method to obtain the thermophysical data of high undercooling liquid metal. Molecular dynamics simulation is a computer method for studying multi-body system which atoms and molecules are allowed to interact for a fixed period of time, then the physical movements of atoms and molecules could be given. Copper is commonly used for electrical applications because of high ductility, electrical and thermal conductivity. In this paper, the atom distribution and thermophysical properties including melting temperature, density, specific heat and self-diffusion coefficient of liquid copper have been studied by molecular dynamics simulation. Mishin and Zhou’S embedded-atom method potential, and the modified embedded-atom method potential proposed by Bakes are used over the temperature range of 800~2400 K, the maximum undercooling is 556 K. The simulated results are in good agreement with the reported experimental results and simulated results. The crystal-liquid-crystal structures is used to simulate the melting point. As to the density, it’s can be easily calculated from the mass and the volume. The enthalpy of the system could be received from the internal energy, pressure and volume. It is found that the enthalpy increases linearly with the rise of temperature. We can get the specific heat from the derivation of enthalpy, specific heat hardly changes with the variation of the undercooling degree. The mean square displacement is a measure of the deviation time between the position of atoms and reference positions. From the first derivative of the MSD at different temperatures, the self-diffusion coefficient can be obtained. The calculated self-diffusion coefficient is exponentially dependent on the temperature. The structure of liquid copper changes with the temperature, so the pair distribution function is applied to investigate the atom distribution. The pair distribution function tends to 1 with the increase of the separation between two atoms, and it describes the distribution of distances between two atoms. It indicates that the atomic ordered degree is weakened with the rise of temperature in the short atomic range. The system is ordered within 3~4 atom neighbor distance.

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