Cu-Ni合金结构的分子动力学模拟

采用EAM作用势对Cu Ni合金的结构特性进行了MD模拟研究 .通过FZ结构因子可发现 ,Cu含量的变化对结构因子的波动影响很小 ,键取向序参数和键对也表现出相似的变化规律 ,这表明液态Cu Ni合金对成份变化不敏感 ,体系中的化学序较弱 .将Cu70 Ni3 0 合金熔体的FZ结构因子与Waseda的实验结果进行对比 ,发现二者吻合得较好 ,表明EAM势可以很好地描绘Cu Ni合金的结构特性 .在快速冷却过程中 ,除了Cu2 0 Ni80 合金外 ,其他合金成份的双体分布函数的第二峰都发生了劈裂 ,标志着体系最终形成了非晶结构 ,而Cu2 0 Ni80 合金的双体分布函数却表现出晶体峰的特征 .通过对键取向序参数、键型指数以及铜镍原子的有效扩散系数的分析表明 ,在快速冷却过程中 ,Cu2 0 Ni80 合金最终形成了hcp晶体结构     

Al70Cu30合金液态RDF高斯分解与局域结构计算

运用密度泛函B3LYP方法对Al_mn₃₀(m，n≤4)团簇结构进行量子化学计算，得到团簇的稳定构型。对不同温度下X-射线衍射实验所得的径向分布函数(RDF)在0.2～0.4nm范围内做高斯分解，结合计算结果对高斯峰的意义做了解释，认为计算所得部分团簇构型可以代表Al₇₀Cu₃₀合金熔体的内部局域结构。     

Reverse Monte Carlo study on structural order in liquid and glassy AlFe alloys

This paper reports that anomalous local order in liquid and glassy AlFeCe alloy has been detected by x-ray diffraction measurements. The addition of the element Ce has a great effect on this local structural order. The element Ce favours interpenetration of the icosahedra by sharing a common face and edges. It argues that frustration between this short-range order and the long-range crystalline order controls the glass-forming ability of these liquids. The obtained results suggest that a system having a stronger tendency to show local icosahedral order should be a better glass-former. This scenario also naturally explains the close relationship between the local icosahedral order in a liquid, glass-forming ability, and the nucleation barrier. Such topological local order has also been analysed directly using the reverse Monte Carlo method. It also estimated the fraction of local ordered and disordered structural units in a glassy AlFeCe alloy.     

金属Cu熔化结晶过程的分子动力学模拟

采用常温、常压分子动力学模拟技术,研究了在周期性边界条件下,由８６４个Ｃｕ原子构成的模型系统的熔化、结晶过程。原子间相互作用势采用ＥＡＭ势。模拟结果表明：在连续升温过程中,金属Ｃｕ在１５２０Ｋ熔化;以不同的冷速进行冷却,在较慢冷却条件下,液态Ｃｕ在１０１０Ｋ结晶;当冷速较快时,液态Ｃｕ形成非晶态。分析了升降温过程中熔体偶分布函数、原子体积、能量、ＭＳＤ随温度的变化特征。     

Cu-Ni合金结构的分子动力学模拟

采用EAM作用势对Cu-Ni合金的结构特性进行了MD模拟研究.通过FZ结构因子可发现,Cu含量的变化对结构因子的波动影响很小,键取向序参数和键对也表现出相似的变化规律,这表明液态Cu-Ni合金对成份变化不敏感,体系中的化学序较弱.将Cu70Ni30合金熔体的FZ结构因子与Waseda的实验结果进行对比,发现二者吻合得较好,表明EAM势可以很好地描绘Cu-Ni合金的结构特性.在快速冷却过程中,除了Cu20Ni80合金外,其他合金成份的双体分布函数的第二峰都发生了劈裂,标志着体系最终形成了非晶结构,而Cu20Ni80合金的双体分布函数却表现出晶体峰的特征.通过对键取向序参数、键型指数以及铜镍原子的有效扩散系数的分析表明,在快速冷却过程中,Cu20Ni80合金最终形成了hcp晶体结构.     

中介尺度Au纳米团簇凝固过程的分子动力学模拟

采用分子动力学模拟技术,研究了原子个数N=1088的Au纳米团簇的凝固过程的微观结构、热力学和动力学参数的变化.模型采用的是Johnson的EAM作用势.模拟结果表明:液态团簇在两种不同的冷速下冷却得到两种不同的固态组织:晶体团簇和非晶团簇.当冷速为1.5625×1013K/s时,能量随温度的变化呈线性关系,且偶分布函数的第二峰发生劈裂,体系形成非晶态;当冷速为1.5625×1012K/s时,能量-温度曲线上出现拐点,且偶分布函数显示明显的晶体峰特征,说明体系形成了晶体.另外,计算了不同冷速下原子的平均平方位移随温度的变化,发现原子位置的重排对冷却速度非常敏感.当冷速较快时,原子只在很小的范围内运动;而结晶过程是原子不断扩散重新排列的过程.     

Nanocrystallization behaviour of a ternary amorphous alloy during isothermal annealing： a Monte Carlo simulation

The nanocrystallization behaviour of Zr70Cu20Ni10 metallic glass during isothermal annealing is studied by employing a Monte Carlo simulation incorporating with a modified Ising model and a Q-state Potts model. Based on the simulated microstructure and differential scanning calorimetry curves, we find that the low crystal-amorphous interface energy of Ni plays an important role in the nanocrystallization of primary Zr2Ni. It is found that when T〈T1max （where T1max is the temperature with maximum nucleation rate）, the increase of temperature results in a larger growth rate and a much finer mierostrueture for the primary Zr2Ni, which accords with the microstructure evolution in ＂flash annealing＂. Finally, the Zr2Ni/Zr2Cu interface energy σG contributes to the pinning effect of the primary nano-sized Zr2Ni grains in the later formed normal Zr2Cu grains.     

Medium-Range Order Structure and Fragility of Superheated Melts of Amorphous CuHf Alloys

The structural factors of amorphous CuHf alloys at different temperatures are determined by using a high temperature x-ray diffractometer. It is found that not only the short-range order structure but also the medium-range order structure exists in amorphous CuHf alloys. The dynamic viscosities of CuHf alloy melts are measured by a torsional oscillation viscometer. The fragility of superheated melts of CuHf alloys is calculated based on the viscosity data. The experimental results show that the glass-forming ability of the CuHf alloys is closely related to the fragility of their superheated melt. The relationship between the medium-range order structures and the fragility of superheated melts has also been established in amorphous CuHf alloys. In contrast to the fragility of supercooled liquids, the fragility of superheated liquids promises a better approach to reflecting the dynamics of glass forming liquids.     

Cu3Au合金熔体的中程有序结构

采用紧束缚(Tight-binding,简称TB)原子间相互作用势,利用分子动力学模拟(Molecular Dynamics,简称MD)的方法研究了Cu₃Au合金熔体的微观结构,发现Cu₃Au合金体系在高于熔点以上的400K～500K的温度范围内,结构因子上存在预峰,且在此范围内,随着温度的升高,预峰的强度逐渐降低。当温度超过1764K时,预峰开始消失。通过Lorentzian近似和Scherrer公式,可得预峰所对应的原子团簇尺寸位于1.35nm～1.85nm之间,属于中程有序结构范畴。Bhatia-Thornton(BT)偏结构因子表明,预峰的起源应归咎于体系中存在的化学序与拓扑序。BT形式的双体分布函数也证实,体系中存在着较强的化学序,且团簇中原子间的配位倾向于同类原子的配位。     

二元合金Ag50Rh50从液态到非晶的分子动力学计算

本文对贵重金属银铑合金Ag50Rh50的液态结构和激冷过程进行了分子动力学模拟研究,原子间作用势采用紧束缚势,模拟在施加了周期性边界折常压状态下进行。采用了偶关联函数,键对分析技术和键取向序参, 分子动力学模拟计算方法揭示了Ag50Rh50的液态结构存在原子偏聚特征以及在快速凝固过程形成原子偏聚的不均匀非晶,并与同族过渡金属进行了非晶形成能力的比较。