纳米MgO微晶的热分析特性和晶格畸变

对纳米MgO微晶的系列样品进行了差热分析（DTA）测量和X射线衍射（XRD）实验研究。结合所获得的晶粒度和XRD微结构参数，发现纳米晶MgO的晶粒组元中存在着晶格畸变；随着温度的升高，纳米MgO晶粒长大且其微结构呈现出明显的变化，其晶格畸变与晶粒度有着比较密切的关系。     

纳米晶体Fe2O3点阵参量的研究

对γ相和α相纳米晶体Fe_2O_3的系列样品进行了X射线衍射点阵参量实验研究和计算。结合所得到的晶粒度和微结构参数，发现纳米晶体Fe_2O_3的晶粒组元中存在着晶格畸变；随着温度的升高，γ相和α相纳米晶体Fe_2O_3的点阵参量呈现出了明显的变化，其晶格畸变与晶粒度和温度有较密切的关联。     

Dynamic Failure Behavior of Nanocrystalline Cu at Atomic Scales

Large-scale molecular dynamics (MD) simulations are used to investigate the effects of microstructure and loading conditions on the dynamic failure behavior of nanocrystalline Cu. The nucleation, growth, and coalescence of voids is investigated for the nanocrystalline metal with average grain sizes ranging from 6 nm to 12 nm (inverse Hall-Petch regime) for conditions of uniaxial expansion at constant strain rates ranging from 4x107 s - 1 to 1010 s - 1. MD simulations suggest that the evolution of voids can be described in two stages: The first stage corresponds to the nucleation of voids and the fast linear initial growth of all the individual voids. The second stage of void growth corresponds to the steady (slower) growth and coalescence of the void aggregates/clusters. The evolution of void fraction is found to be strongly dependent on the loading strain rates, but is less dependent on the grain size of the nanocrystalline metal. Higher strain rates require larger plastic strains to nucleate voids, whereas the larger grain sizes require lower plastic strains to nucleate voids in the inverse Hall-Petch regime. The spall strength of the nanocrystalline metal is less affected by the grain size, but is strongly affected by the loading strain rates.     

聚合物中小分子扩散的分子动力学模拟

采用分子动力学(MD)方法,以研究低聚体在聚甲基丙烯酸甲酯中的扩散为例,通过分析高分子链长、低聚体含量、聚合度和温度对扩散系数的影响,揭示小分子在聚合物中扩散过程.通过比较扩散系数的模拟值与实验值,发现两者比值在4左右.为获得小分子在聚合物中的扩散系数提供了一种较好的方法.     

聚乙烯热裂解行为的分子动力学模拟

基于AMBER力场,采用周期性边界条件对聚乙烯模化物的热解过程进行了分子动力学模拟,模拟温度为300～1200 K.模拟结果表明,当温度高于600K时,C-C键开始发生断裂,整个分子链发生解聚,形成各种大分子碎片,随着温度的进一步升高,大分子碎片进一步分解成小分子碎片.聚乙烯的热解是典型的无规裂解,运用自由基链反应理论分析了各种热解主要产物的形成机理.     

Simulation on Grain Boundary Sliding during Superplastic Deformation Using Molecular Dynamics Method

Grain growth and grain boundary sliding are the two main superplastic deformation mechanisms. In the paper, simulation work is focused on the sliding of a∑3 (111) symmetric twist coincidence grain boundary, a ∑13 (110) asymmetric tilt coincidence grain boundary, and a ∑3 (110) symmetric tilt coincidence grain boundary in AI, and the energies of grain boundary for each of equilibrium configurations are computed. An embedded atom method (EAM) potential was used to simulate the atomic interactions in a bicrystal containing more than 2000 atoms. At 0 K, the relationships between total potential energy and time steps for ∑3 (111) symmetric twist coincidence grain boundary and ∑3 (110) symmetric tilt coincidence grain boundary during sliding at 2 m/s represent the periodic characteristic. However, the relationship between total potential energy and time steps for ∑13 (110) asymmetric tilt coincidence grain boundary represents the damp surge characteristic. It is found that grain boundary sliding for ∑3 (110) symmetric tilt coincidence grain boundary is coupled with apparent grain boundary migration.     

材料科学中的分子动力学模拟研究进展

本文综述了几种常见条件下的分子动力学模拟方法以及分子动力学模拟的最新发展趋势，介绍用分子力学模拟方法研究固体的体相结构，表面问题，界面问题以及薄膜形成过程等方面的研究成果。     

氧气在 PVDF 片材中扩散的分子动力学模拟

目的研究气体在PVDF片材中的扩散。方法采用分子动力学模拟方法研究了氧气在其片材中的扩散行为,得到氧气在PVDF片材中的扩散系数,并讨论了时间、聚合度、温度及残余压力对扩散系数的影响。结果模拟时间太短对模拟结果不利,应以大于1000 fs为宜。当聚合度由400增加到800时,扩散系数由4.77×10-6cm2/s下降到1.78×10-6cm2/s;当温度从298 K提高到303 K时,扩散系数由1.06×10-6cm2/s增加到1.42×10-6cm2/s;当残余压力由60 kPa增大到100 kPa时,扩散系数由7.07×10-6cm2/s下降到3.06×10-6cm2/s。结论氧气在PVDF片层中的扩散系数随聚合度和残余压力的增大而变小,随温度的提高而变大。     

Properties,Benefits, and Application of Nanocrystalline Structures in Magnetic Materials

The magnetic properties of nanocrystalline hard magnetic and soft magnetic are summarized. When the grain size becomes of the order f the magnetic exchange length exchange coupling occurs. The different concepts of exchange coupling in these materials are discussed. Exchange coupling leads in isotropic hard magnetic materials to a remanence enhancement. Soft magnetic materials exhibit due to exchange coupling a lower coercivity, lower losses and consequently also improved properties.     

聚乳酸玻璃化转变行为的分子模拟

采用等温等压(NPT)正则系综,用分子动力学方法研究了聚乳酸的玻璃化转变行为,获得了玻璃化转变温度.在230～440K范围内,通过模拟体系的密度、比体积及相关径向分布函数等参数,最终确定了聚乳酸的玻璃化温度,模拟计算的结果与实验值吻合.     

纳米铝晶界内耗峰的连续变温研究

采用低温球磨结合热压烧结技术制备了块体纳米铝晶体材料,在多功能内耗仪上采用受迫振动连续变温(25～450℃)的方式测量了纳米铝材料在低频率(0.2～3.0Hz)条件下的内耗和相对动力学模量。结果表明,纳米铝晶体材料受迫振动时,在升温和降温的内耗-温度谱上均出现一个内耗峰;伴随着内耗峰的出现,相对动力学模量明显下降;随着离散振动频率的增加,内耗峰峰位向高温方向移动,说明该内耗峰具有弛豫性;根据Arrhenius关系,得到该内耗峰的激活能为(2.21±0.04)×10-19 J、指数前因子τ0为10-14 s,表明该内耗峰是晶界内耗峰,其机制为铝原子在铝/铝晶界的自扩散。     

Computer Simulation of Plastic Deformation in GrainBoundary Region under High Rate Loading

The computer simulation of Al three-dimensional crystallite containing grain boundary of special type was carried out and its behaviour under high rate loading was investigated. The molecular dynamics method was used and interaction betwen atoms was described based on pseudopotential method. Vortical character of the atom movements in the grain boundary region is realized under shear loading in certain directions. Back and forth movements of atoms in the direction which is perpendicular to the shear also arise. Amplitude of such movements is approximately equal to an interplanar distance in this direction.     

Measurement of Grain Growth in Nanocrystalline Materialsby Means of Differential Scanning Calorimetry

In this work, we demonstrated that the differential scanning calorimetry (DSC) is not always reliable in measuring thermal stability and grain growth process in nanocrystalline materials by a quantitative analysis and comparison of the DSC data measured in nanocrystalline Ni-P and Hf-Ni samples.     

分子结构对高分子材料动态力学性能影响的研究进展

从材料的阻尼性能的表征出发,系统总结了高分子材料阻尼机理研究状况。主要以LA和TA分析法为例,从分子设计角度,总结阐述了近年来有关分子结构对高分子材料动态力学性能影响的研究成果和存在的问题,并对未来此方面的研究进行了简单的预测。     

Atomistic Simulation of Interaction between Grain Boundary and Dislocations in Ni_3Al

The embedded atom type potentials and static relaxation method combined with a steepest decentcomputational technique have been used to simulate the interaction between the grain boundary(GB) and dislocations in Ni_3Al alloys.The focus has been placed on the energy feature of theinteraction,the distortion of GB structural units,and the dislocation core structure near the GB.Im-plication has also been made on the results for the understanding of the mechanism responsible forB-enhanced ductility.     

Effect of Grain Size on Phase Transformation and Photoluminescence Property of the Nanocrystalline ZrO_2 Powders Prepared by Sol-Gel Method

Nanocrystalline zirconia （ZrO2） powders were prepared by a sol-gel process followed by annealing treatments from 500 to 1200 ℃. Phase transformation, microstructural features and photoluminescence properties were characterized by X-ray diffraction, transmission election microscopy and photoluminescence spectra, respectively. The results show that both monoclinic phase and tetragonal phase exist in the nanocrystalline ZrO2 powders at annealing temperature in the range of 500-900 ℃, and the concentration of monoclinic phase increases with increasing the annealing temperature. Tetragonal phase is totally transformed to monoclinic phase when annealing temperature is up to 900 ℃. The average grain size of the powders also increases when annealing temperature increases. Two emission peaks centered at 390 nm （named as /390） and 470 nm （named as /470） exist in the photoluminescence spectra, and the intensity ratio of /390 to /470 decreases with increasing annealing temperature. The grain size is proposed to be responsible for the phase transformation in the nanocrystalline ZrO2 powders.     

三维泡泡布点方法及网格生成

本文研究如何在三维区域上生成高质量的节点集并基于节点集进行网格生成.根据区域边界的几何描述和理想间隔控制函数,先后对曲面及区域内部用泡泡布点法进行节点布置.节点布置结束后,对区域边界的节点集运用高质量点集的局部网格生成算法(BLMG)进行网格剖分,对区域内部的点集直接进行Delaunay三角剖分.通过计算节点集生成Delaunay网格单元的质量来评价区域节点集的质量.泡泡均匀分布与非均匀分布的算例均表明,该算法生成的节点具有较高的质量并且在泡泡非均匀分布时具有很好的渐进性.     

分子动力学模拟纳米铜晶体中晶界对空穴扩展的影响

用分子动力学方法模拟了∑9对称倾侧晶界铜双晶在拉伸变形过程中晶界对空穴扩展的影响.模拟结果表明:晶界对空穴沿界面的扩展起促进作用,但同时又阻碍空穴越过晶界向另一晶粒扩展;空穴离晶界较远时,晶体在变形过程中表现出比较明显的塑性;空穴的存在会降低晶体的强度,并且空穴离晶界越近晶体强度越低.     

硅晶体中点缺陷结合过程的分子动力学模拟

本文采用分子动力学方法模拟了硅晶体中空位与间隙原子的结合过程.利用Stillinger-Waber三体经验势函数表征原子间的相互作用,采用Verlet积分算法,在VC＋＋环境下使用C＋＋语言编程,进行计算机模拟.结果表明,空位和间隙原子倾向于通过＜111＞方向结合,并且在运动过程中存在着势垒,势垒值为0.5～1.2eV.