液态金属大系统急冷过程中微结构转变机制的模拟研究

首次对于由50000个Al原子组成的液态金属系统在由急冷形成非晶态结构的过程中所出现的微观结构组织的变化进行了分子动力学模拟研究。探讨各种有关键型、原子团结构组态的转变机制,得到一幅十分清晰的关于金属原子成团及其演变的图景,同时也对模拟计算结果的微观机理给了相应的讨论。这对于深入理解非晶态结构的形成机制及其微观过程,将有重要的启示作用。     

Short-to-medium range order of Al-Mg metallic glasses studied by molecular dynamics simulations

Molecular dynamics simulations of Al-Mg metallic glasses with a wide composition range have been conducted. We made use of a variety of analytical methods to study their amorphous structure. Pair distribution functions were constructed to determine the interatomic distances, and we found good agreement with reported simulation and experimental results. Coordination number analyses revealed that Mg atoms are more likely to serve as neighbour atoms in Al-centred icosahedral clusters in the middle concentration range or to form larger polyhedra at the Al-rich end. The presence of the 155-type pairs demonstrated that icosahedral ordering is predominant in the Al-Mg alloy. Results of Voronoi tessellation showed that Al-centred icosahedra are abundant in most compositions of the Al-Mg alloy and will lead to the formation of short-range order. The icosahedral clusters are highly shared with one another forming the medium-range order and there are less than 3% isolated icosahedra in most of the compositions of the Al-Mg alloy. Finally, the sharing schemes of icosahedra are represented by the splitting of the second peak of each pair distribution function.     

Parallel algorithm of solidification process simulation for large-sized system of liquid metal atoms

1　INTRODUCTIONItiswellknownthatinthestudyofmicrostruc turesofmaterials ,sometimesitisdifficulttogetthedesiredresultsbecauseofthelimitofexperimentcon ditions .Forexample ,theX raydiffractioncannotbeusedtoshowtherealmicrostructuresofliquidoramorphousmetalswithintheirshort rangeorder .Duringtherapidcoolingprocessesfromliquidtoglassmetals,itisalsodifficulttoobservethetransientchangeoftheirmicrostructuresbyinstruments ,andsoon .Withthedevelopmentofcomputerscienceandtechnology ,however ,thoser…     

Icosahedral clustering with medium-range order and local elastic properties of amorphous metals

The paper focuses on the relationship between icosahedral clustering with medium-range order in amorphous metals and local elastic properties. Using a Cu–Zr binary amorphous model constructed by rapid quenching in the framework of molecular dynamics simulations, Voronoi polyhedra analysis shows that the icosahedra are not randomly distributed in space, but form characteristic interpenetrating icosahedral clustering with medium-range order. It is shown that the center atoms of icosahedra within the highly developed interpenetrating icosahedral clusters have higher local elastic moduli than those of independently existing icosahedra and other polyhedra with lower coordination numbers.     

液态Ca70Mg30合金快速凝固过程中纳米团簇结构形成演变特性模拟

采用分子动力学方法对液态Ca70Mg30合金快速凝固过程中纳米团簇结构的形成和演变特性进行模拟。采用原子团类型指数法(CTIM)对凝固过程中纳米团簇结构的演变进行分析。结果表明：系统在5×1011 K/s的冷速条件下形成以1551、1541和1431为主的非晶态结构,非晶转变温度约为530 K;(120120)二十面体基本原子团对系统非晶结构的形成起到决定性的作用,并且原子半径较小的Mg原子更容易占据二十面体基本原子团中心原子的位置;同时,纳米团簇主要是通过中等尺寸团簇的合并而形成,纳米级大团簇的形成演变过程呈现出类似于非晶晶化过程的3个阶段式的变化。     

Molecular dynamics simulation of amorphous segregation in Ag-Rh alloys

Molecular dynamics simulation was carried out to investigate the liquid and amorphous microstructures of binary Agx-Rh(100-x) (x = 25, 50, 75 in atom fraction) alloys. Segregation feature of homogeneous interatomic binding of Ag-Rh liquid was found and probed, which can be retained into amorphous solids upon rapid cooling. Homogeneous binding may occur when the difference in the elemental atomic sizes is less than 10%. The icosahedra in liquid before the formation of amorphous state exist in a stable state and the network formed by 1551-clusters in molten alloys would inhibit the crystallization and diffusion of atoms. A higher degree of 1551-clusters will be favorable to form metallic glasses.     

液态金属Al快凝过程中纳米级大团簇结构的形成特性模拟研究

采用分子动力学方法，对含有400000个Al原子的液态金属大系统在快凝过程中纳米级团簇结构的形成特性进行了模拟研究，并采用原子团类型指数法(CTIM)来描述各种类型的团簇结构组态。结果显示：二十面体原子团(120120)及其组合在微观结构转变中起着最重要的作用；纳米级大团簇(150个原子)是由一些中等原子团结合而成，等原子团由小原子团组成；这种结构与由其它方法获得的纳米级大团簇的结构完全不同，后者是以某一个原子为中心按八面体结构堆积起来的多壳层晶体结构。这些结果正好可以用来解释用不同方法所形成的Al的团簇结构组态之间的本质区别。     

Weighted Voronoi tessellation technique for internal structure of metallic glasses

Voronoi tessellation technique has been widely used to describe the atomic structure of amorphous materials, such as short-range order of icosahedra, because of the relative simplicity of calculation. In the ordinary Voronoi tessellation technique, a face is placed halfway between equal-sized atoms. However, as the atoms are not of the same size, bisection cannot be the exact plane to represent the polyhedron. It also produces errors during estimation of volume of each atom and the number of faces on the polyhedron. In this paper, we solve this problem using Richards's method, a kind of weighted Voronoi tessellation technique. The results show over 50% differences in the number of faces and the atomic volume for the binary metallic glasses.     

非晶态合金晶化过程的一种新微观机制SCIEI

根据对非晶态合金微观结构的分析和原位加热TEM观察非晶态Ni-P合金薄膜动态晶化过程的实验结果,本文提出了一个新的晶化微观机制,即非晶态合金的晶化过程由两个不同过程组成;(1)单原子由非晶态问晶胚(或晶体)表面的扩散过程;(2)有序原子团的长大及切变合并或切变沉积过程。部分晶化非晶态Ni-P合金的TEM观察结果为新晶化微观机制的适用性提供了证据。并用此机制解释了晶化过程中的初生晶体结构形态等实验结果。     

Cations in Inorganic Solids

Abstract

Until recently, cations have been considered as small “isolated” entities, occupying the spaces in close-packed arrays of large anions. An inspection however of cation subarrays reveals that some kind of interaction must exist between them, as they reproduce both the topology and the distances of their parent metal structures.

Up to now, the existence of clusters has been identified with metal-rich compounds or with compounds in which the metal atoms have unsaturated valences. However, from the results reported here, it can be stated that cations recognize themselves in forming aggregates in such a way that the world of clusters also comes into the field of fully ionic compounds, wherein metal atoms have saturated valences.

This kind of interaction has already been observed in silver(I) and gold(I) compounds (and is known as the auriphilic effect or as d ¹⁰-d ¹⁰ interactions); but examples are reported here of similar interactions between cations of the alkaline-earth metals. Group 13 elements, lanthanides, Sc, Ti and Y, indicating that this effect is a general feature of inorganic solids. Although some explanations have been reported, the reasons for such interactions remain unclear. This is an open question challenging theoretical chemists.

These new ideas are placed in the context of similar ones developed recently, which give to cations a more relevant ôle in determining crystal structures. Thus, the old ideas of Lebedev regarding the protagonism of “large” cations in the formation of crystal structures is discussed together with the more recent ideas of O'Keeffe and Hyde which describe the crystal structures of oxides as oxygen-stuffed alloys.

In many oxides, the cations occupy octahedral or tetrahedral holes in close-packed arrays of anions. It is true that in many other structures, the cations reproduce the topology of the structures of elements or simple alloys, but it is also true that the structure of the parent metal is often preserved in its oxides.     

金属体积成形模拟技术

综述了体积成形过程数值模拟的发展历史和研究进展,评述了物理模拟的重要性,分析了体积成形模拟发展趋势。     

3D FEM SYSTEM FOR ANALYSIS OF NDUSTRIAL METAL FORMING PROCESSES

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Simulation of metal forming – Visualization of invisible phenomena in the digital era

The simulation of manufacturing processes has significant importance. The research and development of metal forming simulation started in the 1960s from the elastoplastic analysis of a simple plastic deformation, and it now covers a wide range of forming processes. The accuracy and applicability of metal forming simulation have significantly progressed, driven by the development of plasticity theory and numerical methods such as the remeshing technique and contact analysis algorithm. Now the targets of metal forming simulations are undergoing a transition from the macroscale analysis of deforming bodies to coupled analyses of deformations of deforming bodies and tools, and multiscale analyses of microstructure and texture. Past achievements of metal forming simulation show that it has reached the level of ‘visualizing forming phenomena’, but it will continue to evolve in the digital era, impacting the digital society and factories of the future, where machines work autonomously without human intervention. Emergent technologies require advanced materials, augmented reality, and, of course, metal forming simulation. In this paper, we reinforce the role of simulation as a means of performing computational (virtual) experiments and as a tool for the high-fidelity numerical visualization and quantification of unknown, unmeasurable, and invisible phenomena in formed components and their assembly. We will also discuss simulation–machine interactions, such as online simulation with process operation, to realize the triad of ‘process operation – data – simulation’ in the near future.     

板料成形数值模拟进展

在给出板料成形的典型成形过程、物理过程与力学模型的基础上，评述了板料成形数值模拟的发展历史和最新进展，包括成形过程与成形缺陷模拟发展，常用材料模型与壳体模型，接触摩擦处理及汽车覆盖件成形应用，文末指出了该领域的发展趋势。     

Efficient atomic packing-chemistry coupled model and glass formation in ternary Al-based metallic glasses

An efficient atomic packing-chemistry coupled model has been described for ternary Al-based metallic glasses based upon efficient atomic packing and electrochemical potential equalization principle. For Al-TM (transition metal)-RE (rare earth) system, RE-centered clusters are arranged in a mode of spherical periodic order, and TM atoms locate at the interstitial sites between RE-centered clusters to form an efficient atomic packing. The equalization of electrochemical potential between the RE-centered clusters and the TM-centered clusters accounts for the stability of amorphous structure. Further, complementary inverse structure is utilized to select efficient clusters and solute elements for the best glass-forming ability. The validity of this model was testified in the Al–Ni-RE (Y, Ce, La, Gd) systems. A new Al–Ni–Ho glass with a wedge thickness of about 718 μm has been discovered at the predicted composition.     

The geometry,topology and structure of amorphous solids

Clusters of atoms can be divided into three categories depending on their topology. One of the categories provides the basis for development of a model of a perfectly random structure (ideal amorphous solid) using the non-equilateral triangle topology in the coordination shell. Metallic glasses solidify as amorphous solids with random arrangement of atoms. A model of Zr-based metallic glass has been constructed and described in terms of cluster topology, and compared with a recently published dynamic molecular model of the same alloy. It is shown that the pair distribution function for the ideal amorphous model relates to the pair correlation function obtained from the dynamic model. Debye X-ray scattering computations reveal the presence of vacancies and other flaws relative to the ideal amorphous solid. A shift in the peak position can be predicted using the Erhenfest formula. Two atomic displacement mechanisms involving a five-atom sub-cluster are identified as the fundamental means of compositional redistribution between clusters in the alloy.     

Al_(80)Cu_(20)合金液态原子微观结构及其与非晶形成能力的关系

通过对Al80 Cu2 0 非晶的晶化过程的DSC分析以及粘度测试分析 ,并运用分子动力学模拟的方法 ,研究了液态Al80 Cu2 0 合金中存在的原子团簇及其随温度的变化 ,分析了液态中原子团簇对非晶形成能力的影响。研究了Al80 Cu2 0 合金液态的非晶形成能力与液态微结构以及液态粘度的关系。发现Al80 Cu2 0 的液态粘度对其非晶形成能力有着重要的影响。     

Formation and evolution properties of clusters in liquid metal copper during rapid cooling processes

Based on the quantum Sutton-Chen many-body potential, a molecular dynamics simulation was performed to investigate the formation and evolution properties of clusters in liquid Cu with 50 000 atoms. The cluster-type index method（CTIM） was used to describe the complex microstructure transitions. It is demonstrated that the amorphous structures are mainly formed with the three bond-types of 1551, 1541 and 1431 in the system, and the icosahedral cluster （12 0 12 0） and other basic polyhedron clusters of （12 2 8 2）, （13 1 10 2）, （13 3 6 4）, （14 1 10 3）, （14 2 8 4） and （14 3 6 5） play a critical and leading role in the transition from liquid to glass. The nano-clusters formed in the system consist of some basic clusters and middle cluster configurations by connecting to each other, and distinguish from those obtained by gaseous deposition and ionic spray. From the results of structural parameter pair distribution function g（r）, bond-types and basic cluster-types, it is found that the glass transition temperature Tg for liquid metal Cu is about 673 K at the cooling rate of 1.0 × 10^14 K/s.     

添加Al对Cu基合金非晶形成能力影响的团簇模型

在二元Cu-Zr合金中添加Al元素可明显提高合金的非晶形成能力.根据非晶与其晶化相存在结构遗传关系,以Cu-Zr基非晶晶化相Cu10Zr7中的Cu6Zr5阿基米德反棱柱为团簇模型,利用离散变分方法从电子层次研究了Al元素对Cu基非晶合金团簇稳定性的影响.结果表明:当团簇中加入一个Al原子时,Fermi能级处的态密度明显降低,团簇稳定性提高;但继续加入Al原子,Fermi能级处的态密度又开始上升,态密度处于较高位置,团簇稳定性下降;计算结果与实验结果相吻合.     

Bulk forming of sheet metal

Ever increasing demands on functional integration of high strength light weight products leads to the development of a new class of manufacturing processes. The application of bulk forming processes to sheet or plate semi-finished products, sometimes in combination with conventional sheet forming processes creates new products with the requested properties. The paper defines this new class of sheet-bulk metal forming processes, gives an overview of the existing processes belonging to this class, highlights the tooling aspects as well as the resulting product properties and presents a short summary of the relevant work that has been done towards modeling and simulation.