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期刊介绍
  《npj 计算材料学》是在线出版、完全开放获取的国际学术期刊。发表结合计算模拟与设计的材料学一流的研究成果。本刊由中国科学院上海硅酸盐研究所与英国自然出版集团(Nature Publishing Group,NPG)以伙伴关系合作出版。
  主编为陈龙庆博士,美国宾州大学材料科学与工程系、工程科学与力学系、数学系的杰出教授。
  共同主编为陈立东研究员,中国科学院上海硅酸盐研究所研究员高性能陶瓷与超微结构国家重点实验室主任。
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Atomic-scale structural signature of dynamic heterogeneities in metallic liquids(金属液体中动态异质性的原子尺度结构特征) 
Alain Pasturel & Noel Jakse
npj Computational Materials 3:33 (2017)
doi:10.1038/s41524-017-0034-y
Published online:17 August 2017
Abstract| Full Text | PDF OPEN

摘要:液体如果具有足够高的冷却速度,将会越过其平衡熔融温度,并可在固化之前保持在亚稳、过冷状态。过冷液体的研究展示了几个有趣的动态现象,同时,由于液体结构和液体动力学之间存在明显的却又难以识别的联系,揭示与这些现象之间潜在的结构联系仍是一个重大挑战。第一性原理的从头算分子动力学(AIMD)模拟在原子尺度细节方面的描述是特别有效的方法,足以指导实验。基于把Cr加入Al基液体中的AIMD研究,我们首次证明:组分扩散的解耦与过冷状态下动态异质性之间存在紧密联系。此外,我们还证明了两种现象的起源都与结构异性(structural heterogeneity)相关,结构异性由化学短序列(CSRO)和局部五倍拓扑(ISRO)在液相短程之间的强相互作用引起,它在过冷时发展成以二十面体为主的中程序列(IMRO)。本研究结果表明,温度相关的金属-金属耦合分布函数中也观测到这种结构特征,从而为更详细的实验研究奠定了基础。   

Abstract: With sufficiently high cooling rates, liquids will cross their equilibrium melting temperatures and can be maintained in a metastable undercooled state before solidifying. Studies of undercooled liquids reveal several intriguing dynamic phenomena and because explicit connections between liquid structure and liquids dynamics are difficult to identify, it remains a major challenge to capture the underlying structural link to these phenomena. Ab initio molecular dynamics (AIMD) simulations are yet especially powerful in providing atomic-scale details otherwise not accessible in experiments. Through the AIMD-based study of Cr additions in Al-based liquids, we evidence for the first time a close relationship between the decoupling of component diffusion and the emergence of dynamic heterogeneities in the undercooling regime. In addition, we demonstrate that the origin of both phenomena is related to a structural heterogeneity caused by a strong interplay between chemical short-range order (CSRO) and local fivefold topology (ISRO) at the short-range scale in the liquid phase that develops into an icosahedral-based medium-range order (IMRO) upon undercooling. Finally, our findings reveal that this structural signature is also captured in the temperature dependence of partial pair-distribution functions which opens up the route to more elaborated experimental studies. 

Editorial Summary

Metallic liquids: Connection between liquid structure and liquid dynamics (金属液体:液体结构和液体动力学之间的连接) 

本研究基于计算模拟结果揭示了金属液体中原子尺度结构和动力学之间存在强烈联系。当液体材料快速冷却时,可避开结晶,形成亚稳态过冷状态。这样的系统表现出一系列有趣的动态现象,但是在实验上很难看到液体结构和液体动力学之间的相互作用。Grenoble Alpes大学的Alain Pasturel和Noel Jakse使用从头算分子动力学模拟表明,铬掺杂的铝基液体中,铬扩散与铝扩散有很强的去耦。这与动态异质性的出现密切相关,因为这两种效应都具有结构性的起源。他们的研究找到了液体结构和液体动力学之间的密切关系,并可能引起更进一步的实验研究。

Simulations show a strong connection between the atomic-scale structure and dynamics in metallic liquids. When a material is cooled rapidly it can avoid crystallization, forming a metastable undercooled state. Such systems exhibit a range of interesting dynamic phenomena but it is experimentally difficult to look at the interplay between the liquid structure and liquid dynamics. Using ab initio molecular dynamic simulations, Alain Pasturel and Noel Jakse from the University Grenoble Alpes show that in chromium-doped aluminum-based liquids there is a strong decoupling of the chromium diffusions from the aluminum diffusion. This is closely related to the emergence of dynamic heterogeneities, as both effects have a structural origin. These insights provide a close connection between structure and liquid dynamics and could lead to more elaborate experimental studies.

 

Construction of ground-state preserving sparse lattice models for predictive materials simulations(构建能保持基态稀有晶格的模型以预测模拟材料) 
Wenxuan HuangAlexander UrbanZiqin RongZhiwei DingChuan Luo & Gerbrand Ceder
npj Computational Materials 3:30 (2017)
doi:10.1038/s41524-017-0032-0
Published online:07 August 2017
Abstract| Full Text | PDF OPEN

摘要:基于第一原理的集群扩展模型是根据从头算热力学理论研究晶体混合的主要方法,可以预测相图和基态。然而,尽管近来取得了一些进展,由于默认参数会导致各种各样的问题,仍需要耗时费力地手动调整参数才能保证构建模型的准确性。本研究提出了一种系统的、数学上可靠的方法,确保基态与参考数据一致的簇扩展模型。基于新开发的压缩感知途径方法,我们建立了集群扩展模型,并采用二次规划对模型参数加以约束。对于锂离子电池阴极有关的两种锂过渡金属氧化物(Li2xFe2(1-x)O2和Li2xTi2(1-x)O2),我们构建了极具挑战的、带有压缩感知能力的簇扩展模型,证明了本方法的强大实用性。研究证明,我们的方法不仅保证了为模型构建而使用的参考结构集的基态准确,而且通过快速收敛迭代保证了样本之外尺寸较大的超胞基态准确。本法提供了一种通用工具,可用来构建强实用的、压缩的、受约束的、有预测功能的物理模型。   

Abstract: First-principles based cluster expansion models are the dominant approach inab initiothermodynamics of crystalline mixtures enabling the prediction of phase diagrams and novel ground states. However, despite recent advances, the construction of accurate models still requires a careful and time-consuming manual parameter tuning process for ground-state preservation, since this property is not guaranteed by default. In this paper, we present a systematic and mathematically sound method to obtain cluster expansion models that are guaranteed to preserve the ground states of their reference data. The method builds on the recently introduced compressive sensing paradigm for cluster expansion and employs quadratic programming to impose constraints on the model parameters. The robustness of our methodology is illustrated for two lithium transition metal oxides with relevance for Li-ion battery cathodes, i.e., Li2x Fe2(1−x)O2 and Li2xTi2(1−x)O2, for which the construction of cluster expansion models with compressive sensing alone has proven to be challenging. We demonstrate that our method not only guarantees ground-state preservation on the set of reference structures used for the model construction, but also show that out-of-sample ground-state preservation up to relatively large supercell size is achievable through a rapidly converging iterative refinement. This method provides a general tool for building robust, compressed and constrained physical models with predictive power.

Editorial Summary

Materials simulations: Constructing models guaranteed to preserve the ground states(材料模拟:构建能确保维持基态的模型) 

该研究开发了用于材料模拟、不需手动调整输入参数的方法。第一原理密度泛函理论计算是计算材料学研究中最常用的一种工具,但难于应用到含数千个原子的大型结构模拟。这样的系统通常使用集群扩展模型来模拟,但存在一个问题:需要手动调整参数以保持基态——这个调整很重要,因这一调整通常决定了材料的属性。现在来自美国麻省理工学院、加州大学伯克利分校和劳伦斯伯克利国家实验室的Gerbrand Ceder教授(美国2017年新科工程院院士)领导的国际研究团队,提出了构建集群扩展模型的方法,可以保证基态准确而无需手动调整参数。

A method has been developed for performing materials simulations without needing to perform manual parameter tuning for the ground-state. First-principles density functional theory calculations are one of the most commonly used tools for computational materials science research but they cannot easily be applied to large structures that contain many thousands of atoms.In such systems, cluster expansion models are often used but they have a problem: manual parameter tuning is required to preserve the ground-state --- important as this usually governs the materials properties. An international team of researchers led by Gerbrand Ceder from Massachusetts Institute of Technology, the University of California Berkeley and Lawrence Berkeley National Laboratory now present a procedure for constructing cluster expansion models that can preserve the ground states without any need for tuning.

 

Hydrogen embrittlement of grain boundaries in nickel: an atomistic study (镍晶界的氢脆化:原子水平上的研究)
Shan Huang, Dengke ChenJun SongDavid L. McDowell & Ting Zhu
npj Computational Materials 3:28 (2017)
doi:10.1038/s41524-017-0031-1
Published online:14 July 2017
Abstract| Full Text | PDF OPEN

摘要:氢对金属的化学力学性能的削弱作用已有大量观察,但其原子尺度上的作用机理尚不清楚。本研究从原子水平上探讨了氢对镍晶界的脆化作用。通过将晶界划分为由原子组成的多面体堆积单元,可以确定出给定任意晶界的所有可能的氢间隙位点。计算得到各个间隙位点氢的偏聚能并代入Rice-Wang界面脆化热力学理论模型中。通过计算氢偏聚晶界的分离功的变化可以定量评估氢脆化效果。我们研究了快速和慢速分离极限,他们分别对应固定氢浓度和氢化学势条件下的晶界断裂。据此我们还进一步分析了局部电子密度对于氢吸附能的影响,从而揭示了晶界氢脆化的物理极限。   

Abstract: The chemomechanical degradation of metals by hydrogen is widely observed, but not clearly understood at the atomic scale. Here we report an atomistic study of hydrogen embrittlement of grain boundaries in nickel. All the possible interstitial hydrogen sites at a given grain boundary are identified by a powerful geometrical approach of division of grain boundary via polyhedral packing units of atoms.Hydrogen segregation energies are calculated at these interstitial sites to feed into the Rice–Wang thermodynamic theory of interfacial embrittlement. The hydrogen embrittlement effects are quantitatively evaluated in terms of the reduction of work of separation for hydrogen-segregated grain boundaries. We study both the fast and slow separation limits corresponding to grain boundary fracture at fixed hydrogen concentration and fixed hydrogen chemical potential, respectively.We further analyze the influences of local electron densities on hydrogen adsorption energies, thereby gaining insights into the physical limits of hydrogen embrittlement of grain boundaries. 

Editorial Summary

Metals: hydrogen probe divides nickel into grains(金属:氢使镍裂解为晶粒) 

确定金属晶界处所有氢吸附位点,使金属材料失效的定量预测成为可能。由佐治亚理工学院的Ting Zhu领导的国际研究团队发展了一种方法,将氢原子嵌入金属镍晶格中并按照几何结构特征将金属镍划分成由原子组成多面体堆积单元,由此得到了所有可能的氢的吸附位点。通过对被氢吸附的晶界原子水平模拟,发现氢通过电子效应与镍结合并在较高温度下恶化、破坏晶界。晶界强度降低不仅取决于氢嵌入镍中的位置,也取决于晶界处的氢浓度。建立用于量化氢吸附造成金属失效的计算模拟框架将有助于减轻含氢压力容器和管道的失效。

Identifying all hydrogen absorption sites at metallic grain boundaries allows for a quantitative prediction of metal failure. An international team of researchers led by Ting Zhu at Georgia Institute of Technology developed a method to geometrically divide nickel metal into polyhedral packing units of atoms by embedding hydrogen atoms into the nickel atomic lattice. By using atomistic simulations to examine the boundaries through these atomic packing units, they showed that hydrogen binds to nickel via an electronic effect and that grain boundary failure due to hydrogen worsens at higher temperatures. Reducing grain boundary strength therefore depended on the location of hydrogen embedded in nickel as well as hydrogen concentration at the grain boundaries. Establishing a framework to quantify metal failure due to hydrogen absorption may help up mitigate failure in hydrogen-containing pressurized vessels and pipelines.

 

Empirical interatomic potentials optimized for phonon properties (针对声子性能研究优化的经验性原子间相互作用势 
Andrew Rohskopf,Hamid R. Seyf,Kiarash Gordiz,Terumasa Tadano&Asegun Henry
npj Computational Materials 3:27(2017)
doi:10.1038/s41524-017-0026-y
Published online:12 July 2017
Abstract| Full Text | PDF OPEN

摘要:分子动力学模拟已被广泛用于研究并理解声子的性质,然而由于缺乏描述具体体系内部原子间相互作用的经验势函数(empirical interatomic potentials),模拟结果直接与实验数据比较通常比较困难,这已成为阻碍先进的原子水平模拟实际应用的主要障碍。本研究提出了一种通用方法,基于第一原理计算的结果作为输入,针对声子输运性能来研究优化经验性原子间相互作用势。本方法采用遗传算法,针对决定声子输运性能的一系列关键属性进行拟合,从而获得了相互作用经验势的参数。   

Abstract: Molecular dynamics simulations have been extensively used to study phonons and gain insight, but direct comparisons to experimental data are often difficult, due to a lack of accurate empirical interatomic potentials for different systems. As a result, this issue has become a major barrier to realizing the promise associated with advanced atomistic-level modeling techniques. Here, we present a general method for specifically optimizing empirical interatomic potentials from ab initio inputs for the study of phonon transport properties, thereby resulting in phonon optimized potentials.The method uses a genetic algorithm to directly fit the empirical parameters of the potential to the key properties that determine whether or not the atomic level dynamics and most notably the phonon transport are described properly. 

Editorial Summary

Molecular dynamics: Optimized potentials for studying phonons (分子动力学:针对声子研究优化的原子间相互作用势) 

本研究开发了一个优化原子间相互作用势的计算框架,基于此可借助经典分子动力学方法更加精确地研究声子。分子动力学模拟是研究原子间相互作用不可或缺的工具。然而尽管该方法已得到广泛应用,但通常缺乏准确的原子间相互作用势参数来准确描述材料中声子的行为,因此难以阐释诸如热导率等相关材料性能。美国佐治亚理工学院的Asegun Henry教授领导了一个国际研究小组,提出了基于遗传算法和第一原理计算结果为输入,优化经验性原子间相互作用势的计算框架,由此可利用经典分子动力学模拟更精确地研究声子。该方法已经成功应用到硅、锗等半导体体系中,并有望延伸应用到合金和无序等系统中。

A framework has been developed that can optimize the potentials needed to more accurately study phonons using molecular dynamics. Molecular dynamics simulations are an indispensable tool for studying how atoms interact.Despite their widespread use, however, it is often difficult to determine the potentials needed to accurately describe the various interactions involved for phonons, which are the excitations that underpin physical properties such as thermal conductivity.An international team of researchers led by professor Asegun Henry from the Georgia Institute of Technology presents an approach, based on a genetic algorithm, that can optimise the empirical interatomic potentials for phonons from first principles inputs, that can be used in classical molecular dynamics simulations.And although they demonstrate this method with semiconducting silicon and germanium, it should be extendable to alloys and disordered systems.

 

Data analytics using canonical correlation analysis and Monte Carlo simulation(基于正则相关分析和蒙特卡洛模拟的数据分析) 
Jeffrey M. RickmanYan WangAnthony D. RollettMartin P. Harmer Charles Compson
npj Computational Materials 3, Article number: 26(2017)
doi:10.1038/s41524-017-0028-9
Published online:05 July 2017
Abstract| Full Text | PDFOPEN

摘要:正则相关(canonical correlation)分析是数据统计分析中的通用参数模型,数据包含相关或相互依赖的输入、输出变量。作为一种降维策略,它在数据分析中特别有用:通过把识别最小相关变量进行相对较少的组合,从而实现多维参数空间的简化。然而,正则相关分析仅仅提供使这些相关性最大化的变量的线性组合。考虑到这一点,本研究建立了一种多功能的基于Monte-Carlo的方法,可用于确定描述输入/输出变量强相关性的非线性函数。通过两个材料科学领域重要实验研究证明了此方法可显著增强变量相关性,(1)确定了与掺杂多晶氧化铝相关的加工和微结构变量间的相互依赖性,(2)将微结构描述符与基于CuInSe2吸收体的薄膜太阳能电池的电器和光电性能关联起来。最后,我们还描述了本方法如何有助于实验规划和过程控制。   

Abstract: A canonical correlation analysis is a generic parametric model used in the statistical analysis of data involving interrelated or interdependent input and output variables.It is especially useful in data analytics as a dimensional reduction strategy that simplifies a complex, multidimensional parameter space by identifying a relatively few combinations of variables that are maximally correlated.One shortcoming of the canonical correlation analysis, however, is that it provides only a linear combination of variables that maximizes these correlations. With this in mind, we describe here a versatile, Monte-Carlo based methodology that is useful in identifying non-linear functions of the variables that lead to strong input/output correlations. We demonstrate that our approach leads to a substantial enhancement of correlations, as illustrated by two experimental applications of substantial interest to the materials science community, namely: (1) determining the interdependence of processing and microstructural variables associated with doped polycrystalline aluminas, and (2) relating microstructural descriptors to the electrical and optoelectronic properties of thin-film solar cells based on CuInSe2 absorbers. Finally, we describe how this approach facilitates experimental planning and process control. 

Editorial Summary

Data analytics: Non-linear model for establishing correlations (数据分析:建立相关性的非线性模型) 

该研究提出了一种用于定量化非线性关系的方法,为理解材料微结构-性质关系提供基础。正则相关分析就是用于量化两组变量之间关系的常用技术,但当关系是非线性时,该技术通常就难办了。现在来自美国Lehigh大学的Jeffrey Rickman及其领导的国际团队,提出了一个基于Monte-Carlo的扩展正则相关分析,可用来解决有潜在非线性变量依赖性的情况。他们通过建立描述陶瓷氧化物中异常晶粒生长的变量之间的相关性,和建立微结构与某些太阳能电池的电气和光电性能最重要变量之间的相关性,来证实上述相关分析方法的可靠性,并揭示了该方法所适用的材料系统范围。

A method for quantifying non-linear relationships provides insight into the connections between microstructure and properties of materials. Canonical correlation analysis is a common technique used to quantify the relationship between two sets of variables but it is often difficult to apply when the relationships are non-linear. An international team of researchers led by Jeffrey Rickman from Lehigh University now present a Monte-Carlo-based extension of canonical correlation analysis that can be applied to scenarios where non-linear variable dependencies are likely. They demonstrate this approach by establishing correlations between the variables responsible for abnormal grain growth in a ceramic oxide, as well as the variables that are most important in connecting the microstructure to the electrical and optoelectronic properties of certain solar cells, showing the range of materials systems that this approach could be used for.

 

Dislocations interaction induced structural instability in intermetallic Al2Cu (金属间化合物Al2Cu中位错相互作用诱导结构不稳定性行为) 
Qing ZhouJian WangAmit MisraPing HuangFei Wang & Kewei Xu
npj Computational Materials 3:24 (2017)
doi:10.1038/s41524-017-0030-2
Published online:04 July 2017
Abstract| Full Text | PDF OPEN

摘要:金属间析出物广泛应用于调控结构合金的力学性能,但其在塑性变形过程中常常不稳定。本研究通过原子尺度模拟,阐明了模型体系Al2Cu中与位错运动相关的金属间析出物结构不稳定机制。非共面<001>位错偶极子在塑性变形过程中的相互作用引起了异常反应:产生了空位,同时出现了与位错核心变化相关的<001>位错攀爬和集体滑移,并伴随着出现了大规模原子重排(atomic shuffle)——造成了金属间化合物Al2Cu的结构不稳定。随着非共面位错分离不断减少和温度持续升高,这种位错诱导结构不稳定性变得更为严重,并且该变化规律也可能存在于其它非立方金属间化合物的位错诱导结构不稳定过程。   

Abstract:Intermetallic precipitates are widely used to tailor mechanical properties of structural alloys but are often destabilized during plastic deformation. Using atomistic simulations, we elucidate structural instability mechanisms of intermetallic precipitates associated with dislocation motion in a model system of Al2Cu. Interaction of non-coplanar <001> dislocation dipoles during plastic deformation results in anomalous reactions—the creation of vacancies accompanied with climb and collective glide of <001> dislocation associated with the dislocation core change and atomic shuffle—accounting for structural instability in intermetallic Al2Cu. This process is profound with decreasing separation of non-coplanar dislocations and increasing temperature and is likely to be operative in other non-cubic intermetallic compounds as well. 

Editorial Summary

Intermetallics: dislocation climb promotes precipitate dissolution(金属间化合物:位错攀爬促进了析出物溶解) 

金属间析出物的位错因相互作用而攀爬(并非滑移),留下了诸多缺陷。来自中国西安交通大学的Qing Zhou团队及其美国合作伙伴,采用分子动力学模拟,研究了铝-铜合金变形过程中金属间析出物位错的相互作用机制。他们的研究表明,非共面位错是靠攀爬(而非传统的滑移)进行相互作用的,之后再沿着新的原子平面滑移,位错并没有相互抵消,反而产生了空穴。温度升高,缺陷形成加快,位错核心得以扩展,空穴簇也变得更大,促进了析出物溶解。因此,深入研究变形过程中的金属间化合物稳定性,有可能帮助避免采用析出物强化合金时出现的失效问题。

Instead of gliding, dislocations in intermetallic precipitates interact to climb, leaving defects behind. Qing Zhou and colleagues at Xi’an Jiaotong University in China and their collaborators in the United States of America used molecular dynamics simulations to investigate the interactions of dislocations in intermetallic precipitates in aluminium-copper during deformation. They showed that instead of traditional glide, dislocations that do not lie on the same plane can interact by climbing then gliding along a new atomic plane without cancelling each other out, leaving vacancies behind. This defect creation happened faster at higher temperatures, creating extended dislocation cores and vacancy clusters that could facilitate precipitate dissolution. Research into intermetallic stability during deformation may thus help us avoid failure of alloys strengthened with precipitates. 

 

Ultra-large-scale phase-field simulation study of ideal grain growth (理想晶粒生长的超大规模相场模拟研究) 
Eisuke MiyoshiTomohiro TakakiMunekazu OhnoYasushi ShibutaShinji SakaneTakashi Shimokawabe & Takayuki Aoki
npj Computational Materials 3:25 (2017)
doi:10.1038/s41524-017-0029-8
Published online:03 July 2017
Abstract| Full Text | PDF OPEN

摘要: 晶粒生长,是伴随曲率驱动边界迁移的竞争性生长,是冶金学及其他相关学科中最重要的现象之一。然而,即使是最简单、最“理想”的晶粒生长,其真实物理图像也还是争议不断,要解决这个问题非通过大规模数值模拟不可。本研究通过超大规模相场模拟分析了理想晶粒的生长,阐明了相应的真实的统计行为。所进行的数值模拟在时空尺度上比之前所谓最大规模的模拟还要大十倍以上,通过对统计学数量足够多晶粒大规模模拟,强有力展示晶粒的真实、稳态生长行为。此外,我们对理想晶粒生长行为进行全面理论分析,并进行了相关定量化。本研究为理想晶粒生长提供了结论性理解,为研究真实晶粒生长过程奠定基础。   

Abstract: Grain growth, a competitive growth of crystal grains accompanied by curvature-driven boundary migration, is one of the most fundamental phenomena in the context of metallurgy and other scientific disciplines. However, the true picture of grain growth is still controversial, even for the simplest (or ‘ideal’) case.This problem can be addressed only by large-scale numerical simulation. Here, we analyze ideal grain growth via ultra-large-scale phase-field simulations on a supercomputer for elucidating the corresponding authentic statistical behaviors. The performed simulations are more than ten times larger in time and space than the ones previously considered as the largest; this computational scale gives a strong indication of the achievement of true steady-state growth with statistically sufficient number of grains. Moreover, we provide a comprehensive theoretical description of ideal grain growth behaviors correctly quantified by the present simulations. Our findings provide conclusive knowledge on ideal grain growth, establishing a platform for studying more realistic growth processes. 

Editorial Summary

Grain growth: Simulations elucidate statistical behavior (晶粒生长:计算模拟阐明了其统计行为) 

本研究采用超大时空尺度的相场计算,模拟理想条件下的晶粒生长,以便阐明晶粒生长的统计行为。来自日本京都理工大学的Tomohiro Takaki及其团队对理想条件下的晶粒生长行为进行了大规模的相场模拟。模拟中所用的时空尺度比之前报道的尺度要大10倍以上,以足够多的晶粒数量确保了统计学意义,使这些模拟能够达到真正的稳态近似。基于模拟结果导出了一个全面理论解释,用来理解理想晶粒的生长行为。这些研究结果为理解真实材料复杂影响因素提供一个理论模型,从而为研究真实晶粒生长过程奠定基础。 

Grain growth under ideal conditions is simulated by phase-field simulations in ultra-large time and space scales to elucidate the statistical behaviors. A team led by Tomohiro Takaki at Kyoto Institute of Technology in Japan performed large scale phase-field simulations to study ideal grain growth behavior. The time and space scales used in the simulations are more than ten times larger than those in previous reports, enabling them to reach a true steady-state with a statistically significant number of grains. A comprehensive theoretical description was derived to understand the ideal grain growth behavior based on the simulations. The knowledge provided by these findings may offer a model to understand the effects of complicated factors present in real materials and thus establish a platform to study more realistic grain growth phenomena in the future.

Atomic and electronic basis for the serrations of refractory high-entropy alloys(难熔性高熵合金锯齿形变形行为:原子和电子基础) 
William Yi Wang,Shun Li Shang,Yi Wang,Fengbo Han,Kristopher A. Darling,Yidong Wu,Xie Xie,Oleg N. Senkov,Jinshan Li,Xi Dong Hui,Karin A. Dahmen,Peter K. Liaw,Laszlo J. Kecskes&Zi-Kui Liu
npj Computational Materials 3, Article number: 23 (2017);
doi:10.1038/s41524-017-0024-0
Published online:29 June 2017
Abstract| Full Text | PDF OPEN

摘要:难熔性高熵合金具有引人注目的力学性能,即高屈服强度和断裂韧性,使其成为结构应用的潜在候选材料。从原子和电子相互作用层面上揭示高熵合金形成机制及其结构-主导的力学性能的物理本质至关重要,这种策略为进一步开发出预测方法、进而实现先进材料快速设计提供基础与保障。本研究报道了高熵合金和高熵金属玻璃[包括MoNbTaWMoNbVWMoTaVWHfNbTiZrVitreloy-1GG Zr41Ti14Cu12.5Ni10Be22.5]中的价电子浓度分类原理valenceelectron-concentration-categorized principles),观察了锯齿行为的原子和电子相互作用理论基础。我们发现高熵合金和高熵金属玻璃的屈服强度是由局部原子排列决定,电子功函数的幂函数定律。此外,键合电荷密度的相关性提供了对材料中松散键合位点性质的全新认识。强化学键团簇和弱化学键连接原子的同时出现暗示的高熵合金的锯齿形变形行为,进而揭示了缺陷运动的间歇性崩塌行为。  

Abstract:  Refractory high-entropy alloys present attractive mechanical properties, i.e., high yield strength and fracture toughness, making them potential candidates for structural applications. Understandings of atomic and electronic interactions are important to reveal the origins for the formation of high-entropy alloys and their structure−dominated mechanical properties, thus enabling the development of a predictive approach for rapidly designing advanced materials. Here, we report the atomic and electronic basis for the valence−electron-concentration-categorized principles and the observed serration behavior in high-entropy alloys and high-entropy metallic glass, including MoNbTaW, MoNbVW, MoTaVW, HfNbTiZr, and Vitreloy-1 MG (Zr41Ti14Cu12.5Ni10Be22.5). We find that the yield strengths of high-entropy alloys and high-entropy metallic glass are a power-law function of the electron-work function, which is dominated by local atomic arrangements. Further, a reliance on the bonding-charge density provides a groundbreaking insight into the nature of loosely bonded spots in materials. The presence of strongly bonded clusters and weakly bonded glue atoms imply a serrated deformation of high-entropy alloys, resulting in intermittent avalanches of defects movement.

Editorial Summary

High-entropy alloys: cluster-and-glue atoms behind exceptional properties(高熵合金:簇-胶原子模型揭示其优异性能) 

原子排列的“聚集-粘合模型”(cluster-and-glue model)解释了高熵合金的屈服强度和力学响应。受到金属玻璃的启发,来自中国西北工业大学的William Yi Wang带领的研究团队及其美国合作者,采用分子动力学模拟方法构建了由≥4元素组成的难熔高熵合金的不同原子排列方式。根据各原子尺寸与在周期表中位置,一些原子被划归聚合团簇,一些则被划 归为对团簇有粘结作用的原子。当合金从一个原子排列变化为另一个原子排列时,伴随着塑性变形中的化学键断裂与形成,高熵合金和高熵金属玻璃出现缺陷崩塌,从而解释了高熵合金的锯齿形力学响应。因此合金原子排列的理论将有助于预测高熵合金性质。 

A cluster-and-glue model of atomic arrangements explains the yield strength and mechanical response of high entropy alloys. Inspired by metallic glass, a team led by William Yi Wang at China’s Northwestern Polytechnical University and collaborators in the United States of America used molecular dynamics to build different atomic arrangements of refractory high entropy alloys consisting of four or more elements. Depending on atomic size and the periodic table group of each atom, some atoms organized into clusters while others glued the clusters together. Chemical bonds broke and formed with plastic deformation as the alloys went from one atomic arrangement to another via the glue atoms, causing defect avalanches explaining the serrated mechanical response of high entropy alloys.Taking into account atomic arrangement may thus help us predict the properties of high entropy alloys.

In silico designing of power conversion efficient organic lead dyes for solar cells using todays innovative approaches to assure renewable energy for future (太阳能电池中高转换效率有机铅染料:基于当前计算模拟的创新设计、确保未来的可再生能源) 
Supratik KarJuganta K. Roy & Jerzy Leszczynski
npj Computational Materials 3, Article number: 21 (2017)
doi:10.1038/s41524-017-0023-1
Published online:24 May 2017
Abstract| Full Text | PDF OPEN

摘要: 设计新型有机染料敏化剂并用于高转换效率的染料敏化太阳能电池可推动太阳能电池技术的进步,以避开硅基太阳能电池的诸多缺点。计算模拟研究包括定量构-性关系分析及量子化学分析可洞察碘电解质(11个不同化学族群中273个芳基胺有机染料)的主要电子转移机理和光物理特性。直接定量构-性关系模型能够识别化学分子的基本电子属性和结构属性,为11类芳胺有机染料分子性能的量化提供必要的前提条件,是筛选出染料敏化太阳能电池的高转换效率染料分子的基础。探索采用四氢喹啉,NN'-二烷基苯胺和二氢吲哚作为芳基胺有机染料用于染料敏化太阳能电池的研究却鲜见报道。因此,本研究在铅染料设计中采用了上述类别的相应定量构-性关系模型对染料性质进行计算识别。然后对设计的染料的一系列电化学和光物理参数作了计算预测,以确定染料敏化太阳能电池中所需要的电子流动参量。最终通过组合计算技术给出了7种有前途的铅染料,分别用于所考察的所有三类分子(四氢喹啉,NN'-二烷基苯胺和二氢吲哚)。与现有染料的最高实验转换效率相比,这三类染料的最高预测转换效率值(%,experimental %power conversion efficiency value)分别增加了130%183%46%,可满足所需的电化学参数。   

Abstract: Advances in solar cell technology require designing of new organic dye sensitizers for dye-sensitized solar cells with high power conversion efficiency to circumvent the disadvantages of silicon-based solar cells. In silico studies including quantitative structure-property relationship analysis combined with quantum chemical analysis were employed to understand the primary electron transfer mechanism and photo-physical properties of 273 arylamine organic dyes from 11 diverse chemical families explicit to iodine electrolyte. The direct quantitative structure-property relationship models enable identification of the essential electronic and structural attributes necessary for quantifying the molecular prerequisites of 11 classes of arylamine organic dyes, responsible for high power conversion efficiency of dye-sensitized solar cells. Tetrahydroquinoline, N,N′-dialkylaniline and indoline have been least explored classes under arylamine organic dyes for dye-sensitized solar cells. Therefore, the identified properties from the corresponding quantitative structure-property relationship models of the mentioned classes were employed in designing of “lead dyes”. Followed by, a series of electrochemical and photo-physical parameters were computed for designed dyes to check the required variables for electron flow of dye-sensitized solar cells. The combined computational techniques yielded seven promising lead dyes each for all three chemical classes considered. Significant (130, 183, and 46%) increment in predicted %power conversion efficiency was observed comparing with the existing dye with highest experimental %power conversion efficiency value for tetrahydroquinoline, N,N′-dialkylaniline and indoline, respectively maintaining required electrochemical parameters. 

Editorial Summary

Photovoltaics: computers help design efficient solar cells (光伏电池:电脑帮助设计高效的太阳能电池) 

本研究定量设计了21种有望用于太阳能电池的染料,避免了冗长的帅选实验研究。来自西班牙杰克逊州立大学的Jerzy Leszczynski及其团队研究了11个化学分子家族中的数百种有机染料,将计算结果与实验数据相比较,确定了能提高太阳能电池效率的最重要的分子特性。以这些重要的分子特性作为准则,可设计一系列新型染料。其光学和电化学性质的计算模拟可使筛选的范围缩小。最后,他们预测了这些分子在染料敏化太阳能电池中的性能。采用组合计算技术他们确定了二十多种有前景的染料,能让实验科学家更快地合成和测试用所组装的太阳能电池。该方法还有助于设计更多其他化学家族中的分子用作太阳能电池染料。 

Twenty-one promising dyes for solar cells are designed numerically, avoiding lengthy screening experiments. A team led by Jerzy Leszczynski at the Jackson State University studied a collection of hundreds of organic dyes, in eleven chemical families, compared computational results to experimental data, and identified the most important molecular properties that lead to high solar cell efficiency. Using these important molecular properties as guidelines, a series of new dyes were designed. Simulations of their optical and electrochemical properties allowed narrowing down the selection. Finally, their performance in dye-sensitized solar cells was predicted. Using combined computational techniques, the researchers identified two dozen promising dyes for experimentalists to synthesize and to test solar cells more rapidly. The methodology may help design more molecules in other chemical families. 

Continuum understanding of twin formation near grain boundaries of FCC metals with low stacking fault energy (在连续介质尺度上揭示低堆垛层错能量的FCC金属晶界处孪晶形成机制)
Jaimyun JungJae Ik YoonJung Gi KimMarat I. LatypovJin You Kim & Hyoung Seop Kim
npj Computational Materials 3, Article number: 21 (2017)
doi:10.1038/s41524-017-0023-1
Published online:24 May 2017
Abstract| Full Text | PDF OPEN

摘要:低堆垛层错能量的面心立方金属晶界处,常可观察到变形孪晶发生deformation twinning。孪晶发生于晶界处的一个可能的促进因素是变形时的晶粒间相互作用。但这种相互作用对孪晶演化有何影响,人们却不太清楚。同时,微结构特征与孪晶形成之间的因果关系尽管已做了大量实验和模拟研究,却仍缺乏对大量晶粒聚集体之间清晰关系的理解。本研究通过室温下单轴拉伸变形的孪晶诱导可塑钢全场晶体可塑性模拟,探查了晶界附近的形变孪晶,从而表征了晶粒间相互作用的微观力学行为。首先通过电子反散射衍射技术观察了微结构,获得数据后,再经微结构合成建造技术(synthetic microstructure building),重建了统计学上等效的微结构。通过分析晶粒间微观力学响应,来研究拉伸变形条件下微结构大量要素在总体上的孪晶发生行为。模拟结果分析表明,晶粒相互作用可通过晶边处的应力转移或晶界附近的应力局域化,来改变晶界附近的局部力学行为。 

Abstract: Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy. One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation. Nonetheless, the influence of mechanical interaction among grains on twin evolution has not been fully understood. In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior, a clear relation among the large aggregate of grains is still lacking. In this work, we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature. Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building. Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation. Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary. 

Editorial Summary(自然研究宣传稿)

Metals: grain neighbours influence twin formation during deformation(金属:相邻晶粒的相互作用影响变形过程中的孪晶形成)

不利于孪晶形成的晶粒却由于周围的晶粒相互作用显示出对孪晶形成的促进作用。来自韩国浦项科技大学的金贤勋及其同事,基于变形钢的位错滑移和孪生机制,对由各种取向晶粒合成而来的金属微观结构中变形行为进行模拟。孪晶首先起始于晶粒边界附近并依赖初始晶粒的取向,但随着进一步的变形,晶界一侧强大的孪晶活性,又在该晶界的另一侧引发了强烈的孪晶活性。甚至当边界另一边的晶粒不利于孪晶发生的时候,孪晶也照样能够发生。因此,研究相邻晶粒间的邻接关系很可能有助于优化由孪晶形成的合金。

Grains that should not favour twin formation exhibit twinning as a result of surrounding grains acting on their boundaries. A team led by HyoungSeop Kim at the Pohang University of Science and Technology in the Republic of Korea simulated the deformation of synthetic metallic microstructures with many grains of different orientations, based on steels that deform by both dislocation slip and twinning mechanisms. Twinning first started near grain boundaries and depended on initial grain orientation but, with further deformation, strong twin activity on one side of a boundary triggered strong twin activity on the other side of that boundary. This happened even when the grain on the other side of the boundary was unfavourable to twinning. Taking into account grain neighbourhood may therefore help in optimising twin-forming alloys.

 

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