非晶态合金Cu_xPd_(1-x)形成过程合金效应及微观结构转变特性的模拟研究(英文)

本文根据量子Sutton-Chen多体势,采用分子动力学方法对含有50000个原子大系统液态二元合金Cu_xPd_(1-x)(CuPd的原子半径比为1.14)在快速凝固过程中的微观结构转变特性进行模拟研究.运用Honeycutt-Andersen(HA)键型指数法和原子成团类型指数法(CTIM)分析了液态和固态的微观结构特性.研究结果发现:在7.73×10~(13)K/S冷却速率下,Cu_xPd_(1-x)合金形成以1551、1541和1431三种键型为主的非晶态结构;系统以1551键型和由1551键型构成的(12 0 12 0)二十面体团族在所有的键型和团簇中占主导地位,并且在液态合金Cu_xPd_(1-x)微观结构转变中起着关键性作用.通过分析键型、团簇和平均原子体积,我们发现液态合金Cu_xPd_(1-x)的玻璃转变温度是573K.同时还发现,原子的平均配位数的变化与1551,1441,1661键型的变化趋势相当接近,这反映出体系对称性结构的变化规律与配位数的变化有关.     

Formation of Fe-Nb-X (X=Zr, Ti) amorphous alloys from pure metal elements by mechanical alloying

Fe-based amorphous powders of Fe₅₆Nb₆Zr₃₈ and Fe₆₀Nb₆Ti₃₄ based on binary eutectic were prepared by mechanical alloying starting from mixtures of pure metal powders. The amorphization behavior and thermal stability were examined by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. Results show that Fe₅₆Nb₆Zr₃₈ alloy has a better glass forming ability and a relatively lower thermal stability comparing with Fe₆₀Nb₆Ti₃₄ alloy. The prepared amorphous powders have homogeneous element distribution and no obvious contaminants coming from mechanical alloying. The synthesized amorphous powders offer the potential for consolidation to full density with desirable mechanical properties through the powder metallurgy methods.     

Magnetic properties and large magnetocaloric effects in amorphous Gd-Al-Fe alloys for magnetic refrigeration

A series of the amorphous Gd75-55Al25-5Fe0-40 alloy ribbons were prepared by melt spinning.The structure,magnetic properties and magnetocaloric effect(MCE) of these alloys were investigated.The prepared samples have shown the characteristics of a second-order phase transition with zero hysteresis loss and the Tc can be tuned by changing the Fe contents.For the different compositions,the magnetic entropy change(--Sm) for a field change of 0-5 T reached a maximum value of 7.14 J kg-1 K-1 in the Gd70Al20Fe10 a...     

Zr基大块非晶中添加元素对非晶形成能力及耐蚀性的影响

运用实空间递归方法研究了添加元素Nb,Ta,Y,La对Zr基非晶合金的非晶形成能力和耐腐蚀性能的影响.用计算机编程构造了Zr基非晶中初始晶化相Zr₂Ni的原子结构模型,用Zr₂Ni中的二十面体原子团簇模拟非晶中的二十面体团簇.计算了替代二十面体中心或顶角位置原子前后Ni,Zr及合金元素的局域态密度、团簇中心Ni与近邻Zr原子及Ni与替代元素Nb,Ta,Y,La间的键级积分,还计算了合金元素替代前后团簇的费米能级.局域态密度计算结果表明：合金元素Cu占据二十面体团 关键词： 电子结构 Zr基大块非晶 非晶形成能力 耐蚀性     

各向异性场对非晶态合金应力阻抗效应的影响

在非晶态合金材料中引入应力感生各向异性场及磁各向异性场,根据Maxwell方程组及带Gilbert项的Landau-Lifshitz方程,得到了能揭示非晶态合金材料应力阻抗效应的理论,理论结果可定性地解释实验结果. 对不同各向异性场参数下的应力阻抗效应进行了大量计算,获得了一些对理论和应用具有一定参考价值的结论. 关键词： 应力阻抗效应 应力感生各向异性 横向有效磁导率 非晶态合金     

铁基软磁非晶/纳米晶合金研究进展及应用前景

非晶合金通常是将熔融的金属快速冷却、通过抑制结晶而获得的原子呈长程无序排列的金属材料.由于具有这种特殊结构,铁基软磁非晶合金具有各向同性特征、很小的结构关联尺寸和磁各向异性常数,因而具有很小的矫顽力H_c,但可和晶态材料一样具有高的饱和磁感强度B_s.优异的软磁性能促进了铁基软磁非晶合金的应用研究.目前,铁基软磁非晶/纳米晶合金带材已实现大规模工业化生产和应用,成为重要的高性能软磁材料.本文回顾了软磁非晶合金的发现和发展历程,结合成分、结构、工艺对铁基非晶/纳米晶合金软磁性能的影响,介绍了相关基础研究成果和工艺技术进步对铁基软磁非晶/纳米晶合金研发和工业化应用的重要贡献.并根据结构、性能特征将铁基软磁非晶合金研发与应用分为三个阶段,指出了目前铁基软磁非晶合金研发与应用中面临的挑战和发展方向.     

Mg-Ni-Nd非晶合金晶化温度与晶化驱动力的预测

通过对Buschow提出的预测二元非晶态合金晶化温度的“最小空位”模型进行扩展,并进一步结合Miedema理论得到了一种预测三元非晶态合金晶化温度和晶化驱动力的理论方法.利用该方法计算了(Mg_70.6Ni_29.4)_1-xNd_{x(x＝5,10,15)非晶态合金的晶化温度、晶化驱动力以及晶化焓.其中晶化温度和晶化焓的理论预测值与实验值的相对误差分别小于8%和7%.同时发现较高的晶化驱动力会降低 关键词： 非晶态合金 晶化温度 晶化驱动力}     

液态金属凝固过程原子团簇结构表征的新方法（英文）

采用分子动力学方法对液态金属钠的凝固过程进行了模拟计算,运用团簇结构表征新方法――团簇类型指数法(CTIM)对凝固过程中的团簇结构进行了识别.为了阐明CTIM在识别团簇结构上的准确性和效率,将其与广为采用的Voronoi多面体方法 (VPM)进行比较.结果表明:当采用CTIM和VPM分别对液态金属钠凝固结构中的原子团簇结构进行表征时,它们所得到的微观结构特征是一致的.非晶态结构中,原子团簇类型的分布呈现明显的区段特征,每一区段都存在一种主要团簇类型,它们分别是二十面体或其缺陷结构.晶体结构中,体系形成以BCC团簇为主体的晶态结构.同时发现,VPM不易区分不同团簇构型之间的细微差别,不同构型的原子团簇可能被归为同种结构类型;而CTIM根据近邻原子之间相对位置关系,直接准确描述原子团簇的构型.不但由CTIM分析获得的凝固体系结构特征与VPM的分析结果一致;而且CTIM抓住了体系微观结构特征的主要方面,简化了团簇结构的表征形式,这在大尺度模拟体系的结构分析中将具有较高效率.     

非晶态合金与氢相互作用的研究进展

非晶态合金在力学性能、耐磨耐蚀性、磁性等方面比传统晶态合金具有显著优势,是一类有优良应用前景的新型结构与功能材料.非晶态合金与氢相互作用可以产生很多有趣的物理化学现象和应用.本文从物理基础和材料应用两个方面评述非晶态合金和氢相互作用的研究进展,在物理基础研究方面,从氢在非晶态合金中的存在状态出发,讨论氢在非晶态合金中的溶解、分布、占位和扩散等相关物理问题,进而分析氢对非晶态合金的热稳定性、磁性、内耗、氢脆等的影响.在材料应用研究方面,对非晶态储氢合金、非晶态合金氢功能膜、吸氢改善非晶态合金的塑性和玻璃形成能力、氢致非晶化、利用非晶态合金制备纳米储氢材料等方面的研究进展进行评述.最后总结并展望有关非晶态合金与氢相互作用的研究和应用.     

冷速对液态金属Na凝固过程中微观结构影响的模拟研究

采用分子动力学方法对液态金属Na在四种不同冷速下的快速凝固过程进行了模拟跟踪研究.采用双体分布函数g(r)曲线、Honeycutt-Andersen键型指数法和原子团类型指数法对凝固过程中微观结构的变化进行了分析.结果表明：冷却速率对微结构的转变有决定性影响，当冷速为1.0×10¹⁴和1.0×10¹³K/s时，系统形成以1551和1541键型或以缺陷多面体基本原子团(13 1 10 2)和二十面体基本原子团(12 0 12 0)为主体的非晶态结构；当冷速为1.0×10¹²和1.0×10¹¹K/s时，系统则形成以1441和1661键型或以体心立方基本原子团(14 6 0 8)为主体的晶态结构.同时发现：不同冷速对液态金属Na在液态和过冷态时微观结构的影响甚小；但不同冷速对其固态(非晶态利晶态)时的微观结构有显著的影响，且要在液-固转变点(分别在玻璃转变温度T_g和晶化起始温度T_c)附近或以后才能充分展现出来.根据这一特点，有可能建立另一种确定液态金属T_g和T_c的新方法.原子团类型指数法比键型指数法更有利于研究液态、非晶态等无序体系和一些晶化体系的具体结构特征. 关键词： 液态金属Na 凝固过程 分子动力学模拟 原子团类型指数法     

Formation of L10-FeNi hard magnetic material from FeNi-based amorphous alloys

L1₀-FeNi hard magnetic alloy with coercivity reaching 861 Oe was synthesized through annealing Fe₄₂Ni_41.3Si₈B₄P₄Cu_0.7 amorphous alloy, and the L1₀-FeNi formation mechanism has been studied. It is found the L1₀-FeNi in annealed samples at 400 ℃ mainly originated from the residual amorphous phase during the second stage of crystallization which could take place over 60 ℃ lower than the measured onset temperature of the second stage with a 5 ℃/min heating rate. Annealing at 400 ℃ after fully crystallization still caused a slight increase of coercivity, which was probably contributed by the limited transformation from other high temperature crystalline phases towards L1₀ phase, or the removal of B from L1₀ lattice and improvement of the ordering quality of L1₀ phase due to the reduced temperature from 520 ℃ to 400 ℃. The first stage of crystallization has hardly direct contribution to L1₀-FeNi formation. Ab initio simulations show that the addition of Si or Co in L1₀-FeNi has the effect of enhancing the thermal stability of L1₀ phase without seriously deteriorating its magnetic hardness. The non-monotonic feature of direction dependent coercivity in ribbon segments resulted from the combination of domain wall pinning and demagnetization effects. The approaches of synthesizing L1₀-FeNi magnets by adding Si or Co and decreasing the onset crystallization temperature have been discussed in detail.     

Accurate prediction method for the microstructure of amorphous alloys without non-metallic elements

A new structural parameter of amorphous alloys called atomic bond proportion was proposed, and a topological algorithm for the structural parameter was proven feasible in the previous work. In the present study, a correction factor, λ, is introduced to optimize the algorithm and dramatically improve the calculation accuracy of the atomic bond proportion. The correction factor represents the ability of heterogeneous atoms to combine with one another to form the metallic bonds and it is associated with the uniformity of the master alloy, mixing enthalpy, cooling rate during preparation, and annealing time. The correction factor provides a novel pathway for researching the structures of the amorphous alloys.     

A reversion of atomic segregation under ion bombardment of Nix Pdy alloys

The angular distribution of atoms sputtered from Ni_xPd_y alloys (x, y=1, 5) under 3 and 10 keV Ar⁺ ion bombardment has been studied experimentally and using computer simulations. A collector technique combined with RBS to analyze the distribution of collected material was used. It was found that the Pd/Ni yield ratio increases with the polar ejection angle θ for all targets excluding NiPd₅. This peculiarity of sputtering was explained by a reversion of atomic segregation at high initial concentrations of Pd atoms in the target.     

Fe基纳米晶合金晶粒尺寸反常变化的物理机制

晶粒尺寸在很大程度上决定了Fe基纳米晶合金的磁学性能,其随退火温度变化的物理机理是纳米晶领域重要的研究内容.研究了初始晶化温度与二次晶化温度之间退火1 h Fe基纳米晶合金晶粒尺寸随退火温度的变化,并建立了相应的模型.利用提出的模型分析了该温度范围内Fe基纳米晶合金晶粒尺寸随退火温度升高先减小后增大的物理机制. 研究发现,在初始晶化温度与二次晶化温度之间等时退火,当退火温度约为Fe基纳米晶合金熔点的0.6倍时其晶粒尺寸最小.在研究的温度区间内,理论研究结果与实验符合得较好. 本研究提供了一种快速获得小晶粒尺寸纳米晶合金的方法.     

Computer simulation of the structure of MZr2 liquid and amorphous alloys

In the present study, we compare the structure of NiZr₂ and CuZr₂ disordered (liquid and amorphous) alloys. While Cu and Ni have similar atomic radii, the formation heats of these alloys differ by more than a factor of two. Moreover, the most stable crystal phase in the CuZr₂ alloy has the C11b lattice while the most stable phase in the NiZr2 alloy has the C16 lattice. Comparing these two alloys allows us to directly explore how the chemistry and atomic size affect the disordered phase structure. We find that all differences in the structures of the disordered alloys are readily explained by the smaller Ni–Zr separation driven by the higher heat of mixing and the structure of the disordered alloys does not necessarily resemble the local packing structure of their crystalline counterparts. Comparison of the disordered alloys and their most stable crystal phase structures explains the better glass formability of the CuZr₂ alloy.     

Successive defects asymmetric simple exclusion processes with particles of arbitrary size

This paper uses various mean-field approaches and the Monte Carlo simulation to calculate asymmetric simple exclusion processes with particles of arbitrary size in the successive defects system. In this system, the hopping probability p (p<1) and the size d of particles are not constant. Through theoretical calculation and computer simulation, it obtains the exact theoretical results and finds that the theoretical results are in agreement with the computer simulation. These results are helpful in analysing the effect of traffic with different hopping probabilities p and sizes d of particle.     

冷速对液态金属Pb凝固过程中微观团簇结构演变影响的模拟研究

采用分子动力学方法对六种不同冷却速率对液态金属Pb凝固过程中微观团簇结构演变的影响进行了模拟跟踪研究.采用双体分布函数、Honeycutt-Andersen键型指数法、原子团类型指数法(CTIM-2)、平均配位数等方法对凝固过程中微观团簇结构的演变进行了分析.结果表明：系统存在一个形成非晶态或晶态结构的临界冷速(介于5×10¹²与1×10¹²之间),大于这个临界冷速时,系统将形成以1551,1541和1431键型为主的非晶态结构;当小于这个临界冷速时,系统将先形成以1441和1661键型或以bcc基本原子团(14 6 0 8 0 0)为主的晶态结构,并稳定存在一段时间,然后又迅速转变为以1421和1422键型为主或以fcc基本原子团(12 0 0 0 12 0)和hcp基本原子团(12 0 0 0 6 6)以一定比例并存的部分晶态结构;同时发现,冷速对系统中fcc结构和hcp结构的相对比例有明显的影响,冷速越低,fcc结构所占的比例越多,越倾向于形成完美的fcc晶态结构. 关键词： 液态金属铅 凝固过程 团簇结构演变 分子动力学模拟     

同步辐射技术在无序合金结构与性能研究中的应用

同步辐射装置作为大科学装置和多学科的实验平台,已成为物质结构,特别是无序物质结构研究最有效、最先进的手段之一.文章简单介绍了同步辐射技术在研究无序合金结构、液态合金结构、非晶多形态相变以及块体金属玻璃力学行为等方面的应用.随着第三代的上海同步辐射光源（SSRF）的建立,国内用户利用先进的同步辐射技术开展研究又多一个选择, 相信上海光源对中国科研的发展将起到积极的推动作用.     

有机超微粒的制备及其尺寸效应的研究

有机超微粒是国际上刚刚起步的研究领域,是纳米科技领域和有机光电子领域的重要前沿课题.文章从有机功能小分子出发,在制备粒径和形状可控的、高度单分散的纳米超微粒的基础上,首次系统地研究了有机超微粒的电子态随尺寸大小的变化过程.发现有机超微粒和无机超微粒一样具有显著的尺寸效应,而且更具多样性.该项研究工作为探索和比较无机和有机材料介观尺寸效应的异同点这一科学问题奠定了坚实的基础,对于理解有机分子晶体这类传统材料中的基本过程和现象以及开发新型光电材料和器件也极具意义.     

The temperature dependence of the magnetoelastic characteristics of cores for force sensors utilizing Fe<Subscript>70</Subscript>Ni<Subscript>8</Subscript>Si<Subscript>10</Subscript>B<Subscript>12</Subscript> amorphous alloy

This paper presents the results of investigation on the influence of temperature on magnetoelastic characteristics of the two ring-shaped cores, made of Fe₇₀Ni₈Si₁₀B₁₂ amorphous alloy. The cores were annealed for 1 h at 350 and 400°C, respectively. The compressive force F was applied perpendicular to the direction of the magnetizing field H in the sample. Special cylindrical backing enables application of the uniform compressive stress σ to the wound ring sample. A resistive furnace heated the experimental set-up. Results presented in the paper indicate a significant influence of the temperature on the magnetoelastic characteristics of Fe₇₀Ni₈Si₁₀B₁₂ amorphous alloy. Information about the magnetoelastic characteristics of this material may be useful in the magnetoelastic sensor development. Also this will create new possibilities in the development of physical model of magnetoelastic effect.