A simulation study of rapid solidification and crystal configuration of Cu70Ni30 alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

A simulation study of rapid solidification and crystal configuration of Cu<Subscript>70</Subscript>Ni<Subscript>30</Subscript> alloy

A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu₇₀Ni₃₀ adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2×10¹² K/s, the Cu₇₀Ni₃₀ formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be, further understood.     

Cu50Ni50合金快速凝固的分子动力学模拟

采用分子动力学模拟的方法研究了Cu₅₀Ni₅₀合金在不同冷却速度下的凝固过程,利用均方位移、径向分布函数和结构可视化等方法分析其微观结构.并对凝固模型进行拉伸模拟,通过应力应变曲线和直观结构变化分析其性能.研究表明：冷却速度对Cu₅₀Ni₅₀合金凝固形成的结构有较大影响,随着冷却速度的升高,凝固形成的结构中晶体含量减少,在较低的冷却速度下,如冷却1×10¹²K/s时,Cu₅₀Ni₅₀合金凝固形成晶体结构;在较高的冷却速度下,如1×10¹⁴K/s时,Cu₅₀Ni₅₀合金凝固形成非晶体结构,且非晶Cu₅₀Ni₅₀合金的抗拉性能要优于晶体Cu₅₀Ni₅₀合金.     

Effect of Ni on growth kinetics,microstructural evolution and crystal structure in the Cu(Ni)–Sn system

Abstract

The role of Ni addition in Cu on the growth of intermetallic compounds in the Cu–Sn system is studied based on microstructure, crystal structure and quantitative diffusion analysis. The diffraction pattern analysis of intermetallic compounds indicates that the presence of Ni does not change their crystal structure. However, it strongly affects the microstructural evolution and diffusion rates of components. The growth rate of (Cu,Ni)₃Sn decreases without changing the diffusion coefficient because of the increase in growth rate of (Cu,Ni)₆Sn₅. For 3 at.% or higher Ni addition in Cu, only the (Cu,Ni)₆Sn₅ phase grows in the interdiffusion zone. The elongated grains of (Cu,Ni)₆Sn₅ are found when it is grown from (Cu,Ni)₃Sn. This indicates that the newly formed intermetallic compound joins with the existing grains of the phase. On the other hand, smaller grains are found when this phase grows directly from Cu in the absence of (Cu,Ni)₃Sn indicating the ease of repeated nucleation. Grain size of (Cu,Ni)₆Sn₅ decreases with further increase in Ni content, which indicates a further reduction of activation barrier for nucleation. The relations for the estimation of relevant diffusion parameters are established considering the diffusion mechanism in the Cu(Ni)–Sn system, which is otherwise impossible in the phases with narrow homogeneity range in a ternary system. The flux of Sn increases, whereas the flux of Cu decreases drastically with the addition of very small amount of Ni, such as 0.5 at.% Ni, in Cu. Analysis of the atomic mechanism of diffusion indicates the contribution from both lattice and grain boundary for the growth of (Cu,Ni)₆Sn₅ phase.     

A combined XPS/AES study of Cu segregation to the high and low index surfaces of a Cu-Ni alloy

Quantitative information was obtained regarding the equilibrium segregation of Cu to the high index surfaces (cut 5° off the (100) plane in the [001] and [011] directions) and low index surfaces ((100), (111) and (110)) of a Cu: Ni, 5: 95% alloy crystal. Data regarding segregation to the (111) surface of a Cu: Ni, 50: 50% alloy crystal was also obtained. Equilibrium surfaces were obtained by careful annealing in the temperature range 850–920 K to avoid Cu loss by evaporation. The surface composition profile was calculated using data from the combination of the X-ray Photo-electron Spectroscopy and Auger Electron Spectroscopy techniques. Using these techniques, a wide range of electron kinetic energies and associated electron escape depths can be probed, yielding information about the topmost layer concentration and about the concentration profile into the bulk. Extensive Cu segregation was observed for the 5% and 50% Cu alloys. Topmost layer compositions of 85–100% Cu were found for both the high and low index surfaces of the 5% Cu alloy. In the next two or three atomic layers the composition was found to drop swiftly to near bulk Cu levels. For atomic layers deeper than this, some experimental evidence suggested a rise in Cu composition over three or four layers to 8–17% Cu before bulk levels were finally regained. For the 50% Cu alloy sample, a topmost layer composition was found of 95–100% Cu. Bulk levels of Cu were regained in about four atomic layers. These results are discussed in relation to other theoretical and experimental studies of segregation in these Cu-Ni alloys. The significance of the measured composition in relation to an equilibrium surface is also considered.     

Oscillations in the compositional depth profile of Cu/Ni alloys: A study by UPS

The composition in the surface region of a (110) oriented single crystal of Cu/Ni alloy was studied by ultraviolet photoemission spectroscopy (UPS) in the energy range hv = 32–240 eV. The data indicate a surface enrichment of Cu and that the composition, as a function of depth below the surface, does not approach the bulk value in a monotonic manner but shows at least one oscillation. The depth sampled by the UPS experiment was varied by changing the photon energy and thus the escape length of the photoemitted electrons. Two surfaces of a single bulk crystal (bulk atomic composition 90% Ni and 10% Cu) were studied. One was the high temperature equilibrium surface (AES measurements yielded a surface composition of ~65% Cu and 35% Ni); the second surface was higher in Ni concentration (AES measurements gave ~65% Ni and 35% Cu) and was obtained by annealing at a lower temperature. Theories based on the quasi-chemical and regular solution models predict a surface enrichment of Cu for the alloy, but do not predict any oscillation in composition below the surface.     

Simulation study for atomic size and alloying effects during forming processes of amorphous alloys

1 Introduction Since amorphous alloys were successfully prepared by Duwez et al.[1] in the 1960s by rapid cooling from the eutectic alloy of Ag-Cu system, the investigation about atomic size and alloying effects during the formation process of amorphous alloys has become such an important area that many people paid a good deal attention. From the experiments that AgxCu1-x alloys formed amorphous structures, Takayama[2] has determined the content range of amorphous alloys, being x = 35—65, …     

热处理温度对铜镍镀层的光谱性能的影响

采用电沉积法在镍表面制备铜镍镀层,并将该铜镍镀层在不同温度下进行热处理。分别用扫描电镜法(SEM)、能谱法(EDAX) 和X衍射法(XRD)等对热处理后的铜镍镀层进行表征,研究热处理温度对铜镍镀层的光谱性能的影响。用电镀的方法获得的铜镍镀层表面是由节瘤组成,热处理温度在25~600 ℃范围,随着热处理温度的升高,铜镍镀层表面的节瘤变小;热处理温度在600~900 ℃范围,随着热处理温度的升高,铜镍镀层表面的节瘤变小,铜镍镀层表面的节瘤间的分界线越不明显。热处理温度在25～900 ℃范围,随着热处理温度的升高,铜镍镀层中铜的含量减小,从82.52 at%减小到78.30 at%;镍的含量增加,从17.48 at%增加到21.70 at%。铜镍镀层为Cu_0.81Ni_0.19立方晶型结构,热处理温度在25～300 ℃范围,随着热处理温度的升高,Cu_0.81Ni_0.19的晶型结构更完整;热处理温度在600～900 ℃范围,铜镍镀层中可能有部分的Cu_0.81Ni_0.19立方晶型结构转变为Cu_3.8Ni立方晶型结构;随着热处理温度的升高,有利于Cu_3.8Ni(311)和Cu_0.81N_i0.19(311) 晶面的生长。     

快速凝固Co-Cu包晶合金的电学性能

研究了Co-Cu包晶合金快速凝固过程中的相选择和组织形成特征, 探索了冷却速率、组织结构和晶体位向与合金电阻率之间的相关规律.实验发现, 快速凝固可使Co在(Cu)中的固溶度扩展至20%.Cu含量大于80%时, L+αCo→(Cu)包晶转变被抑制, (Cu)可从过冷熔体中直接形核析出.Cu含量在40%—70%范围时, Co-Cu合金的液相分离受到抑制, 凝固组织沿条带厚度方向分为两个晶区.细晶区中αCo和(Cu)相竞争形核并生长, αCo枝晶形态细密，细小的（Cu）等轴晶均匀分布于αCo的基体之中.粗晶区αCo相为领先相, 富Cu相分布于αCo枝晶的晶界处.随着冷速的增大, 合金组织显著细化, 晶界增多,对自由电子的散射作用增强, 合金电阻率显著增大.当晶界散射系数r＝0996—0999时, 可采用M-S模型综合分析快速凝固Co-Cu合金的电阻率. 关键词： 电阻率 快速凝固 相结构 晶体生长     

Regularity of self-organization of the atomic structure of the interphase boundary in a crystal-nanoparticle heterosystem

The structure of the (001) fcc/(001) fcc interphase boundary of a system consisting of a hemispherical Ni (or Cu) crystal nanoparticle and a Pd crystal substrate was studied depending on the nanoparticle rotation angle θ = 15°, 20°, 25°, and 30°. A molecular dynamics simulation including multiparticle potentials calculated in the framework of the embedded atom method was used in this study. It was shown that, under given annealing conditions, the nanoparticle rotation depends on the size; namely, the annealing of small nanoparticles leads to their rotation to the position corresponding to the coincidence orientation at the interphase boundary, while the position of large islands remains practically unchanged. It was established that the atomic rearrangement at the interphase boundary affects only lattices with a larger parameter.     

脉冲激光沉积的金属原子团簇的电子状态及生长的研究

 介绍了采用X射线光电子谱(XPS)等技术研究脉冲激光沉积在Ni、Mo、C、NaCl(100)表面的Cu、Au原子团簇的电子状态;结合Cu₂p_3/2 X射线光电子谱峰和Cu L₃M_4,5M_4,5俄歇跃迁分离了电子结合能的初态和终态贡献,得出了它们随Cu表面浓度变化的关系,并对之作出了解释。使用XPS、RBS、TEM三项技术研究了Au在NaCl(100)表面的生长过程,通过计算得出了在不同表面浓度下Au原子团簇的平均高度和表面覆盖率。     

热镀铜层冷凝过程的分子动力学模拟

采用常温、常压分子动力学模拟方法和FS(Finnis Sinclair)势 ,研究了在周期性边界条件下由 5 0 0个原子构成的液态Cu模型系统的凝固过程 ,考察了不同降温速率下Cu的凝固行为 ,得到了不同温度、不同冷却速率下Cu的双体分布函数 ;采用HA键型指数法统计了各种小原子团在不同温度下所占比例 ,采用键取向序分析了体系降温全过程的局域取向对称性 ,得到原子体系微观结构组态变化的重要信息 ;最后 ,利用能量分析的方法对体系微观结构的变化进行了说明 ,给出了液态Cu冷凝过程中微观结构转变的重要信息 .     

On the origin of the substrate-induced oxidation of Ni/NiO(001) studied by X-ray Photoelectron Spectroscopy and Molecular Dynamics Simulations

Metallic Ni, vapor-deposited on NiO(001) near room temperature, could be gradually oxidised upon annealing between 800 K and 940 K in Ultra High Vacuum (UHV), as evidenced by X-ray Photoelectron Spectroscopy for initial Ni coverage of 1.6, 3.8 and 7.5 equivalent monolayers (ML). The time dependence of the oxidation process was consistent with a diffusion mechanism, supplying oxygen via the NiO crystal to a coalesced particulate deposit and resulting in an oxide shell, which grew over the entire surface and enclosed a shrinking metallic core. Similar to the well known behaviour upon gas phase oxidation, the process was fast within a depth of two atomic layers of Ni, limited by the diffusive supply of oxygen from the substrate. Molecular Dynamics Simulations for 0.06, 0.11 and 0.22 ML of Ni ions deposited on a model NiO(001) substrate indicated the formation of NiO islands via oxygen ions transferred from the surface and near-surface layers of the crystal. A significant atomic concentration of oxygen vacancies of the order of 10 to 20% could be created in each underneath layer, before the next one started donating lattice anions. This suggests a possible explanation for the aforementioned NiO-substrate-induced oxidation of deposited Ni, whereby the formation of oxygen vacancies inside the crystal supplies the necessary oxygen.     

Effects of Ni buffer layer on giant magnetoresistance in Co/Cu/Co sandwich

In order to increase the sensitivity of Co/Cu/Co sandwiches, different thickness Ni layers were used as buffer layer. It was found that in the Co 55 Å/Cu 35 Å/Co 55 Å sandwiches with different thickness Ni buffer layers, MR ratios between 3.5% and 5.6% could be obtained, and the coercive forces were about 12 Oe. Hence, the maximum field sensitivity could be enhanced to about 1%/Oe. Further investigation from the results of atomic force microscopy showed the improvement of the interfacial flatness in the sandwiches with Ni buffer layer. The microstructure observed by high-resolution electron microscope demonstrated the different structure of the two Co layers in the Ni buffered sandwich, which directly determined the small saturation field of the sandwich. This was confirmed by the magnetic behaviors of the two Co layers calculated from the experimental hysteresis loops. All these showed that the usage of a Ni buffer layer could result in interfacial improvement, different crystalline structure, and small saturation field in the Co/Cu/Co sandwich. These enhanced the electron spin scattering at the Co–Cu interfaces and finally enlarged the giant magnetoresistance and the sensitivity in the sandwich.     

Non-steady state solidification of the Nd-123 superconducting oxides

Crystal growth of the melt-textured bulk Nd_1+xBa_2−xCu₃O_6+d (Nd123) superconducting oxides was investigated by employing isothermal undercooling solidification with hot-seeding in air. From the relationship between growth length and holding time, the Nd123 crystal was found to have almost stopped growing after a certain growth period, while the growth length increased proportionally to the holding time at an early stage of the crystal growth. As a result of quantitative analysis for the Nd123 crystal of which solidification was terminated, the distribution of the Nd/Ba substitution was observed to decrease in the Nd123 single crystal matrix from the seed crystal to the edge of the Nd123 crystals. Also, the substitution content at the edge of the Nd123 crystal, which corresponds to that at the final stage of the crystal growth, was found to be in good agreement with the minimum substitution of the Nd123 solid solution phase in the equilibrium phase diagram at this process temperature. These compositional changes could be explained using the equilibrium phase diagram as associated with the solid solution formation, which is responsible for the non-steady state solidification of the Nd123 crystals even for the isothermal undercooling processing.     

Ag/Ni和Cu/Ni界面的分子动力学模拟

用分子动力学方法对金属界面在弯曲状态下的力学行为做了模拟计算．在自行设计的两种弯曲模型中，首先比较了Ａｇ／Ｎｉ在不形成界面、形成界面（错配比约为１５％）以及Ｃｕ／Ｎｉ形成界面（错配比约为３％）时在动态弯曲过程中的势能－应变曲线，应力－应变曲线，模量－应变曲线，通过比较得出的结论是：界面的存在影响很大，失配位错影响界面的性质，并且错配比不同界面的力学性质亦不相同．同时，对计算元胞的尺寸效应做了详细的讨论，给出了用于计算机模拟中比较适宜的计算元胞的尺寸．最后，利用圆弧弯曲模型将静态平移周期性边界条件应用于动态 关键词：     

An X-ray absorption spectroscopy investigation of the local atomic structure in Cu–Ni–Si alloy after severe plastic deformation and ageing

The local atomic structure of Cu–Ni–Si alloy after severe plastic deformation (SPD) processing and the decomposition of supersaturated solid solution upon annealing were investigated by means of X-ray absorption spectroscopy. The coordination number and interatomic distances were obtained by analyzing experimental extend X-ray absorption fine structure data collected at the Ni K-edge. Results indicate that the environment of Ni atoms in Cu–Ni–Si alloy is strongly influenced by the deformation process. Moreover, ageing at 973 K affects strongly the atomic structure around the Ni atoms in Cu–Ni–Si deformed by equal channel angular pressing and high pressure torsion. This influence is discussed in terms of changes and decomposition features of the Cu–Ni–Si solid solution.     

Epitaxial growth of ultra-thin NiO films on Cu(1 1 1)

The very first stages of the growth of NiO on Cu(1 1 1) is examined on a microscopic scale. The paper focuses on the morphological and structural characterization of nanostructures formed in the 0-1 Å thickness range. Ultra-thin NiO films, obtained through evaporation of a Ni rod under an oxygen atmosphere were grown at 550 K. In the early stages of the growth the oxide film morphology shows 10-30 nm large, monolayer high, islands with a partial incorporation of metallic Ni in the first Cu(1 1 1) surface plane. The first layer is formed by an epitaxial atomic layer exhibiting a STM contrast similar to the one observed on adsorbed oxygen on Cu(1 1 0). A NiO cluster nucleation and coalescence mechanism is proposed in order to explain the formation of the second NiO layer. A α-Ni₂O₃ hexagonal phase, or a structural distortion of the NiO(1 1 1)()R30° structure could both explain the complex LEED patterns.     

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.     

d Band structure and alloying effects in crystalline and amorphous ZrCo and ZrNi

We study the electronic structure by photoemission of amorphous Zr₇₀Co₃₀, Zr₇₅ Ni₂₅ and crystalline Zr₂Co, Zr₂Ni. The results show that the electronic structures for the amorphous and crystalline states are quite similar. The valence bands of the amorphous alloys do not present features attributable specifically to the amorphous state. In both cases the valence band indicate a strong localization of the d levels and can be interpreted as a superposition of the Zr 4d levels in the upper part of the band, the Co or Ni 3d levels being centered in the low part of the part of the band. The present results and previous ones on ZrCu amorphous alloys show that the binding energies of the 3d levels increase with the distance between the alloying elements in the periodic table. Moreover the full width at half maximum of Co, Ni or Cu d levels is noticeably less than for pure elements. These results are considered at the light of atomic structure and theoretical models ; in particular it seems that the coordination number of the atoms plays a dominant role in the structure of the d levels.