液态Ga-In合金中的团簇分离现象

与以往试验及模拟计算方法不同,文章利用从头计算分子动力学研究了液态Ga, In及Ga-In合金的偏结构. 发现合金偏双体相关函数gGaGa(r), gInIn(r)的第一峰的位置分别与液态纯Ga和纯In的第一峰 位置接近, gGaIn(r)第一峰位置大于纯Ga和纯In第一峰位置的平均值,说明液态Ga-In合金中异类原子 呈现排斥倾向, Ga-Ga, In-In团簇更容易出现.在纯Ga, 纯In中占据最高含量的1311键对在液态合金中占主导 地位,说明Ga-Ga, In-In团簇共存于液态Ga-In合金中. Voronoi多面体分析发现,随着In含量的增加, 在Ga_100-xIn_x(30 ≤x≤qslant 50 at.% ) 区域内, Ga原子周围主配位数出现突变,由12降为10,证明Ga-Ga和In-In团簇倾向于分离.该研究结果不同于 通常的微观不均匀模型,揭示了液态Ga-In合金中团簇分离的机制.     

二元室温金属流体热导率的理论计算与实验研究

室温金属流体在芯片散热领域中正日益显示重要价值,但相关材料的热物性比较缺乏.本文基于Faber-Ziman理论和Wiedemann-Franz-Lorenz定律,采用Ashcroft-Langrethp硬球模型偏结构因子以及空核心模型赝势计算了液态二元镓铟及钠钾合金的热导率.结果表明:相比于钠钾合金的热导率随原子组分浓度呈抛物线变化,镓铟合金的热导率与原子组分浓度呈单调变化关系,同时镓铟合金的热导率随着温度升高而升高.作为对比,本文同时也对镓铟合金的热导率进行了实验测定.结合所获数据及钠钾合金文献数据对比,表明计算结果与实验值符合得较好.本文工作为进一步研究二元合金热导率打下了基础.     

Hallkoeffizient,spezifischer elektrischer Widerstand und magnetische Suszeptibilität flüssiger Hg-In-und Ga-In-Legierungen

The Hall coefficient and the magnetic susceptibility of the liquid alloys Hg-In and Ga-In have been measured and compared with the free electron model. The deviation of the measured from the calculated Hall coefficient for Hg-In is discussed. The susceptibility of carriers in Hg and Hg-In deviates strongly from the Pauli-Landau-susceptibility. This behaviour can be understood by assuming a minimum of the density of states at the Fermi level of Hg. The susceptibility data accounts for the Knight-shift ofSeymour andStyles. For liquid Ga-In, the Hall-coefficient and the magnetic susceptibility agree with the free electron model.     

Concentration dependence of Fe segregation near the surface in V-Fe alloys after V+ ion irradiation

The effect of Fe segregation near the free surface of V model alloys containing 2, 5, or 7 at % Fe is investigated by x-ray photoelectron spectroscopy. Segregation is induced by 50-keV V⁺ ion irradiation at a temperature of 30–40°C with fluences ranging from 10¹⁹ to 10²¹. Young’s moduli in these alloys are measured by the torsion pendulum method. The degree of Fe segregation is estimated, and its dependence on the irradiation dose and iron concentration in these alloys is analyzed. Correlation is found between the behavior of Young’s moduli and the degree of iron surface segregation as functions of the Fe concentration in the alloys.     

Analysis of the effect of the energy of interatomic interaction and the structure of Fe-Cr alloys on the processes of radiation-induced segregation after ion etching

We present the results of a comparative analysis of profiles of the radiation-induced segregation of chromium after irradiation of model alloys Fe-(9, 11, 14) at % Cr by He⁺ ions with the energy of 30 keV with fluences 10¹⁹–10²¹ ions/m² at 450°C and data on varying the moduli of normal elasticity and the structure of these alloys depending on the Cr concentration. It is shown that an interstitial migration mechanism is the determining factor in the case of chromium segregation near the surface. A correlation between the character of varying the elasticity moduli, order, and value of surface segregation and swelling of the Fe-Cr alloys depending on the Cr concentration is established.     

An auger investigation of oxygen-enhanced tin segregation on a liquid Pb−Sn alloy

Summary Auger measurements of the surface composition have been performed on solid and molten Pb-5at%Sn alloys. They confirm the theoretical predictions that, in the absence of oxygen, liquid or solid alloys exhibit no significant surface segregation. On the contrary, surface composition measurements and simultaneous surface tension measurements clearly show that oxygen adsorption strongly affects the segregation of tin at the liquid-vapour interface. This surface enrichment is driven by the contribution of the reaction free energy and of the products surface tension.     

Surface tension modelling of liquid Cd–Sn–Zn alloys

The thermodynamic model in conjunction with Butler equation and the geometric models were used for the surface tension calculation of Cd–Sn–Zn liquid alloys. Good agreement was found between the experimental data for limiting binaries and model calculations performed with Butler model. In the case of ternary alloys, the surface tension variation with Cd content is better reproduced in the case of alloys lying on vertical sections defined by high Sn to Zn molar fraction ratio. The calculated surface tension is in relatively good agreement with the available experimental data. In addition, the surface segregation of liquid ternary Cd–Sn–Zn and constituent binaries has also been calculated.     

Characterisation of Interfaces Between Liquid Tin and Alumina in the Presence of Titanium Alloy Additions

Neutron reflection spectroscopy has been used to characterise the composition of interfaces between liquid Sn-Ti alloys and Al₂O₃. The reflectivity profiles for both 1% and 3% Ti alloys are consistent with the presence of a layer approximately 2 nm thick at the liquid/solid interface, showing extensive segregation of Ti. The composition of this layer is not pure Ti but shows a greater Ti content than any known Ti oxide composition. In all interfaces exposed to liquid metals at elevated temperature (including pure Sn) there is a layer of thickness 20–100 nm on the alumina surface with slightly lower neutron scattering length density than pure alumina. This is interpreted as evidence for surface roughening of the Al₂O₃ surface during exposure to the liquid metal.     

Application of X-ray radioscopic methods for characterization of two-phase phenomena and solidification processes in metallic melts

X-ray attenuation techniques are an important diagnostic tool for investigating liquid metal two-phase flows or solidification studies in metallic alloys. X-ray visualization enables a general, intuitive understanding of flow phenomena or pattern formation in opaque liquid metal systems. Real-time and in-situ observations of the density distribution within thin solidifying samples achieve a spatial resolution of a few microns and contribute significantly to an improved understanding of dendritic growth processes. Moreover, X-ray radioscopy is a useful tool for a non-invasive, in-situ visualization and characterization of gas bubbles in nontransparent melts or for observations of the formation of metal foams. In this paper we consider three different fields of application which are under intensive investigation at HZDR and TUD: the bottom-up solidification of Ga-In alloys under the influence of buoyancy-driven and electromagnetically driven convection, the injection of Ar gas into liquid GaInSn, the study of Al foams with respect to foam formation and the characterization of their internal structure.     

Thermodynamics and surface properties of liquid Al–Ga and Al–Ge alloys

The surface properties of Al–Ga and Al–Ge liquid alloys have been theoretically investigated at a temperature of 1100 K and 1220 K respectively. For the Al–Ga system, the quasi chemical model for regular alloy and a model for phase segregating alloy systems were applied, while for the Al–Ge system the quasi chemical model for regular and compound forming binary alloys were applied. In the case of Al–Ga, the models for the regular alloys and that for the phase segregating alloys produced the same value of order energy and same values of thermodynamic and surface properties, while for the Al–Ge system, the model for the regular alloy reproduced better the thermodynamic properties of the alloy. The model for the compound forming systems showed a qualitative trend with the measured values of the thermodynamic properties of the Al–Ge alloy and suggests the presence of a weak complex of the form Al₂Ge₃. The surface concentrations for the alloys show that Ga manifests some level of surface segregation in Al–Ga liquid alloy while the surface concentration of Ge in Al–Ge liquid alloy showed a near Roultian behavior below 0.8 atomic fraction of Ge.     

Energetics of mixing in Bi-Pb and Sb-Sn liquid alloys

We have analysed the energetics of mixing of Bi-Pb and Sb-Sn liquid alloys at respective temperatures 700 and 905 K through the study of their thermodynamic functions and surface properties using four atom cluster model and quasichemical approximation (QCA) approach, respectively. Our study reveals that the two systems exhibit chemical order or heterocoordination, with the degree of chemical order in Sb-Sn being more than that of Bi-Pb. We also observed that while Bi-atoms segregate to the surface of Bi-Pb alloy, Sb-atoms segregate to the surface of Sb-Sn alloys. The degree of segregation of Sb-atoms being more than that of Bi-atoms.     

Pairing interactions and Gibbs adsorption at the liquid bi-in surface: a resonant X-ray reflectivity study

Resonant x-ray reflectivity measurements from the surface of liquid Bi(22)In(78) find only a modest surface Bi enhancement, with 35 at. % Bi in the first atomic layer. This is in contrast to the Gibbs adsorption in all liquid alloys studied to date, which show surface segregation of a complete monolayer of the low surface tension component. This suggests that surface adsorption in Bi-In is dominated by attractive interactions that increase the number of Bi-In neighbors at the surface. These are the first measurements in which resonant x-ray scattering has been used to quantify compositional changes induced at a liquid alloy surface.     

Selected topics in low-energy ion scattering: Surface segregation in Cu/Ni alloys and ion neutralization

The usefulness of ion scattering for studies of surface segregation in alloys has been demonstrated for the Cu/Ni system. A strong surface enrichment in Cu is found. As a step towards understanding the mechanism of neutralization of ions at a surface, the scattering of Ne⁺ from Au has been studied. The importance and origin of oscillations in the energy dependence of the ion fraction is discussed.     

铜基大块非晶合金添加微量元素对腐蚀行为的影响机理研究

通过分子动力学方法模拟了Cu-Al合金液相,然后模拟降温过程得到Cu-Al非晶合金.通过计算机编程建立了Cu-Al-M非晶基体、Cu-Al-M非晶表面及吸附O原子Cu-Al-M非晶表面原子结构模型.利用实空间连分数方法,研究了添加微量合金元素Zr,Nb,Ta,V,Y,Sc对Cu基大块非晶合金的腐蚀行为的影响机理.研究发现合金元素Zr,Nb,Ta,V,Sc不向清洁Cu基非晶表面偏聚,但除Y外向有氧吸附的表面偏聚,说明有氧吸附后Cu基非晶表面偏聚发生逆转.键级积分计算表明Zr,Nb,Ta,V,Y,Sc元素均增大与氧之间的结合力,易形成氧化膜,提高Cu基大块非晶的耐蚀性.稀土Y提高Cu基大块非晶的耐蚀性可能是由于它向合金与氧化膜界面偏聚并提高了合金与氧化膜的结合力.     

Surface segregation in liquid GaSn alloys by AES

The surface segregation of Sn in liquid GaSn alloys has been studied by Auger electron spectroscopy as a function of bulk concentration at 350° C. The Sn was found to be strongly adsorbed at the surface. The surface concentrations of Sn and Ga were calculated from the Auger measurements using inelastic mean free paths and backscattering factors estimated in recent theoretical work. The values found for the surface concentrations are essentially in agreement with those deduced from surface tension measurements using Gibbs adsorption theory. This result supports a monolayer adsorption distribution in the GaSn system.     

A Monte Carlo study of surface segregation in alloys

The Monte Carlo method has been applied to the study of surface segregation in a multi-layer, regular solution model of alloy surfaces. Three different alloy configurations have been investigated: semi-infinite slabs, thin films and small particles. The results show that the alloy component with the lowest surface energy tends to segregate to the first three or four surface atom layers and that segregation is greater in clustering alloys than in ordering alloys. Furthermore, segregation is more pronounced in low coordination surfaces, as evidenced by a comparison of {110} and {100}-oriented surfaces of fcc alloys. The degree of surface segregation in thin films and small particles (in the particle size range studied) tends to be smaller than in semi-infinite slabs, because of mass conservation constraints, and decreases with decreasing film thickness and particle size. The results obtained are contrasted with previous calculations and possible avenues for improving surface segregation models are discussed.     

ISS measurement of surface composition of AuCu alloys by simultaneous ion bombardments with Ar+ and He + ions

Surface composition of Au-Cu(43 at%) alloy under 1.5–5 keV argon ion bombardment has been investigated by ion scattering spectroscopy (ISS). In this experiment, we adopted a specific technique to use mixed He⁺ and Ar⁺ ions as primary beam in order to perform sputtering (Ar⁺) and ISS measurement (He⁺) simultaneously. The outermost atom layer of Au-Cu alloys under Ar⁺ ion bombardment is Au-rich leading to the conclusion that Ar⁺ ion bombardment of AuCu alloys causes the preferential sputtering of Cu atoms, resulting in a Au-rich outermost atom layer and a depletion layer of Au atoms beneath the outermost atom layer due to ion-beam-enhanced surface segregation. This result explains the experimental results obtained by AES as well.     

Physical and mathematical model of the surface segregation in binary alloys of transition metals

The surface segregation in binary alloys of transition metals based on platinum and palladium with different surface-face orientations are simulated via the electron-density functional method. The concentrations of the surface-active components of the binary alloys and displacements of the surface ion planes thereof are calculated self-consistently. The influence of surface segregation and lattice relaxation on the surface energy and electron work function on the surface of alloys of transition metals with various concentrations is investigated. The simulation results are compared with experimental data.     

Surface segregation in Pt-Au alloys studied using Auger electron spectroscopy

Temperature dependent surface segregation studies using Auger electron spectroscopy have been performed on three different Pt-Au alloys, containing 2, 5 and 90 wt% Au. By utilizing Auger transitions of different kinetic energies and model segregation profiles, an estimate of the in-depth variation in composition was made. Strong surface segregation of Au was observed in the three alloys.     

Analysis of the effect of interatomic interaction energy in V-Fe alloys with different iron concentrations on segregation and swelling processes after ion irradiation

Comparative analysis of iron segregation profiles near the free surfaces of V-(2, 5, 7) at % Fe alloys irradiated with 50-keV V⁺ ions at temperatures 30–40°C with doses from 1 × 10¹⁹ to 1 × 10²¹ ions/m² has been performed. Data on the change in the moduli of normal elasticity and the values of swelling of these alloys with a change in Fe concentration in them are reported. A correlation between the character of the concentration dependence of the degree of Fe segregation, partial diffusion coefficients of the alloy components, the Young moduli, and the preference factors for vacancies and interstitials between dislocations and voids in these alloys is established.