Al-Sc金属间化合物的电子结构及稳定性和热力学性质

采用基于密度泛函理论的赝势平面波法,计算Al-Sc的4个稳定相的电子结构,分析其成键情况,并采用基于第一性原理的热力学计算公式,计算各相的生成焓、结合能、德拜温度、体弹模量和自由能。结果表明:Al-Sc金属间化合物在费米面以下,主要通过Al3s-Sc3d和Al3p-Sc3d杂化成键,在费米面以上则以Sc3d成键为主;随着Al在各相中所占比例的增大,体系中共价性增大,稳定性提高,且Al2Sc与Al3Sc在低能级区成键电子较多,结构较为稳定。在4个化合物中,0K时合金化形成能力最强的是Al2Sc(H0=-52.02kJ/mol),最弱的是AlSc2(H0=-35.93kJ/mol)。自由能计算所得曲线表明:Al2Sc的结构稳定性最好,AlSc2的最差;随着温度的升高,晶体稳定性都降低。所有热力学计算值与试验值吻合良好。     

The effect of atomic volume on the hydrogen storage capacity of hexagonal metals/intermetallics

A detailed analysis of a large number of data on the gravimetric hydrogen (H) capacity of hexagonal metals and intermetallic alloys shows that their maximum gravimetric hydrogen capacity increases linearly with increasing atomic volume, starting from some threshold value of about 120×10⁻⁴ nm³/atom.     

Evolution of CuSn intermetallics between molten SnAgCu solder and Cu substrate

The evolution of SnCu intermetallic compounds (IMCs) between a molten SnAgCu alloy and the Cu under-bump metallization (UBM) throughout reflow is presented based on interruption of soldering reactions in experiments by removing the liquid solder from the substrate. This allows to capture and visualize interfacial reactants at arbitrary moments of the soldering process, and to gain an insight into their formation characteristics. The results show that the interfacial Cu₆Sn₅/Cu₃Sn structure is formed at an early stage of reflow and is maintained throughout the process. Based on the experiments, formation mechanisms of interfacial CuSn IMCs are discussed.     

A technique for rapid characterization of intermetallics and interfaces

The production, testing and characterization of intermetallics is expensive and time consuming. In view of the wide range of intermetallics which need to be explored, the development of rapid and simple methods for classifying intermetallics is of importance. In the current work we will describe a method of producing layered or graded materials containing a sequence of intermetallics by controlled dissolution and solidification. The scale of the structure is such that hardness and toughness can be assessed by the use of microhardness indentation and, in addition, the properties of specific interfaces can be assessed. An example is shown for the copper–aluminum system where the sequence of intermetallics CuAl₂, CuAl, Cu₉Al₄ can be created. Interfacial fracture between the CuAl₂ (tetragonal phase) and the CuAl (monoclinic/orthorombic phase) has been observed and characterized by Atomic Force, Scanning and Transmission Electron Microscopes.     

A correlation between electrochemical parameters and stress corrosion cracking

Measurements of relaxation times for passivation, by means of a.c. impedance measurements, have been made and a correlation with susceptibility to stress corrosion cracking obtained, for low carbon steels in carbonate/bicarbonate solutions at 70°C.     

Comparison between X-ray micro-computed tomography and optical scanning tomography for full 3D strain measurement by digital volume correlation

In this study, we present three-dimensional (3D) measurements by digital volume correlation (DVC) with images from X-ray micro-computed tomography (XμCT) and optical scanning tomography (OST). In this article, we compare both techniques and we define their field of application by evaluating their measurement uncertainty in the case of rigid body translations, homogeneous strain tests and localised compression tests. For displacement, measurement uncertainty is around 0.037 voxel for OST and 0.049 voxel for XμCT which correspond to a measured strain about 0.1%. For larger strain, uncertainty increases with strain intensity but relative error remains constant about 10%. To resume, measurement uncertainties given by DVC are similar to the ones which we obtain generally for a two-dimensional (2D) study with DIC.     

Effect of solution heat treatment on galvanic coupling between intermetallics and matrix in AA7075-T6

Susceptibility to localised corrosion is strongly affected by heat treatments performed on Al-Zn-Cu-Mg alloys. In order to study how galvanic coupling between intermetallics and matrix is affected by solution heat treatment, AA7075-T6 and solution heat treated AA7075 have been characterised by means of scanning electron microscopy and scanning Kelvin probe force microscopy. Solution heat treatment strongly increased the Volta potential difference between the intermetallics and the surrounding matrix showing a strong increase in galvanic coupling. This is explained by Zn and Mg enrichment of the matrix caused by dissolution of strengthening particles during solution heat treatment.     

A correlation between Malva sylvestris extracts molecules and their corrosion inhibition capabilities

Experimental and quantum chemical investigations have been coupled in order to determine anticorrosion potential of Malva sylvestris extract molecules. The plant extract is a mixture of chemicals of which only four are abundant. Two groups of molecules are evidenced using quantum chemical parameters. The electrochemical investigation has classified the plant extract as a mixed-type inhibitor. The %EI has been only 54.5% due to antagonistic effects of the extract molecules.     

A critique of internal oxidation in alloys during the post-wagner era

Wagner's classical treatment of internal oxidation (generic name allowing for reaction with oxygen, nitrogen, carbon or sulfur) assumed ideal conditions such as uninhibited dissolution of the gas, formation of spherical particles, diffusion of the oxidant in the solvent as the rate-controlling step, equilibrium conditions, etc. However, during the 45 years since his treatment, many observations have been made to complicate the idealized situation suggested by Wagner. This paper examines the most important modifications with respect to Wagner's original analysis. The following items are discussed. (a) The role of solute concentration: The parabolic kinetics are much higher than expected for Ni–Al alloys due to rapid interfacial diffusion of oxygen along the interfaces between cylindrical rods of Al₂O₃ (perpendicular to the surface) and the matrix. (b) Precipitate morphology: Spherical precipitates seem almost to be the exception. A wide variety of forms have been observed, including Widmanstätten platelets, cylindrical rods, hexagonal plates, dendritic or fishbone products, etc. The competition between nucleation and growth is useful to explain the observed structures. (c) Intergranular internal oxidation: Rapid oxygen diffusion in grain boundaries may lead to a wide variety of intergranular-precipitate structures. (d) Internal-oxide bands: Wavy, approximately parallel bands form at a finite distance beneath the surface in certain alloys having very reactive solutes, e.g., Ag–Mg. It is postulated that high stresses generated by precipitation play a major role. (e) Surface nodules of pure solvent metal: High stresses generated during precipitation cause extrusion of solute through dislocation pipes, leading to extensive nodule formation on either grain boundaries or on the grains (or both), depending on the alloy and oxidizing conditions. (f) Nonstoichiometric precipitates: Either hypo- or hyperstoichiometric particles can form as very small clusters in certain alloys (Ag–Al). The nature of precursors and changes in stoichiometry during reaction are discussed. (g) Trapping of oxidant: Diffusion of the oxidant may be slowed appreciably by trapping with the solute, although no precipitates need to form. Lower-than-expected kinetics (based on normal diffusivities of the oxidant) result. (h) High-solubility-product precipitates: Concentration profiles of solute, oxidant and precipitate are quite different than those expected for low-solubility-product precipitates as considered by Wagner. In particular, a variable mole fraction of precipitate exists, and further precipitation occurs in the reaction zone after the front has passed by. Linear kinetics have been observed for some Nb-base alloys at very high temperatures and low oxygen pressures. The rate-controlling step is the arrival of oxygen at the surface and not oxygen diffusion in the metal. (i) Dual oxidants: Two gases may diffuse·simultaneously and each forms its own product with the solute. The thermodynamically most-stable compound forms near the surface, and the less-stable compound deeper in the alloy. The less-stable compound is subsequently converted to the more-stable compound with a concomitant release of the second oxidant. Although numerous examples have been reported of systems which do not behave as predicted by Wagner, his theory still remains as the cornerstone of our understanding and is still the starting point for virtually every study in internal oxidation.     

基于生物信息学的胃癌特征基因网络关键节点及预后关联分析

目的:本研究旨在利用生物信息学筛选胃癌的特征基因,探索胃癌的恶性机制。方法:通过GEO数据库筛选胃癌相关基因芯片作为训练集,并利用GEO2R工具分析胃癌组织相较于正常组织的差异基因,进而在验证集患者中对所筛选基因进行验证;采用String数据库计算其蛋白质-蛋白质相互作用(protein-protein interaction,PPI)网络。根据Cytoscape软件的Centiscape等插件分析PPI网络中的关键节点,分析蛋白相互作用相关性;并利用DAVID数据库对差异基因和PPI关键模块基因进行基因功能富集及注释。随后对关键节点基因进行生存分析。结果:所筛选出的63个特征差异基因对胃癌与正常组织区分度良好,主要参与调控细胞外基质受体相互作用、PI3K-AKT信号通路等。PPI网络中关键节点调控肿瘤增殖、转移。对关键节点基因进行生存性分析发现,ITGB1、COL1A2表达高的患者,其生存率远低于低表达患者（P<0.05）。结论:本文可为寻找胃癌发生发展的关键基因,探索胃癌治疗新靶点提供一定的理论依据。     

Linear analysis on the stability of lanthanide vapor complexes LnAl3Cli2(Ln = La to Lu)

The reactions LnCl3 (s) + (3/2)Al2Cl6 (g) = LnAl3Cl12 (g) for Ln = La to Lu were studied by quenching experi-ments in roughly the same temperature and pressure ranges (588-851 K and 0.01-0.22 MPa). Stability constants Kθ oflanthanide complexes LnAl3Cl12 were calculated from the measurements. The values of lg Kθ change linearly with theionpotential (Z+/r) of lanthanide(Ⅲ) from La to Gd and from Tb to Lu, respectively, indicating the Gd break. There exist in-clined W effect between lg Kθ and the total angular momentum L of lanthanide(Ⅲ). And hereby lanthanide elements aredivided into four segments, La-Nd, Pm-Gd, Tb-Ho, and Er-Lu. In each segment, the linearity is maintained.     

The correlation between the electronic structure and elastic properties of nanolaminates

Upon reviewing the correlation between the electronic structure and the elastic properties of nanolaminates based on the previously published ab-initio data, the authors suggest that nanolaminates can be described as interleaved layers of high and low electron density. M_n+1AX_n phases (space group P6₃/mmc) can be characterized by stacking of layers of high (MX) and low (A) electron density. Furthermore, the M_n+1AX_n phases possess the bulk-modulus-to-C₄₄ ratio of 1.2–1.7, which in turn gives rise to a combination of ceramic and metallic properties. This design criterion is not only limited to the M_n+1AX_n phases, but it can be found in many other phases crystallizing in the same space group (ternary phosphides, Al₃BC₃, Zr₂Al₃C₅, and W₂B₅ based phases) and the related space group P6/mmm (Y_n+1Co_3n+5B_2n) as well as in the phases of the cubic symmetry (perovskite borides and nitrides).     

A correlation between deviations in circularity, cylindricity, roughness and size tolerances

It is often necessary to prescribe size and form tolerances when specific workpiece accuracy is demanded. On the basis of published data and investigations carried out by the author a correlation has been developed between deviations in form for circularity and cylindricity, and International Organization for Standardization (ISO) tolerances. The range of application is for nominal sizes up to 10 000 mm and for tolerance grades 4–16. This correlation can help constructors and workshop workers to choose the size of form tolerances for circularity and cylindricity when a certain workpiece accuracy is demanded. The proposed correlation is verified by measurements of the fitting of workpieces for industrial production and the evaluation of measuring data.     

Measuring the mechanical properties of Pb-free solder and Sn-based intermetallics by nanoindentation

The technique of nanoindentation coupled with an atomic force microscope has been used to measure mechanical properties of Cu-Sn and Ag-Sn intermetallics at length scales similar to those observed in real solder joints. This article describes the experiment and discusses the results in terms of the effect of intermetallics on the reliability of microelectronic packages. The results show that, despite their high hardness, the intermetallics deform plastically without cracking at the small loads and length scales of nanoindentation testing. For more information, contact Richard R. Chromik, Lehigh University, Materials Research Center, 5 East Packer Avenue, Bethlehem, Pennsylvania 18015; (610) 758-6879, fax (610) 758-3526, email chromik@lehigh.edu.     

A correlation between the Pilling-Bedworth ratio and the radius of curvature of metallic substrates with coherent thin oxide layers

A correlation between the radius of curvature of metallic substrates with strainfree coherent monolayers of oxides and the Pilling-Bedworth ratio was found to follow the expression ¦R¦19.5/¦–1¦ for a large number of metal- oxide systems in which the metal and the oxide have identical cubic structures. For any given Pilling-Bedworth ratio , the radius of curvature of basally oriented hexagonal substrates was lower than that when the surface was perpendicular to the basal plane.     

Beneficial and detrimental Effects of Nitrogen on the oxidation behaviour of TiAl-based intermetallics

The isothermal oxidation of binary and ternary, Nh-containing titanium aluminides was studied at 900°C in air and Ar/O₂. It was found that the presence of nitrogen in the atmosphere is in some cases beneficial, in others detrimental. For an interpretation of the effects of nitrogen it is necessary to consider the various oxidation stages in which the mechanisms of titanium aluminide oxidation fundamentally differ. For High-Al alloys, which tend to form protective alumina based scales in the early oxidation stages, nitrogen always scenes to he detrimental because it promotes the formation of a more rapidly growing mixed alumina/titania scale. After this shift to mixed oxide scales, nitrogen can be detrimental as well as beneficial. It is proposed that the last mentioned case prevails if a near-continuous Ti-rich nitride layer is stable at the oxide/alloy interface, thereby preventing internal oxidation of aluminium. This beneficial effect, of nitrogen was found under all studied conditions for the Nb-containing alloys but only in some cases for the binary alloys.     

Deduction of plastic work rate per unit volume for unified yield criterion and its application

A unified linear expression of plastic work rate per unit volume is deduced from the unified linear yield criterion and the associated flow rule. The expression is suitable for various linear yield loci in the error triangle between Tresca's and twin shear stress yield loci on the π-plane. It exhibits generalization in which the different value of criterion parameter b corresponds to a specific linear formula of plastic work rate per unit volume. Finally, with the unified linear expression of plastic work rate and upper-bound parallel velocity field the strip forging without bulge is successfully analyzed and an analytical result is also obtained. The comparison with traditional solutions shows that when b=1/(1+(√3)) the result is the same as the upper bound result by Mises' yield criterion, and it also is identical to that by slab method with m=1, σ0=0.     

Effect of O impurity on structure and mechanical properties of NiAl intermetallics: A first-principles study

We have investigated the effects of O on the structure and mechanical properties of NiAl intermetallics using a first-principles pseudopotential total-energy method based on the density functional theory with the generalized gradient approximation. We found that the impurity O atom can either replace Ni atom or go into the tetrahedron interstitial site depending on the surrounding environment. In both cases, O tends to form an Al₂O₃-like tetrahedron structure with its nearest Al or Ni atoms, leading to the formation of the stronger O–Al bond containing covalent component. We demonstrate that the presence of O will cause an increase of the brittleness and a decrease of the ductility of NiAl based on the calculated elastic constants and the empirical criterions for both substitutional and interstitial cases. Our calculations provide a way to suppress the negative effect of O by adding the alloying element with lower electronegativity than that of Al.     

On a correlation between the electronic structure and passivability of Fe-Cr alloys

The chromium (5.8 to 30.7 wt. %) effect on the superfine magnetic structure and surrounding electrons of the ⁵⁷Fe nuclei in quenched and annealed Fe-Cr alloys is studied with the use of nuclear -resonant (Mö ssbauer) spectroscopy. The following parameters of the Mössbauer spectra are calculated by using PC with a Normos software: the effective magnetic intensity H _ef (in kOe), the isomeric (chemical) shift ° (in mm/s), the quadrupole electric splitting eq (in mm/s), and the area fraction S (%) of the superfine-structure subspectrum. Significant changes in the superfine magnetic structure and the electron surrounding of the ⁵⁷Fe nuclei are revealed as functions of the chromium content in the alloys. The conclusion on a correlation between the electronic structure of the alloys and their passivability is drawn.Translated from Zashchita Metallov, Vol. 41, No. 2, 2005, pp. 127–132.Original Russian Text Copyright © 2005 by Kasparova, Baldokhin, Solomatin.