Surface properties of liquid In-Zn alloys

The measurements of surface tension and density of zinc, indium and liquid In-Zn alloys containing 0.9, 0.85, 0.75, 0.70, 0.60, 0.40, 0.25 and 0.10 mole fraction of In were carried out using the method of maximum pressure in gaseous bubbles (MBP) as well as dilatometric technique. The technique of sessile drop was additionally applied in the measurements of surface tension for pure indium and zinc. The measurements were performed at temperature range 474-1151 K. The isotherms of surface tension calculated based on Butler's equation at 700 and 1100 K corresponded well with the experimental values for zinc content lower than 0.6 mole fraction. The surface tension calculated for alloys of higher zinc concentrations (0.6 < X_Zn < 0.95) had a positive value of the surface tension temperature coefficient (dσ/dT), which did not coincide with the experimental results. The density as well as molar volume of liquid In-Zn alloys showed almost identical behaviour like the ideal solutions. The observed little deviations were contained within assessed experimental errors.     

Thermodynamic Analysis of the System Bi-Au2Bi

Results of the experimental thermodynamic investigations of the system Bi-Au₂Bi obtained by using Oelsen calorimetry are presented in this paper. Activities, activity coefficients and partial molar quantities for bismuth in the temperature interval 600-1000 K are determined. Based on the values of the thermodynamic parameters, negative deviation from Raoult law was obtained for the investigated system. Also, bismuth activities and activity coefficients dependence on composition and temperature is calculated by the nonlinear programming using gradient method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Using capillary electrophoresis to study the chemical conditions within cracks in aluminum alloys

The environment-assisted cracking (EAC) susceptibility of some aluminum alloys used for airplane structural components currently limits their use in the peak strength condition. Understanding the mechanism of EAC will facilitate the development of crack-resistant alloys with optimum mechanical properties. One component towards understanding the fundamental processes responsible for EAC is a comprehensive knowledge of the chemical conditions within cracks. The present work uses capillary electrophoresis (CE) to quantify the crack chemistry in order to provide insight into the nature of the mechanism controlling cracking. The highly restricted geometry of cracks in metals means that a crack typically contains less than 10 μl of solution. The high mass sensitivity combined with the inherently robust nature of CE makes it an ideal analytical technique for this application. Complicating factors in the accurate determination of the crack environment include high levels of sodium present from the test solution. Low sample volume and analyte matrix complexity necessitated the development of specific sampling, extraction and analysis methods. Analysis of the crack solutions in EAC-susceptible material revealed high levels of Al³⁺, Mg²⁺, Zn²⁺, and Cl⁻ near the crack tip. Cations arise from the anodic dissolution of the alloy, whereas chloride ingress from the external environment occurs to maintain solution electroneutrality within the crack. In contrast, EAC-resistant material exhibited significantly lower concentrations of dissolution products.     

Microstructural evolution of AZ31 magnesium alloy subjected to sliding friction treatment

Microstructural evolution and grain refinement mechanism in AZ31 magnesium alloy subjected to sliding friction treatment were investigated by means of transmission electron microscopy. The process of grain refinement was found to involve the following stages: (I) coarse grains were divided into fine twin plates through mechanical twinning; then the twin plates were transformed to lamellae with the accumulation of residual dislocations at the twin boundaries; (II) the lamellae were separated into subgrains with increasing grain boundary misorientation and evolution of high angle boundaries into random boundaries by continuous dynamic recrystallisation (cDRX); (III) the formation of nanograins. The mechanisms for the final stage, the formation of nanograins, can be classified into three types: (i) cDRX; (ii) discontinuous dynamic recrystallisation (dDRX); (iii) a combined mechanism of prior shear-band and subsequent dDRX. Stored strain energy plays an important role in determining deformation mechanisms during plastic deformation.     

Theory of hydrogen solubility in binary iron alloys based on ab initio calculation results

Interaction of hydrogen atoms with three substitutional impurities (X?=?Pd, Ti, Cr) in bcc iron base solid solution was modelled ab initio using the WIEN2k package. It was shown that in spite of attraction between H and X atoms, excess energy of the H atom in tetrahedral sites in the first sphere of coordination of the X atom has a significant positive value, while the lowest negative values are observed in the second (Pd, ?0.087?eV; Ti, ?0.091?eV) or the third (Cr, ?0.032?eV) sphere. A new thermodynamic theory of hydrogen solubility in dilute bcc Fe–X alloys was developed on the basis of these results. The resulting equation was used to analyze existing experimental data on H solubility in a number of Fe–X alloys, and X–H interaction energies were determined for each case. The energies determined from high-temperature solubility data for Fe–Pd, Fe–Ti and Fe–Cr are somewhat greater than those obtained in ab initio calculations. The theory gives a new basis for analyzing hydrogen behaviour in iron-base solid solutions.     

高碘酸钾法测钢铁及合金中锰的改进建议

试样经酸溶解后,以磷酸-高氯酸混合酸(4 1)或(9 1)氧化至冒烟.在硫酸、磷酸介质中,用高碘酸钾将锰氧化到七价,测其吸光度.     

Effect of the shear layer on the etching behavior of 6060 aluminum extrusion alloys

The occurrence of preferential grain etching (PGE) during alkaline etching of aluminum extrusion alloys from the 6XXX series is often linked to the presence of certain impurity elements such as zinc, causing an undesired etching appearance. In the presented work, an additional culprit in this context is identified, which has not been investigated yet. A clear relation between PGE and the presence of a subsurface shear layer is identified for extruded Al 6060 alloys containing 0.02 and 0.06 wt% Zn. This shear layer can be distinguished from the bulk of the metal by its difference in crystallographic texture as visualized by electron backscatter diffraction (EBSD). For the Zn enriched alloy, the <111>//ND grains are etched away faster than grains with other orientations, resulting in the grainy appearance typical for PGE. Independent of the Zn content in the alloy, once the shear layer is removed and <111>//ND grains are practically absent on the new surface, the depths variations caused by preferential etching disappear. Instead, the surface of the alloy is attacked uniformly by the caustic etch bath.     

基于LIBS技术的钢铁合金中元素多变量定量分析方法研究

针对钢铁合金样品元素组成相对复杂,基体效应较严重的问题,利用激光诱导击穿(LIBS)光谱技术对钢铁合金中的元素进行了定量分析。以Nd∶YAG脉冲激光器基频1 064 nm波长激光作为激发光源,采用中阶梯光栅光谱仪和ICCD分光探测钢铁合金样品的LIBS光谱。通过优化实验确定最佳探测延时为1.5 μs,最佳探测门宽为2 μs,激光聚焦点位置在实验样品靶面以下1.5 mm。采用单变量定量分析、多变量线性回归和偏最小二乘(PLS)三种方法分析钢铁合金中Cr元素和Ni元素的含量。结果表明,采用单变量定标方法定标曲线相关系数不高,对待测样的预测误差相对较大,难以有效地定量分析基体元素复杂的钢铁合金中金属元素的含量;采用多变量线性回归分析方法能有效提高定量分析的精度;采用PLS方法得到的Cr和Ni元素的拟合曲线相关系数r分别为0.981和0.995,对两个待测样品中Cr元素和Ni元素的预测相对误差在6.4%和7.1%以内,分析结果优于多变量线性回归方法。可见,采用多变量校正的PLS方法能更有效地校正基体效应对定量分析的影响,提高定量分析的精度。     

Electron Dispersion in Liquid Alkali and Their Alloys

Ashcroft's local empty core (EMC) model pseudopotential in the second-orderperturbation theory is used to study the electron dispersion relation, theFermi energy, and deviation in the Fermi energy from free electron value forthe liquid alkali metals and their equiatomic binary alloys for the firsttime. In the present computation, the use of pseudo-alloy-atom model (PAA)is proposed and found successful. The influence of the six different formsof the local field correction functions proposed by Hartree (H), Vashishta-Singwi (VS), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F), andSarkar et al. (S) on the aforesaid electronic properties is examined explicitly,which reflects the varying effects of screening. The depth of the negativehump in the electron dispersion of liquid alkalis decreases in the orderLi →K, except for Rb and Cs, it increases. The results of alloys are in predictive nature.     

Three dimensional large deformation analysis of phase transformation in shape memory alloys

Shape memory alloys（SMAs）have been explored as smart materials and used as dampers,actuator elements,and smart sensors.An important character of SMAs is its ability to recover all of its large deformations in mechanical loading-unloading cycles without showing permanent deformation.This paper presents a stress-induced phenomenological constitutive equation for SMAs,which can be used to describe the superelastic hysteresis loops and phase transformation between Martensite and Austenite.The Martensite fraction of SMAs is assumed to be dependent on deviatoric stress tensor.Therefore,phase transformation of SMAs is volume preserving during the phase transformation.The model is implemented in large deformation finite element code and cast in the updated Lagrangian scheme.In order to use the Cauchy stress and the linear strain in constitutive laws,a frame indifferent stress objective rate has to be used.In this paper,the Jaumann stress rate is used.Results of the numerical experiments conducted in this study show that the superelastic hysteresis loops arising with the phase transformation can be effectively captured.