Synthesis and characterization of mechanical-alloyed Ti–xMg alloys

The synthesis and characterization of Ti–xMg (x=4, 9, 12, 15, 21, 24 at%) alloys using mechanical alloying was investigated. A nanometer-sized Ti–24Mg alloy was produced. During mechanical alloying, the height of the XRD peaks of the Mg in the Ti–9Mg alloy decreased, and then disappeared, whereas the Ti XRD peaks broadened, and the grain size decreased with increasing milling time. The Mg firstly dissolved in the grain boundaries of the Ti, and then diffused into the Ti grain interiors. The grain boundaries played an important role in enhancing the solid solubility of Mg in Ti. With increasing Mg content the volume fraction of grain boundaries increased, and a decrease in grain size occurred after mechanical alloying for 48 h.     

Micromilling of Lamellar Ti6Al4V: Cutting Force Analysis

The aim of this article is to study the influence of a Ti6Al4V microstructure on cutting forces during the micromilling process. Samples were annealed above the β-transus at three different temperatures—1020, 1050, 1080°C—and then cooled in a furnace, air, and water, in order to produce different Widmastätten microstructures. Micromilling tests were carried out on heat-treated samples, and the cutting forces were measured by means of a load cell. The results were correlated to the sample microstructures, which were thoroughly investigated by means of an optical microscope, X-ray diffraction, and microhardness measurements.

The highest cutting forces were observed for soft and ductile furnace-cooled samples, suggesting that the most important factor affecting workability is the material ductility, while hardness is a less relevant parameter.     

Spinodal decomposition and clustering in III/V alloys

The criteria for clustering and spinodal decomposition in III/V pseudobinary and quaternary solid alloys are examined. A chemical driving force for clustering and phase separation exists in some ternary and most quaternary alloys. However, single crystalline alloys are shown to be stabilized by the coherency strain energy inherent in any clustering or spinodal decomposition in alloys where lattice parameter is a function of composition. Analytical expressions are derived for T_s, the temperature above which no clustering or phase separation should occur. Most III/V pseudobinary and quaternary alloys are stable at all temperatures. Numerical techniques are used to calculate spinodal isotherms. Results are presented for the systems Ga_xIn_1−x As P_1−y, A1_xGa_1−xAs_ySb_1−y, and Ga_xIn_1−x As P_1−y. This work was supported by the Department of Energy, contract No. DE-AT 03-81 ER 10934.     

Structural,electronic and thermodynamic properties of SrxCd1−xO: A first-principles study

First principles calculations have been performed within the framework of density functional theory to investigate the structural, electronic and thermodynamic properties of Sr_xCd_1?xO ternary alloys. The exchange-correlation potential for structural properties was calculated by the standard local density approximation (LDA) and GGA (PBE), a more accurate nonempirical density functional generalized gradient approximation (GGA), as proposed by Wu and Cohen [Physical Review B 73 (2006) 235116], while for electronic properties, the Engel and Vosko GGA (EVGGA) and the modified Becke–Johnson (MBJ) of the exchange-correlation energy and potential, respectively, are used. Deviation of the lattice constants from Vegard's law and bulk modulus from linear concentration dependence (LCD) were observed for the ternary alloys. The MBJ band gaps values agree well with the available experimental results. In addition the thermodynamic stability of the alloys was investigated by calculating the critical temperatures of alloys.     

Guidelines for establishment of correlations between mechanical properties and microstructure in Al–Si alloys

Abstract

This paper reports an analysis of the accuracy and sensitivity of ultimate tensile strength and strain to failure to changes in microstructure constituents in Al–Si alloys ranging from 7 to 18%Si. The influence of amount of constituents, namely dendrites, eutectic, silicon particles and intermetallics as well as their geometrical features, namely secondary dendrite arm spacing, silicon eutectic thickness and intermetallics thickness on both ultimate tensile strength and strain to failure is evaluated. This study provides information that will be useful in the establishment of robust correlations between mechanical properties and metallurgical features, since they are highly dependent on their sensitivity and accuracy.     

Ligand effects in heterogeneous catalysis and electrochemistry

Ligand effects in surface reactivity are discussed on the basis of extensive density functional theory calculations. The d-band model is reviewed and it is shown that it can be used to rationalize trends in reactivity in heterogeneous catalysis and electrochemistry.     

In situ scanning tunneling microscopy study of selective dissolution of Au3Cu and Cu3Au (0 0 1)

We present an electrochemical study of Au₃Cu (0 0 1) single crystal surfaces in 0.1 mol dm⁻³ H₂SO₄ and 0.1 mol dm⁻³ H₂SO₄ + 0.1 mmol dm⁻³ HCl, and of Cu₃Au (0 0 1) in 0.1 mol dm⁻³ H₂SO₄. The focus is on in situ scanning tunneling microscopy experiments. The changes of the surface morphology, which are time- and potential-dependent, have been observed, clearly resolving single atomic steps and mono-atomic islands and pits. Chloride additives enhance the surface diffusion and respective morphologies are observed earlier. All surfaces have shown considerable roughening already in the passive region far below the critical potential.     

Comparative Analysis of Energetic Properties of Ti6Al4V Titanium and EN-AW-2017A(PA6) Aluminum Alloy Surface Layers for an Adhesive Bonding Application

The purpose of this article is to present energetic properties of surface Ti6Al4V titanium as well as surface EN-AW-2017A(PA6) aluminum alloy layers. Values of surface free energy after selected mechanical operations and ozonation were compared. In addition, the influence of different values of ozone concentration on surface layer energetic activation was analyzed. Dispersive and polar components of surface free energy were of particular concern. Comparative evaluation of shearing strength of Ti6Al4V titanium and EN-AW-2017A(PA6) aluminum alloy single-lap adhesive bonded joints were presented. Results can be used as pro-ecological methods of titanium and aluminum alloys preparing for applications where adhesive phenomenon is important.     

HDPE-g-GMA反应性增容PA66/UHMWPE共混合金性能研究

以甲基丙烯酸缩水甘油酯接枝高密度聚乙烯(HDPE-g-GMA)作为聚酰胺66/超高摩尔质量聚乙烯(PA66/UHMWPE)共混合金的增容剂,采用熔融法制备了PA66/uHMwPE/HDPE-g-GMA共混合金.通过Molau试验、SEM观察和力学性能测试,研究了HDPE-g-GMA在熔融共混过程中对PA66/UHMWPE共混合金的增容作用.结果表明:HDPE-g-GMA与PA66发生了化学反应,所生成的接枝共聚物对PA66/UHMWPE共混合金有较好的增容作用;PA66/UHMWPE共混合金的界面形态和力学性能均有较大改善,吸水率也有所降低.     

Quantitatively comparing phase-field modeling with direct real time observation by synchrotron X-ray radiography of the initial transient during directional solidification of an Al-Cu alloy

The initial transient during directional solidification of an Al-4 wt.% Cu alloy was simulated by a quantitative phase-field model solved with the adaptive finite element method. The simulated solidification process was compared with the related analytical theory and in situ and real time observations by means of X-ray radiography at the European Synchrotron Radiation Facility. The simulated velocity of the planar interface and solute profile ahead of the solidification front in the liquid are close to the predictions of the Warren-Langer model of the initial planar solidification transient, but in fair quantitative agreement with experimental results only at early stages of planar solidification. After the accelerated flat interface lost its stability a transition to cellular solidification was initiated. The initial cell spacing predicted by the phase-field simulation agreed well with the experimental observations in the region where the cell growth direction was perpendicular to the fluid flow, whereas a discrepancy was obvious in the corners where the fluid flow was parallel to growth. An analytical relation describing the wavelength of the initial solid-liquid interface corrugations under diffusion-limited transport is screened out by comparing the phase-field simulation data with expressions based upon the Mullins-Sekerka linear stability analysis theory or derived for primary spacing. The gravity-driven natural convection in the experiment resulted in misfits between the phase-field predictions and the experimental observations in the late stage of planar solidification, onset and development of morphological instability.