Solidification behaviour of ceramic particle reinforced Al-alloy matrices

Novel metal matrix composites have been produced by cast production route. TiC and WC ceramic reinforcing particles have been successfully introduced into Al 6060, Al 319, Al 356, Al–7Si–5Mg, Al–20Cu and Al 2007 alloys. Refined grain structure and various intermetallic phase formation have been observed. Particle–melt and particle–solidification front interactions, solidification sequence and particle–matrix interfacial characteristics have been examined by means of metallography, SEM examination and EDX analysis. Particle distribution, intermetallic phase formation and location and grain structure are discussed in terms of ceramic-melt wetting characteristics, alloying element interfacial segregation and particle–solidification front thermal behaviour.     

Effects of Cu and Al on the crystal structure and composition of η (MgZn2) phase in over-aged Al–Zn–Mg–Cu alloys

Heat treatable Al–Zn–Mg alloys can be strengthened by the precipitation of second phase particles. In this paper, Al–6.57%Zn–2.83%Mg and Al–6.57%Zn–2.83%Mg–3.92%Cu alloys (in wt%) in T7 state (140 °C for 96 h) have been prepared. The effects of Cu and Al on the concentration and structure of equilibrium η (MgZn₂) phase have been investigated by high resolution transmission electron microscopy, aberration-corrected scanning transmission electron microscopy, selected election diffraction pattern simulations, and first-principles calculations. The effects of Cu and Al substitution on the diffraction characteristics of the η phase and the general rule of Cu and Al substitution in the η phase have been discussed.     

Using direct hot-rolling approach to obtain dual-phase weathering steel Cu–P–Cr–Ni–Mo

A weathering steel Cu–P–Cr–Ni–Mo has been developed which exhibits special continuous cooling transformation characteristics which permit the desired dual-phase (DP) microstructure to be obtained by direct hot-rolling. Hot-rolling procedures to obtain DP microstructures have been designed based on the continuous cooling transformation diagram of weathering steel Cu–P–Cr–Ni–Mo. The results show that the microstructures of DP weathering steels Cu–P–Cr–Ni–Mo are characterized by an irregular distribution of island-shaped martensite–austenite in the matrix of polygonal ferrite grains. DP weathering steel Cu–P–Cr–Ni–Mo with favorable corrosion resistant property, weldability and mechanical properties, such as, high strain hardening exponent values, a lower ratio of yield to tensile strength, and higher strengths; and is obtained successfully by direct hot-rolling.     

Thermal-Conductivity Measurements and Predictions for Ni–Cr Solid Solution Alloys

Thermal conductivities of Ni–Cr solid solution alloys have been measured to develop a prediction equation for thermal conductivities as functions of temperature and chemical composition. Samples used were Ni–x at% Cr (0 ≤ x ≤ 22) and commercial alloys of Nichrome Nos. 1 and 2. Thermal conductivity measurements were carried out using the transient hot-strip method over a temperature range from 293 K to 1273 K. The thermal conductivities of the alloys increased with increasing temperature and decreased with increasing Cr concentration at constant temperature. The Smith–Palmer equation has been examined to relate the thermal conductivities of the alloys to the electrical resistivities. The thermal conductivity and electrical-resistivity data, respectively, in the present work and in the literature have confirmed that the Smith–Palmer equation applies to Ni–Cr solid solutions and Nichrome alloys. On the basis of this equation, the thermal conductivity of Ni–Cr solid solution alloys has been expressed as a function of temperature and chemical composition. This analysis has also been applied to Ni–Fe and Cu–Ni solid solution alloys.     

Strain–life curves of steels and methods for determining the curve parameters. Part 1. Conventional methods

The available publications give much consideration to strain–life curves which are usually described by the Basquin–Manson–Coffin equation. The parameters of this equation are related to those of the Ramberg–Osgood equation that represents the cyclic stress–strain diagram. Many different methods have been put forward for the assessment of parameters of these equations on the basis of static strength and plasticity characteristics. Most of the methods rely on a fairly small body of experimental evidence. Using the experimental data on static and cyclic strength and plasticity characteristics of about 200 various steels from the well-known publications, a statistical analysis of parameters of Basquin–Manson–Coffin and Ramberg–Osgood equations has been performed by each of the assessment methods, revealing their advantages and disadvantages.     

Pearlite in hypoeutectoid iron–nitrogen binary alloys

In this study, hypoeutectoid Fe–N binary specimens have been prepared by gas nitriding pure iron in austenite domain at 840 °C. The slow cooling of these specimens led to the α-ferrite + γ′-Fe₄N pearlitic microstructure which is similar to the pearlite in Fe–C binary system. This pearlitic microstructure has been characterized by electron microscopy. The crystal structure of the γ′-Fe₄N nitride has been identified by electron microdiffraction and the Nishiyama–Wassermann (N–W) and near Kurdjumov–Sachs (K–S) orientation relationships have been found between the α-ferrite and the γ′-Fe₄N.     

Analysis of three-dimensional structures in complex turbulent flows

The basic integral relations used in analyzing various images of flows are given. The differences in the Abel transform for laminar and turbulent flows have been shown. The integral Uberoi–Kovasznay transform used in analyzing direct-shadow images of turbulent flows has been described. The present possibilities of digital laser speckle-photography for analyzing speckle-images of turbulent flows with the use of integral Erbeck–Merzkirch transforms have been analyzed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 8–17, January–February, 2009.     

Simulation of the supersonic turbulent flow around a cylinder with coaxial disks

The turbulent axisymmetric flow around a stepped body — a cylinder with coaxial front and rear disks — has been calculated with the aid of a VP2/3 package based on multiblock computational technologies and the generalized procedure of pressure correction. The computational model has been tested with the example of a supersonic flow around a sphere. The numerical forecasts made with the use of Spalart–Allmares shear stress transfer and eddy viscosity transfer models have been compared with the data of the aeroballistic experiment, wind tunnel tests, and the results of the calculation of the flow around the disk–cylinder arrangement by a simplified zonal model in a wide range of variation of the incident flow Mach number (from 1.5 to 4). We have obtained a good agreement between the calculated transverse flow density distributions in the front stalling zone and those determined from the interferograms for the wave-drag-rational disk–cylinder arrangement. The influence of the rear disk on the drag of the disk–cylinder–disk arrangement has been estimated.     

Electrical conductivity, thermoelectric power and viscosity of liquid Sn-based alloys

Shear viscosity of liquid Sn–Ag, Sn–Cu and Sn–Ag–Cu eutectics from melting temperature up to 1100 K and their electrical conductivity and thermoelectric power up to 850 K have been investigated. The electrical properties of liquid Sn with additions of Fe and Ni have also been studied. It is shown that small amounts of metal admixtures affect noticeably the behavior of the physical properties of liquid Sn.     

Microstructure features of failure and mechanical properties of ultra-fine grained Ti–6AL–4V ELI alloy at 300–77 K

Experimental investigation of mechanical characteristics and failure regularities of the ultra-fine grained Ti–6Al–4V ELI alloy, produced by equal channel angular pressing (ECAP), have been carried out under the uniaxial tension at 300 and 77 K. These characteristics have been compared for the different structural states of the Ti–6Al–4V ELI alloy, distinguished by the average grain size and by the morphology of α and β phases. It has been established that the combination of the heat treatment, ECAP, and the extrusion of the Ti–6Al–4V ELI alloy leads to a considerable increase of the alloy’s strength in comparison with the initial state (54% at 300 K and 78% at 77 K) with preserving the reasonable values of the ductility (3–4% elongation to the neck beginning and 5–10% to the failure). For all investigated structural states of the Ti–6Al–4V ELI alloy only ductile failure was observed at 300 and 77 K. The fracture surface consists of regions failed under normal and shear stresses. In shear failure regions of fracture surface only elongated dimples were present.     

Wear characteristics of spray formed Al-alloys and their composites

In the present investigation, different Al based alloys such as Al–Si–Pb, Al–Si, Al–Si–Fe and 2014Al + SiC composites have been produced by spray forming process. The microstructural features of monolithic alloys and composite materials have been examined and their wear characteristics have been evaluated at different loads and sliding velocities. The microstructural features invariably showed a significant refinement of the primary phases and also modification of secondary phases in Al-alloys. The Pb particles in Al–Si–Pb alloy were observed to be uniformly distributed in the matrix phase besides decorating the grain boundaries. The spray formed composites showed uniform distribution of SiC particles in the matrix. It was observed that wear resistance of Al–Si alloy increases with increase in Pb content; however, there is not much improvement after addition of Pb more than 20%. The coefficient of friction reduced to 0.2 for the alloy containing 20%Pb. A sliding velocity of 1 ms⁻¹ was observed to be optimum for high wear resistance of these materials. Alloying elements such as Fe and Cu in Al–Si alloy lead to improved wear resistance compared to that of the base alloy. The addition of SiC in 2014Al alloy gave rise to considerable improvement in wear resistance but primarily in the low pressure regime. The wear rate seemed to decrease with increase in sliding velocity. The wear response of the materials has been discussed in light of their microstructural features and topographical observation of worn surfaces.     

ZnO/Si solar cell fabricated by spray pyrolysis technique

The ZnO/Si heterojunctions have been prepared by depositing n-ZnO films doped with aluminium on p-Si by spray pyrolysis method. Heterojunction solar cells were fabricated using the configuration Al/ZnO/Si/In. The electrical properties of the heterojunction are investigated by means of current–voltage measurements in the temperature range 295–375 K. The cells show the rectifying behaviour characterized by the current–voltage (I–V) measurement under a dark condition, while photoelectric effects have been exhibited under the illumination. As a result, the conversion efficiency of the fabricated cell of about 6.6% was obtained.     

Sol–gel processing and UVA patterning of epoxy-based hybrid organic–inorganic thin films

Sol–gel processed photosensitive hybrid organic–inorganic films, deposited from 2-(3,4-epoxycyclohexylethyltrimethoxysilane) (EETMOS), have been studied. EETMOS sols have been optimized with respect to several criteria that guarantee a good quality, photosensitivity, and reproducibility of derived films. Photo-sensitivity of EETMOS-based films has been assessed by UVA exposure experiments. Optimized films have been photo-patterned using a mercury lamp or a He–Cd laser source, both emitting in the UVA spectral range. Promising micronic size motives have been laser patterned. The quality of derived motives is discussed with respect to photopolymerization mechanisms and photo-patterning parameters.     

Tuning the stress induced martensitic formation in titanium alloys by alloy design

Two novel titanium alloys, Ti–10V–2Cr–3Al and Ti–10V–1Fe–3Al (wt%), have been designed, fabricated, and tested for their intended stress-induced martensitic (SIM) transformation behavior. The results show that for Ti–10V–1Fe–3Al the triggering stress for SIM transformation is independently affected by the β domain size and β phase stability, when the value of the molybdenum equivalent is higher than ~9. The triggering stress was well predicted using the equations derived separately for the commercial Ti–10V–2Fe–3Al alloy. For samples containing β with a lower molybdenum equivalence value, pre-existing thermal martensite is also present and this was found to have an obstructive effect on SIM transformation. In Ti–10V–2Cr–3Al, the low diffusion speed of Cr caused local gradients in the Cr level for many heat treatments leading even to martensite free zones near former β regions.     

Yield stress of SiC reinforced aluminum alloy composites

This article develops a constitutive model for the yield stress of SiC reinforced aluminum alloy composites based on the modified shear lag model, Eshelby’s equivalent inclusion approach, and Weibull statistics. The SiC particle debonding and cracking during deformation have been incorporated into the model. It has been shown that the yield stress of the composites increases as the volume fraction and aspect ratio of the SiC particles increase, while it decreases as the size of the SiC particles increases. Four types of aluminum alloys, including pure aluminum, Al–Mg–Si alloy, Al–Cu–Mg alloy, and Al–Zn–Mg alloy, have been chosen as the matrix materials to verify the model accuracy. The comparisons between the model predictions and the experimental counterparts indicate that the present model predictions agree much better with the experimental data than the traditional modified shear lag model predictions. The present model indicates that particle failure has important effect on the yield stress of the SiC reinforced aluminum alloy composites.     

Investigation of the dynamics of radiative micropinch discharges

The dynamics of plasma cylinder compression by current pulses with a rise time of ∼100 nsec in the Z-pinch geometry has been considered. The numerical simulation has been performed in the approximation of one-dimensional magnetic radiation gas dynamics. In the calculations, real thermodynamic, transport, and optical properties of the plasma have been used. The radiation transfer is described in the multigroup approximation by the photon energy. The calculations have been performed for a pinch in xenon (radius ∼0.5 cm, energy E₀ = 10–30 J, maximum current ∼30 kA). A detailed pattern of the dynamics of pinches has been investigated and the energy-to-radiation conversion efficiency has been determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 216–222, March–April, 2008.     

The role of Chinese–American scientists in China–US scientific collaboration: a study in nanotechnology

In this paper, we use bibliometric methods and social network analysis to analyze the pattern of China–US scientific collaboration on individual level in nanotechnology. Results show that Chinese–American scientists have been playing an important role in China–US scientific collaboration. We find that China–US collaboration in nanotechnology mainly occurs between Chinese and Chinese–American scientists. In the co-authorship network, Chinese–American scientists tend to have higher betweenness centrality. Moreover, the series of polices implemented by the Chinese government to recruit oversea experts seems to contribute a lot to China–US scientific collaboration.     

Changes on the nanostructure of cementitius calcium silicate hydrates (C–S–H) induced by aqueous carbonation

The nanostructure of the main binding phase of the hydrated cements, the calcium silicate hydrates (C–S–H), and their structural changes due to aqueous carbonation have been characterized using TEM, nitrogen physisorption, and SAXS. Synthetic C–S–H has been used for this purpose. Two different morphologies were identified, similar to the high density and low density C–S–H types. When submitting the sample to a CO₂ flux, the low density phase was completely carbonated. The carbonation by-products, calcium carbonate, and silica gel were also identified and characterized. The precipitation of the silica gel increased the specific surface area from 95 to 132 m²/g, and its structure, formed by particles of ~5 nm typical radius, was observed by small angle X-ray scattering. In addition, the resistance of the high density C–S–H to carbonation is reported, and the passivating effect of the precipitated calcium carbonate is also discussed. Finally, the results have been compared with carbonation features observed in Portland cement carbonated experimentally at downhole conditions.     

Electrical characterization of LiTaO<Subscript>3</Subscript>:P(VDF–TrFE) composites

Composites of pyroelectric ceramics and polymers are very important as their unique features and properties can be easily tailored for various specific applications. Lithium tantalatum oxide (LiTaO₃, LT), the pyroelectric ceramic powder has been incorporated into a polyvinylidene fluoride–trifluoroethylene [P(VDF–TrFE) 70/30 mol%] copolymer matrix to form 0–3 composites. The composite films were prepared using ‘solvent casting’ (SC) method to disperse the ceramic powder homogeneously in the P(VDF–TrFE) copolymer matrix with various wt% of LT powder. In order to derive high pyroelectric performance, the samples were poled. Electric properties, such as the dielectric constant, dielectric loss, and pyroelectric coefficient, have been measured as a function of temperature and frequency. In addition, material figures-of-merit, very important factors for assessing many sensor applications have also been calculated. The results show that the fabricated lead free lithium tantalite: P(VDF–TrFE) composite materials have a good potential for pyroelectric infrared sensor applications.