Influence of heat treatment and particle shape on mechanical properties of infiltrated Al2O3 particle reinforced Al–2 wt-% Cu

Abstract

Carbon dioxide (CO₂) generation by ultraviolet irradiation of poly(ethyleneterephthalate) (PET) films in oxygen was monitored by in situ Fourier transform infrared spectroscopy. Typically, the CO₂ absorbance increased by ～100 × 10^?4 in 180 min, with no evidence of hindrance by restricted diffusion of O₂ into, or CO₂ out of, the films. It was concluded that Fourier transform infrared spectrometry monitoring of CO₂ conveniently, reliably and rapidly measures PET films photostability.

Quantitative analysis of the CO₂ evolved from progressively thinner films from successive stages of the biaxial film drawing process indicated that CO₂ was generated within a few microns of the film surface and that the same amounts were generated from the irradiated surface of 540 μm cast, 150 μm uniaxially drawn and 85 μm biaxially drawn films. Although drawing increased film crystallinity, photoreactivity appeared to be unchanged. However, total CO₂ formation followed the pattern PET cast相似文献   

Optimal heat exchanger network synthesis using particle swarm optimization

Heat exchanger network (HEN) synthesis has been a well-studied subject over the past decades. Many studies and methodologies were proposed to make possible the energy recovery, minimizing the utilities consumption and the number of heat transfer equipment.     

Effect of post-weld heat treatment on heat affected zone microstructures of microalloyed C–Mn submerged arc welds

Abstract

The effect of various post-weld heat treatment (PWHT) cycles on the as welded heat affected zone (HAZ) microstructures of C–Mn steels microalloyed with niobium, or niobium plus vanadium, has been studied. Single pass welds were produced at an arc energy of 3·5 kJ mm^?1; examination was carried out using optical and electron microscopy, along with hardness and crack tip opening displacement testing. As welded, the C–Mn–Nb HAZ contained a significant proportion of auto tempered martensite. After PWHT at 550°C, isolated hard regions remained, but at 600°C all hard regions had been removed, with a concomitant increase in cleavage resistance. In contrast, ferrite with aligned second phase with lower hardness was found mainly in the as welded HAZ of the C–Mn–Nb–V steel. When the PWHT temperature was raised, HAZ hardness increased to a maximum at 600°C; overaging would be required to obtain improved toughness, although this would soften the parent plate. The results indicate that the current practice of specifying a common heat treatment procedure for steels to a given specification is not satisfactory; allowance should be made for the particular composition and as welded HAZ microstructure.

MST/1190     

The influences of particle–particle interaction and viscosity of carrier fluid on characteristics of silica and calcium carbonate suspensions-coated Twaron® composite

The effects of particle–particle interaction and viscosity of carrier fluid on steady and dynamic rheological responses and quasi-static penetration resistance of Twaron® fabrics treated with shear thickening and shear thinning suspensions have been investigated. The suspensions have been made by mechanically dispersing 60 nm silica (SiO₂) and calcium carbonate (CaCO₃) nanoparticles in poly ethylene glycol (PEG) with molecular weights of 200 and 400 g/mol. The CaCO₃ suspensions display shear thinning behaviour along with the total dominance of the elastic state over the viscous state while the SiO₂ suspensions exhibit shear thickening behaviour with the emergence of both the elastic and viscous states. With the increase of molecular weight of PEG, viscosity, viscoelastic modules and instability of the suspensions increase and critical shear rate and frequency of transition to elastic state diminish. The PEG200 and PEG400-contained SiO₂ suspensions-treated Twaron® composites at 35 wt.% have quasi-static penetration resistances which are nearly 2.63 and 2.48 times and maximum absorbed energies which are about 1.54 and 1.55 times higher, respectively, than those of the corresponding CaCO₃ ones. However, the influence of increasing the PEG's molecular weight is not as considerable as the effect of particle–particle interaction on the enhancement of penetration resistance performance.     

Effects of particle–particle collisions on sudden expansion gas-particle flows via a two-phase kinetic energy-particle temperature model

In the framework of the gas–particle two-fluid mode, an improved gas–particle two-phase kinetic energy incorporating into a particles collision model (k–k_p–θ) is proposed to study the sudden expansion gas–particle turbulent flows in a cylindrical pipe section. Anisotropy of gas–solid two-phase stress and the interaction between two-phase stresses are considered by means of a transport equation of two-phase fluctuation velocity correlation. Xu and Zhou [10] experimental data is used to quantitatively validate k–k_p–θ and k–k_p model for analysis the effects of particle–particle collision. Numerical predicted results show that time-averaged velocity, fluctuation velocity of gas and particle and correlation of two-phase fluctuation velocity considering particles collision are better than those of the without particle temperature model and they are in good agreement with experimental data. Larger particle concentration and particle temperature located at shear layer adjacent to wall surface and re-circulation region. Energy dissipation due to smaller scale particles collision contributes to homogeneous distribution of Reynolds stress and affects the particle transportation behavior together with particle inertia.     

What dominates heat transfer performance of hybrid nanofluid in single pass shell and tube heat exchanger?

Influence of nanoparticle volume concentration and proportion on heat transfer performance (HTP) of Al₂O₃ – Cu/water hybrid nanofluid in a single pass shell and tube heat exchanger is analyzed. Multiphase mixture model is adopted to model the flow. Three-dimensional governing equations and associated boundary conditions are solved using finite volume method. The numerical results are validated with the experimental results. Results indicate that optimized nanoparticle volume concentration and proportion dominate HTP of hybrid nanofluid. Heat transfer coefficient and Nusselt number are monotonic increase functions of nanoparticle volume concentration and proportion. The percentage increase in heat transfer coefficient of hybrid nanofluid is 139% than water and 25% than Cu/water nanofluid. At higher Reynolds number, the increment in Number of Transfer Units (NTU) between water and hybrid nanofluid is close to 75%. Maximum enhancement in Nusselt number for hybrid nanofluid exceeds 90% when compared to nanofluid (Al₂O₃/Water nanofluid). Consequently, highest heat transfer performance is attained for hybrid nanofluid systems. Effectiveness of heat exchanger increases almost to 124% when hybrid nanofluid is employed. We show that it is higher than water as well (conventional coolant). Results are expected to be helpful in further industrial-scale deployment of nanofluids, which is an area that is currently relevant for ongoing academia-industry partnership efforts worldwide.     

An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

Effect of particle size on in vitro cytotoxicity of titania and alumina nanoparticles

Aluminium oxide (Al₂O₃) and titanium dioxide (TiO₂) nanoparticles (NPs) have been widely used in nanotechnology-based products. Recently, researchers and the public have raised concerns about the adverse effects of these NPs in biological systems, particularly in humans. The aim of this study was to investigate the possible adverse effects of these two common metal oxide NPs on human lung epithelium cells (A549) and to investigate NP size-dependent effects on these cells, considering both the primary and hydrodynamic particle size. NPs were found to inhibit cell viability and proliferation at the highest concentration level (10?mg/mL) included in this study, as measured by a clonogenic assay. Moreover, cell viability, proliferation and metabolism were impaired to a greater extent by the smaller NPs (5?nm TiO₂ and 10?nm Al₂O₃) relative to the larger particles (200?nm TiO₂ and 50?nm Al₂O₃) included in this study, as measured by cell proliferation and metabolism. Notably, the observed cytotoxic effects correlated to the primary size, rather than the hydrodynamic size. Similarly, NP cytotoxicity was found to be correlated with the NP surface area. These findings highlight the importance of including primary size and surface area information in NP characterisation in cytotoxicity studies.     

Effect of β heat treatment on phase transformations of TC21 during rolling

Phase transformations during hot rolling is determined for the forged and β heat treated TC21 titanium alloys. The results show that β heat treatment has a great effect on phase constitution. Three types of precipitates, namely, α₂, ω and (Ti, Zr)₅Si₃ phase is observed in the rolled forged materials, whereas the rolled β heat treated materials exhibites the presence of lamellar α and type 2α precipitate. The influence of β heat treatment on the phase transformations has been discussed on the basis of alloying elements, and β heat treatment can eliminate or decrease elemental segregation.     

Development of microstructure during heat treatment of high carbon Cr–Mo steel

Abstract

Stainless steels containing enhanced chromium and carbon contents are particularly attractive for applications requiring improved wear and corrosion resistance. The as cast microstructure of such steels is composed mainly of ferritic matrix along with a network of interdendritic primary carbides. It has been shown that heat treatment of these steels results in microstructures that contain more than one type of carbide. A selective dissolution technique has been employed to isolate carbides from the matrix. Scanning electron microscope and X-ray diffraction studies of the as cast steels have shown that the primary carbides are essentially of M₇C₃ type, whereas in heat treated specimens both M₇C₃ (primary) and M₂₃C₆ (secondary) type carbides have been observed. The relative amounts of these carbides are found to be dependent on the heat treatment temperature. In addition, nucleation of austenite occurs above 950°C and at ～1250°C the matrix transforms entirely to austenite, which is retained completely on quenching to room temperature.     

Investigation of two-phase heat transfer coefficients of argon–freon cryogenic mixed refrigerants

Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon–freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.     

Development of a procedure for spherical alginate–boehmite particle preparation

Herein we describe a versatile new strategy for producing spherical solid particles with 2 mm in size using integrated gelling process. The method involves the formation of spherical droplets by using a peristatic pump device and shaping the droplets in a liquid calcium chloride solution. The shape and size of these calcium alginate macroparticles depend strongly on the calcium solution concentration. The shaping mechanism of the macroparticles and the impact of the experimental conditions on particle shape and size are investigated. This method has the following features: (1) A new level of control over the shapes of the particles is offered. (2) The procedure can be scaled up to produce large numbers of particles. (3) The final porous structure of the developed particle can be designed for a specific application (adsorption, catalysis).     

Inertia of measurements with “auxiliary-wall” type heat meters

The article examines the problem of thermal inertia on the basis of an auxiliary-wall type heat meter, it demonstrates the boundaries of applicability of the approximate relationship for calculating non-steady-state heat fluxes.Notation q() non-steady-state heat flux through the heat meter - _i,a _i thermal conductivity, thermal diffusivity, and thickness of the heat meter, respectively - ₂,a ₂ thermal conductivity and thermal diffusivity, respectively, of the base of the heat meter - t() temperature gradient over the thickness of the heat meter - index of thermal inertia - time - s parameter of Laplace transform - t₁ (x, ) temperature of the heat meter at point x - t₂(x, ) temperature of the base - t_c ambient temperature - Y_q(s) transfer function from the heat flux q() to the temperature gradient t() Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 298–305, August, 1980.     

Control of particle interfaces — the critical issue in nanoparticle technology

In the field of particle technology, processes cannot yet be designedfroma basic molecular understanding. Nanotechnology, however, begins to bridge this gap between molecules and particles, and may thus not only open new ways for the production and handling of particulate matter, but also for the engineered design of advanced material properties. The visions and applications in nanoparticle technology cover a broad range, e.g. quantum dots in information technology, refractory particles for advanced ceramics, highly active substances in pharmacy, catalysts and micro- and mesoporous adsorbents to name only a few applications. Starting from the concept of product engineering we investigate the basic preconditions for tailoring nanoparticulate properties, i.e. the control of the particle interactions. This concept is then applied to precipitation as an example for particle synthesis and to particulate thin film formation as an example for structure formation.     

Preparation and properties of cast aluminium alloy–sillimanite particle composite

An attempt has been made to explore the possibility of using natural mineral namely sillimanite for synthesizing aluminium alloy composite through a solidification technique. The sillimanite particles were characterized in terms of X-ray, differential thermal analysis in order to examine their suitability for preparing the composite. An aluminium alloy (BS:LM6) was used as the matrix alloy. The sillimanite particles of mean size 140 μm (major axis) were used as reinforcement. The sillimanite particles were added into the matrix melt by creating a vortex with the help of a mechanical stirrer and the melt temperature was maintained between 750 and 800°C. The cast composite was characterized in terms of microstructural, mechanical and abrasive wear properties. It was noted that the sillimanite particles were reasonably uniformly distributed within the matrix and exhibited good mechanical bonding with the matrix. The strength of the composite was noted to be marginally lower than that of the base alloy but the hardness and the wear resistance of the composite were found to be significantly higher than those of the base alloy.     

Experimental investigation of heat transfer enhancement in helical coil heat exchangers using water based CuO nanofluid

The present work deals with the study of heat transfer enhancement using water based CuO nanofluids in the helical coil heat exchanger. Nanofluids were prepared using two-step method by using wet chemical method. Nanofluids with various volume percentage between 0 and 0.5 of CuO nanoparticles and their flow rate between 30 and 80 LPH (Reynolds number ranging from 812 to 1895, Laminar flow regime) were considered in the present study. The setup consists of a test section (helical coil), cooler, reservoir, pump, flow meter, thermocouples and flow controlling system. The temperature measurements were carried out with the help of thermocouples. The investigation was carried out to study the effect of particle loading and flow rate on heat transfer coefficient and Nusselt number. It has been found that the increase in the loading of CuO nanoparticles in base fluid shows a significant enhancement in the heat transfer coefficient of nanofluid. In the present study, at 0.1 vol% concentration of CuO nanoparticles in nanofluid, enhancement in heat transfer coefficient was 37.3% as compared to base fluid while at 0.5 vol%, it is as high as 77.7%. Also with the increase in the flow rate of the CuO nanofluid, significant increase in heat transfer coefficient was observed.     

Effect of heat treatment on morphology of Fe-rich intermetallics in Al–Cu alloys

The iron-rich intermetallics are considered to be stable in aluminium alloys and usually hard to dissolve into the matrix during solution heat treatment (SHT). Nevertheless, solid-state transformations between Fe-rich intermetallics may happen and will play a great role in breaking-up of the large Fe-rich intermetallics particle during hot deformation process. In this study, the solid-state phase transformation of the iron-rich intermetallics from Al_mFe to β-Fe (Al₇Cu₂Fe) has been studied using SEM, XRD and deep-etched technique in a 2xxx Al–Cu cast alloy during SHT. The mechanism of solid-state transformation for the Fe-rich intermetallics was discussed, including the solid-state reaction, nucleation and growth of iron-rich intermetallics and Al phases.     

Detailed analysis of particle–substrate interaction based on a centrifugal method

The interaction between particles and inclined substrates in a centrifuge was investigated theoretically and experimentally. First, the balance of the force acting on a particle adhering to the substrate, with an inclination angle from 0 to 90° to the horizontal, was formulated separately in the normal and tangential directions. The adhesion force was then derived based on the point-mass model as a function of the angular velocity. Next, the balance of the moments of the forces acting on a particle adhering to the substrate was formulated; theoretical equations for the adhesion force and the effective contact radius were then derived from the angular velocities, obtained at any two inclination angles, based on the rigid-body model. Finally, the removal fraction curves of spherical/nonspherical particles with median diameters of less than 10 µm were experimentally obtained by increasing the angular velocity at each inclination angle. The experimentally obtained angular velocities were substituted into the theoretical equations to compare the point-mass and rigid-body models. The effects of the particle shape on the adhesion force and effective contact radius and that of the inclination angle on the removal fraction curves based on the theoretical equation were also investigated.