Effect of wetting behavior on generation of uniform aluminum droplets obtained by pneumatic drop-on-demand technique

Micro metal droplet is the basic building block of three-dimensional metal parts fabricated by micro droplet deposition manufacturing (MDDM) technique. In this paper, the effect of wetting behavior between liquid metal and spray nozzle on the generation of micro aluminum droplets produced by pneumatic drop-on-demand (DOD) technique was investigated by simulation and experiment. A finite element model of liquid–gas flow was established based on the improved level set method (LSM). Then the generation of micro liquid aluminum droplets under different wetting conditions was simulated. A series of spraying experiments were also performed on micro droplet deposition experiment platform. The results show that the generation and flight of micro aluminum droplets are influenced by wetting condition between liquid metal and the nozzle surface significantly. Additionally, the effect of wetting behavior on the droplet size was analyzed to achieve the smallest building block. It was found that the droplet radius decreased with the increase of contact angle exponentially, which agreed with the numerical calculation and experiment results. On this basis, a wettability criterion was proposed for selecting nozzle materials. These works would be helpful for the processing optimization and equipment improvement of MDDM technique.     

Effect of process parameters on copper droplet ejecting by pneumatic drop-on-demand technology

Stable generation of copper droplets is a key issue in fabricating copper parts by drop-on-demand (DOD) technology. The process parameters such as supply pressure and electronic pulse width have significant effect on pressure variation and droplet formation. In the present work, a pressure acquisition system was first set up to measure the pressure variation in crucible. Then the measured pressure data were applied on a 2D axisymmetric model as inlet conditions to study the influence of process parameters on copper droplet formation. The results indicated that the peak pressure in crucible increased linearly with the increase of supply pressure. As supply pressure increased, the jet velocity and the limiting length increased to critical value and droplet could be generated. The peak width increased with the rise of electronic pulse width. By increasing the electronic pulse width, the time of pressure above threshold value increased and the jet limiting length grew to critical value for breakup. However, if supply pressure and electronic pulse width were too large, satellite droplets would be formed. Pure copper droplet generating experiments were conducted to obtain appropriate parameters. Single droplet was generated while supply pressure was between 60 kPa and 100 kPa and pulse width was between 550 μs and 1550 μs. Also the range of pulse width varied as the supply pressure increased for generating single droplet. The statistics of droplet diameter suggested that droplet diameter increased with the increase of supply pressure. Electronic pulse width had influence on the droplets size and the standard deviation increased with the increase of electronic pulse width. So small supply pressure and electronic pulse width should be used for generating uniform droplets.     

Formation of aluminide coatings on Ni and austenitic 316 stainless steel by a low temperature FBCVD process

The experimental formation of aluminide coatings on 316 stainless steel grades and Ni by use of a chemical vapour deposition via the fluidised bed technique at relatively low temperatures (550, 560 and 570 °C for the steel and 550-650 °C for Ni) was studied. A mathematical model that predicts the growth rate of the coating for both substrates is being proposed. The experimental results were evaluated by means of optical microscopy. Uniform coatings even for reduced treatment times of a few minutes were produced. The measured coating thickness was compared to the predicted results from the model. The results indicate a linear correlation of coating thickness and treatment time for short treatment times and a parabolic correlation for longer ones. The low treatment temperature allows for energy saving and the mechanical properties of the treated parts remain unaffected.     

Synthesis and characterization of metal oxide multilayers obtained via MOCVD as protective coatings of graphite against oxidation

Zirconia (ZrO₂) titania (TiO₂) and alumina (Al₂O₃) thin films were deposited on a graphite substrate both in mono- and in multi-layer systems, using the metal organic chemical vapor deposition technique, to test their practical qualities as protective coatings against oxidation at high temperatures. The depositions were performed using a hot wall reactor at reduced pressure (0.6 Torr) in the temperature range 350–500 °C, using, as precursors, (η⁵-C₅H₅)₂Zr(CH₂C(CH₃)₃)₂, Ti(OCH(CH₃)₂)₄, and (CH₃CH₂)₂Al(OCCH₃CHCCH₃O), respectively. Surface and topographical analysis of the deposits using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy techniques as well as thermogravimetric measurements (TG and DTA) in an oxygen flux of mono- and multi-layer systems are reported and examined.     

Preparation and characterization of superhydrophobic silica-based surfaces by using polypropylene glycol and tetraethoxysilane precursors

Preparation of superhydrophobic silica-based surfaces via sol-gel process by adding polypropylene glycol (PPG) polymer into the precursor solution has been developed. Surface roughness of the films was obtained by removing the organic polymer at 500 °C and then the hydrophobic groups bonded onto the films were obtained by chemical reaction with hexamethyldisilazane (HMDS). Physical properties of the as-prepared films were analyzed by contact angle measurements, scanning electron microscopy (SEM), UV-VIS scanning spectrophotometer and Fourier transform infrared (FT-IR) spectrophotometer. The experimental parameters were varied by the type of silane species, the weight ratio of PPG solution to precursor solution, the hydrolysis time of the precursor solution, the molecular weight of PPG, the casting temperature and the evaporation temperature. The phase separation of the PPG polymer rich domain occurred on the substrates at a lower temperature. The result showed that the contact angles of the films prepared at 5 °C were greater than 150° when the weight ratio of PPG solution to precursor solution was 5. In addition, the transmittance of the films was greater than 80% simultaneously.     

FEA modeling and simulation of shear localized chip formation in metal cutting

The finite element analysis (FEA) has been applied to model and simulate the chip formation and the shear localization phenomena in the metal cutting process. The updated Lagrangian formulation of plane strain condition is used in this study. A strain-hardening thermal-softening material model is used to simulate shear localized chip formation. Chip formation, shear banding, cutting forces, effects of tool rake angle on both shear angle and cutting forces, maximum shear stress and plastic strain fields, and distribution of effective stress on tool rake face are predicted by the finite element model. The initiation and extension of shear banding due to material's shear instability are also simulated. FEA was also used to predict and compare materials behaviors and chip formations of different workpiece materials in metal cutting. The predictions of the finite element analysis agreed well with the experimental measurements.     

A theoretical and experimental study on forming limit diagram for a seamed tube hydroforming

The purpose of this work is to establish the forming limit diagram (FLD) for a seamed tube hydroforming. A new theoretical model is developed to predict the FLD for a seamed tube hydroforming. Based on this theoretical model, the FLD for a seamed tube made of QSTE340 sheet metal is calculated by using the Hosford yield criterion. Some forming limit experiments are performed. A classical free hydroforming tool set is used for obtaining the left hand side forming limit strains, and a novel hydroforming tool set is designed for the right hand side of FLD. The novel device required the simultaneous application of lateral compression force and internal pressure to control the material flow under tension–tension strain states. Furthermore, the suitable loading paths for the left hand side of FLD by theoretical formulas and for the right hand side of FLD by finite element (FE) simulations are calculated. Finally, a comparison between the theoretical results and experimental data is performed. The theoretical predicting results show good agreement with the experimental results.     

Effects of particle arrangement and particle damage on the mechanical response of metal matrix nanocomposites: A numerical analysis

The spatial distribution of reinforcement particles has a significant effect on the mechanical response and damage evolution of metal matrix composites (MMCs). It is observed that particle clustering leads to higher flow stress, earlier particle damage, as well as lower overall failure strain. In recent years, experimental studies have shown that reducing the size of particles to the nanoscale dramatically increases the mechanical strength of MMCs even at low particle volume fractions. However, the effects of particle distribution and particle damage on the mechanical response of these metal matrix nanocomposites, which may be different from that observed in normal MMCs, has not been widely explored. In this paper, these effects are investigated numerically using plane strain discrete dislocation simulations. The results show that non-clustered random and highly clustered particle arrangements result in the highest and lowest flow stress, respectively. The effect of particle fracture on the overall response of the nanocomposite is also more significant for non-clustered random and mildly clustered particle arrangements, in which particle damage begins earlier and the fraction of damaged particles is higher, compared to regular rectangular and highly clustered arrangements.     

Workpiece surface roughness and integrity after WEDM of Ti-6Al-4V and Inconel 718 using minimum damage generator technology

Following a brief review of EDM and its use on advanced aerospace alloys including workpiece integrity constraints, data are presented after machining Ti-6Al-4V and Inconel 718. Roughing and finishing (multiple trim cut) strategies were employed on two high specification machines with pulse generators designed to provide minimum workpiece integrity damage. Results include productivity, 3D topographic maps of workpiece surfaces, microstructural and microhardness depth profile data. Average recast thickness was <11 μm, several trim passes showing no apparent recast or damage. Similarly, no significant change in workpiece microhardness variation was observed with cracking confined to the recast layer.     

Elastic fields generated by a semi-spherical hydride particle on a free surface of a metal and their effect on its growth

The formation of a metal hydride is associated with a large increase of volume relative to the parent metal and therefore in large strain energies. Effects of elastic energy on the hydriding of metals are revealed in the microstructural evolution and kinetics of hydride growth on free surfaces. In the present work, we study in detail the elastic fields set up by a semi-spherical hydride particle growing at a free surface of metal with cubic symmetry, with and without an oxide layer. These systems combine geometric (structural) and material anisotropies.Three stages along the microstructural evolution on the surface of some hydride forming metals exposed to hydrogen at constant pressure were described experimentally. For these stages along hydride growth, correlations with the elastic fields are suggested as follows. (a) A hydride particle at the free surface generates regions of tensile and compressive hydrostatic stress in the surrounding matrix. This may induce a preferred nucleation of new hydrides and formation of clusters of hydrides precipitates, which is indeed observed experimentally. (b) Clustering, on the other hand, may contribute to the cease of growth due to competition on hydrogen. In addition, as the particle grows, changes in the stress fields may retard further diffusion from the surface and be another contribution to the cease of growth. (c) A growing hydride increases the stress in the oxide layer and may finely break it. Then the elastic energy per unit volume drops to its minimum value and the growth may accelerate. The formation of such “growth center” is favored for that hydride precipitate that grow alone and not in a cluster.     

Synthesis and characterization of cubic boron nitride thin films using the ME-ARE method

Cubic boron nitride (cBN) films were deposited by a magnetically enhanced activated reactive evaporation (ME-ARE) technique. Pulsed DC instead of r.f. power was used to bias the substrate. The effect of deposition parameters such as substrate bias voltage, plasma discharge current and gas flow ratio on the formation of cBN was investigated. BN films were characterized by FTIR and TEM. CBN films with a high content of cubic phase were successfully synthesized. It was found that formation of cBN film requires the bombardment of ions with both high flux and high energy. TEM observation showed that the cBN film had grain sizes of 15-50 nm and that a non-cubic phase BN, 10-15 nm was initially grown.     

Selective separation of Cu(II), Zn(II), and Cd(II) by solvent extraction

An experimental investigation was presented on the separation of Cu (II), Zn (II), and Cd (II) from a rich sulfate leachate of zinc slag by solvent extraction. The results of orthogonal experiments indicate that LIX 984N is highly selective and very efficient in the extraction of Cu (II), and the analysis of variance indicates that the sequence of parameters according to their influence on the separation efficiency is phase ratio>LIX 984N concentration>pH value>extraction time. The optimal condition for copper extraction is obtained as 25% of LIX 984N concentration, 7 min of extraction time, 3:2 of phase ratio O/A, and pH=1.7. The separation of Zn (II) and Cd (II) was performed after the copper extraction from the raffinate. Comparative analysis of the separation with di-2-ethylhexyl phosphoric acid (D2EHPA), D2EHPA-tributyl-phosophate (TBP) synergistic extracting system, and 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (HEHEHP) was made at pH=2.0. It is demonstrated that the extraction efficiency with D2EHPA is improved after being saponified by sodium hydroxide, and D2EHPA-TBP synergistic extracting, as well as HEHEHP, has a superior selectivity to Zn (II) over Cd (II).     

焊缝管液压胀形模拟建模及变形规律的研究

基于周向显微硬度的分布及经验公式法,确立了STKM11A焊缝管热影响区的流动应力;通过对热影响区进行分片的方式,建立了包含焊缝和热影响区的焊缝管液压胀形的有限元模拟模型。基于该模型,模拟分析了STKM11A焊缝管液压胀形时的变形规律,如截面轮廓形状、周向壁厚分布和成形极限等,并与胀形实验结果进行对比。结果表明,液压胀形后焊缝管的截面轮廓形状不对称、壁厚分布不均匀,最小壁厚位于热影响区;包含焊缝及热影响区的有限元模型在预测焊缝管液压胀形的变形规律、极限载荷和潜在胀裂位置等方面,较其他常规模型更加精确。     

Amperometric detection of gold by differential pulse voltammetry using a DNA biosensor

A DNA biosensor with [Ru(DA-bpy)3]Cl2(DA-bpy:4,4'-diamino-2,2'-bipyridine) (RuL) as the electrochemical probe was prepared on pyrolytic graphite electrode (PGE) through the supramolecular interaction between RuL complex and DNA template. Cyclic voltammetry of RuL-DNA film showed a pair of stable and reversible peaks corresponding to the Ru(III)/Ru(II) redox potential of -0.165 V versus Ag|AgCl in pH 7.4 0.1 mol·L-1 Tris-HCl. The electron transfer was expected across the double-strand DNA by an "electron tunneling" mechanism. When the DNA biosensor was immerged in gold (III) buffer solution, the current peak signal (I) of the RuL-DNA supramolecular depressed and △I was linear in the concentration range of Au ion from 1 × 10-7 to 2 × 10-5 mol·L-1 with a regression coefficient of 0.9879. The detection limit was 5 × 10-8 mol·L-1. The developed procedures were applied to the analysis of synthetic samples of real materials with good sensitivity and selectivity.     

Structural integrity of direct metal laser sintered parts subjected to thermal and finishing treatments

Direct Metal Laser Sintering (DMLS) is a rapid manufacturing technology that is starting to be used for the manufacturing of functional components. Therefore, properties of DMLS manufactured parts must be carefully analyzed to determine if they satisfy technical requirements under fatigue conditions.     

Liquid metal embrittlement susceptibility of T91 steel by lead–bismuth

Previous studies on T91 steel in its standard metallurgical state do not provide evidence for liquid metal embrittlement by eutectic Pb–Bi. In this paper, we show that this steel can be embrittled by Pb–Bi when direct contact between the steel and the liquid metal is obtained by prior ion beam sputtering of the native oxidized film.     

企业建模方法及ARIS建模过程应用研究

面对环境变化,建立企业模型成为企业管理的重要手段。文章首先介绍了企业建模的概念,其次比较了常用的建模工具,然后着重探讨了集成信息系统体系结构(ARIS)建模过程的视图结构与建模层次,最后以实例介绍了采用ARIS工具对业务流程进行建模的具体过程。     

Development of cold work tool steel based-MMC coating using HVOF spraying and its HIP densification behaviour

The aim of the present study is to develop a Fe-based metal matrix composite (MMC) coating using high velocity oxy-fuel spraying (HVOF) process. A ledeburitic high alloyed cold work tool steel (X220CrVMo13-4) and NbC with an average size of 2 µm at different volume fractions have been considered as metal matrix and hard particles respectively. MMC coatings were deposited on austenitic stainless substrates and the coatings were subsequently densified by hot isostatic pressing (HIP) with and without encapsulation. Microstructural analysis of the as-sprayed and HIPed coatings were characterized by SEM and XRD methods. Results showed that the feedstock preparation involving fine NbC was an influencing factor on the coating deposition. A relatively homogeneous dispersion of fine NbC up to 30 vol.% in cold work tool steel matrix was possible using optimized HVOF spraying. Besides, HVOF spraying and its subsequent HIP treatment induced significant microstructural and phase changes in the MMC coatings. The study showed the potential of HVOF spraying for the development of steel based MMC coatings and its subsequent densification can be achieved by HIP process with and without encapsulation.