Tribological Properties of Reactive Magnetron Sputtered V2O5 and VN–V2O5 Coatings

Next generation of advanced hard coatings for tribological applications should combine the advantages of hard wear resistant coatings with low-friction films. In this study, the tribological behaviour of vanadium pentoxide (V₂O₅) single-layer as well as VN–V₂O₅ bi-layer coatings was investigated in the temperature ranging between 25 and 600 °C. For VN–V₂O₅ bi-layer coatings, the V₂O₅ top-layers were deposited by dc and bipolar-pulsed dc reactive magnetron sputtering, where the V₂O₅ phase shows preferred growth orientation in (200) and (110), respectively. The V₂O₅ single-layer coatings were prepared by dc reactive magnetron sputtering with a substrate bias of −80 V which leads to a preferred (200) growth orientation. Tribological properties were evaluated using a ball-on-disc configuration in ambient air with alumina balls as counterpart. The structure of the as-deposited films and eventual changes after tribometer testing were identified using X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The friction coefficient of VN–V₂O₅ bi-layer coatings deposited in dc and pulsed dc mode decreases from room temperature to 600 °C, where the pulsed dc VN–V₂O₅ coatings have a significantly lower coefficient of friction over the whole testing temperatures reaching a value of 0.28 at 600 °C. Up to 400 °C, V₂O₅ single-layer coatings showed almost the same coefficient of friction as pulsed dc VN–V₂O₅ bi-layer coatings but reached a value of 0.15 at 600 °C. It seems that thermal activation of crystallographic slip systems is necessary for V₂O₅ films to show a low-friction effect.     

Thermal–structural analysis of bi-metallic conformal cooling for injection moulds

In injection moulding process, cooling time greatly affects the total cycle time. As thermal conductivity is one of the main factors for conductive heat transfer in cooling phase of IMP, a cooling channel made by higher thermal conductive material will allow faster extraction of heat from the molten plastic materials, thus resulting in shorter cycle time and higher productivity. The main objective of this paper is to investigate bi-metallic conformal cooling channel design with high thermal conductive copper tube insert for injection moulds. Thermal–structural finite element analysis has been carried out with ANSYS workbench simulation software for a mould with bi-metallic conformal cooling channels and the performance is compared with a mould with conventional straight cooling channels for an industrial plastic part. Experimental verification has been carried out for the two moulds using two different types of plastics, polypropylene (PP) and acrylonitrile butadiene styrene, in a mini injection moulding machine. Simulation and experimental results show that bi-metallic conformal cooling channel design gives better cycle time, which ultimately increases production rate as well as fatigue life of the mould.     

Numerical analysis of rubber dams using fluid–structure interactions

Rubber dams are flexible cylindrical inflatable structures attached to a rigid base and inflated by air and/or water. Due to elasticity of the structure and continuous variation of its shape during operation, a rubber dam structural and hydraulic analysis is more complicated than a rigid dam.This paper deals with numerical analysis of the rubber dams for solving the flow based problem and static and dynamic structural analysis, simultaneously. The three dimensional fluid–structure interactions are analyzed both under the stationary hydrostatic and overflow conditions, based on different internal pressures, and upstream and downstream water depths. The water free-surface was obtained based on two-phase air–water flow interface. The flow separation downstream of the dam was modeled using shear stress transport turbulence model. The results describing height, cross-sectional profile and cross-sectional area of the dams were compared with these of former studies and good agreement was obtained. Altogether, the fluid–structure interaction analysis provides two new correlations to predict the equilibrium height of the rubber dam and its discharge coefficient based on the dam equilibrium height and the total upstream head. It was found that the rubber dam equilibrium height is a function of its thickness, modulus of elasticity, internal pressure and foot width.     

高温真空分解V2O5制备VO2

尝试采用真空分解V2O5熔体的方法制备高纯度的VO2,通过XRD和SEM等方法进行了分析。结果表明,该方法可以直接获得高纯度的VO2的沉积层,沉积层为连续单相多晶组织。当熔体以小于10℃/h的升温速率加热到1350℃,真空度控制为10-6atm,所获得的沉积层的电阻突变量级达到最大为4~5,相变温度为68℃,相变温度滞后为1℃~2℃。     

A coupled thermal–mechanical analysis of a mold-billet system during continuous casting

The three-dimensional (3-D) thermal–mechanical behavior of a mold–billet system under actual casting conditions is investigated with an finite element approach, taking into account the main influencing factors, such as solidification heat, latent heat released during phase transformation, heat transfer, as well as the interaction between the moving billet and the mold. It is based on the coupled thermal–mechanical analysis for the whole mold–billet system, instead of analyzing the thermal–mechanical behavior of the mold and the billet individually, as is often used in practice. Comparison shows that the former approach can provide satisfactory results without making use of the empirical estimation of the heat flux through the inboard surface of the mold based on the difference between the temperature of inlet and outlet cooling water at steady-state and the temperature distribution near the surface of the inboard plate measured experimentally, which are usually necessarily required for the latter approach to be applied in practice.     

V2O5掺杂对ZnNb2O6介质陶瓷性能的影响

采用传统的固相反应法制备了V2O5掺杂ZnNb2O6介质陶瓷,借助XRD、SEM和LCR测试仪等研究了陶瓷的烧结特性及介电性能.结果表明V2O5掺杂能有效地降低ZnNb2O6陶瓷的烧结温度,提高介电常数,改善频率温度系数,但介电损耗有所增加.经1050℃烧结,1.0%V2O5掺杂的ZnNb2O6陶瓷具有较好的介电性能,εr=28,tanδ=0.000 6,τf=-42.50×10-6℃-1.     

Evaluation of performance of nanofluid using multiwalled carbon nanotubes for machining of Ti–6AL–4V

Machining of titanium alloys generate very high temperature in the cutting zone. This results in rapid tool wear and poor surface properties. Therefore, improvement in cutting performance in machining of titanium alloys is very much dependent on effectiveness of the cooling strategies applied. In the present work, performance of nanofluid using multiwalled carbon nanotubes (MWCNTs) dispersed in distilled water and sodium dodecyl sulfate (SDS) as surfactant is evaluated for turning operation on Ti–6Al–4V workpieces. Turning operations were carried out under three different conditions – dry, with conventional cutting fluid and with nanofluid. Nanofluid application was limited to 1 L/h and it was applied at the tool tip through gravity feed. Various machining responses like cutting force, surface finish and tool wear were analyzed while turning at optimum cutting parameters as 150 m/min, 0.1 mm/rev and 1 mm depth of cut. Later on, machining performance of nanofluid is confirmed at low cutting speed of 90 m/min. Nanofluid outperformed conventional cutting fluid with 34% reduction in tool wear, average 28% drop in cutting forces and 7% decrease in surface roughness at cutting speed of 150 m/min.     

Prediction of abrasive wear rate of in situ Cu–Al2O3 nanocomposite using artificial neural networks

In this work, artificial neural networks (ANNs) technique was used in the prediction of abrasive wear rate of Cu–Al₂O₃ nanocomposite materials. The abrasive wear rates obtained from series of wear tests were used in the formation of the data sets of the ANN. The inputs to the network are load, sliding speed, and alumina volume fraction. Correlation coefficients between the experimental data and outputs from the ANN confirmed the feasibility of the ANNs for effectively model and predict the abrasive wear rate. The comparison between the ANNs and the multi-variable regression analysis results showed that using ANNs technique is more effective than multi-variable regression analysis for the prediction of abrasive wear rate of Cu–Al₂O₃ nanocomposite materials. Optimization of the training process of the ANN using genetic algorithm (GA) is performed and the results are compared with the ANN trained without GA. Sensitivity analysis is also done to find the relative influence of factors on the wear rate. It is observed that load and alumina volume fraction effectively influence the wear rate.     

钙化焙烧冶烧V2O5新工艺研究

钙化焙烧碳化浸出冶炼钒的新工艺具有环境污染低,钒回收率高等特点。本文介绍了该工艺的原理,生产流程及各项技术指标。     

与Y2O3共同掺杂下Sb2O5掺杂量对SnO2陶瓷压敏电阻电性能的影响

通过在SnO2陶瓷压敏电阻中共同掺杂Sb2O5和Y2O3(0.05％,物质的量分数),采用扫描电镜和阻抗仪研究了Sb2O5掺杂量(0,0.05％,0.10％,0.15％,物质的量分数)对SnO2压敏电阻微观形貌、电压梯度和晶粒电阻的影响.结果表明:随Sb2O5掺杂量增加,SnO2压敏电阻的晶粒尺寸和界面态密度先增大后减...     

Electrochemical determination of hydrogen peroxide using a novel prussian blue–polythiophene–graphene oxide membrane-modified glassy carbon electrode

A polythiophene–graphene oxide compound membrane and Prussian blue were deposited sequentially on the surface of a glassy carbon electrode by cyclic voltammetry. Due to its excellent electrocatalysis and its analogy with peroxidase enzymes, Prussian blue has been widely used in amperometric biosensors. The polythiophene–graphene oxide compound membrane exhibited good electroconductibility and a large specific surface area. The fabricated Prussian blue/polythiophene/graphene oxide/glassy carbon electrode was characterized by transmission electron microscopy, scanning electron microscopy, and cyclic voltammetry. Under the optimal experimental conditions, the detection of hydrogen peroxide was studied by its amperometric current–time curve. Due to the presence of polythiophene–graphene oxide compound membrane and Prussian blue, the hydrogen peroxide sensor shows a linear calibration range of 1.0?×?10^?6–1.0?×?10^?4?mol?L^?1, detection limits of 3.2?×?10^?7?mol?L^?1 at a signal-to-noise ratio of 3, and recoveries from 95.0 to 105.0%. The results show that the modified glassy carbon electrode has potential practical application for the determination of hydrogen peroxide based on its sensitivity and long-term stability.     

光纤传感用的TiO2：V2O5湿敏光学薄膜

用溶胶—凝胶法制备ＴｉＯ２∶Ｖ２Ｏ５光学薄膜，研究了它的湿敏光学特性，并用表面吸附理论、电子理论较好地解析了湿敏—光学特性机理。     

Enhanced magnetic abrasive finishing of Ti–6Al–4V using shear thickening fluids additives

The available magnetic field assisted finishing process is considered as the critical stage for improvement of workpiece surface quality. This paper aims to investigate the key quality performance of an enhanced magnetic abrasive finishing in achieving nanolevel finish on Ti–6Al–4V workpieces with initial micrometer surface roughness values. The finishing media, combining the intelligent shear thickening fluids (STFs), carbonyl iron particles and SiC particles, is developed. Finishing experiments for Ti–6Al–4V workpieces are conducted using an established platform, aiming to investigate the effects of varying STFs concentration, working gap, feed rate and spindle rotational speed. It is observed from the experimental results that the developed finishing media is effective for surface finishing comparing to the finishing media without STFs. The surface roughness of 54 nm was achieved from the initial value of 1.17 μm, which improved by over 95%, under the experimental conditions of 0.8 mm working gap, 15000 mm/min feed rate, 900 rpm spindle rotational speed and 15 wt% STFs. Surface observations showed that a smooth surface without obvious scratches was obtained.     

Wear analysis of Cu–Al coating on Ti–6Al–4V substrate under fretting condition

Fretting behavior of Cu–Al coating on Ti–6Al–4V substrate was investigated with and without fatigue load. Soft and rough Cu–Al coating resulted in abrasive wear and a large amount of debris remained at the contact surface, which caused an increase in tangential force during the fretting test under gross slip condition. Fretting in the partial slip condition also showed the wear of coating. To characterize wear, dissipated energies during fretting were calculated from fretting loops and wear volumes were obtained from worn surface profiles. Energy approach of wear analysis showed a linear relationship between wear volume and accumulated dissipated energy. This relationship was independent of fatigue loading condition and extended from partial slip to gross slip regimes. As an alternate but simple approach for wear analysis, accumulated relative displacement range was correlated with the wear volume. This also resulted in a linear relationship as in the case of accumulated dissipated energy suggesting that the accumulated relative displacement range can be used as an alternative parameter for dissipated energy to characterize the wear. When the maximum wear depth was equal to the thickness of Cu–Al coating, harder Ti–6Al–4V substrate inhibited further increase in wear depth. Only when a considerable energy was supplied through a large value of the applied displacement, wear in the substrate material could occur beyond the thickness of coating.     

Analysis of dry sliding friction and wear behaviour of AA6351–SiC–B4C composites using grey relational analysis

Abstract

This paper describes the multifactor based experiments that are applied to investigate the dry sliding wear system of aluminium matrix alloy (AA6351) with 5 wt-% silicon carbide (SiC), 5 wt-% and 10 wt-% of boron carbide (B₄C) reinforced metal matrix composites (MMCs). Stir casting route was adopted to prepare the composites and the tribological experiments were carried out on pin-on-disc type wear machine. The effects of parameters like applied load, sliding velocity, wt-% of B₄C on the dry sliding wear and frictional coefficient of aluminium MMCs using grey relational analysis (GRA) are reported. The orthogonal array with L9 layout and analysis of variance were used to investigate the influence of the parameters. It is observed that the dry sliding friction and wear behaviour of the composites are influenced by the applied load, sliding velocity and wt-% of B₄C with a contribution of 60·82%, 21·72% and 14·28% respectively. The optimal design parameters were found by grey relational grade and a good agreement was observed for 95% level of confidence.     

In-process prediction of surface roughness in turning of Ti–6Al–4V alloy using cutting parameters and vibration signals

In this work, an attempt has been made to use vibration signals for in-process prediction of surface roughness during turning of Ti–6Al–4V alloy. The investigation was carried out in two stages. In the first stage, only acceleration amplitude of tool vibrations in axial, radial and tangential directions were used to develop multiple regression models for prediction of surface roughness. The first and second order regression models thus developed were not found accurate enough (maximum percentage error close to 24%). In the second stage, initially a correlation analysis was performed to determine the degree of association of cutting speed, feed rate, and depth of cut and the acceleration amplitude of vibrations in axial, radial, and tangential directions with surface roughness. Subsequently, based on this analysis, feed rate and depth of cut were included as input parameters aside from the acceleration amplitude of vibrations in radial and tangential directions to develop a refined first order multiple regression model for surface roughness prediction. This model provided good prediction accuracy (maximum percentage error 7.45%) of surface roughness. Finally, an artificial neural network model was developed as it can be readily integrated into a computer integrated manufacturing environment.     

Surface quality improvement of EDMed Ti–6Al–4V alloy using plasma etching and TiN coating

This paper seeks to improve the surface quality of electrical discharge machining (EDM) Ti–6Al–4V using plasma etching treatment and TiN coating. The EDM parameter setting is optimized firstly based on grey-Taguchi method. Four EDM parameters, including current (A), voltage (V), pulse duration (μs), and duty factor (%), are selected for multiple performance of lower electrode wear rate (EWR), higher material removal rate (MRR), and better surface roughness (SR). An orthogonal array, signal-to-noise (S/N) ratios, and analysis of variance (ANOVA) are used to analyze the effects of these EDM parameters. Normality tests show that all the distributions fit normality assumption with p?=?0.276, 0.688, and 0.663, respectively. The EDM process is stable over time monitored by Shewhart control charts. It is observed that there is an EDM damaged layer on the surface consisting of debris, microcracks, molten drops, and solidified metals by scanning electron microscopy. The plasma etching and TiN coating are employed to improve surface quality of the EDMed Ti–6Al–4V alloys. The results demonstrate that using the oxygen plasma etching treatment, the damaged phenomena are decreased, and the mean SR value is reduced from Ra?=?2.91 to Ra?=?2.50 μm. In addition, when the plasma-treated alloy is coated with Ti buffer/TiN coating by physical vapor deposition, the surface morphology exhibits less defects and a better surface finish. The mean SR values are further reduced from Ra?=?2.50 μm to Ra?=?1.48 μm (for 740 nm TiN film) and Ra?=?0.61 μm (for 1450 nm TiN film), respectively.     

热处理对V2O5薄膜的结构及光学性能的影响

用射频平面磁控溅射法在Ar/O2气氛中溅射V2O5粉末靶制得V2O5薄膜,然后在大气中对样品薄膜作250℃～400℃的热处理试验.用XRD分析表明薄膜随着热处理温度的升高,除了晶粒尺寸不断长大以外,薄膜的组分也在发生不断的变化,在低温下处理时出现的某些结构在高温处理后消失,同样在高温下处理后也出现了一些低温下没有出现的新结构.这种结构变化导致在300℃以下的温度处理后的薄膜在可见光和近红外波段都有异常大的吸收;在350℃以上的温度处理后的薄膜在可见光和近红外波段的吸收显著地减小.     

热处理对V2O5薄膜的结构及光学性能的影响

用射频平面磁控溅射法在Ar/O2气氛中溅射V2O5粉末靶制得V2O5薄膜,然后在大气中对样品薄膜作250℃～400℃的热处理试验.用XRD分析表明薄膜随着热处理温度的升高,除了晶粒尺寸不断长大以外,薄膜的组分也在发生不断的变化,在低温下处理时出现的某些结构在高温处理后消失,同样在高温下处理后也出现了一些低温下没有出现的新结构.这种结构变化导致在300℃以下的温度处理后的薄膜在可见光和近红外波段都有异常大的吸收;在350℃以上的温度处理后的薄膜在可见光和近红外波段的吸收显著地减小.