Effect of particle size on tribological behavior of Ni3Al matrix high temperature self-lubricating composites

The Ni₃Al matrix high temperature self-lubricating composites with different particle size were fabricated by the powder metallurgy technique. The effect of particle size on the mechanical and tribological properties of the composites was investigated in this paper. The results showed that the coarse particle composite exhibited the lowest friction coefficient and wear rate compared to the fine particle ones at a wide temperature range from room temperature to 1000 °C. The reason for the low wear rate was that the coarse bulk phase could provide better deformation resistance and higher load bearing capacity than the fine microstructure.     

Effect of particle size on tribological behavior of Ni3Al matrix high temperature self-lubricating composites

The Ni₃Al matrix high temperature self-lubricating composites with different particle size were fabricated by the powder metallurgy technique. The effect of particle size on the mechanical and tribological properties of the composites was investigated in this paper. The results showed that the coarse particle composite exhibited the lowest friction coefficient and wear rate compared to the fine particle ones at a wide temperature range from room temperature to 1000 °C. The reason for the low wear rate was that the coarse bulk phase could provide better deformation resistance and higher load bearing capacity than the fine microstructure.     

Effect of particle size and composition of powdered nanocrystalline molybdenum disulfide on its tribological behavior

The tribological behavior of two types of nanocrystalline molybdenum disulfide produced from natural molybdenum disulfide by monolayer dispersion in the presence of water (nano-MoS₂(H₂O)) and acetonitrile (nano-MoS₂(CH₃CN)) is studied. The study of the friction of these materials against polished and ground steels, as well as XPS examinations, show the advantage of the more thermally stable nano-MoS₂(CH₃CN), which is primarily due to the origin of low-molecular products adsorbed on the surfaces of nanoparticles.     

Tribological behavior of graphite-containing nickel-based composite as function of temperature,load and counterface

Nickel-based graphite-containing composites were prepared by powder metallurgy method. Their mechanical properties at room temperature and friction and wear properties from room temperature to 600 °C were investigated by a pin-on-disk tribometer with alumina, silicon nitride and nickel-based alloy as counterfaces. The effects of graphite addition amount, temperature, load, sliding speed and counterface materials on the tribological properties were discussed. The micro-structure and worn surface morphologies were analyzed by scanning electron microscope (SEM) attached with energy dispersive spectroscopy (EDS). The results show that the composites are mainly consisted of nickel-based solid solution, free graphite and carbide formed during hot pressing. The friction and wear properties of composites are all improved by adding 6–12 wt.% graphite while the anti-bending and tensile strength as well as hardness decrease after adding graphite. The friction coefficients from room temperature to 600 °C decrease with the increase of load, sliding speed while the wear rates increase with the increasing temperature, sliding speed. The lower friction coefficients and wear rates are obtained when the composite rubs against nickel-based alloy containing molybdenum disulfide. Friction coefficients of graphite-containing composites from room temperature to 600 °C are about 0.4 while wear rates are in the magnitude of 10^?5 mm³/(N m). At high temperature, the graphite is not effective in lubrication due to the oxidation and the shield of ‘glaze’ layer formed by compacting back-transferred wear particles. EDS analysis of worn surface shows that the oxides of nickel and molybdenum play the main role of lubrication instead of graphite at the temperature above 400 °C.     

土壤粒径大小对蒽荧光特性的影响及校正

为了准确检测土壤中的多环芳烃,以土壤中典型多环芳烃污染物蒽为检测对象,研究了土壤粒径大小对其荧光特性的影响,并提出了一种校正土壤粒径大小对多环芳烃标准曲线影响的方法。研究了蒽在土壤中的荧光特性,指出蒽在421nm、442nm和470nm处出现较强的荧光峰。接着,制备7种不同粒径大小的蒽土壤样品,并以土壤粒径大小为外扰,构建了同步和异步二维相关荧光谱,研究了蒽荧光强度和304nm处瑞利散射光强随土壤粒径大小的变化。结果显示,随着土壤粒径增大,蒽荧光强度和304nm处瑞利散射光强度都有增强。最后,分别建立了80目和160目土壤粒径下定量分析土壤蒽浓度的标准曲线,并通过304nm处瑞利散射光对蒽荧光进行校正。结果表明:该方法有效降低了土壤粒径大小对蒽标准曲线的影响。     

Effect of temperature on wear behavior of high-entropy alloys

The wear behavior of a FeCoNiCrMn (counterbody)–Ti₃₀Zr₂₅Hf₁₅Nb₂₀Ta₁₀ (finger) friction pair in the temperature range of 77–873 K has been determined. It has been found out that the finger wear significantly decreases with an temperature increase compared with the counterbody due to the spur increase in the hardness of the friction surface structures of up to 18.0 GPa due to the formation of a high-temperature oxide. It has been revealed that the depth of secondary structures increases with temperature, while at 523 K and higher, it reaches 40 μm.     

Effect of ash fraction and particle size on ash deposition during pulverized coal combustion

Coal is an important energy source to increase consumption continuously. However, the ash residues from coal combustion have produced ash deposition that causes slagging and fouling in boilers. The goal of this study is to examine the characteristics of ash deposits (i.e., the effects of the ash fraction and particle size) in pulverized coal combustion. For this study, five coals (Suek, Macqurie, Berau, Lanna and Vitol) are used, which have similar chemical components in the ash but differences in the ash fraction. A Thermomechanical analysis technique (TMA) and Drop tube furnace (DTF) are used to analyze the tendencies in the ash fusibility and deposition with temperature, respectively. Moreover, the size and morphology of the fly ash are analyzed for physical changes by using a particle-sizedistribution analyzer and Scanning electron microscopy (SEM), respectively. In the TMA results, all coal types have a similar fusibility because of the similar chemical components in the ash. The order of the deposited mass is Suek, Macqurie, Berau, Vitol and Lanna in accordance with the ash fraction in the DTF. The ash fraction in coal is a major factor in the ash deposit according to these results. The size of the fly ash changed compared to that of the raw coal according to the results of a particle-size analysis and SEM owing to physical processes such as fragmentation, shedding and coalescence during coal burning. On this basis, a deposition model is developed with the ash fraction and particle size. The model results are in good agreement with the measurements. The results demonstrate that the particle size and ash fraction influence the deposit.

     

High stress abrasive wear behaviour of aluminium hard particle composites: Effect of experimental parameters, particle size and volume fraction

High stress abrasive wear behaviour of aluminium alloy (ADC-12)–SiC particle reinforced composites has been studied as a function of applied load, reinforcement size and volume fraction, and has been compared with that of the matrix alloy. Two different size ranges (25–50 and 50–80 μm) of SiC particles have been used for synthesizing ADC-12–SiC composite. The volume fraction of SiC particles has been varied in the ranges from 5 to 15 wt%. It has been noted that the abrasive wear rate of the alloy reduced considerably due to addition of SiC particle and the wear rate of composite decreases linearly with increase in SiC content. It has also been noted that the wear resistance of composite varies inversely with square of the reinforcement size. The wear rate of the alloy and composite has been found to be a linear function of applied load but invariant to the abrasive size; at critical abrasive size, transition in wear behaviour is noted. This has been explained through analytically derived equations and wear–surface examination.     

Effect of droplet size on the droplet behavior on the heterogeneous surface

Journal of Mechanical Science and Technology - The characteristics of a three-dimensional hemispherical droplet on a heterogeneous surface were studied using the Lattice Boltzmann method (LBM). The...     

A lower bound to the creep rupture time of pressurised thick cylinders

A lower bound to the creep rupture time of internally pressurised thick cylinders is derived. Material behaviour is described by a phenomenological creep rupture theory that accounts for all phases of creep, and for the full coupling between the deformation and damage processes. To obtain the desirable lower bound, the effective stress and the equivalent rupture stress, which represent the effects of multiaxial stress states on the creep strain and damage rates, respectively, were approximated by the maximum shear stress in the constitutive equations. By comparing the lower bound estimations for a wide range of cylinder dimensions and different engineering materials with the rupture times determined from accurate finite element calculations, it is shown that the lower bound estimations provide quite conservative lifetime predictions.     

Effect of the size of bimetallic plates on the critical temperature on heating

A static 3D model of an elastic-plastic body is considered with the dependence of material capabilities on temperature taken into account. The effect of the size of the plate on deformation and stress at each point of the plate is analyzed to identify such instances of heating in which the plate would function without destruction.     

Effect of grain size and hardness on fretting wear behavior of Inconel 600 alloys

The effects of grain size and bulk hardness on fretting wear behaviors were investigated by solution annealing and subsequently fretting wear test in Inconel 600 alloys. The results indicated that, with increase of solution temperature, the grain size increased while the hardness decreased. The average friction coefficients were the almost same, independent of grain size and hardness; while the wear volume decreased with increase of grain size, but the hardness played little role. The smaller grain was conductive to formation of tribological transformed structure (TTS) layer, and produced shorter delamiantion cracks in the TTS layer than larger one.     

Effect of lubricating oil additives on particle size distribution and total number concentration in diesel engine

This paper investigates the characteristics of particle size distribution in exhaust gas of engine fuelled with pure diesel and with diesel mixed with base oil or with oil additives. The experiments are conducted on a turbocharged diesel engine with fast particulate spectrometer DMS 500 connected to the exhaust pipe. Base oil and two kinds of commonly used lubricating oil additives, antioxidant additives and antifoaming additives, are chosen to be added into the fuel, with the concentrations being 0.5%, 1.0% and 1.5% of fuel weight individually. The particle size distribution is measured under medium load (100 Nm) and full load at different speeds. The results indicate that the existence of base oil or oil additives shows great influence on particle size distribution. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermo-viscoelastic residual stress analysis of metal liner-inserted composite cylinders

One of the most significant problems in the processing of composite material is residual stress. The high residual stress may cause cracking in the matrix without external loads and degrade tile integrity of composite structures. In this Study, thermo-viscoelastic residual stresses occurred in an aluminum liner-inserted composite cylinder are investigated. This type of the structure is used for rocket fuselage due to the convenience to attach payloads and equipment to the metal liner by machining. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. Thee equations are solved with the finite element method to predict the residual stresses in the composite cylinder and also in the interface between the liner and file composite dining cure.     

Effect of particle size, forging and ageing on the mechanical fatigue characteristics of Al6082/SiCp metal matrix composites

Addition of inexpensive silicon carbide particulates (SiC_p) in the aluminium alloy matrix results in materials with properties non-obtainable in monolithic materials. The forging process results in improved properties as well as forms a shape of the final product. The age-hardening processes accelerate the coarse hardening process of the composites and improve strength and ductility. The size, morphology and volume fraction are the key controlling factors that control the plasticity and the thermal residual stresses in the matrix and thereby it’s mechanical and fatigue properties. This research paper focuses on the effect of particle size, forging and ageing on the mechanical and fatigue properties of the cast, forged and age-hardened aluminium 6082 (AI6082) reinforced with SiC_p. Al6082 reinforced with three different particle sizes of SiC_p (average particles size of 22, 12 and 3 µm) in the forged and ageing conditions were studied. The samples were characterised by optical microscopy, hardness, tensile and fatigue tests. The forged microstructure shows a more uniform distribution of SiC_p in the aluminium matrix. The addition of SiC_p results in improved tensile strength, yield strength and elastic constants of the composites with reduction in ductility. It also increases the fatigue strength of the composites by increasing the number of cycles required for fatigue failure of the composites for the given value of stress. The results also show considerable improvements in mechanical fatigue properties due to forging and ageing heat treatment of the metal matrix composites     

光阻法颗粒粒径测量验证实验

针对低浓度液体介质中颗粒物的数目和粒径检测问题,基于几何光学原理和Mie光散射理论分析,研究光阻法对球形颗粒的检测,采用角散射并结合图像法验证信号测量的一致性。搭建了一套能采用3种方法同步测试的实验系统,通过对实验测得的6种标准颗粒的光阻信号进行标定,对不同标准颗粒脉冲幅值进行统计平均后拟合和优化,通过拟合公式进一步测定了其他颗粒的粒径。结果表明,对于标称为15.0μm和63.6μm标准颗粒的数目中位径与标称值偏差均小于2%,同时对于混合颗粒也具有较好的区分能力。     

Effect of current density,MoS2 content and bath agitation on tribological properties of electrodeposited nanostructured Ni-MoS2 composite coatings

ABSTRACT

Nanostructured nickel coatings with molybdenum disulphide particles were electrodeposited to form composite coatings. Three different current densities, i.e. 3, 5 and 7?A/dm² were investigated initially. The best results were obtained with 5 A/dm² for codeposition of nanostructured Ni-MoS₂ composite coatings. With the addition of 1–4?g/L molybdenum disulphide to the bath, the weight percentages of MoS₂ particles in the coatings were 23–38%. This increase of MoS₂ content was accompanied with decrease in friction coefficient of the coatings from 0.35 to 0.08. Wear resistance of the coatings was increased with increasing MoS₂ content and the weight loss was decreased from 1.4 to 0.7?mg. Hardness was decreased from 585 to 400 VHN with increasing the MoS₂ content. By increasing bath agitation speed up to 150?rpm, more MoS₂ particles were embedded in the matrix and the coatings showed better wear resistance. However, increase of agitation speed from 150 to 200?rpm caused a decrease of MoS₂ particles in the nickel matrix due to the turbulent motion of particles in the bath. Overall, it was shown that the lubricating effect of MoS₂ in the coating was more influential than the nanocrystallinity of the nickel matrix in improving tribological properties of these composite coatings.     

马尔文激光粒度仪在测定铬系催化剂粒度分布中的应用

介绍了用马尔文激光粒度仪湿法测定铬系催化剂样品粒度分布的方法。催化剂样品均匀分散在蒸馏水中并以一定流速通过激光束，衍射光由检测器收集，并将信号转换为粒度分布。讨论了应用中的经验。该方法容易建立，精密度高，非常适合在生产过程中应用。     

Simultaneous particle size and concentration measurements using a back-lighted particle imaging system

A back-lighted particle imaging system (BLPIS) is developed to simultaneously measure particle size distribution and volume concentration of suspended particles in water. Based upon optical principles, a modified in-focus parameter, incorporating optical conditions, particle shape, overlapping, and depth-of-field variations due to particle size, is developed to identify particles. BLPIS is calibrated with a precise graticule with an accuracy of particle sizes within the measurement uncertainty of image pixel size resolution. For volume concentration, BLPIS employs an adaptive sampling volume methodology that varies with each particle size based upon a critical in-focus parameter value. Experiments show that under lower volume concentration, measured and actual particle size distributions are in good agreement. For higher volume concentration, measured particle concentration is corrected using a Poisson-based distribution to account for overlapping. Overall the volumetric concentration measurement is reliable and accurate with a relative error of approximate 10%. Finally BLPIS is applied to accurately measure both size and concentration of flowing particles near the bottom boundary with resuspension and sedimentation processes.