Effects of particle size and distribution on the mechanical properties of SiC reinforced Al-Cu alloy composites

This paper studied the combined effects of particle size and distribution on the mechanical properties of the SiC particle reinforced Al-Cu alloy composites. It has been shown that small ratio between matrix/reinforcement particle sizes resulted in more uniform distribution of the SiC particles in the matrix. The SiC particles distributed more uniformly in the matrix with increasing in mixing time. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength and elongation. Yield strength and ultimate tensile strength of the composite reinforced by 4.7 μm sized SiC particles are higher than those of composite reinforced by 77 μm sized SiC particles, while the elongation shows opposite trend with yield strength and ultimate tensile strength. Fracture surface observations showed that the dominant fracture mechanism of the composites with small SiC particle size (4.7 μm) is ductile fracture of the matrix, accompanied by the “pull-out” of the particles from the matrix, while the dominant fracture mechanism of the composites with large SiC particle size (77 μm) is ductile fracture of the matrix, accompanied by the SiC particle fracture.     

Fatigue behaviour and crack growth rate of cryorolled Al 7075 alloy

The effects of cryorolling (CR) on high cycle fatigue (HCF) and fatigue crack growth rate behaviour of Al 7075 alloy have been investigated in the present work. The Al 7075 alloy was rolled for different thickness reductions (40% and 70%) at cryogenic (liquid nitrogen) temperature and its tensile strength, fatigue life, and fatigue crack growth mechanism were studied by using tensile testing, constant amplitude stress controlled fatigue testing, and fatigue crack growth rate testing using load shedding (decreasing ΔK) technique. The microstructural characterization of the alloy was carried out by using Field emission scanning electron microscopy (FESEM). The cryorolled Al alloy after 70% thickness reduction exhibits ultrafine grain (ufg) structure as observed from its FESEM micrographs. The cryorolled Al 7075 alloys showed improved mechanical properties (Y.S, U.T.S, Impact energy and Fracture toughness are 430 Mpa, 530 Mpa, 21 J, 24 Mpa m^1/2 for 40CR alloy) as compared to the bulk 7075 Al alloy. It is due to suppression of dynamic recovery and accumulation of higher dislocations density in the cryorolled Al alloys. The cryorolled Al alloy investigated under HCF regime of intermediate to low plastic strain amplitudes has shown the significant enhancement in fatigue strength as compared to the coarse grained (CG) bulk alloy due to effective grain refinement. Fatigue crack growth (FCGR) resistance of the ufg Al alloy has been found be higher, especially at higher values of applied stress intensity factor ΔK The reasons behind such crack growth retardation is due to diffused crack branching mechanism, interaction between a propagating crack and the increased amount of grain boundaries (GB), and steps developed on the crack plane during crack-precipitate interaction at the GB due to ultrafine grain formation.     

机械合金化(Mg+Mg2 Ni)+TiO2合金的储氢性能

用机械合金化法合成了(Mg Mg2Ni) TiO2储氢合金,借助XRD分析了TiO2的加入对合金的物相结构的影响,SEM考察了合金的形貌.TiO2在合金的吸放氢过程中起到很好的催化作用,降低合金放氢温度并且提高合金储氢量,(Mg Mg2Ni) 10wt%TiO2合金在573K下的储氢量是5.84wt%.     

Effect of SiC particle size on the physical and mechanical properties of extruded Al matrix nanocomposites

In this work, the effect of SiC particle size and its amount on both physical and mechanical properties of Al matrix composite were investigated. SiC of particle size 70 nm, 10 μm and 40 μm, and Al powder of particle size 60 μm were used. Composites of Al with 5 and 10 wt.% SiC were fabricated by powder metallurgy technique followed by hot extrusion. Phase composition and microstructure were characterized. Relative density, thermal conductivity, hardness and compression strength were studied. The results showed that the X-ray diffraction (XRD) analysis indicated that the dominant components were Al and SiC. Densification and thermal conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Scanning electron microscope (SEM) studies showed that the distribution of the reinforced particle was uniform. Increasing the amount of SiC leads to higher hardness and consequently improves the compressive strength of Al–SiC composite. Moreover, as the SiC particle size decreases, hardness and compressive strength increase. The use of fine SiC particles has a similar effect on both hardness and compressive strength.     

Artificial neural network analysis of the effect of matrix size and milling time on the properties of flake Al-Cu-Mg alloy particles synthesized by ball milling

In this study, the effect of matrix size and milling time on the particle size, apparent density, and specific surface area of flake Al-Cu-Mg alloy powders was investigated both by experimental and artificial neural networks model. Four different matrix sizes (28, 60, 100, and 160?µm) and five different milling times (0.5, 1, 1.5, 2, and 2.5?h) were used in the fabrication of the flake Al-Cu-Mg alloy powders. A feed forward back propagation artificial neural network (ANN) system was used to predict the properties of flake Al-Cu-Mg alloy powders. For training process, the ANN models of the flake size, apparent density, and specific surface area have the mean square error of 0.66, 0.004, and 0.01%. For testing process, it was obtained that the R² values were 0.9984, 0.9998, and 0.9932 for the flake size, apparent density, and specific surface area, respectively. The degrees of accuracy of the prediction models were 95.145, 99.705, and 94.25% for the flake size, apparent density, and specific surface area, respectively.     

CaCO3粉体气流粉碎/静电分散粒径分布规律研究

气流粉碎是近年来发展起来的一种新型微纳米粉体制备技术,然而采用该方法制备的粉体在一定程度上会自发团聚形成团聚体。将静电分散与气流粉碎相结合,研究了不同粒径的原始粉料经气流粉碎/静电分散方法处理后的粒径分布以及粒径随时间的变化关系,得到了气流粉碎/静电分散中荷电电压对所制备粉体粒径分布的影响规律和颗粒荷电分散的时效性,结果表明荷电电压越高粉体分散性越好,经J/E处理后粉体粒径随时间变化关系满足d=Aet/B+d0。     

Effects of particle size and properties on the microstructures,mechanical properties,and fracture mechanisms of 7075Al hybrid composites prepared by squeeze casting

To investigate the effects of particle size and properties on the mechanical properties of 7075Al matrix composites, hybrid composites reinforced using three different reinforcement combinations, 40 vol. % 7 μm SiC_p with 5 vol. % 7 μm SiC_p, 35 μm SiC_p, and 35 μm Ti, were prepared using squeeze casting. The failure mechanisms and the microstructure–property relationships of hybrid composites were studied using SEM, TEM, and tensile tests. The composite containing Ti particles achieved the highest tensile strength of 626 MPa and an elongation of 1.2 %. Fracture mechanism analyses imply that the reduced strength for the 35 μm SiC_p-containing composite are caused by the inefficient load transfer capability resulting from the preferential breakage of larger-sized SiC_p particles during the deformation process. In contrast, micro-zones formed by Ti particles at the center and matrix alloy with few dislocations around release stress and deform synergistically during deformation, which decreases the breakage of SiC_p and improves the plastic deformation ability of the matrix alloy, resulting in a good combination of strength and ductility.     

Prediction of cutting force based on machining parameters on AL7075-T6 aluminum alloy by response surface methodology in end milling

Cutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075-T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.     

Effect of particle size on fatigue behaviour in SiC particulate-reinforced aluminium alloy composites

The effect of particle size on rotary bending fatigue behaviour was studied for powder metallurgy 2024 aluminium alloy composites reinforced with 10 wt% silicon carbide particles (SiC_p ). Average particle sizes of 5, 20 and 60 μm were evaluated. Particle size had a significant influence on fatigue strength, indicating an increased fatigue strength with decreasing particle size. The composite with 5 μm SiC particles showed higher fatigue strength than the unreinforced alloy. The incorporation of 20 μm SiC particles led to an increase in fatigue strength at a high stress level, but the improvement diminished with decreasing stress level, and a slightly decreased fatigue strength was observed at low stress level, as compared with the unreinforced alloy. The composite with 60 μm SiC particles exhibited a considerable decrease in fatigue strength. Fatigue cracks initiated at several different microstructural features, e.g. surface defects, inclusions and particle–matrix interfaces, and crack initiation was considerably affected by particle size. Fatigue strength was found to depend strongly on the resistance to crack initiation, because there was no discernible difference in small crack growth between the unreinforced alloy and the composites, particularly at a low maximum stress intensity factor.     

Effect of varying the ratio of matrix/dispersoid particle size on the piezoresistivity of alumina/carbon-black composite ceramics

Alumina/carbon-black composite ceramics with different percolation thresholds were fabricated by changing the size ratio of constituent particles. The dependence of resistivity on pressure was established for each sample. The compositional dependence of resistivity can be explained by percolation theory. The percolation threshold decreases with increasing alumina/carbon-black particle size ratio. The pressure dependence of the resistivity increases as the composition approaches the percolation threshold. When the relative composition at the percolation threshold is fixed, the sensitivity increases with increasing matrix/dispersoid initial particle size ratio.     

Effect of ball milling time on the structural characteristics and mechanical properties of nano-sized Y2O3 particle reinforced aluminum matrix composites produced by powder metallurgy route

Mechanical milling presents an effective solution in producing a homogenous structure for composites. The present study focused on the production of 0.5 wt% yttria nanoparticle reinforced 7075 aluminum alloy composite in order to examine the effects of yttria dispersion and interfacial bonding by ball milling technique. The 7075 aluminum alloy powders and yttria were mechanically alloyed with different milling times. The milled composites powders were then consolidated with the help of hot pressing. Hardness, density, and tensile tests were carried out for characterizing the mechanical properties of the composite. The milled powder and the microstructural evolution of the composites were analyzed utilizing scanning and transmission electron microscopy. A striking enhancement of 164% and 90% in hardness and ultimate tensile strength, respectively, were found compared with the reference 7075 aluminum alloy fabricated with the same producing history. The origins of the observed increase in hardness and strength were discussed within the strengthening mechanisms' framework.     

Effect of the milling method and particle structure on the color tone of (Cr,Fe)2O3 inorganic black masterbatch pigment

(Cr, Fe)₂O₃ pigment was milled using different techniques into the same particle sizes to investigate the influence of milling processes on its properties. The research showed that milling type resulted in significant color differences, accompanied by the pigment color changing from intense reddish-brown to dark brown. Differences in the morphology of the particles embedded in the plastic matrix led to different light scattering, which is observed as a decrease in the color saturation of the pigment. Particle size distribution (PSD) was characterized by measuring with a laser diffraction particle size analyzer. Pigments were milled down to 4 µm in all milling methods. The very small particles in the pigment affected the light scattering and the color tone. The particle size of the pigment milled by the planetary mill was D₁₀ = 0.035 μ ± 0.1. Color values of the plastic plates were measured according to CIE laboratory analysis. The pigment milled with the planetary mill was lighter, greener, and yellower (ΔL*=4.15, Da*=3.68, Db*=2.96). The pigment milled with the jet-mill was closest to the pigment color after calcination. The pigment milled with ball mill was slightly greener than the values after calcination (Da*=1).     

Synthesis and structural characterization of nanocrystalline silicon by high energy mechanical milling using Al2O3 media

High energy mechanical milling was used to fabricate nanoparticulate Si using Al₂O₃ grinding media. Two ratios of grinding media to charge of 5 and 10 were used with milling times, such as 7, 10, 13, 16, and 19 h. Morphology of the milled powders was investigated by scanning and transmission electron microscopy. Crystallinity of the milled powders was found to be preserved for all milling conditions without amorphization. Crystallite size of the milled powders was calculated from x-ray diffractograms by various methods. From morphology and crystallite size it was observed that 13 h of milling is the optimum time to produce well dispersed Si nanoparticulates. Further increase in milling duration clearly indicated agglomeration of the powders and cold welding of the crystallites for samples of both media-to-charge ratios. X-ray diffractograms and Raman spectrographs of the milled samples were used to calculate the strain induced in the materials, which indicated progressive increase in strain with milling duration. The results indicate that Al₂O₃ milling media can be used with optimized process conditions for the production of large quantities of nanoparticulate Si.     

原位合成TiC/Al(7075)复合材料的组织及力学性能

采用原位合成法制备TiC/Al(7075)复合材料,研究原位TiC颗粒的存在形式、分布状态及不同原位TiC颗粒含量对TiC/Al(7075)复合材料的微观组织及力学性能的影响。结果显示,TiC颗粒多以近球形团聚态存在于7075铝基体中,颗粒团大小约为1μm。当原位TiC颗粒质量分数小于6%时,原位TiC颗粒分布较为均匀,随着颗粒含量的增加,TiC/Al(7075)复合材料的铸态组织由蔷薇状组织逐渐转变为等轴晶组织,晶粒尺寸也随着原位TiC颗粒含量的增加而减小。当原位TiC颗粒的质量分数大于6%时,组织中出现气孔。复合材料的硬度和抗冲击韧性测试表明,TiC/Al(7075)复合材料的硬度随TiC颗粒含量的增加而增加,最高硬度达HB 108,冲击韧性在颗粒质量分数为6%时达到最佳,较基体提升31.55%。     

Impact of graphite particle on milling of Al/15Al2O3 and Al/15Al2O3/5Gr composites

ABSTRACT

Hybrid Metal Matrix Composites (MMCs) are a new class of composites, formed by a combination of the metal matrix and more than one type of reinforcement having different properties. Machining of MMCs is a difficult task because of its heterogeneity and abrasive nature of reinforcement, which results in excessive tool wear and inferior surface finish. This paper investigates experimentally the addition of graphite (Gr) on cutting force, surface roughness and tool wear while milling Al/15Al₂O₃ and Al/15Al₂O₃/5Gr composites at different cutting conditions using tungsten carbide (WC) and polycrystalline diamond (PCD) insert. The result reveals that feed has a major contribution on cutting force and tool wear, whereas the machined surface roughness was found to be more sensitive to speed for both composite materials. The incorporation of graphite reduces the coefficient of friction between the tool–workpiece interfaces, thereby reducing the cutting force and tool wear for hybrid composites. The surface morphology and worn tool are analyzed using scanning electron microscope (SEM). The surface damage due to machining extends up to 200 µm for Al/15Al₂O₃/5Gr composites, which is beyond 250 µm for Al/15Al₂O₃ composites.     

Influence of controlled particle size on pore size distribution and mechanical resistance of agarose beads for bioadsorption application

ABSTRACT

In this work the influence of fabrication conditions (ion strength, surfactant utilization) on the macro- (particle size distribution, PSD) and microscopic [pore size distribution (PoSD), specific surface area] structure of agarose beads was investigated. The main purpose was achieving uniform sized and porous beads with improved mechanical strength for bioseparation and chromatography applications. Therefore, PSD, PoSD, mechanical resistance, and flux through packed bed of the fabricated beads (4, 6, and 8% wt/wt) were analyzed. Based on porosimetry results, it was found that increasing ion concentration or presence of surfactant (the key variable for narrowing PSD) decreases the span value of PSD (p-value <0.05); thus, leading to a more uniform distribution. Moreover, as a result of controlling PSD, the PoSD changes from micro- to meso- and macropores in higher ion charged solutions. Furthermore, the obtained PoSD affects mechanical resistance of the prepared microspheres either as single beads or packed in a column. Mesoporous 6%-agarose beads showed the highest flux due to elevated mechanical resistance and elastic characteristic. Mesoporous 4%-beads showed the highest elasticity, and thus lower flux through column. These results demonstrate that manipulation of both macro- and microscopic characteristics of the beads should be commensurate with the intended application i.e., bioadsorption chromatography.     

颗粒粒度分布对树脂基磁致伸缩复合材料性能的影响

已有研究在Terfenol-D颗粒粒径及粒度分布对树脂基磁致伸缩复合材料性能的影响规律上存在分歧。本文中以Terfenol-D为磁致伸缩颗粒,以不饱和聚酯树脂为基体,采用5 种窄分布颗粒(30～53μm、53～150μm、150～300μm、300～450μm、450～500μm)和1种宽分布颗粒(30～500μm)制备颗粒体积分数为20 %的磁致伸缩复合材料,并测试其动静态磁致伸缩系数、磁机械耦合系数、弹性模量及抗压强度等性能参数。在窄分布颗粒制备的试样中,以53～150μm制备的复合材料的磁致伸缩性能最佳;而采用宽分布颗粒制备的试样其性能优于窄分布颗粒制备的试样。该结果表明,增大颗粒粒径同时具有积极作用与消极作用, 其对复合材料磁致伸缩性能的影响取决于哪一个居主导地位。      

机械球磨对Ti/Al混合粉末组织和热稳定性影响的研究

为了探索一种制备高综合性能TiAl基金属间化合物的新方法，研究了机械球磨对Ti、Al粉末微观组织及其热稳定性的影响，结果表明，在机械球磨的作用下Al粉末晶粒以高于Ti的速率细化，最终形成局部含少量Ti 纳米晶的非晶，但在整个过程中未发现Ti、Al元素相互扩散形成Ti-Al金属间化合物中间相；不同球磨时间作用下的Ti/Al粉末中贮有不同的能量，且随时间的延长而增加，以非晶化粉末最为显著，内能的增加是由于机械合金化过程引入了大量的微观缺陷所致，对不同球磨时间的粉末进行热处理显示，球磨时间的增加可大幅度降低形成Ti-Al金属间化合物的温度，球磨75h的复合粉末甚至在350℃，保温1h即可转变成金属间化合物。     

Effect of mechanical milling and heat treatment on the structure and magnetic properties of gas atomized Mn-Al alloy powders

Ferromagnetic Mn-Al alloy powders were fabricated by mechanical milling and heat treatment with gas-atomized powders. Different processes, i.e., heat treatment before ball milling and ball milling before heat treatment, result in different microstructures and magnetic properties of the powders. It was found that H_c increased and M_r decreased with the size reduction regardless of the sequence of heat treatment and ball milling. However, tendency of the change in H_c and M_r depended on the sequence. Further annealing of the powders ball-milled after heat treatment resulted in slight decrease of H_c and large increase of M_r. The magnetic properties, M_r = 41.2 emu/g, H_c = 3.1 kOe, were obtained from the powders ball-milled for 5 h after heat treatment at 650 °C for 20 min, and subsequent annealing at 280 °C for 20 min.     

Al_2O_3粒径与形貌对尼龙复合材料导热性能影响研究

以尼龙(PA)为基体、三氧化二铝(Al2O3)为导热填料经熔融共混、模压成型后制得尼龙导热复合材料。通过扫描电子显微镜、导热分析仪对复合材料微观形貌、导热性能进行表征。结果表明,Al2O3在尼龙基体中具有良好的分散性;Al2O3填料含量、粒径和形貌都对复合材料导热率有影响,当粒径为5μm的片状Al2O3的填充量达到50%(质量分数)时,其导热率可达0.838 W/(m·K);不同形貌的Al2O3填料复配使用可以有效构建导热通路、提高复合材料热扩散系数,但会降低材料热容、使复合材料导热系数减小。