包覆混料对镀铜混合尺寸SiCp/Fe力学性能的影响

为探索提高SiCp/Fe力学性能的途径,采用包覆混料工艺,研究了该工艺对镀铜SiCp/Fe力学性能的影响,以及该工艺下增强粒子混合尺寸的影响.结果表明:包覆混料相比于普通混料,可显著改善SiC粒子在基体中分散的均匀性,而镀铜的作用是显著消除界面缺陷;性能的改善是包覆混料改善粒子分散性和镀铜改善界面结合的综合结果.对于体积分数30%SiCp/Fe的抗拉强度,通过包覆改善均匀性的贡献可提高7.2%,通过镀铜消除界面缺陷的贡献可提高12.5%,因此减少界面缺陷对颗粒增强复合材料力学性能的提高更重要.混合尺寸粒子对力学性能的增强效果明显高于其对应单一尺寸,这是由于小尺寸粒子能有效地提高基体的强度,而大尺寸颗粒更有效地承担载荷传递的作用.     

Erosive wear behaviour of aluminium based composites

Al-MMCs reinforced with short fibres or particles of ceramics such as alumina, titanium diboride and silicon carbide result in composites of high specific strength and stiffness, suitable for advanced engineering applications such as in the aerospace and automotive industries. This paper studies the erosion wear behaviour of Al-based composites reinforced with alumina-fibre and in-situ TiB₂ particles using a water/SiC particles slurry jet. From the results of our experiment, the erosion resistance of reinforced Al-MMCs depends on that of the Al-alloy and the reinforcing ceramics, as well as on the bonding strength between the matrix and ceramic fibres or particles. Some design strategies to enhance the erosion resistance of Al-MMCs reinforced with short fibres and particles have been discussed.     

搅拌摩擦加工制备颗粒增强铝基复合材料的研究现状及展望

铝合金作为现代工程和高新技术领域发展的关键材料之一,具有密度小、比强度和比刚度高、耐蚀性好等特点。通过在铝基体中添加增强相颗粒,制备得到的颗粒增强铝基复合材料既有铝合金良好的强度、韧性、易成形性等特点,又有颗粒的高强、高模等优点,是近年来应用最广的一类金属基复合材料。 目前,制备铝基复合材料的方法主要有粉末冶金法、铸造以及超声波法等,但这些方法在制备过程中需要较高的温度,颗粒与金属基体容易发生不良的界面反应,从而影响界面结合效果,降低复合材料的性能。搅拌摩擦加工(FSP)作为一种新型的固相加工技术,可同时实现材料微观组织的细化、致密化和均匀化。目前,FSP直接法已在铝基复合材料制备方面取得应用,主要是将增强相颗粒通过打盲孔或开槽的方式预置在金属基体内再进行FSP,进而制备出高致密度的颗粒增强铝基复合材料。因为FSP过程的温度低,颗粒与铝基体不会发生界面反应,所以该方法也被用于制备具有形状记忆效应(SME)的铝基功能复合材料。 近年研究结果表明,颗粒相对FSP制备的铝基复合材料晶粒细化起到显著作用,这有助于提高复合材料的拉伸强度、显微硬度及疲劳强度等力学性能。随着颗粒含量的增加和颗粒尺寸的减小,复合材料的力学性能得以增强。再者,减小颗粒尺寸有利于改善颗粒与基体之间的结合。另外,通过优化搅拌头的结构、形状和尺寸,以及FSP工艺参数,已经可以实现加工后颗粒相在基体中的均匀分布。 鉴于搅拌摩擦加工(FSP)直接法在制备颗粒增强铝基复合材料方面所具备的短流程、高效能以及基体与增强相颗粒界面无杂质等优势,本文对目前FSP直接法制备颗粒增强铝基复合材料的最新研究现状进行了总结。主要综述了FSP制备颗粒增强铝基复合材料过程中颗粒的含量、类型及尺寸对复合材料组织与力学性能的影响,并对颗粒分布均匀性以及颗粒与铝基体的界面问题做了阐述。文章最后深入分析了当前研究中的不足之处并展望了未来的研究方向。     

In situ processing of TiCp-Al composites by reacting graphite with AI-Ti melts

Aluminum has been a key material, particularly in the aerospace and automotive industries, owing to its low density, high specific strength, good corrosion resistance and recyclability. Aluminum based metal matrix composites have also become attractive candidates for various applications where monolithic aluminum alloys cannot meet the strict design requirements. Recently, particulate reinforced aluminum composites have attracted a great deal of attention. Among various techniques which have been employed in the synthesis of these composites, incorporation of the reinforcing phase particles directly into the melt is practical and economic; yet it is not trouble-free. In situ processing of particulate reinforced composites, on the other hand, yields superior microstructures and thus better properties. In the present work, such a method to manufacture TiC_p-Al composites and the microstructures obtained thereof will be described.     

稀释中间复合材料法制备SiCP/356Al的研究

本文探索了一种制备SiC_P/Al的新工艺方法,即稀释中间复合材料法,以避免通常用来制备SiC_P/Al的复合铸造法中存在的浸润性差、气孔率高、存在氧化夹杂及颗粒偏聚等问题。结果表明,用该法能成功地制备10vol%和15vol%SiC_P/Al复合材料,其拉伸性能比用复合铸造法制备的同样材料高10%,且气孔率显着降低,X-rays衍射和TEM分析结果表明,该工艺过程中没有发生明显的界面反应,工艺参数的选择是合理的。     

Influence of reinforcing particles on microstructure and mechanical properties of friction stir processed aluminium alloy AA7075-T651

This paper emphasis the improvement of mechanical properties of AA7075-T651 using friction stir processing through localized surface modification by adding nano boron carbide particles. The reinforcement techniques such as the groove and blind hole methods were used by changing reinforcements of nano boron carbide and a matrix of AA7075-T651 surface composites volume percentages (2 %, 4 %, and 6 %) along with tool rotational speed and processing speeds. Optical microscopy, scanning electron microscope and x-ray diffraction analysis were used to examine the particle dispersion for the surface composites and to correlate with the enhanced mechanical properties. Results revealed that high input parameters have given grain coarsening and precipitate agglomeration and low input parameters provide poor nugget metal consolidation and no vertical material flow. The L9 orthogonal Array designed and optimized the process parameters for enhancing the surface properties of processed samples. Mechanical properties like ultimate tensile strength, yield strength, hardness, percentage of elongation and impact strength were evaluated for the groove friction stir processing method and blind-hole friction stir processing methods. From the results, it has been observed that the blind-hole technique resulted in higher hardness and the homogenous dispersion of nano boron carbide particles in the stir zone than the groove method. Consequently, for blind-hole friction stir processing, grey relational analysis (GRA) and particle swarm optimization (PSO) approaches were proposed to optimise process parameters. From the compared optimization results between grey relational analysis and particle swarm optimization, particle swarm optimization approach was shown the best optimization results. Successively, the optimum condition in the respective experimentation is accomplished. Based on these observation and results, final validation tests were carried by changing the volume percentages of reinforcement keeping tool rotation speed and tool processing speed as constant. It is apparent that dynamic recrystallization in aluminium alloy at the processed zone due to presence of heterogeneous nucleation sites with nano boron carbide particles.     

Cryogenic Processing: A Study of Materials at Low Temperatures

Cryogenics is an exciting, important and inexpensive technique that already has led to main discoveries and holds much future assurance. Cryogenic processing is the treatment of the materials at very low temperature around 77 K. This technique has been proven to be efficient in improving the physical and mechanical properties of the materials such as metals, alloys, plastics and composites. It improves the wear, abrasion, erosion and corrosion resistivity, durability and stabilizes the strength characteristics of various materials. Cryogenic refines and stabilizes the crystal lattice structure and distribute carbon particles throughout the material resulting a stronger and hence more durable material. In present paper, we have reviewed the effect of cryogenic treatment on some metals, alloys, plastics and composites.     

Comparison of Al-Cu-Fe quasicrystalline particle reinforced Al composites fabricated by conventional casting and extrusion

Aluminum matrix composites reinforced by Al₆₂Cu₂₆Fe₁₂ gas atomized powders were produced by conventional metallurgical processes, such as gravity casting with stirring and hot extrusion. This investigation was mainly focused on the dependency of the yield stress at room temperature as a function of the volume fraction of reinforcement, but other variables such as the matrix, coating layer around the particles, and processing were also investigated. For as-extruded composites, the addition of the Al-Cu-Fe particles improved the yield stress, although not dramatically owing to the large particle size. In contrast, it was found that the yield stress was considerably enhanced for the as-cast composites up to 10%(AlCuFe)p, while an asymptotic value was observed afterward. The dominant parameter appeared to be the strength of the matrix, which was found to be proportional to the volume fraction of the reinforcement. These results are discussed in relation with the possible strengthening mechanisms in order to estimate the role of the icosahedral and related crystalline phases on the increase of yield stress.     

Particle-reinforced aluminum matrix composites produced from powder mixtures via friction stir processing

Particle-reinforced aluminum matrix composites were produced from powder mixtures of aluminum and silicon by using multiple passages of friction stir processing (FSP). In the composites, the Si particles with an average size of ∼1.5 μm are uniformly dispersed in the aluminum matrix which has a fine-grained structure (∼2 μm). The strengthening mechanism of the composites is discussed. It indicates that the fine grain size of aluminum, the Orowan strengthening due to intragranular particles and the dislocations generated by thermal mismatch all contribute significantly to the composite yield strength.     

NOVEL PROCESSING APPROACHES TO INTERMETALLIC MATRIX COMPOSITES

Intermetallic compounds have been recognized as potentially useful structural materials. They form the basis for high temperature materials of the future. Intermetallic compounds based on aluminum have attractive characteristics of high strength at elevated temperatures, good corrosion and oxidation resistance, and low densities. This research focuses on the use of the nickel aluminide (Ni₃Al) intermetallic compound as a matrix for high temperature composites. The powder processing approach has been adopted for the consolidation of these composites. This paper describes research on powder injection molding (PIM) of an alumina fiber reinforced nickel aluminide intermetallic. Major problems are associated with the debinding process. They have been resolved and composite structures formed. Preliminary investigations on a reactive hot isostatic pressing approach for forming these nickel aluminide matrix composites, are briefly discussed.     

The fabrication of metal matrix composites by a pressureless infiltration technique

A novel technique for fabricating metal matrix composites by the spontaneous (pressureless) infiltration of filler preforms with molten aluminium alloys is described. Numerous reinforcing materials, including Al₂O₃ and SiC of various configurations, such as particles, agglomerates, and fibres, have been incorporated as fillers. The effects of processing variables, such as alloy chemistry, process temperature, and filler material, on the infiltration kinetics and resultant microstructures are discussed. Comparisons with existing infiltration technology and preliminary composite properties are presented.     

Composites and nanocomposites of ABS: Synergy between glass fiber and nano-sepiolite

One of the latest steps in polymer nano-technology is polymer/clay/glass fiber composites because of the synergistic effects of both reinforcing particles. Acrylonitrile–butadiene–styrene (ABS) – sepiolite nanocomposites have been developed, and glass fiber has been added to this system in order to study a synergistic behavior between both reinforcing particles. Properties such as Young modulus, impact strength and heat deflection temperature have been measured to characterize the nanocomposites. Morphology has been studied by means of optical and electron microscopy.     

Tensile behaviour and fracture toughness of EPDM filled with untreated and silane-treated glass beads

The Essential Work of Fracture (EWF) theory has been applied to study the fracture behaviour of untreated and silane-treated glass bead-filled EPDM composites. The experimental values of both Young's modulus and tensile strength have been compared with those predicted by the main theoretical and semiempirical models, and the influence of the composite processing temperature on the tensile properties has been studied, noticing a marked drop of stiffness and strength from a processing temperature of 200 °C. A good adhesion between EPDM matrix and glass beads was achieved with the silane Z-6032, resulting in higher tensile strength, and it has been observed that glass bead presence induces plasticity in the EPDM matrix. No differences of the specific essential work of fracture were found in the three filled samples, although results show that the higher adhesion degree between matrix and particles, the higher value of the specific plastic work of fracture, and also the higher final instability in crack propagation.     

Discontinuously-reinforced aluminum matrix composites

This article reviews the literature relating to aluminum matrix composites reinforced by ceramic particles, short fibers or whiskers. The main reinforcements which have been used are presented with respect to their nature, morphology and mechanical behavior. The influence of matrix alloying elements on ceramic-metal compatibility is discussed. Most fabrication techniques which have been proposed are described and particular attention is paid to the methods suitable for large scale production. The mechanical characteristics of this kind of composite are reported and compared in relation to processing parameters. Finally, models giving a rough prediction of the mechanical behavior of the composites are discussed.     

Processing techniques for particulate-reinforced metal aluminium matrix composites

The critical need for high strength, lightweight and high stiffness materials has, in recent years, resurrected much interest in discontinuously reinforced powder metallurgy metal matrix composites. These hybrid materials have combined both standard wrought alloys of aluminium and a wide variety of discontinuous reinforcements such as particulates and whiskers of ceramic materials. Renewed interest in these materials as attractive candidates for use in the aerospace and transportation industry has resulted from an attractive and unique combination of physical and mechanical properties, and an ability to offer near isotropic properties coupled with the low cost of these materials when compared with existing monolithic materials. In this paper, the primary processing categories for discontinuously-reinforced metal-matrix composites are highlighted and the salient features of the various techniques in each category are discussed. The variables involved in each processing technique are examined, and the influence of alloy chemistry highlighted. Novel processing techniques for these materials such as the variable co-deposition method is presented as a means to process these novel engineering materials in order to improve their overall mechanical performance.     

Study on nonlinear conductivity and breakdown characteristics of zinc oxide–hexagonal boron nitride/EPDM composites

The ethylene–propylene–diene monomer (EPDM) has been widely used in HVDC cables accessories. The nonlinear conductivity of EPDM-based composites plays an important role on relieving the distortion of electric field. In this study, the zinc oxide (ZnO) particles are selected as fillers for improving the nonlinear conductivity of EPDM. The result shows that nonlinear conductivity characteristics of ZnO/EPDM becomes more and more pronounced with the increase of ZnO doping content, however, the breakdown strength of ZnO/EPDM composites has been seriously deteriorated with the increase of ZnO doping content. The excellent breakdown strength of composites is very important for ensuring the safe operation of cable accessories, so the hexagonal boron nitride (h-BN) with good electrical insulation has been employed for improving the breakdown strength of ZnO/EPDM. The results indicate that both of non-linear conductivity and good breakdown strength have been obtained in ZnO–h composite-BN/EPDM composites. This work provides a novel way for constructing the composites with excellent electrical performances which are used for cable accessories.     

Graphene-reinforced metal matrix nanocomposites – a review

The research works of graphene-reinforced metal matrix composites will be summarised in this paper. Comparatively, much less research works have been undertaken in this field. Graphene has been thought to be an ideal reinforcement material for composites due to its unique two-dimensional structure and outstanding physical and mechanical properties. It is expected to yield structural materials with high specific strength or functional materials with exciting thermal and electrical characteristics. This paper will introduce all kinds of graphene-reinforced metal matrix composites that have been studied. The microstructure and mechanical properties, processing techniques, graphene dispersion, strengthening mechanisms, interfacial reactions between graphene and the metal matrix and future research works in this field will be discussed.     

Experimental investigation on mechanical properties and wear characterization of Al-Si12CulMg1 aluminium alloy reinforced with titanium diboride and boron carbide particulate hybrid composites using stir casting process

LM13 aluminium alloy (Al−Si12CulMg1) with titanium diboride (TiB₂) and boron carbide (B₄C) particulate hybrid composites have been prepared using stir casting process. Wt% of titanium diboride is varied from 0–10 and constant 5 wt% boron carbide particles have been used to reinforce LM13 aluminium alloy. Microstructure of the composites has been investigated and mechanical properties viz., hardness, the tensile strength of composites have been analyzed. Wear behavior of samples has been tested using a pin on disc apparatus under varying load (20 N–50 N) for a sliding distance of 2000 m. Fracture and wear on the surface of samples have been investigated. Microstructures of composites show uniform dispersion of particles in LM13 aluminium alloy. Hardness and tensile strength of composites increased with increasing wt % of reinforcements. Dry sliding wear test results reveal that weight loss of composites increased with increasing load and sliding distance. Fracture on the surface of composites reveals that the initiation of crack is at the interface of the matrix and reinforcement whereas dimples are observed for LM13 aluminium alloy. Worn surface of composites shows fine grooves and delamination is observed for the matrix.     

High energy density processing of a free form Nickel-alumina nanocomposite

The development of a free form bulk Nickel reinforced Alumina matrix nano composites using Air Plasma Spray and laser processing has been presented. The process consumes less time and requires further minimal machining and therefore is cost effective. The relative differences in using APS over laser processing in development of bulk metal-ceramic nanocomposites have been discussed. The process intricacies involved during processing such as material specific mandrel selection, plasma-particle interaction are highlighted. Electroless coating has been used to uniformly disperse Nickel in alumina matrix as a source material. The electroless Ni coated alumina particles are subjected to both laser processing and Air Plasma Spraying with optimized parameters. Consolidation by laser processing could not be achieved as the laser beam was reflective to Nickel. On the other hand, APS Ni-alumina nanocomposite with a cylindrical shape of 1.2" OD x 1" ID x 1.5" length has been fabricated with minimum or no surface defects. HRTEM pictures revealed the nanostructure retention thereby corroborating the fact that bulk nanostructures can be made using Air Plasma Spray. XRD analysis confirmed the phase transformation from alpha alumina to gamma alumina and oxidation of Ni to NiO. Subsequent reduction of NiO to metallic nickel using hydrogen atmosphere has also been demonstrated. Mechanical properties such as, hardness (1025 HV) and fracture toughness (5 MPa m1/2) for the nanocomposite are presented herein.