During the past decade, considerable research effort has been directed towards the development of in situ metal matrix composites (MMCs), in which the reinforcements are formed in situ by exothermal reactions between elements or between elements and compounds. Using this approach, MMCs with a wide range of matrix materials (including aluminum, titanium, copper, nickel and iron), and second-phase particles (including borides, carbides, nitrides, oxides and their mixtures) have been produced. Because of the formation of ultrafine and stable ceramic reinforcements, the in situ MMCs are found to exhibit excellent mechanical properties. In this review article, current development on the fabrication, microstructure and mechanical properties of the composites reinforced with in situ ceramic phases will be addressed. Particular attention is paid to the mechanisms responsible for the formation of in situ reinforcements, and for creep failure of the aluminum-based matrix composites.

Microstructural and mechanical characteristics of in situ metal matrix composites

Roles of minor additions in formation and properties of bulk metallic glasses

Production and mechanical properties of Al2O3 particle-reinforced 2024 aluminium alloy composites

Lightweight metal matrix nano-composites (MMNCs) (metal matrix with nano-sized ceramic particles) can be of significance for automobile, aerospace and numerous other applications. It would be advantageous to produce low-cost as-cast bulk lightweight components of MMNCs. However, it is extremely difficult to disperse nano-sized ceramic particles uniformly in molten metal. This paper presents a new method for an inexpensive fabrication of bulk lightweight MMNCs with reproducible microstructures and superior properties by use of ultrasonic nonlinear effects, namely transient cavitation and acoustic streaming, to achieve uniform dispersion of nano-sized SiC particles in molten aluminum alloy A356. Microstructural study was carried out with an optical microscope, SEM, EDS mapping, and XPS. It validates a good dispersion of nano-sized SiC in metal matrix. It also indicates that partial oxidation of SiC nanopartilces results in the formation of SiO2 in the matrix. Mechanical properties of the as-cast MMNCs have been improved significantly even with a low weight fraction of nano-sized SiC. The ultrasonic fabrication methodology is promising to produce a wide range of other MMNCs.

Study on bulk aluminum matrix nano-composite fabricated by ultrasonic dispersion of nano-sized SiC particles in molten aluminum alloy

Microstructure and interface characteristics of B4C, SiC and Al2O3 reinforced Al matrix composites: a comparative study

The physical and mechanical properties that can be obtained with metal matrix composites (MMCs) have made them attractive candidate materials for aerospace, automotive and numerous other applications. More recently, particulate reinforced MMCs have attracted considerable attention as a result of their relatively low costs and characteristic isotropic properties. Reinforcement materials include carbides, nitrides and oxides. In an effort to optimize the structure and properties of particulate reinforced MMCs various processing techniques have evolved over the last 20 years. The processing methods utilized to manufacture particulate reinforced MMCs can be grouped depending on the temperature of the metallic matrix during processing. Accordingly, the processes can be classified into three categories: (a) liquid phase processes, (b) solid state processes, and (c) two phase (solid-liquid) processes. Regarding physical properties, strengthening in metal matrix composites has been related to dislocations of a very high density in the matrix originating from differential thermal contraction, geometrical constraints and plastic deformation during processing.

Particulate reinforced metal matrix composites — a review

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.

Processing techniques for particulate-reinforced metal aluminium matrix composites

The present study addresses the wetting and interfacial behaviour in a SiCp reinforced aluminium-lithium alloy processed by spray atomization and deposition. The microstructural characteristics of the spray atomized and deposited Al-Li-SiCp metal matrix composites were investigated as a function of processing history and thermal exposure. The present results show that there was sufficient interfacial activity at the Al-Li/SiC interface during deposition to establish a stable bond. Furthermore, the absence of interfacial reaction products suggests that the temperature during deposition remained relatively low. When the spray deposited material was exposed to temperatures in excess of 600 °C, severe interfacial reactions and the formation of oxide phases were noted. The microstructural studies were accomplished using optical microscopy, scanning electron microscopy (with energy dispersive X-ray spectroscopy), transmission electron microscopy, and X-ray diffractometry.

Wetting and interfacial reactions in Al-Li-SiCp metal matrix composites processed by spray atomization and deposition

Leaching of a low grade Egyptian chromite ore

This investigation is aimed at determining the influence of agro-wastes as substrates on the nutritional quality of Pleurotus pulmonarius and Pleurotus ostreatus. Cassava peels, banana leaves and amended sawdust (sawdust mixed with rice bran in ratio 4:1) were used as growth substrates. Proximate and mineral analyses were carried out using DA 7250 NIR Analyzer and Atomic Absorption of Spectrophotometer machine (AA320N). Both species in amended sawdust had the highest stipe length and pileus diameter of the fruiting body. Starch was the most abundant proximate constituent in the two species. The starch was the most abundant proximate constituent in the two species but highest starch contents were observed in . P. pulmonarius grown in cassava peels substrate and P. ostreatus raised in banana leaves substrate. Fat appeared to be the lowest proximate constituent in the two species. Potassium was predominant among the minerals in both P. pulmonarius and P. ostreatus and the highest value (68.204 mg/L) was observed in P. ostreatus cultivated in amended sawdust. Other minerals varied considerably and as they were differential affected by the substrates. The mushrooms contained useful nutritional constituents however their quantities were influenced by the substrates used in raising them.

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I. A. Ibrahim

Papers

Particulate reinforced metal matrix composites — a review

Processing techniques for particulate-reinforced metal aluminium matrix composites

Wetting and interfacial reactions in Al-Li-SiCp metal matrix composites processed by spray atomization and deposition

Leaching of a low grade Egyptian chromite ore

Influence of substrates on the nutritional quality of Pleurotus pulmonarius and Pleurotus ostreatus