This review summarises the research work carried out in the field of carbon nanotube (CNT) metal matrix composites (MMCs). Much research has been undertaken in utilising CNTs as reinforcement for composite material. However, CNT-reinforced MMCs have received the least attention. These composites are being projected for use in structural applications for their high specific strength as well as functional materials for their exciting thermal and electrical characteristics. The present review focuses on the critical issues of CNT-reinforced MMCs that include processing techniques, nanotube dispersion, interface, strengthening mechanisms and mechanical properties. Processing techniques used for synthesis of the composites have been critically reviewed with an objective to achieve homogeneous distribution of carbon nanotubes in the matrix. The mechanical property improvements achieved by addition of CNTs in various metal matrix systems are summarised. The factors determining strengthening achieved by CNT reinforcement are elucidated as are the structural and chemical stability of CNTs in different metal matrixes and the importance of the CNT/metal interface has been reviewed. The importance of CNT dispersion and its quantification is highlighted. Carbon nanotube reinforced MMCs as functional materials are summarised. Future work that needs attention is addressed.

Carbon nanotube reinforced metal matrix composites - a review

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

Metal matrix composites reinforced by nano-particles are very promising materials, suitable for a large number of applications. These composites consist of a metal matrix filled with nano-particles featuring physical and mechanical properties very different from those of the matrix. The nano-particles can improve the base material in terms of wear resistance, damping properties and mechanical strength. Different kinds of metals, predominantly Al, Mg and Cu, have been employed for the production of composites reinforced by nano-ceramic particles such as carbides, nitrides, oxides as well as carbon nanotubes. The main issue of concern for the synthesis of these materials consists in the low wettability of the reinforcement phase by the molten metal, which does not allow the synthesis by conventional casting methods. Several alternative routes have been presented in literature for the production of nano-composites. This work is aimed at reviewing the most important manufacturing techniques used for the synthesis of bulk metal matrix nanocomposites. Moreover, the strengthening mechanisms responsible for the improvement of mechanical properties of nano-reinforced metal matrix composites have been reviewed and the main potential applications of this new class of materials are envisaged.

/pdf/metal-matrix-composites-reinforced-by-nano-particles-a-206fp650x1.pdf

Metal Matrix Composites Reinforced by Nano-Particles—A Review

Rapid innovation in nanotechnology in recent years enabled development of advanced metal matrix nanocomposites for structural engineering and functional devices. Carbonous materials, such as graphite, carbon nanotubes (CNT's), and graphene possess unique electrical, mechanical, and thermal properties. Owe to their lubricious nature, these carbonous materials have attracted researchers to synthesize lightweight self-lubricating metal matrix nanocomposites with superior mechanical and tribological properties for several applications in automotive and aerospace industries. This review focuses on the recent development in mechanical and tribological behavior of self-lubricating metallic nanocomposites reinforced by carbonous nanomaterials such as CNT and graphene. The review includes development of self-lubricating nanocomposites, related issues in their processing, their characterization, and investigation of their tribological behavior. The results reveal that adding CNT and graphene to metals decreases both coefficient of friction and wear rate as well as increases the tensile strength. The mechanisms involved for the improved mechanical and tribological behavior is discussed.

Mechanical and tribological properties of self-lubricating metal matrix nanocomposites reinforced by carbon nanotubes (CNTs) and graphene – A review

Mechanically alloyed nanocomposites

Effect of carbon nanotube (CNT) content on the mechanical properties of CNT-reinforced aluminium composites

Powder metallurgy techniques have emerged as promising routes for the fabrication of carbon nanotube (CNT) reinforced metal matrix composites. In this work, planetary ball milling was used to disperse 2 wt% MWCNT in aluminum (Al) powder. Despite the success of ball milling in dispersing CNTs in Al powder, it is often accompanied with considerable strain hardening of the Al powder, which may have implications on the final properties of the composite. Both un-annealed and annealed Al–2 wt% CNT composites were investigated. It was found that, ball-milled and extruded (un-annealed) samples of Al–2 wt% CNT demonstrated high notch-sensitivity and consistently fractured outside the gauge length during tensile testing. In contrast, extruded samples annealed at 400 and at 500 °C for 10 h prior to testing, exhibited more ductile behavior and no notch sensitivity. Under the present investigated processing conditions, ball milling for 3 h followed by hot extrusion and annealing at 500 °C resulted in enhancements of around 21% in tensile strength compared with pure aluminum with the same process history. The ball-milling conditions used were found to result in the creation of a nanostructure in all samples produced, as shown by XRD and TEM analysis. Such nanostructure was retained after prolonged exposures to temperatures up to 500 °C. The tensile testing fracture surfaces showed uniform dispersion and alignment of the CNTs in the aluminum matrix but also showed CNTs acting as nucleation sites for void formation during tensile testing. This has contributed to the observation of CNT pull-out due to the poor bond between the CNTs and the matrix.

Fabrication and properties of dispersed carbon nanotube–aluminum composites

Ball milling was used to disperse MWCNTs of two different morphologies (stiff and straight vs. bent and entangled) and diameters (very large diameter and 3.5 times smaller diameter) in aluminium powders, which were subsequently hot consolidated by hot extrusion. Characterization of the produced composites revealed that the CNT morphology plays an important role in affecting dispersion. It was found that the smaller diameter bent and entangled CNTs were more difficult to disperse with increase in CNT content compared to the larger diameter stiff and straight ones; which in turn affected the tensile properties and hardness of the composites. Furthermore, cold welding of the milled powders as well as carbide formation in the final composite was found to depend on the CNT diameter. The smaller diameter CNTs – having a larger effective interfacial contact area with the aluminium matrix compared to the larger ones for a given CNT wt.% – were found to reduce particle welding during milling and to be more affected by carbide formation. Nano-sized particles of aluminium oxide as well as nano-rods of aluminium carbide, in addition to CNT damage were observed upon TEM analysis of the smaller diameter CNTs.

The influence of carbon nanotube (CNT) morphology and diameter on the processing and properties of CNT-reinforced aluminium composites

Ball-milled aluminum (Al) and Al–carbon nanotube (CNT) composite (2.5 wt.% CNT loading) powders have been consolidated using a spark plasma extrusion (SPE) process. Compared with spark plasma sintering (SPS), SPE has the added advantages of allowing the production of powder-based materials of extended geometries and bulk deformation under the influence of electric current which may yield materials with unique properties. The process is discussed in this short communication together with resulting microstructures and properties for the investigated materials.

Spark plasma extrusion (SPE) of ball-milled aluminum and carbon nanotube reinforced aluminum composite powders

The interest in carbon nanotube (CNT) aluminum composites has been growing significantly over the past decade. Most work has focused on the generation of composite materials with homogeneously dispersed carbon nanotubes. On the other hand, the dual matrix composite microstructural design, where the matrix is selectively reinforced in localized regions within the microstructure separated by ductile unreinforced matrix, may present significant benefits. Primarily these benefits include an ability to tailor the properties of the final composite which may give rise to controlled properties and enhanced formability. This paper discusses dual- and single-matrix CNT–Al composites and milled aluminum processed via Spark Plasma Extrusion (SPE) and discusses the effect of the microstructural design on the mechanical properties.

A. Sayed

Papers

Effect of carbon nanotube (CNT) content on the mechanical properties of CNT-reinforced aluminium composites

Fabrication and properties of dispersed carbon nanotube–aluminum composites

The influence of carbon nanotube (CNT) morphology and diameter on the processing and properties of CNT-reinforced aluminium composites

Spark plasma extrusion (SPE) of ball-milled aluminum and carbon nanotube reinforced aluminum composite powders

Properties of single and dual matrix aluminum–carbon nanotube composites processed via spark plasma extrusion (SPE)