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.

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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

Microstructurally inhomogeneous composites: Is a homogeneous reinforcement distribution optimal?

The present work investigated the effects of hot compression and heat treatment on the microstructure and tensile property of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy with a widmanstatten microstructure. During hot compression at 995 °C, the lamellar α phase in the widmanstatten structure was distorted, and an equiaxed microstructure was obtained by subsequent duplex annealing of the hot-compressed sample. The tensile strength and elongation were significantly improved by hot compressing at 995 °C. Duplex annealing treatment resulted in a further increase in ductility at the expense of slight decrease in strength. A good combination of tensile strength (990 MPa) and elongation (12.8%) has been obtained by hot compression at 995 °C followed by the duplex annealing treatment.

Effects of hot compression and heat treatment on the microstructure and tensile property of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy

Simultaneous enhancement of the strength and ductility in metal-matrix nanocomposites with high content nano-reinforcements is crucial for the development of novel composite materials. Here SiC/Al nanocomposites with ultrafine Al grains and intragranular 10 vol% SiC nanoparticle were prepared by mechanical alloying and hot pressure sintering followed by hot extrusion. The results show that nanocrystalline Al grains and uniformly distributed SiC nanoparticles (SiCnp) in the composite powders are obtained after ball-milling. The prior particle boundary (PPB) in the composite powders cannot be fully removed by sintering at 580 °C under 20 MPa, but can be eliminated by subsequent hot extrusion at 450 °C with a ratio 25:1. The extruded nanocomposites possess ultrafine Al grains with diameter 320 nm and intragranular SiCnp created by the dynamic recrystallizations (DRX). Such optimal microstructure favors a significant improvement of 284% in yield strength (YS) and 259% in ultimate tensile strength (UTS) compared with monolithic Al, and more interestingly, maintains an elongation up to 12% due to the homogeneous nanoparticles in fine Al grains. Theoretical analysis shows that the dominant strengthening factor is Orowan strengthening related to the high content intragranular SiCnp, with second factor grain boundary strengthening due to ultrafine Al grains.

Enhanced combination of strength and ductility in ultrafine-grained aluminum composites reinforced with high content intragranular nanoparticles

Fabrication and characteristics of in situ Al12W particles reinforced aluminum matrix composites by reaction sintering

The Ti–(SiC p /Al) laminated composite was prepared by roll bonding of pure Ti and SiC p /Al foils. The microstructure analysis shows that the work-hardening of Ti reduces the deformation compatibility of the Ti and SiC p /Al layers with increasing the rolling reduction. A nano-sized TiAl 3 interfacial layer was formed at the interface between the Ti and SiC p /Al layers, which resulted in a good interlaminar bonding strength and an improved ductility of the laminated composite due to the nano-sized effect. A good strength–ductility balance, 307 MPa yield strength and 21.4% elongation to failure, was achieved. Combining with the low density of 3.62 g/cm 3 , 20% lower than that of Ti, this Ti–(SiC p /Al) laminated composite presents the potential application in the aerospace field.

Mechanical properties of Ti–(SiCp/Al) laminated composite with nano-sized TiAl3 interfacial layer synthesized by roll bonding

In the present work, TiAl 3 layers were synthesized by reaction annealing of a multi-laminated Ti-(SiC P /Al) composite at 650 °C. It was found that Si dissolved in the TiAl 3 layers during annealing. The effect of Si in the TiAl 3 layers on mechanical properties was investigated both by experiment and theory. The experimental results show that after annealing at 650 °C for 3 h, the solid solubility of Si in the TiAl 3 layer is about 6 at%, which leads to the lattice distortion of TiAl 3 . Due to the solid solution of Si in TiAl 3 , the elastic modulus and nanohardness increased up to 280 Gpa and 10.7 Gpa, respectively. Furthermore, the mechanism of increased modulus due to the solid solution of Si is verified by first-principles calculation of the theoretical elastic properties and can be explained from the electronic structure: (i) a new hybridization between Si3s and Al3s; (ii) primarily covalent interactions along Al3Si bonds.

A.B. Li

Papers

Effects of hot compression and heat treatment on the microstructure and tensile property of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy

Enhanced combination of strength and ductility in ultrafine-grained aluminum composites reinforced with high content intragranular nanoparticles

Fabrication and characteristics of in situ Al12W particles reinforced aluminum matrix composites by reaction sintering

Mechanical properties of Ti–(SiCp/Al) laminated composite with nano-sized TiAl3 interfacial layer synthesized by roll bonding

Effect of solid solution of Si on mechanical properties of TiAl3 based on the multi-laminated Ti-(SiCP/Al) composite system