With using the carbon nano-tube (CNT) of high chemical activity, nano-TiCx particles with different growth shapes were synthesized through the self-propagating high temperature in the 80 wt.% metal (Cu, Al, and Fe)-Ti-CNT systems. The growth shapes of the TiCx particles are mainly octahedron in the Cu- and Al-Ti-CNT systems, while mainly cube- and sphere-like in the Fe-Ti-CNT system.

The morphologies of the transition metal carbide (TMC) (ZrC x , NbC x , and TaC x ), transition metal nitride (TMN) (TiN x ), and transition metal diboride (TMD) (NbB 2x and TaB 2x ) particles formed during the selfpropagating high-temperature synthesis (SHS) were investigated. The results indicate that the ceramics with wide stoichiometric ranges all show a stoichiometry-induced morphology evolution, i.e., octahedron → truncated-octahedron → spherelike → sphere, for TMCs and TMNs, and hexagonal prism → polyhedron → spherelike, for TMDs. For TMCs and TMNs, the increase in the stoichiometry leads to the increase in the growth rate in the ⟨111⟩ crystalline direction. Hence, their morphologies show an evolution process of gradual exposure of the {100} surfaces and shrinkage of the {111} surfaces. When the exposed {100} surfaces are roughed because of the extremely high combustion temperatures during the SHS and thus turn round, the growth shapes of the TMC and TMN crystals change to spherelike. On the other hand, when the TMCs and TMNs are stoichiometric or near stoichiometric, the critical transition temperature for thermodynamic roughening of the {100} surfaces could be very high. Then, the rounded {100} will restore to the flat surfaces, and the cubic and truncatedcubic TMCs and TMNs particles are formed. For TMDs, the morphology evolution could be caused by the decrease in the stability of the {0001} and {101̅ 0} surfaces at high stoichiometries. With the increase in the stoichiometry, these two surfaces are less-exposed gradually while the {11̅ 01} surfaces are exposed and expand. The growth shapes of TMDs change from regular hexagonal prism to polyhedron. With the rounding (roughening) transition of the {11̅ 01} surfaces at high temperatures, the TMDs particles become spherical.

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Compared to the micro-sized particle-reinforced metal matrix composites, the nano-sized particle-reinforced metal matrix composites possess superior strength, ductility, and wear resistance, and they also exhibit good elevated temperature properties. Therefore, the nano-sized particle-reinforced metal matrix composites are the new potential material which could be applied in many industry fields. At present, the nano-sized particle-reinforced metal matrix composites could be manufactured by many methods. Different kinds of metals, predominantly Al, Mg, and Cu, have been employed for the production of composites reinforced by nano-sized ceramic particles such as carbides, nitrides, and oxides. The main drawbacks of these synthesis methods are the agglomeration of the nano-sized particles and the poor interface between the particles and the metal matrix. This work is aimed at reviewing the ex situ and in situ manufacturing techniques. Moreover, the distinction between the two methods is discussed in some detail. It was agreed that the in situ manufacturing technique is a promising method to fabricate the nano-sized particle-reinforced metal matrix composites.

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