Abstract:
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.
Introduction
Metal matrix composites (MMCs) reinforced with nano-particles, also called Metal Matrix
nano-Composites (MMnCs), are being investigated worldwide in recent years, owing to their
promising properties suitable for a large number of functional and structural applications. The reduced
size of the reinforcement phase down to the nano-scale is such that interaction of particles with
dislocations becomes of significant importance and, when added to other strengthening effects
typically found in conventional MMCs, results in a remarkable improvement of mechanical
properties.
The main issue to be faced in the production of MMnCs is the low wettability of ceramic nano-particles with the molten metal matrix, which do not allow the production of MMnCs by conventional casting processes. Small powder aggregates are in fact prone to form clusters, losing their capability to be homogeneously dispersed throughout the matrix for an optimal exploitation of the strengthening potential. For this reason, several alternative methods have been proposed in order to overcome this problem.
The production methods can be categorized into two major groups: ex situ and in situ. The first synthesis route consists of adding nano-reinforcements to the liquid or powdered metal, while in situ
processes refer to those methods leading to the generation of ceramic nano-compounds by reaction
during processing, for example by using reactive gases.
Several methods have been developed for ex situ synthesis of MMnCs. In particular, different powder metallurgy techniques were successfully employed. Moreover, ultrasound-assisted casting plays a particularly promising role for its high potential productivity. Alternative methods are listed and discussed in a following section.
The methods used for the characterization of MMNCs are the same of those used for conventional
MMCs and alloys. Of course, the downsizing of the reinforcement implies the use of higher resolution
techniques for characterization of morphology and local chemistry of the constituents. In the literature, different kinds of matrix metals have been coupled with several types of nanometric phases. Ceramic compounds (SiC, Al2O3, etc.), intermetallic materials and carbon allotropes were used to reinforce Al, Mg, Cu and other metals and alloys.
Particular importance is assigned to carbon nanotubes (CNT), which are characterized by very high strength, stiffness and electrical conductivity. These properties confer higher mechanical strength while improving electrical and thermal properties of the base material [5,6]. Moreover, MMnCs revealed to be able to improve other interesting engineering properties, such as damping capacity [7,8], wear resistance and creep behavior.
This paper is aimed at reviewing the theoretical and experimental background related to bulk MMnCs and the major results achieved in this field. Structural properties and mechanical performance induced by nano-particle and nano-tube addition to base metals will be presented and the state of art of the synthesis methods will be described.
Mau donasi lewat mana?
Donate with PaypalGopay-