Nanoparticle-reinforced MMCs

The critical issue in nanoparticle-reinforced MMCs is the retention of the nanosize in the composite after processing. There are several factors controlling this issue, as discussed in the following sections. 

Figure 14.2 SiC nanoparticle-reinforced MMC processed by an ex situ technique at (a) low and (b) bigb magnifications.

In general, the addition of nanoparticles into the metal matrix increases its strength. The main strengthening mechanisms of nanoparticle-reinforced MMCs are presented in the following sections. 

Nanoparticle-reinforced MMCs usually exhibit higher microhardness than that of the unreinforced matrix alloy. The increase in hardness can be described as follows (1) strengthening mechanisms arising from restricting or impeding the motion of dislocation, (2) the presence and near-uniform distribution of second-phase particles achieved by optimal processing, and (3) a refinement in grain size. 

In a traditional way, ceramic reinforcements are added to the matrix materials, which are in a molten or powder state, and they can be termed as ex situ MMCs because the reinforcing phases are prepared separately before the composite fabrication (Tjong and Ma, 2000 Zhao-hui et al., 2010). Figure 14.2 shows 5 vol% SiC nanoparticle-remforced A16061 MMC produced by an ex situ method, which was followed by... 

---