EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Nowadays, there is a growing interest in the development of advanced materials capable to achieve high mechanical properties while maintaining lightweight, as the metallic matrix nanocomposites (MMNCs). Although the MMNCs can be reinforced by different nanometric materials, the carbon nanotubes (CNTs) are pointed as the most promising, due to their unique structure and properties, as well as their integration within several metals. The high mechanical properties of MMNCs come from the contribution of several strengthening mechanisms that act simultaneously.
Although the load transfer from the matrix to the reinforcement material is the most widely reported strengthening mechanism, there are other important mechanisms whose study is crucial. Depending on the metallic matrix and its affinity with carbon, the formation of second phase particles may occur and its presence can contribute to the MMNCs strengthening, as already reported in several studies. On other hand, there is also an increase in dislocation density and Orowan hardening and, although less mentioned, grain refinement can even occur.
Metal matrix nanocomposites reinforced with multi-walled carbon nanotubes were produced using a classical powder metallurgy route, by cold pressing of the mixtures and sintering under vacuum. The identification and study of the different strengthening mechanisms were performed through advanced microstructural characterization techniques, namely: scanning electron microscopy (SEM), focusing on electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM).
It was concluded that the presence of CNTs significantly influences the way how the strengthening mechanisms occur in the metal matrix. The effect of the CNTs was especially visible on the load transfer mechanism, the increase of dislocation density and also in the formation of second phase particles. Consequently, the CNTs affect the microstructure of the nanocomposite and, therefore, its mechanical properties.