Interfacial characterization in carbon nanotube reinforced aluminum matrix composites

• The high reactivity between CNT and Al matrix, resulting Al4C3 formation during the sintering process is highlighted.
• We demonstrate, thanks to in-situ TEM observations, that Al4C3 crystals grow into aluminum grains by carbon diffusion.
• The native aluminum oxide around the aluminum particles prevents the diffusion of carbon into the aluminum grains.
• We show that the protective layer can be broken because of its crystallization, leading to the formation of Al4C3.
• SPS, by limiting the sintering duration, is an interesting way for preparing CNT/Al composites without carbide formation.

In this work, the effects of the sintering parameters, such as temperature and the techniques used (HP and SPS), on CNT/Al composite interfaces are studied. The major role of the native aluminum oxide (Al2O3) layer covering the aluminum grains is highlighted. It is shown that, for a sintering temperature below 620 °C, the amorphous Al2O3 layer prevents the reaction between aluminum and carbon. For greater sintering temperatures, the breaking of the oxide layer due to its crystallization leads to the formation of aluminum carbide (Al4C3) by reaction between aluminum and the CNT. The Al4C3 crystals grow perpendicularly to the matrix grain boundaries by thermally activated diffusion of the carbon atoms coming from the CNT. It is also demonstrated that, by limiting the sintering time, which is the case in SPS, it is possible to limit the growth of the Al4C3 crystals and thus to preserve the CNT.