Carbon Nanotubes: Metal Matrix Composites
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The literature on bulk CNT–MMCs is limited to about 20 papers. A pioneering work on processing CNT reinforced aluminum was published by Kuzumaki et al. in 1998. They produced composite wires by hot extrusion of CNT–Al powder blends, which were previously mounted on a silver sheath. The resulting wire microstructure consisted of partially aligned nanotubes on a metal matrix. Transmission electron microscopy (TEM) observations showed that the nanotubes were not damaged by the processing method, and that no reaction at the nanotube/aluminum interface was visible after annealing for 24 hr at 983 K. The tensile strength of the composite wires was similar to that of pure aluminum produced in similar powder metallurgy process, but the wires retained the strength by annealing at 873 K, while the strength of aluminum wires significantly decreased with time. The same authors published a further work on CNT reinforced titanium that was prepared by hot compaction at 1208 K for 2 hr, at 30 MPa, in vacuum. TEM observations revealed that the nanotubes did not react with the Ti matrix. A significant increase in microhardness and elastic modulus (evaluated by ultrasonic spectrum microscopy) was measured and compared with pure titanium obtained by the same processing route.