Metal Matrix Composites (MMCs) using carbon nanotubes (CNTs) as the reinforcing material have generated significant interest in recent years through their ability to produce lightweight components combined with high stiffness and strength. Researchers at Veermata Jijabai Technological Institute in Matunga, Mumbai, India, have been investigating the use of the Powder Injection Moulding (PIM) process to produce value added MMC products with iron powder derived from grinding waste as the base metal.
On its own this type of iron powder would have inadequate properties but when CNTs are added significantly better properties can be achieved. V.J. Pillewan and co-researchers published their findings on the use of PIM to produce Fe-CNT MMCs in the International Journal of Emerging Technology and Advanced Engineering (Vol. 5, No. 5, May 2015).
They stated that carbon nanotubes were added to iron powder in fractions ranging from 1% to 6% by weight. The feedstock for the MMCs was prepared by first mixing the iron powder with stearic acid at 60°C followed by the addition of paraffin wax and CNTs with mixing at 90°C, and finally adding HDPE and mixing at 160°C. The proportions of the various materials used to produce the PIM samples are shown in the Table. Solvent debinding was preferred to thermal debinding because of more complete binder removal. Sintering was done in an inert atmosphere at 1150°C for 2 hr which was found to be sufficient to provide bonding between the iron and CNTs.
Some porosity was found in the sintered PIM samples, but the researchers state that work is underway to improve sintered density and hence to improve strength properties. As the percentage of CNTs increases in the samples it improves the hardness of the Fe-CNT composite. However, adding more CNTs may leading to fracture of these samples, and further optimisation is required. Hardness values ranged from 55 to 87 HRB. Wear tests on the PIM Fe-CNT MMCs are reported.