Synthesis of carbide-free, high strength iron-carbon nanotube composite by in situ nanotube growth

Iron-multiwall carbon nanotube (MWNT) composites have been synthesized by the chemical vapor deposition (CVD) of the nanotubes directly inside an iron matrix. Carbide-free synthesis was achieved as indicated by X-ray diffraction data by the use of a mixture of acetylene and carbon monoxide as the carbon source. A possible mechanism for this formation reaction is proposed. The yield strength of the iron-MWNT composites prepared with 4.5 vol% or 1 wt% of nanotubes increased 36% and 43% for the upper and lower yield points, respectively, compared to similarly heat-treated reference samples of pure iron with the same porosity. The increase in yield strength is likely to be due to the support provided by MWNT bridges formed across the pores of the metal matrix. The Vickers hardness coefficient, which scales with the yield strength, also increased by as much as 97% in these composites relative to the reference samples.