Enhanced yield strength in iron nanocomposite with in situ grown single-wall carbon nanotubes
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D.A. Wiegand and F.J. Owens Armament Research, Development and Engineering Center, Picatinny, New Jersey 07806
Z. Iqbala) Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102 (Received 22 August 2005; accepted 11 November 2005)
The yield strength of iron-carbon nanotube composites fabricated by in situ chemical vapor deposition of 2.2 vol% single-wall carbon nanotubes (SWNTs) inside an iron matrix showed substantial enhancement up to 45%, relative to that of similarly treated pure iron samples without carbon nanotubes of the same piece density. The work hardening coefficient and the Vickers hardness coefficient also significantly increased in these composites relative to the reference samples. X-ray diffraction together with energy dispersive x-ray measurements and micro-Raman spectroscopy indicated no concomitant formation of carbides and very little amorphous carbon during the vapor deposition process. Micro-Raman spectroscopy and scanning and transmission electron microscopy showed spectral signatures and images, respectively, indicating the formation and dispersion of SWNTs within the cavities of the iron matrix. It is suggested that the increased strength of the nanocomposites was due to the mechanical support provided to these cavities by the extremely strong SWNTs.
I. INTRODUCTION
Carbon nanotubes, which have high length-todiameter ratios, are capable of imparting toughness and strength to polymer, ceramic, and metallic composites.1,2 Theoretical modeling3–7 and experimental measurements8–11 have demonstrated that carbon nanotubes have high stiffness and strength, high electrical and thermal conductivity, and are capable of sustaining high elastic strain. Carbon nanotubes have been incorporated in polymer and ceramic matrices12–18 to provide improved mechanical properties. However, only sparse results are available for carbon nanotube–metal composites, with no improvement in mechanical properties reported so far. For example, Kuzumaki et al.19 fabricated aluminum composites using 5 and 10 vol% pre-synthesized arcgrown multi-wall carbon nanotubes (MWNTs) dispersed in an aluminum matrix, but these composites showed no improvement in mechanical properties. Yang and Schaller20 prepared MWNT/magnesium composites by gas pressure infiltration of liquid magnesium into a porous array of nanotubes and investigated their damping a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0061 522
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 2, Feb 2006 Downloaded: 17 Mar 2015
characteristics, but no improvement relative to damping characteristics of conventional metal matrix materials was observed. Flahaut et al.21 fabricated carbon nanotube–iron–Al2O3 composites by hot pressing in-situformed carbon nanotubes using a H2–CH4 mixture as the carbon source. The carbon nanotubes made using this process are, however, damaged during the high temperature (1500–1600 °C) processing step used, and disordered graphene la
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