Research on fabrication process & mechanical behavior of CNT/Cu & CNT/Ni nanocomposite

Abstract

Carbon Nanotubes are considered to be the ideal reinforcement due to superior mechanical properties. Young’s modulus of the order of 1 TPa and high tensile strength (30-200 GPa) with high elongation at break (10-30%). In addition, CNTs have high aspect ratio (>1000), high structural and chemical stability, and remarkable electrical, thermal and optical properties. Many of these outstanding properties can be best exploited by incorporating the nanotubes into some form of matrix, and the preparation of nanotube containing composite materials is now a rapidly growing research area. However critical barriers on fabrication process for metal nanocomposite obstacle the wide use of this fascination material. In this study, molecular level mixing process was modified by introduction of controlled oxidation step for CNT/Cu nanocomposite and direct reduction process step for CNT/Ni nanocomposite. These processes introduced to obtain homogenous distribution of CNT in each metal matrix to consider wettability of metal matrices on CNT. Controlled oxidation process introduced instead of drying and calcination step in order to prevent oxidation of CNTs and to reduce oxygen content which has deteriorative effect on both ductility and electrical conductivity of Cu matrix. In addition, direct reduction process support more ductility in CNT/Ni nanocomposites with low oxygen contents without severe agglomeration of CNT in Ni matrix. Mechanical Properties of CNT/Cu & CNT/Ni nanocomposites were characterized at room temperature to elucidate reinforcement effect of CNT at room temperature. The mechanical property analysis was performed based on microstructural char-acterization of CNT/Cu & CNT/Ni nanocomposite The modified ‘molecular level mixing and controlled oxidation process’ supply uniform 0.3~2um sized CNT/Cu nanocomposite powders. The obtained CNT/Cu nanocomposite powders were consolidated with spark plasma sintered and mechanical property was characterized. The 10vol.% CNT added CNT/Cu nanocomposite shows 3.2 times higher yield strength with 1.7time higher Young’s modulus than pure Cu. This high strengthening effect of carbon nanotubes are believed effective load transfer at the CNT and Cu matrix due to strong functional interfacial bonding. Homogeneous distribution of CNT in Cu matrix also important factor for high strengthening efficiency. The modified ‘molecular level mixing and direct reduction process’ supply uniform 50~200nm sized CNT/Ni nanocomposite powders. The 10vol.% CNT added CNT/Ni nanocomposite shows 4.2 times higher yield strength with 1.5time higher Young’s modulus than pure Ni. The strengthening of CNT in metal matrix originated from effective load transfer and grain size refinement of metal matrix. Mechanical behaviors at room temperature were analyzed. Plastic deformation of CNT reinforced metal occurred by dislocation movement and deformation twin mechanism. Due to majority of generation of deformation twin in deformation the high strain hardening is inhibited in CNT/Metal nanocomposite. The wear loss of 10vol.%CNT/Cu nanocomposites is reduced to 1/3 compared to those of pure Cu matrix. This improvement of wear property of CNT reinforced nanocomposites is expected when the external load can be shared by homogeneously distributed CNTs through the load transfer from matrix to CNTs by sound interfacial strength at CNT/matrix. Self-lubricating effect CNT is also major factor of this wear resistance improvement.

Development of this fabrication process for CNT/Cu and CNT/Ni nancomposite and analysis of mechanical behavior may contribute not only scientific development but also development of strength and high modulus structural materials for industrial development.