Modified embedded atom method study of the mechanical properties of carbon nanotube reinforced nickel composites

We report an atomistic simulation study of the behavior of nanocomposite materials that are formed by incorporating single-walled carbon nanotubes (SWCNTs), with three different diameters, and a multiwalled carbon nanotube (MWCNT) into a single-crystal nickel matrix. The interactions between carbon and nickel atoms are described by a modified embedded atom method potential. Mechanical properties of these nanocomposite materials are predicted by atomistic calculations and compared with that of fcc nickel and pristine CNTs. Our simulations predict that all Ni/CNT composites studied in this work are mechanically stable. Their elastic properties depend on the volume fraction and diameter of embedded CNTs. The single-crystal Young's modulus (E-11) of Ni/SWCNT composites exhibit a large increase in the direction of CNTs alignment compared to that of a single-crystal nickel. However, a moderate but gradual decrease is seen for E-22 and E-33 in the transverse directions with increase in CNT diameters. As a consequence, Ni/SWCNTs show a gradual decrease for the polycrystalline Young's, bulk and shear moduli with the increasing CNT diameters and volume fractions. These reductions, although moderate, suggest that enhancement of mechanical properties for polycrystalline Ni/SWCNT nanocomposites are not achievable at any CNT volume fraction. The Ni/MWCNT composite with high CNT volume fraction shows the highest increase in E-11. Unlike the E-22 and E-33 for Ni/SWCNTs, there is a significant increase in the E-22 and the E-33 for Ni/MWCNT. As a result, polycrystalline Ni/MWCNT composites show slight increase in the elastic properties. This suggests that nickel nanocomposites with enhanced mechanical properties can be fabricated using large volume fractions of larger diameter MWCNTs. Depending on type, alignment and volume fraction, Ni/CNT composites show varying degrees of elastic anisotropy and Poisson's ratio compared to pure Ni. Simulation predicts strong adhesion at the Ni/CNT interface and a significant interfacial stress transfer between CNT and Ni matrix.