Molecular Dynamics Modeling of Mechanical Properties of Nanocrystalline SiC

Molecular dynamics simulations using the Tersoff bond-order potential are employed to study the effects of temperature and grain size on mechanical properties of nanocrystalline silicon carbide. In this work, the simulated nanocrystalline SiC samples have a mean grain size varying from 2.5 to 5 nm and contain about 105 atoms in the model system. Tension tests with periodic boundary conditions and engineering strain rate of 10 – 4 ps – 1 are simulated, which result in the stress-strain curves of the single- and nanocrystalline SiC in terms of the average virial stress and true strain. The elastic moduli of the single- and nanocrystalline silicon carbide are determined from fitting the stress-strain curves. In this work, the Young’s modulus of nanocrystalline SiC is compared with those of the monocrystalline SiC for different temperatures in the range from 300 K to 3000 K. The numerical results show that the temperature has an obvious effect on Young's modulus, which is attributed to the large volume fraction of grain boundaries in nanocrystalline samples. With increasing temperature, the nanocrystalline SiC shows a brittle-to-ductile transition at temperatures above 600 K. In addition, the reduction in Young’s modulus of the nanocrystalline SiC with increasing temperature exhibits a nonlinear trend. It is found that the plasticity of the nanocrystalline SiC samples sharply increases at temperatures above 2000 K. This effect was explained by a decrease in the melting point of the nanocrystalline materials in comparison to monocrystalline solids. The grain size dependence of elastic modulus of nanocrystalline SiC only becomes distinct at high temperatures and at a grain size greater than about 3 nm, while at room temperature elastic properties are almost invariant with the change of grain size. We expect that the quantifications of temperature and grain size dependence of mechanical properties will have implications in the development of nanocrystalline silicon carbide nanostructured materials for high performance structural applications.