Elastic anisotropy and its temperature dependence for cubic crystals revealed by molecular dynamics simulations

The temperature dependent phonon dispersions of BCC iron and tungsten were measured by running molecular dynamics simulations, based on which the elastic constants and elastic anisotropy were derived. It is found that the elastic constants decrease with increasing the temperature, while the elastic anisotropy generally enhances. Detailed analysis reveals that the lattice thermal expansion effect dominates the decreasing of elastic constants, which also tends to weaken the elastic anisotropy. Meanwhile, the lattice thermal vibration effect lowers the elastic constants related to the longitudinal waves, while has little impact on other elastic constants, thereby enhancing the elastic anisotropy. The overall effect of temperature on the elastic anisotropy in turn depends on the competition/compromise between the lattice thermal expansion and the thermal vibrations.