Rate dependence and anisotropy of SiC response to ramp and wave-free quasi-isentropic compression*

Dynamic responses of SiC under compression are investigated using large-scale molecular dynamics simulations.The ramp wave compression applied to single crystal 3C-SiC uses ramp rise times from 10 to 100 ps. Wave-free quasi-isentropic compression loading is also applied with strain rates varying from 10⁸ to 10¹¹ s^-1. Results show that the plastic deformation and phase transition are strongly strain-rate dependent. With increasing strain rate, the threshold strain and longitudinal stress for deformation twinning is anisotropically increased. The threshold longitudinal and shear stresses triggering plasticity are lowest in [001] direction, followed by [110], and highest in [111] SiC at the same strain rate. The threshold pressure for structural phase transition from zinc-blende (ZB) to rock-salt (RS) structure increases with the applied strain rate. As a result, the transition from ZB to RS structure is incomplete and inhomogeneous mixed-phase structures are observed over a wide range of applied stresses, even up to ~180 GPa, which agrees well with experimental observations.