Structural phase transition and amorphization in hexagonal SiC subjected to dynamic loading

Understanding the dynamic behavior of silicon carbide (SiC) at extreme conditions is critical for applications such as coatings and armor. Revealing the plasticity and phase transition in SiC under intensive dynamic loading is among the key concerns. However, the effects of polytypes in SiC as well as the various loading conditions on its dynamic material responses are still not well understood. Here we carry out a series of large-scale molecular dynamics (MD) simulations to explore the inelastic responses of hexagonal SiC subjected to shock and ramp compression along the [0001] direction. The shock responses present three regimes sequentially as the shock particle velocity is increased from 0.5 km/s to 6 km/s: a single elastic wave, a multi-wave structure consisting of an elastic-plastic wave followed by two consecutive phase transition waves, and finally, an overdriven structural phase transformation wave. The original wurtzite structure is observed to transform into a 6-coordinated rock salt structure through a 5-coordinated intermediate structure. Furthermore, slip along the 1120 direction on the (0001) plane causes multiple stacking faults and amorphization when subjected to intense shock compression. The effects of temperature and strain rate on the material responses of hexagonal SiC are decoupled by performing ramp loading simulations. The results reveal that a lower temperature rise impedes atomic motion while a lower strain rate promotes it, highlighting a competitive effect. Besides, due to the limited availability of slip planes, dynamic compression can lead to the formation of nanograins in hexagonal SiC, and nanograins refinement with increasing shock intensity is observed. These results provide important insights into the deformation of SiC polytypes under extreme conditions and promote the understanding of the dynamic properties of hexagonal structure covalent materials.