Elastic instability in graphite single crystal under dynamic triaxial compression: Effect of strain-rate on the resulting microstructure

We focus on the behavior of graphite under triaxial loading at a constant strain-rate using large scale molecular dynamics simulations. Buckling patterns (chevrons) in graphite nucleate from an elastic instability strongly related to the material anisotropy and subsequently grow until the first diamond nuclei appear. We show that the phase transition completely inhibits the growth of chevrons in buckled graphite, the diamond grain size being determined by the size of chevrons at the onset of nucleation. Cubic-diamond clusters nucleate within chevrons of buckled graphite and grow until the parent phase is entirely transformed. This phenomenon leads to nano-structured diamond polycrystals, with orientations of interfaces given by those of the buckled material right before the nucleation process. The buckled graphite microstructure is shown to strongly influence the final microstructure/size of nano-diamonds.