Nanosecond grain reorientation and ductility in shocked nano-polycrystalline diamond (in situ XFEL study)

Diamond is the hardest known material in nature, and there has been considerable interest to develop even harder forms of diamond for industrial and defense applications. Among all such attempts, full-density nano-polycrystalline diamond (NPD), synthesized by compressing and heating highly oriented pyrolytic graphite, is the hardest bulk material that has ever been studied [Irifune et al, 2003, Sumiya et al, 2008]. NPD also has the highest Hugoniot Elastic Limit of any material, as well as an unusually stiff Hugoniot curve, even up to several megabars of pressure [Katagiri et al, 2020]. The deformation mechanisms of NPD that lead to such properties remain to be understood.

We will present in situ X-ray diffraction measurements at SACLA-XFEL that resolve the strain and microstructural evolution of nano-polycrystalline diamond in response to laser-driven shock compression. Within a nanosecond of compression, the initially randomly textured diamond begins to develop a fiber texture aligned with the direction of shock propagation. With supporting molecular dynamics simulations, we will explore the cause of grain reorientation and its connection to dislocation motion and loss of strength.