In situ X-ray Diffraction of Shock-Compressed Nanopolycrystalline Diamond

Over 50 years of shock experiments have demonstrated that planar shock waves deform crystals first along one dimension before the crystal rapidly relaxes along three dimensions. However, previous experiments have lacked the necessary spatiotemporal resolution to resolve this ultrafast lattice dynamics in detail. By performing in-situ x-ray diffraction measurements on shock-compressed full-density nanopolycrystalline diamond (NPD) with an average grain size of 10-20 nm, we accurately measured the evolution of strain in continuous elastic-plastic deformations of NPD. The experiments were performed at EH5 of SPring-8 Angstrom Compact Free Electron Laser (SACLA) where a high-energy drive laser is synchronized to the femtosecond pulsed X-ray Free Electron Laser (XFEL). Our results show that some of the anisotropy of the preceding elastic deformation remains in the subsequent plastic deformation, indicating that the strength of NPD persists even under stresses exceeding its Hugoniot elastic limit. The obtained structural data also show that the diamond structure is stable (or metastable) up to a shock pressure of at least 700 GPa. The detailed view of how ultrahard materials like NPD yield under high strain-rate shock compression gives key insights into the fundamental understandings of material disturbances in Inertial Confinement Fusion, hypervelocity planetary impact, material processing, and high-energy-density experiments that occasionally use a diamond as an ablator.