Imaging Defects in Diamond during Shock Compression

Diamond is well established to have strong resistance to plastic deformation and it’s Hugoniot Elastic Limit (HEL) is large relative to other materials. The HEL of single crystal diamond has orientation dependance: diamonds shocked in the <100> and <110> directions have been shown to have higher HEL than the <111> direction. Grain size of and impurities in diamond are thought to affect the HEL. Additionally, when diamond is shocked to stresses beyond the HEL, its strength drops (like a brittle material). To investigate the wide range of reported diamonds strength, we conduct X-ray topography experiments during laser shock loading at the MEC beamline at LCLS. X-ray topography is a near field imaging technique that images defects by observing contrast in the intensity of the diffracted X-ray beam. By using a line focused X-ray beam coupled with a thick diffracting region, we generate 2D images where defect derived intracrystalline rotations generate a diffraction intensity contrast compared to the defect free regions. We shock <100>, <110> and <111> oriented diamonds that are type Ia, Ib and IIa over a range of stresses to view dislocation avalanches in order to visualize the physics behind the onset of plasticity.

Prepared by LLNL under Contract DE-AC52-07NA27344.