Laser compression of nanocrystalline tantalum

Nanocrystalline tantalum was prepared by high pressure torsion from monocrystalline [100] stock, yielding a grain size of 70nm. It was subjected to laser driven compression at energy levels of ~ 350 J to ~ 850 J in the Omega facility (LLE, U. of Rochester) with corresponding pressures as high as ~ 170 GPa. The laser beam created a crater of significant depth (~ 100 µm). Transmission electron microscopy (TEM) revealed dislocations in the grains but no twins in contrast with monocrystalline tantalum. Hardness measurements were conducted and show the same trend as single crystalline tantalum. The grain size was found to increase close to the energy deposition surface due to the thermomechanical excursion.