LASER COMPRESSION OF NANOCRYSTALLINE METALS

M.A. MEYERS; H. JARMAKANI; E.M. BRINGA; P. ERHART; B.A. REMINGTON; N.Q. VO; Y.M. WANG

Nashville

Congreso; Shock Compression of Condensed Matter 2009; 2009

APS

Shock compression in nanocrystalline nickel is simulated over a range of pressures (10-80GPa) and compared with experimental results. Laser compression carried out at Omega and Janusyields new information on the deformation mechanisms of nanocrystalline Ni. Although conventionaldeformation does not produce hardening, the extreme regime imparted by laser compression generatesan increase in hardness, attributed to the residual dislocations observed in the structure by TEM. Ananalytical model is applied to predict the critical pressure for the onset of twinning in nanocrystallinenickel. The slip-twinning transition pressure is shifted from 20 GPa, for polycrystalline Ni, to 80 GPa,for Ni with g. s. of 10 nm. Contributions to the net strain from the different mechanisms of plasticdeformation (partials, perfect dislocations, twinning, and grain boundary shear) were quantified in thenanocrystalline samples through MD calculations. The effect of release, a phenomenon often neglectedin MD simulations, on dislocation behavior was established. A large fraction of the dislocationsgenerated at the front are annihilated.