### Session D3: Materials Science II: Laser Shock

Chair: Ronald Armstrong, University of Maryland
Room: Hyatt Regency Constellation D

 Monday, August 1, 2005 1:30PM - 1:45PM D3.00001: High-pressure phase synthesis of iron using femtosecond laser-driven shock wave Tomokazu Sano , Akio Hirose , Kojiro Kobayashi , Osami Sakata , Yasuaki Okano , Katsuya Oguri , Hidetoshi Nakano The quenching of the high-pressure phase of iron, which has not been observed under a conventional shock compression, was attained using a femtosecond laser. The lower pressure and temperature alpha-iron (bcc) transforms at higher temperatures to the gamma-iron (fcc) and at higher pressures to the epsilon- iron (hcp). Crystalline structures in a recovered iron sample after the femtosecond laser ($800$ nm, $120$ fs, $10^{13}$ - $10^ {16}$ $\mathrm{W/cm}^2$) irradiation were determined using the electron backscatter diffraction pattern, the electron diffraction, and the synchrotron X-ray diffraction methods. These results show the existence of the hcp structure and a small amount of the fcc structure in the recovered iron. The quenched hcp structure is found to be the high-pressure epsilon phase as a result of the temperature calculations during the shock-loading and shock-release process. The femtosecond laser driven shock wave may have the potential to quench high-pressure phases of other materials. [Ref. T. Sano et al., Appl. Phys. Lett. 83, 3498 (2003).] Monday, August 1, 2005 1:45PM - 2:00PM D3.00002: Near-Isentropic, High Pressure Laser-Driven Deformation Response of Copper J.M. McNaney , B. Torralva , J.S. Harper , M.S. Schneider , E.M. Bringa , B.A. Remington , M. Wall , M.A. Meyers We have developed a new platform for investigating deformation of a material under dynamic high pressure, quasi-isentropic loading. The technique uses a laser to generate a strong shock in a reservoir material. Unloading of the shockwave at the back of the reservoir creates a plasma that stretches across an evacuated gap and induces a quasi-isentropic pressure wave in the solid sample to be investigated. As this wave propagates through the solid material, it steepens and eventually becomes a shock. The large size of the sample minimizes the effect of wave reflection from boundaries. We have used this platform to investigate the response of single crystal copper loaded to a peak pressure of 25 GPa. Transmission electron microscope evaluation of the residual microstructure reveals a distinct difference between the shockless (dislocation cells) and shocked region (stacking faults). This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. Monday, August 1, 2005 2:00PM - 2:30PM D3.00003: Materials response under extreme conditions: a path to materials science above 1000 GPa Invited Speaker: Bruce Remington Solid state experiments at extreme pressures (10-100 GPa) and strain rates (1.e6 -- 1.e8 1/s) are being developed on high-energy laser facilities. [1] A quasi-isentropic, ramped-pressure (shockless) drive is being developed on the Omega laser. [2] Constitutive models for solid-state strength under these conditions are tested with experiments measuring perturbation growth due to the Rayleigh-Taylor instability in solid-state samples. [3] Lattice compression, phase, and temperature are deduced from extended x-ray absorption fine structure (EXAFS) measurements, from which the shock-induced alpha-omega phase transition in Ti is inferred to occur on sub-nanosec time scales. [4] Time resolved lattice response and phase can be inferred from dynamic x-ray diffraction measurements, where the elastic-plastic (1D-3D) lattice relaxation in shocked Cu is shown to occur promptly (sub-nsec). [5] Large-scale MD simulations have elucidated the microscopic dynamics that underlie the 3D lattice relaxation. [6] Deformation mechanisms, such as the slip-twinning transition in shocked single-crystal Cu, are identified by examining the residual microstructure in recovered samples. [7] Designs will be shown for reaching much higher pressures, (greater than 1000 GPa), in the solid state on the NIF laser. [8] *This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48. [1] B.A. Remington et al., Met. Mat. Trans. 35A, 2587 (2004). [2] J. Edwards et al., PRL 92, 075002 (2004). [3] K.T. Lorenz et al., PoP, in press (May, 2005). [4] B. Yaakobi et al., PRL 92, 095504 (2004). [5] A. Loveridge-Smith et al., PRL 86, 2349 (2001). [6] E.M. Bringa et al., Nature, submitted (March, 2005). [7] M.S. Schneider et al., Met. Mat. Trans. 35A, 2633 (2004). [8] B.A. Remington et al., in press, ApSS 298 (July, 2005). Monday, August 1, 2005 2:30PM - 2:45PM D3.00004: Shock-induced deformation mechanisms in nanocrystalline Ni Yinmin Wang , M. Victoria , A.M. Hodge , J. McNaney , E.M. Bringa , A. Caro , B. Remington , R. Smith , B. Torralva , C.A. Schuh , H. Van Swygenhoven The deformation physics of nanocrystalline materials with grain sizes less than 100 nm under shock loading is an interesting but unexplored topic. Here we present, for the first time, experimental observations on deformation behavior of nanocrystalline Ni, shock-loaded at different pressures by laser-driven isentropic compression experiments (ICE). Materials recovered after shocks have been systematically characterized using TEM/HRTEM, X-ray diffractometry, and mechanical testing (nanoindentation). These experimental results, in conjunction with our molecular dynamics simulations presented in a separate talk, provide tremendous new physics insights on deformation mechanisms of nanocrystalline materials at ultrahigh deformation strain rates (higher than 10$^{6}$ /s). This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract of No.W-7405-Eng-48, LDRD 04-ERD-021. Monday, August 1, 2005 2:45PM - 3:00PM D3.00005: Defect substructures in laser shocked and plate impacted monocrystalline copper Bu Yang Cao , Marc A. Meyers , David H. Lassila , Matt S. Schneider , Yong Bo Xu , Daniel H. Kalantar , Bruce A. Remington Monocrystalline copper samples with orientations of [001] and [221] were shocked at pressures ranging from 20 GPa to 60 GPa using two techniques: direct drive lasers and explosively driven flyer plates. The pulse duration for these techniques differed substantially: 2 ns for the laser experiments and 1.1---1.4 us for the flyer-plate experiments. The residual microstructures were dependent on orientation, pressure, and shocking method. The much shorter pulse duration in laser shock yielded recovery microstructures with no or limited dislocation motion. For the flyer-plate experiments, the longer pulse duration allow shock-generated defects to reorganize into lower energy configurations. Calculations show that the post shock cooling occurs in a time scale of 0.2 s for laser shock and 1000 s for plate-impact shock, propitiating recovery and recrystallization conditions for the latter. At the higher pressure level extensive recrystallization was observed in the plate-impact samples, while it was absent in laser shock. An effect that is proposed to contribute significantly to the formation of recrystallized regions is the existence of micro-shearbands, which increase the local temperature.