Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session V5: Materials Science IV |
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Chair: Pablo Escobedo, Los Alamos National Laboratory Room: Renaissance Ballroom D |
Thursday, June 30, 2011 4:00PM - 4:15PM |
V5.00001: Laser Compression of Monocrystalline Tantalum Marc Meyers, Chia-Hui Lu, Bruce Remington, Brian Maddox, Hye-Sook Park, Shon Priesbrey, Bimal Kad, Rain Luo Monocrystalline tantalum with orientations [100] and [111] was subjected to laser driven compression at laser energies of 350 to 685 J, generating shock amplitudes varying from 15 to 100 GPa. The laser beam, with a beam spot diameter of $\sim $1 mm, created a crater of significant depth ($\sim $ 80 to $\sim $ 200 $\mu $m). Twins were observed just below the crater surface ($\sim $ 42 $\mu $m) by back-scattered SEM. Transmission electron microscopy (TEM) revealed profuse mechanical twinning within a distance from the energy deposition surface of about 1.5 mm ($\sim $ 1.3 mm from residual crater vertex) at 684 J compression power, corresponding to an approximate pressure of 35 GPa. The decay of the pulse through the specimens was accompanied by an attendant decrease in the density of shock-generated dislocations. Dislocation densities as a function of pressure were calculated for the case of homogeneous nucleation and for Orowan hardening. The observed results are compared with predictions. Microhardness measurements were conducted on the recovered samples. The experimentally measured threshold stress for twinning is compared with predictions using an analysis based on the constitutive response and the similarities and differences are discussed. [Preview Abstract] |
Thursday, June 30, 2011 4:15PM - 4:30PM |
V5.00002: Laser Compression of Nanocrystalline Tantalum Chia-Hui Lu, Brian Maddox, Bruce Remington, Eduardo Bringa, Megumi Kawasaki, Terence Langdon, Hye-sook Park, Bimal Kad, Marc Meyers Nanocrystlline tantalum was prepared by HPT (High Pressure Torsion) from monocrystalline [100] stock yielding a grain size of 70 nm. It was subjected to laser driven compression at energy levels of $\sim $ 350 J to $\sim $ 850 J in the Omega facility (LLE, U. of Rochester) yielding pressures as high as $\sim $ 180 GPa. The laser beam created a crater of significant depth ($\sim $ 100$\mu $m). Transmission electron microscopy (TEM) revealed dislocations in the grains but no twins in contrast with monocrystalline tantalum. Hardness measurements were conducted and show the same trend as single crystalline tantalum. The grain size was found to increase close to the energy deposition surface. [Preview Abstract] |
Thursday, June 30, 2011 4:30PM - 4:45PM |
V5.00003: Thermophysical Properties of Solid and Liquid Platinum Alloys by a Pulse-Heating Technique Shahid Mehmood, Ulrich E. Klotz, Gernot Pottlacher Thermophysical properties of platinum and four platinum alloys namely, Pt-4Cu Pt96Cu4, Pt68Cu32, Pt50Cu50 and Pt25Cu75 are investigated in the solid and in the liquid phase by a fast pulse-heating technique. In this technique wire shaped samples are resistively volume heated as part of fast capacitor discharge circuit. With heating rates up to 10$^{8}$ K/s the liquid phase is achieved after about 30 $\mu $s. Time resolved measurements with submicrosecond resolution allow the calculation of specific heat, enthalpy, electrical resistivity and temperature in the solid and liquid phase. Densities of these alloys as a function of temperature are determined by an expansion measurement using a fast and specifically designed CCD camera. Thermal conductivity and thermal diffusivity are calculated by means of the Wiedemann-Franz law using resistivity, specific heat and density data. The results are compared with available literature values, pure platinum and pure copper results. [Preview Abstract] |
Thursday, June 30, 2011 4:45PM - 5:00PM |
V5.00004: Femtosecond laser-driven shock hardening of iron and aluminum Tomokazu Sano, Kazuto Arakawa, Takahiro Tsukada, Yutaro Isshiki, Tomo Ogura, Akio Hirose, Kojiro Kobayashi We found that surface layer around 10 um becomes harder than the parent material of iron and aluminum compressed by the femtosecond laser-driven shock wave. Femtosecond laser pulses with wavelength of 800 nm and pulse width of 130 fs were irradiated to the surface of pure iron with purity of 99.99 {\%} and pure aluminum with purity of 99.999 {\%}, respectively, varing the pulse energy. Hardness was measured using nanoindentation. We found that dense dislocation network exists in the hardened regions as a result of the TEM observation. We suggest that rapidly cooling in the femtosecond laser-driven shock compressed region prevent the dislocation network from recovering. [Preview Abstract] |
Thursday, June 30, 2011 5:00PM - 5:15PM |
V5.00005: The Refractive Index and Transparency of Lithium Fluoride Compressed to 800~GPa Dayne Eric Fratanduono, T.R. Boehly, J.H. Eggert, M.A. Barrios, R. Smith, P.M. Celliers, D.G. Hicks, G.W. Collins, D.D. Meyerhofer Lithium fluoride, ramp compressed by direct laser ablation, is observed to remain transparent up to 800 GPa. Simultaneous measurements of the free-surface and interface (particle) velocities in a two-section diamond-LiF target determine the velocity-correction factor and the refractive index of compressed LiF. The refractive index is observed to increase linearly with density over pressures of 30 to 800 GPa. An effective single-oscillator model shows that the refractive index is linear in density as a result of the optical gap closing monotonically with increasing density. Extrapolation of these results indicate that metallization of LiF should occur at pressures significantly higher than the Goldhammer--Herzfeld criterion ($\sim$ 2750 GPa), suggesting that LiF will remain transparent at extremely high pressures. [Preview Abstract] |
Thursday, June 30, 2011 5:15PM - 5:30PM |
V5.00006: Electron Back-Scatter Diffraction Analysis of Pre and Post-Deformation Ti-6Al-4V Taylor Impact Specimens Euan Wielewski, Joshua Eggleston, Clive Siviour, Nik Petrinic Titanium alloys have seen wide spread, and ever increasing, use in the aerospace industry, due to a high specific strength and good resistance to corrosion. However, current understanding of the deformation mechanisms of Titanium alloys under complex high strain rate loading is limited. In order to improve understanding in this area, post-deformation microstructural analyses of Titanium alloys loaded under well controlled, but complex, high strain rate loading conditions, such as the Taylor impact test, are required. This paper presents the results of Taylor impact experiments carried out on specimens cut from the rolling and transverse material directions of two heavily textured Ti-6Al-4V plates with different microstructures. Electron back-scatter diffraction analysis has been performed on pre and post-deformation specimens with comparisons made between the deformed microstructures of the two plates in the rolling and transverse material orientations. [Preview Abstract] |
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