Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session L4: MS: Metals Phase Transitions I |
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Chair: Matt Hudspeth, LANL Room: Pavilion West |
Tuesday, June 18, 2019 4:00PM - 4:15PM |
L4.00001: Studies on the Mg hcp-bcc phase boundary through shock and release Matthew T Beason, Anirban Mandal, Brian J Jensen Despite its relatively simple electronic structure, the phase diagram of Mg is not well understood. It has been shown that the hcp-bcc transition occurs near 50 GPa at room temperature; however, both hcp and bcc Mg are observed from 46-56 GPa. This stems from small free energy differences between the hcp and bcc phases and has resulted in a range of reported phase boundaries for the hcp-bcc transition. As a result, the location of the bcc phase boundary is uncertain. The Mg phase diagram has been examined through a series of shock experiments and dynamic X-ray diffraction performed at the Dynamic Compression Sector (Argonne, IL) and front surface impact (FSI) experiments performed using the 2-stage gas gun at Los Alamos National Laboratory. The results indicate formation of bcc Mg on the ns timescale under shock loading. The shock-release profile observed in the FSI experiments show signs of a phase transition occurring on release from pressures above 30 GPa, providing a method for locating the bcc phase boundary as it approaches the melt boundary. The experimental results and analysis will be presented along with our path forward for studying the dynamic response of Mg. LA-UR-19-21417 [Preview Abstract] |
Tuesday, June 18, 2019 4:15PM - 4:30PM |
L4.00002: Nanosecond freezing of gallium metal under extreme effective cooling rates. Part 1: Experiments Justin Brown, Brian Stoltzfus, Jonathan Belof, Philip Myint Despite considerable interest in the timescales associated with first-order phase transitions, dynamic experiments probing the limits of transformation rates remain sparse. We present results for the first experimental measurements of the dynamic freezing of a metal on nanosecond timescales. Experiments were performed using the pulsed-power machine Thor, which utilizes precision shaping of the current pulse to shocklessly compress thin liquid gallium samples at a range of loading strain rates (10$^{\mathrm{6}}$ -- 10$^{\mathrm{7}}$ s$^{\mathrm{-1}})$ and peak pressures (20 -- 45 GPa). Velocimetry measurements of the rear surface of the cell shows clear evidence of freezing under a subset of loading conditions. We demonstrate how these data can be integrated with a recently developed theoretical description of nucleation and growth to advance our understanding of the dynamic solidification of metals. Results from this model are presented in the following accompanying talk. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. [Preview Abstract] |
Tuesday, June 18, 2019 4:30PM - 4:45PM |
L4.00003: Nanosecond freezing of gallium under extreme effective cooling rates. Part 2: Theory and Simulations Jonathan Belof, Philip Myint, Justin Brown, Brian Stoltzfus Experiments recently performed using the pulsed-power machine Thor, shocklessly compressing thin liquid gallium (Ga) samples at a range of loading rates ($10^6$ -- $10^7$ sec$^{-1}$) and peak pressures (20 -- 45 GPa), demonstrate freezing at very high driving force with nanosecond solidification kinetics, as presented in the previous accompanying talk. Building on a previously developed model for the compression-induced solidification of water to the high-pressure ice VII phase, a transient nucleation and growth theory for the time-dependent phase transition from the liquid to the body-centered tetragonal structure of Ga has been developed and applied toward the analysis of the Ga ramp compression data. Having coupled the solidification kinetics model to the hydrodynamic field equations, numerical simulations reveal an intimate relationship between ramp compression loading rate, wave propagation distance and the observed timescale for solidification kinetics. Simulations of multiple Ga ramp experiments demonstrate nearly quantitative agreement with a single physics-based model, with the high level of accuracy attributed to the explicit inclusion of the liquid-solid interfacial thermodynamics in the kinetics model. [Preview Abstract] |
Tuesday, June 18, 2019 4:45PM - 5:00PM |
L4.00004: Transformation pathways and microstructural evolution in shock-loaded and reshocked Zr and Ti Benjamin Morrow, David Jones, Ellen Cerreta During shock loading, hcp metals (e.g. zirconium and titanium) can experience a phase transformation from hcp alpha phase to hexagonal omega phase. Omega phase is often retained in the microstructure after unloading, and has a strong influence on subsequent mechanical properties. A systematic study of the microstructural evolution under various shock conditions will be presented. Soft-recovered shocked samples were characterized using electron backscatter diffraction (EBSD) to observe and quantify crystal orientations and microstructural features (including twinning, phase variants formed during deformation, and textures) to determine likely transformation pathways. Additionally, several previously shocked, two-phase samples were reshocked, resulting in a further refinement of the microstructure. Experiments at the Advanced Photon Source were performed to measure diffraction patterns during plate impact experiments of single and two-phase material to study the evolution during transformation. The combination of high-rate, in-situ and post-mortem data allow us to probe the mechanism and kinetics of phase transformations. [Preview Abstract] |
Tuesday, June 18, 2019 5:00PM - 5:15PM |
L4.00005: An atomistic view of zirconium during shock compression and release Martin Gorman, Cindy Bolme, David McGonegle, Arianna Gleason, Carl Greef, June Wicks, Patrick Heighway, Kenny Hulpach, Benny Glam, Eric Galtier, Hae Ja Lee, Jon Eggert, Raymond Smith The group IV metal Zirconium (Zr) is an important material in the nuclear, aviation and biomedical industries due to its low neutron cross section, high-resistance to corrosion and low toxicity. Understanding the structural behavior of Zr at extreme pressures (P) and temperatures (T) has therefore been the subject of considerable theoretical and experimental effort. While Zr has already been the subject of numerous shock compression studies, the characterization of its structural behavior at high P-T conditions has been limited by a lack of lattice level information provided in these experiments. Our understanding of the phase transition kinetics associated with the alpha $\to $ omega phase transition has also suffered from the lack of \textit{in situ }structural information. We used both high-quality velocimetry and in situ X-ray diffraction to extend our understanding of the structural and melting behavior of Zr up to 200 GPa. Upon shock release from the high pressure $\omega $ phase, our measurements provide an in situ, atomistic view of the $\omega \quad \to \quad \alpha $ transformation and its kinetics for the first time. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344 [Preview Abstract] |
Tuesday, June 18, 2019 5:15PM - 5:30PM |
L4.00006: Examining the alpha-epsilon phase transition in cerium at high pressures Brian Jensen, Frank Cherne, Nenad Velisavljevic, Matthew Beason, David Holtkamp, Thomas Hartsfield The ability to understand and predict the response of matter at extreme conditions requires knowledge of a materials equation-of-state including the location of~phase boundaries and associated~kinetics.~ For cerium metal, there still remain regions of the phase diagram that are largely unexplored dynamically including the high-pressure region below the melt boundary.~ In this region, diamond anvil cell data show significant disagreement in the existence, location, and slope of the alpha-epsilon phase transition along a high-temperature isotherm.~ In this work, we couple double-shock loading used to generate a secondary Hugoniot below the melt boundary with diamond anvil cell data to study the phase transition directly.~ Shock experiments using pyrometry and X-ray diffraction provide additional insight into the state of the material in this high-pressure region.~ Details of the experimental methods and analysis results will be presented that together provide a more complete picture of this phase transition at high-pressure.~ [Preview Abstract] |
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